Title of Invention	"A PROCESS FOR STORING THE FUEL GASES SUCH AS NATURAL GAS AND ITS BLENDS IN A CONTAINER"
Abstract	The present invention relates to a process for storing the fuel gases and its blends in a container at a pressure of 400 psig to 600 psig at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent, wherein the said fuel gases or its blends from the source of supply to a compressor unit are supplied and passed through a pressure control and metering device followed by passing through a purification unit comprising adsorbent material preferably activated carbon prepared from coconut shells acting as guard bed to remove moisture, carbon dioxide and heavier hydrocarbons to get the purified fuel gases, the said purified gases are finally introduced in a storage container containing adsorbent of microporous carbon particles prepared from coconut shells by means of carbonization and partial oxidation to form the monoliths of high packing density in a container.

Title of Invention

"A PROCESS FOR STORING THE FUEL GASES SUCH AS NATURAL GAS AND ITS BLENDS IN A CONTAINER"

Abstract

The present invention relates to a process for storing the fuel gases and its blends in a container at a pressure of 400 psig to 600 psig at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent, wherein the said fuel gases or its blends from the source of supply to a compressor unit are supplied and passed through a pressure control and metering device followed by passing through a purification unit comprising adsorbent material preferably activated carbon prepared from coconut shells acting as guard bed to remove moisture, carbon dioxide and heavier hydrocarbons to get the purified fuel gases, the said purified gases are finally introduced in a storage container containing adsorbent of microporous carbon particles prepared from coconut shells by means of carbonization and partial oxidation to form the monoliths of high packing density in a container.

Full Text	The present invention relates to a method for the safe storage, off-line transmission and distribution of gaseous fuels such as Natural Gas (NG) and Hythane at low pressure and ambient temperature. The invention also resides in the process for the preparation of the adsorbents used in the purification unit for the storage of gaseous fuels, acting as guard bed to trap high hydrocarbon components of natural gas. The embodiment of the invention resides in the thermal energy storage system comprising phase change materials to mitigate heat effects in the adsorption / desorption of natural gas. The object of the invention is to store the gaseous fuels at low pressures and the transportation and distribution of natural gas and blends of natural gas (particularly, Hythane fuel, which is a mixture in the range of 5 to 20 percent hydrogen and 80 to 95 percent natural gas by volume) for utilization of Natural Gas and /or Hythane as fuel in such applications as barbecue stoves, indoor cooking burners, automobiles and the like. PRIOR ART Presently, the use of liquefied petroleum gas (LPG) consisting mainly of propane and butane for the domestic purposes is widespread. Though LPG is convenient to store as it liquefies at moderate pressure and ambient temperature. However, LPG has several drawbacks as of potential fire hazard. This is due to the fact that propane and butane vapours are heavier than air so that when spilled or leaked they will remain close to ground level thus creating a risk of fire or explosion. Moreover, LPG burning causes substantially larger emissions of CO2 on the basis of per unit of energy generated. The use of Natural gas for such purposes has also been tried because unlike that of LPG, there is an abundant supply of natural gas with world reserves estimated to last more than 100 years. Since natural gas is lighter than air, it is inherently safe because upon accidental leakage it would rapidly disperse. Natural gas also has the advantage of clean-burning characteristics with very low level emissions of toxic and regulated gases such as hydrocarbons, carbon monoxide and nitrogen oxides (NO and NO2). Octane rating of natural gas is about 130, substantially higher than octane rating of propane (105 - 110). The combination of an extensive resource base and environmental advantages makes natural gas a preferred fuel. Natural gas is the least carbon intensive of the fossil fuels and therefore produces the least amount of Carbon dioxide per unit of energy generated. The natural gas not only results in the reduced Carbon dioxide emission, it's combustion also produces less air pollution than other fossil fuels due to lower level of emissions of NOX, SO2,CO and non-Methane hydrocarbons from natural gas fuelled systems. For utilization of natural gas as fuel in cooking appliances, and Hythane as fuel in automobiles in places where pipeline transmission and distribution system of these gaseous fuels does not exist, it is required to provide an alternative cost-effective and convenient means of storage, transportation and distribution of these gaseous fuels in these places. The most commonly perceived way is to store natural gas and its blends under pressures between 3,000 to 5,000 psig. This method of high pressure storage requires use of very heavy and expensive storage cylinders and expensive fuelling equipment. The high pressure gas is also a safety hazard. In the case of an accident, high pressure natural gas and Hythane could explode due to ignition. Therefore, this method of high pressure Natural Gas storage is not acceptable for use in barbecue stoves and indoor burners. Presently, natural gas is used mainly for fuelling stationery systems such as power plant combustors, industrial boilers, residential and commercial space heaters and domestic appliances. In these applications , natural gas is supplied by gas pipe line technology. Its application in mobile systems is limited since the energy density of stored natural gas is low due to its gaseous nature. For the same reason, it has found little application as a domestic fuel in places where it is not available via pipelines. Another way of off-line (non-pipeline) transportation of natural gas and its blends is to supply it in liquid form in thermally-insulated tanks. However, this method of natural gas and Hythane storage and distribution is also not a viable option due to the prohibitively high costs involved in liquefaction and refrigeration, and extraordinary safety precautions that must be taken during the transportation and handling of such dangerous cryogenic liquids. Conventionally, the storage of natural gas is achieved by compression, liquefaction, dissolution, adsorption, clathration and encapsulation. However, in the storage of natural gas , the compression is the widely used technique. The maximum storage pressure is found to be 20.7 Mpa. At this high pressure at ambient temperatures, the energy of compressed natural gas is only 30% of the energy of an equal volume of petrol. The gas cylinders used are made up of steel or reinforced aluminium. Both, these types of cylinders are however, heavier and more expensive than a petrol tank, moreover, at these high pressures the used cylinders have to be rechecked periodically. Another method of concentrating natural gas is to liquefy it at a temperature of -164°C. Natural gas is liquefied by a refrigeration cycle and stored in insulated tankers. The natural gas is reduced to about one six-hundredth of its original volume and the non methane components are largely eliminated. This requires, however, that the liquefied natural gas be kept in insulated containers and stored under refrigeration conditions. This is also not found to be appropriate solution in the circumstances when the storage containers are taken to remote areas. Although liquefied natural gas contains two times more energy per unit volume than compressed natural gas at 2.49mpa, it is not considered to be an economically viable solution due to the higher cost involved in refrigeration and liquefaction compared to its compression. Moreover, the refuelling procedures are more complex and hazardous for liquefied natural gas then for compressed natural gas. Dissolution of natural gas in a liquid is another option of natural gas storage. The dissolved amount of natural gas is generally low, except when the solvent is ethane or propane. These solvents have, however, high volatiles and as the pressure in the container drops and the natural gas gets depleted, the concentration of ethane or propane increases in the gaseous phase, which modifies the physical characteristics of the fuel mixture. However, this requires more complex and expensive ignition system. The part of solvents are lost and also in case of leak, the higher hydrocarbons tend to settle in low height areas instead of escaping to the atmosphere as is the case with natural gas , thus causing a fire or explosion hazard. Hence, the dissolution of the natural gas in heavier hydrocarbons is also not a viable option. The other option is to store natural gas by clathration and encapsulation. Clathrates are formed by inclusion of a guest molecule in a cavity made by several host molecules. The components are not held together by primary valence forces, but the guest molecule is necessary for the stability of the host molecules structure. Natural gas hydrates are a kind of clatharate where methane molecules are held in water molecule cages. These natural gas hydrates account for very large natural gas reserves in deep oceans and in the permafrost. The clathration of methane by either water or other compounds has been tried but methane storage is too low to be of any interest. Further, encapsulation is another method for the storage of natural gas, which is quite similar to clathration, however, the same is also not found suitable as the storage capacity is low, refuelling requires very high pressure and the release mechanism for natural gas is also very complex. To overcome the drawbacks associated with all the above referenced techniques involved in the storage of natural gas , there is a need to use a high surface area material which can adsorb large quantities of natural gas at moderate pressures, where the natural gas molecules are adsorbed within the pores of a high surface area solid material using an adequate adsorbent. The adsorbents are used for storing such Natural Gas at low pressures. Such adsorbents and their compaction and binding technique to fabricate carbon monoliths preferebly from coconut shells have been described in detail in the co-pending Indian Patent Application The invention relates to a method for loading adsorbent material into a suitable storage container for adsorbing the fuel gas onto it at a pressure of 400 to 600 psig and at ambient temperature (5-50°C), which results in storage of the fuel of about 150 litres of gas per litre of adsorbent. The storage of this amount of natural gas in the same container without adsorbent is only possible at a very high pressure of about 2000 psi, which is unsafe and expensive for many applications. The adsorbent used are carbon monoliths of high packing density fabricated by binding and compacting microporous carbon particles, prepared from coconut shells, using an inorganic clay material as binder. Natural gas or Hythane so stored in a suitable container can be transported and distributed by conventional or specially made carriers to any place, thus avoiding the need for pipeline system of distribution. The present invention can better be understood with reference to the accompanying drawings, which are for illustrative purposes and should not in any way be construed to restrict the scope of the invention keeping in view that certain modifications and improvements are possible without deviating from the scope of the invention. STATEMENT OF THE INVENTION According to the present invention there is provided a process for storing the fuel gases such as natural gas and its blends in a container at a pressure of 400 psig to 600 pisg at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent where the said adsorbent is monolithic microporous carbon adsorbent of high packing density comprising: fabricating said adsorbent from granular microporous coconut shell carbon using a binding agent comprising of mixture of a clay and sodium silicate or mixture of a clay and calcium hydroxide or a clay material alone wherein the clay component is chosen from the group comprising of cationic clays and pillared analogues of cationic clays; fabricating a purification unit comprising a filter material acting as a guard bed to remove moisture, carbon dioxide and heavier hydrocarbons to get the purified fuel gases; feeding the said fuel gases or its blends from the natural gas supply line to a compressor unit; passing the said compressed fuel gases through a pressure control and a metering device to control the pressure of compressed natural gas at desired level; passing the said compressed fuel gases through the purification unit; and finally, introducing the said purified gases in a storage container containing the fabricated monolithic adsorbent. DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 depicts the block flow diagram showing various unit operations involved in the preparation of high density monolithic microporous carbon adsorbent from coconut shells for use in the safe storage, off-line transportation and distribution of natural gas and Hythane fuels. Figure 2 depicts the block diagram illustrating a process of storing of natural gas and Hythane with monolithic carbon adsorbent. DETAILED DESCRIPTION OF THE INVENTION As illustrated in Figure 1, microporous carbon for binding and consolidation in accordance with the method disclosed in the copending Indian Patent application No. is prepared from coconut shells by the two-stage process of carbonization and controlled partial oxidation. The raw coconut shells were crushed to particle size of about 5-10 mm, washed with water and dried at a temperature of about 110°C and then subjected to carbonization by heating to a temperature of about 600°C to about 700°C in an inert atmosphere. The char so produced was crushed, screened to 8-30 mesh size and then submitted to controlled partial oxidation with oxidising agents such as carbon dioxide and water vapour/nitrogen mixture at a temperature of about 700°C to about 850°C. The resultant product was a granular microporous carbon having a surface area in the range 1200 - 1800 m2/g. The source of microporous carbon suited for the storage of natural gas and Hythane is coconut shells. However, Microporous carbons derived from other sources such as coal, coal coke, petroleum coke, wood and rice husks can also be used for safe storage, transportation and distribution of natural gas and Hythane. The method comprises : (a) crushing and milling the granular carbon into a fine powder by conventional means preferably in a ball mill; (b) preparing an aqueous dispersion of the binder formulation by adding the ingredients of the formulation to water (25 mL to 50 mL water per gram of binder) and thoroughly agitating the mix; (c) mixing dry or pre-wetted carbon powder of step (a) with the water dispersion of the binder of step (b) in appropriate proportions to make a slurry of carbon and binding agent; (d) drying the carbon-binding agent slurry of step (c) to a desired moisture content ranging from 80% to 100% by weight based on the weight of carbon used in step (c), by evaporating water while stirring in any conventional blending-drying equipment; (e) consolidating carbon-binder mix of step (d) either by compression, at ambient temperature, inside a suitable die under a pressure of 8,000 to 16,000 psi using a suitable pelleting press or by extrusion process using a suitable extruder to provide high density, mechanically strong monoliths of desired shapes and sizes; and (f) subjecting the said monoliths to drying in steps at a temperature of 60°C to 70°C and at temperature of 120°C to 140°C in air atmosphere to provide dried monoliths free of moisture. The said binding agent is a clay material used alone or as a mixture with sodium silicate or calcium hydroxide, wherein the clay component is chosen from a group of cationic clays which are hydrous layer silicates of the so-called phyllosilicate family consisting of such groups as smectite, vermiculite, serpentine-kaolin, talc-pyrophylite, mica, brittle mica, chlorite and sepiolite-palygorskite, typical examples being bentonite, atapulgite, hectorite, beidellite, fuller's earth, halloysite, illite kaolin, montmorillonite and mullite or from a group consisting of pillared analogues of cationic clays which are materials in which small cations of cationic clay are replaced by large polyoxocationic species. The most preferred clays for use in the binding agent formulation include bentonite clay, sodium exchanged bentonite clay, pillared analogues of bentonite clay (such as AI-, Fe-, Cr-, Zr- or Ti- pillared bentonite clay) and combinations thereof. In the said binding agent formulation, the clay content is 5% to 15% by weight, sodium silicate content is 0.5% to 1.5% by weight, and calcium hydroxide content is 0.5% to 1.5% by weight, all based on the weight of carbon used in step (c). In step (d), the moisture content of the carbon-binder paste is controlled in the range from 80% to 100% by weight based on the weight of carbon used in the preparation. The packing density of the monoliths so prepared is nearly twice as much as that of the starting granular material. The binding agents used in this invention are thermally and chemically stable substances which at no stages of monolith fabrication process release obnoxious gases or vapours of any kind and therefore there is no cause for concern from the viewpoint of environmental pollution or occupational health and safety hazard. Unlike prior art, the method of this invention does not require heating of carbon-binder mix during step (e) of the above-described embodiment, thereby providing substantial processing cost savings. Furthermore, since the method does not involve heating and cooling of the material during step (e) of the above-described embodiment, the said carbon-binder mix or paste can be processed to form monoliths in less than 15 minutes, thereby shortening the processing time. Moreover, the subject process does not suffer from any drawback associated with the problem of pore plugging with binder because major ingredient of binder formulation (that is the clay component) is applied as a dispersion in water rather then as a solution wherein size of the clay particulates are too large to penetrate into and occupy the micropores of carbon particles. The method of binding and compaction of microporous carbon powder thus overcomes the difficulties associated with the prior art of pelletization or briquetting of activated carbon powders for use in the storage of natural gas. The process for the storage of natural gas comprises packing the carbon monoliths prepared from coconut shell by the steps of carbonization and partial oxidation with steam or CO2 activation binded together and consolidated into monoliths of high packing density in a storage container (10) of cylindrical or cuboidal geometry. The natural gas or its blends from the source (1) is fed via compressor (2) passes to flow control and metering device (4), via line (3), which is connected to pressure control and metering device (6) through pipe (5), which in turn is connected through a pipe (7) to a purification unit as guard bed (8) packed with suitable solid adsorbent material, preferably activated carbon, carbon molecular sieve, zeolites or a combination thereof, which removes moisture, carbon dioxide and heavier hydrocarbons (C4 and above) constituents present in small amounts in natural gas and Hythane. The exit stream from the purification unit (8) is then introduced via pipe line (9) into the adsorbent packed storage container (10) allowing adsorptive storage of Natural Gas or Hythane fuel under a pressure of 400 psig to 600 psig . The present monolithic adsorbent produced from coconut shell microporous carbons by binding and compaction using the binding agents and method disclosed as above when packed in a container show high reversible uptakes of natural gas and Hythane on a volumetric basis, thus providing an efficient means of storage of natural gas and its blends. The method does not require expensive and heavy storage vessels, saves compression costs of high pressure (3000 -5000 psig) storage, and offers safety because container pressure is limited to between 400 psig and 600 psig. The adsorbent used in the guard bed are prepared from the coconut shell having a packing density of 0.5g/cm2 and a surface area of about 1200 m2/g. The process for the preparation of activated carbon from coconut shells for use as guard bed is a two stage process ; comprises: 1 pyrolysis/carbonization of dried coconut shell at 873 K under an inert atmosphere. 2 Activation of coconut char by partial gasification/controlled oxidation with CO2 at 1073K. The coconut shells were cleaned of loose fibers and traces of kernel, crushed to particle size of about 10mm, washed with water and dried at 383K overnight. In a vessel, crushed and dried coconut shells are loaded , which is purged with N2. The vessel is mounted vertically in a tube furnace and heated at a temperature of 873K for a period of two to four hours and then allowed to cool at room temperature. The char so produced is crushed and screened to 10-30 mesh fraction. The char so produced is treated with dilute Nitric acid at room temperature for four to six hours. The dilute nitric acid treated char is then washed with distilled water till char is free from acid. The washed char is then dried at 383 K overnight. The acid treated char is activated by partial gasification with CO2 under well defined conditions. The activated carbon so obtained thus used as guard bed in the purification unit. The natural gas storage vessel can be filled with the natural gas under two conditions as slow filling and fast filling. When filling is done slowly heat liberated due to adsorption dessipates in the environment, while in case of fast filling , there is very little or no scope of heat dissipation to the environment. As a result, adsorbent bed experiences a substantial rise in temperature. Since, adsorption of natural gas by the adsorbent decreases with increase of temperature, the temperature rise during fast filling causes a lowering of the gas stored by the adsorbent, similarly when the desorption is carried out rapidly, the temperature of the adsorbent bed drops substantially, affecting the discharge of the stored gas. The phase change materials may optionally be introduced in the storage vessel. These phase change materials absorbs the heat liberated during the adsorption cycle by melting and storing the heat at or slightly above the phase change materials melting temperature and then during the desorption cycle releases the stored heat within the phase change material by freezing in the encapsulant and transfer the heat of fusion back to the adsorbent. The Phase change material thus increases the amount of natural gas stored during fast filling and also increases the amount of natural gas to be retrieved from the adsorbent during a rapid discharge cycle. The phase change material may be selected from the group comprising C20 Paraffin, C18 Paraffin, C17 Paraffin, C15 Paraffin, CaCI2.6H2O Storage containers can be filled in a central filling station and distributed therefrom. Thus, the transportation and distribution of natural gas and Hythane by the method of this invention is not dependent upon an extensive pipeline distribution infrastructure. Once a storage container becomes empty, due to, for example, usage of stored natural gas as fuel in kitchen stove, barbeque stove and like, it can be brought back to the filling station, refilled and transported back to the user. In this way the same batch of adsorbent placed in the storage container can be used for storage and distribution of natural gas or Hythane over and over again for years. The subject invention can better be understood with reference to the undermentioned examples, which should not be construed to restrict the scope of the invention. EXAMPLES: EXAMPLE 1 Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 8,000 psi while maintaining the die at ambient temperature. The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature of 600°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 700°C using carbon dioxide as the oxidizing agent. The binding agents used are bentonite clay mixed with sodium silicate. The said carbon-binder mix was prepared by thoroughly blending the fine powder of microporous carbon with the binding agent formulation dispersed in water, and then partially drying the blend (slurry) by evaporation of water under vigorous stirring until the moisture content of the resultant carbon-binder mix corresponded to the 80% by weight based on the weight of dry carbon powder used in the preparation. The binder dispersion was prepared by adding in the binder ingredients 25 mL water per gram of the binding agent and vigorously stirring the binder-water mixture. The clay to carbon ratio in the said carbon binder mix is 0.10g/g, while the ratio of sodium silicate to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.78 g/mL. The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 44.5 grams and having a total geometric volume 56.8 mL was used. The natural gas storage capacity of the adsorbent was found to be 155 litres of natural gas per litre of adsorbent (155 v/v), as shown in Table 1. TABLE 1: (Table Removed) EXAMPLE :2 Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 10,000 psi while maintaining the die at ambient temperature. The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature of 650°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 750°C using water vapour - N2 mixture as oxidising agent. The binding agents used are Bentonite Clay mixed with Calcium Hydroxide. The said Carbon-binder mix was prepared by the process as explained in example 1. The binder dispersion was prepared by adding in the binder ingredients 30 ml water per gram of the binding agent and vigorously stirring the binder-water mixture. The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of calcium hydroxide to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.79 g/mL. The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 36.6 grams and having a total geometric volume 54.9 mL was used. The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 2. TABLE :2 (Table Removed) EXAMPLE : 3 Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 12,000 psi while maintaining the die at ambient temperature. The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature at 660°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 720°C using water vapour - N2 mixture as oxidising agent. The binding agents used are Na-exchanged bentonite clay mixed with calcium hydroxide. The said carbon-binder mix was prepared by the process as explained in example 1. The binder dispersion was prepared by adding the binder ingredients 35 ml_ water per gram of the binding agent and vigorously stirring the binder-water mixture. The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of calcium hydroxide to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.79 g/mL. The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 43.4 grams and having a total geometric volume 54.7 mL was used. The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 3. TABLE :3 (Table Removed) EXAMPLE : 4 Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 11,000 psi while maintaining the die at ambient temperature. The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature of 670°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 735°C using water vapour - N2 mixture as the oxidizing agent. The binding agents used are Al-pillared Bentonite Clay mixed with Sodium Silicate. The binder dispersion was prepared by adding the binder ingredients 40 mL water per gram of the binding agent and vigorously stirring the binder-water mixture. The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of sodium silicate to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.78 g/mL. The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 4. TABLE:4 (Table Removed) EXAMPLE 5 Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 14,000 psi while maintaining the die at ambient temperature. The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature at 665°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 755°C using water vapour - N2 mixture as the oxidizing agent The binding agents used are bentonite clay mixed with sodium silicate. The binder dispersion was prepared by adding the binder ingredients 42 mL water per gram of the binding agent and vigorously stirring the binder-water mixture. The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of sodium silicate to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.89 g/mL. The monoliths were tested for the storage of natural gas under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 36.6 grams and having a total geometric volume 54.9 ml_ was used. The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 5. TABLE 5: (Table Removed) EXAMPLE : 6 Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 16,000 psi while maintaining the die at ambient temperature. The carbon monoliths are prepared from coconut shells as described in the foregoing examples. The binding agents used are bentonite clay mixed with sodium silicate. The binder dispersion was prepared by adding the binder ingredients 50 mL water per gram of the binding agent and vigorously stirring the binder-water mixture. The clay to carbon ratio in the said carbon binder mix is 0.05g/g, while the ratio of Sodium Silicate to carbon ratio in carbon-binder mix is 0.005g/g. The packing density of monolith was found to be 0.87 g/mL. The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 36.6 grams and having a total geometric volume 54.9 ml was used. The natural gas storage capacity of the adsorbent was found to be 154 litres of natural gas per litre of adsorbent (154 v/v), as shown in Table 6. TABLE :6 (Table Removed) In the examples 1-6 , the packing densities of the cylindrical shaped monoliths were ranging from 0.67-0.78, which was determined from their physically measured dimensions and weights. A batch consisting of 5 to 7 monoliths were used in the measurement. The weights were recorded after degassing the monoliths under vacuum at a temperature of 130°C to 150°C. The mechanical strength of the monoliths was tested in an apparatus consisting of a screw-thread type hand press attached to an electronic balance. Monolithic pieces were subjected to a constant compressive pressure of 5 kg/cm2 (applied load divided by cross-sectional area of the monolith) and if found to remain intact it was concluded that the crushing strength of the particular monolith is at least 5 kg/cm2. Packing density of the granular samples was measured by filling a calibrated cylinder with a known sample weight and tapping the cylinder until a constant volume was obtained. The results are reported in Table A. The surface area of granular carbon samples was determined from nitrogen adsorption isotherm measured at liquid nitrogen temperature using BET equation. Packing density of the granular samples was measured by filling a calibrated cylinder with a known sample weight and tapping the cylinder until a constant volume was obtained. The results are reported in TABLE A (Table Removed) The binding and consolidation with the bentonite clay based binding agents result in an increase in the packing density of the microporous carbons prepared by using different oxidizing agents and having different surface areas, thus making these materials suitable for the storage, transportation and distribution of gaseous fuels such as natural gas and Hythane, as illustrated in the Table A. The mechanical strength of the carbon monoliths was found to be greater than 5 kg/cm2 which is adequate for most applications. EXAMPLE :7 The polyvinyl alcohol based binder was also tried to be used in the fabrication of carbon monoliths, where Carbon used was a mixture of two coconut shell carbons (surface area ~ 1100 m2 and ~ 1600 m2/g) in the ratio 80 : 20. The binder was a mixture of 0.06 gram of polyvinyl alcohol (mol. wt. ~ 115,000), 0.004 gram of urea and 0.002 gram of ethylene glycol per gram of carbon. A slurry of carbon and binder ingredients in water was prepared, which was then partially evaporated to obtain a semi-dried mass with a moisture content of 40% by wt. (based on the total wt. of carbon used). Cylindrical shaped carbon monoliths of 20 mm diameter and 15mm thickness were fabricated by pressing the semi-dried mass contained in a cylindrical die by means of a hydraulic press at a pressure of 50,000 psi while slowly heating the die to a temperature of 250°C and holding at that temperature for 1 hour. The average packing density of dried (moisture free) monoliths was 0.84 g/mL The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at ambient temperature (22°C - 25°C). A batch of pellets weighing 44.7 grams and having a total geometric volume of 53.0 mL was used in the test. The natural gas storage capacity of the adsorbent was measured. The natural gas storage capacity of the adsorbent was found to be 155 litres of gas per litre of adsorbent(155v/v), as shown in Table 7. TABLE 7 Natural Gas Storage by Monolithic Microporous Coconut Carbon Monoliths fabricated using Polyvinyl Alcohol based Binder at 500 psig Pressure and Ambient Temperature (Table Removed) EXAMPLE : 8 Microporous carbon particles, prepared from coconut shells by carbonization and partial oxidation with water vapour - N2 mixture and having surface area of about 1240 m2/g, were binded together and consolidated into cylindrical monoliths having 20 mm diameter and 40 mm thickness using a mixture of bentonite clay and sodium silicate as binding agent in the amounts of 0.10 gram of bentonite clay and 0.010 gram of sodium silicate per gram of carbon. The average density of carbon monoliths was 0.79 g/mL. The monoliths were tested for the storage of Hythane fuel (composition : 90 volume percent natural gas and 10 volume percent hydrogen) under a pressure of 550 psig and at ambient temperature 25°C. A batch of monoliths weighing 44.5 grams and having a total geometric volume 56.5 ml was used in the test. The fuel storage capacity of the adsorbent was measured. The Hythane storage capacity of the adsorbent was found to be 154 litres of Hythane per litre of adsorbent (154 v/v), as shown in Table 8. TABLE :8 Hythane Storage by Monolithic Microporous Coconut Carbon at 550 psig Pressure and Ambient Temperature. (Table Removed) Examples 1-6, which deal with the monolithic carbon adsorbent fabricated using clay-based binders according to the method of this invention, clearly illustrate that the concentrated storage of natural gas at low pressures can be achieved by the method and adsorbent materials of this invention, thus avoiding the high pressures needed for storage as compressed gas (CNG) or cryogenic temperatures needed for storage as liquefied natural gas (LNG). Example 7, deals with the monolithic carbon adsorbent monoliths fabricated using PVA-based binder. It is evident from the above mentioned table that PVA-based procedure is not only time-consuming, cumbersome and energy intensive but does not offer any advantages also. The natural gas storage capacity of the adsorbent fabricated using clay-based binders according to this invention, is similar to that of the adsorbent fabricated using PVA-based binder. On the other hand, the clay-based fabrication method has a number of advantages: it is simple and easy-to-practice ; fabrication process does not require costly heating ; and there is no risk of releasing obnoxious gases or vapours. Example 8 illustrates that the method and adsorbent material of this invention is also well suited for low pressure adsorptive storage of Hythane fuel. The natural gas and Hythane stored in portable containers by the method and adsorbent materials of this invention can be safely transported and distributed by conventional transport system. Storage containers can be fuelled in a central filling station. Once the natural gas or Hythane stored in a container is exhausted due to usage as fuel in the desired application, the container can be brought back to the filling station, refilled and transported back to the user. In this way, the same batch of adsorbent can be used for storage and distribution of natural gas or Hythane over and over again for years. While the invention has been described and illustrated herein by references to various specific materials, procedures and examples, it is understood that the invention is not restricted to the particular materials and procedures selected for that purpose. Numerous variations of such details can be employed, as will be appreciated by those skilled in the art without deviating from the scope of the invention. WE CLAIM: 1 A process for storing the fuel gases such as natural gas and its blends in a container at a pressure of 400 psig to 600 psig at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent, comprising: feeding the said fuel gases or its blends from the source of supply to a compressor unit; passing the said compressed fuel gases through a pressure control and metering device to control the pressure of compressed natural gas at desired level; passing the said compressed pressure controlled fuel gases through a purification unit comprising adsorbent material preferably activated carbon prepared from coconut shells acting as guard bed to remove moisture, carbon dioxide and heavier hydrocarbons to get the purified fuel gases, and finally introducing the said purified gases in a storage container containing adsorbent of microporous carbon particles prepared from coconut shells by means of carbonization and partial oxidation to form the monoliths of high packing density in a container. 2 A process as claimed in claim 1, wherein the said adsorbent acting as guard bed in the said purification unit is prepared from the coconut shell by the process comprising - cleaning the coconut shells of loose fibers and traces of kernel, crushing the said cleaned coconut shell to particle size of 8-12mm, washing the said crushed coconut shell with water drying the said washed coconut shell at a temperature of 370-385 K overnight loading the said dried coconut shells in a vessel purged with N2 mounting the said vessel containing said dried coconut shell vertically in a tube furnace and heating the same at a temperature of 870-880K for a period of two to four hours ; cooling the said vessel containing said dried coconut shell at room temperature crushing and screening the said cooled coconut shell to obtain char having mesh size of 10-30 mesh fraction. treating the said crushed char with dilute Nitric acid at room temperature for four to six hours washing the said dilute nitric acid treated char with distilled water till char is free from acid; drying the said washed char at 375-385 K overnight. activation of said acid treated char by partial gasification with CO2 under controlled conditions to obtain activated carbon to be used as guard bed in the purification unit. 3 A process for storing the fuel gases such as natural gas and its blends in a container at a pressure of 400 psig to 600 psig at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent substantially as herein described with reference to accompanying drawings.

Full Text

The present invention relates to a method for the safe storage, off-line transmission and distribution of gaseous fuels such as Natural Gas (NG) and Hythane at low pressure and ambient temperature.
The invention also resides in the process for the preparation of the adsorbents used in the purification unit for the storage of gaseous fuels, acting as guard bed to trap high hydrocarbon components of natural gas.
The embodiment of the invention resides in the thermal energy storage system comprising phase change materials to mitigate heat effects in the adsorption / desorption of natural gas.
The object of the invention is to store the gaseous fuels at low pressures and the transportation and distribution of natural gas and blends of natural gas (particularly, Hythane fuel, which is a mixture in the range of 5 to 20 percent hydrogen and 80 to 95 percent natural gas by volume) for utilization of Natural Gas and /or Hythane as fuel in such applications as barbecue stoves, indoor cooking burners, automobiles and the like.
PRIOR ART
Presently, the use of liquefied petroleum gas (LPG) consisting mainly of propane and butane for the domestic purposes is widespread. Though LPG is convenient to store as it liquefies at moderate pressure and ambient temperature. However, LPG has several drawbacks as of potential fire hazard. This is due to the fact that propane and butane vapours are heavier than air so that when spilled or leaked they will remain close to ground level thus creating a risk of fire or explosion. Moreover, LPG burning causes substantially larger emissions of CO2 on the basis of per unit of energy generated.

The use of Natural gas for such purposes has also been tried because unlike that of LPG, there is an abundant supply of natural gas with world reserves estimated to last more than 100 years. Since natural gas is lighter than air, it is inherently safe because upon accidental leakage it would rapidly disperse. Natural gas also has the advantage of clean-burning characteristics with very low level emissions of toxic and regulated gases such as hydrocarbons, carbon monoxide and nitrogen oxides (NO and NO2). Octane rating of natural gas is about 130, substantially higher than octane rating of propane (105 - 110). The combination of an extensive resource base and environmental advantages makes natural gas a preferred fuel.
Natural gas is the least carbon intensive of the fossil fuels and therefore produces the least amount of Carbon dioxide per unit of energy generated. The natural gas not only results in the reduced Carbon dioxide emission, it's combustion also produces less air pollution than other fossil fuels due to lower level of emissions of NOX, SO2,CO and non-Methane hydrocarbons from natural gas fuelled systems.
For utilization of natural gas as fuel in cooking appliances, and Hythane as fuel in automobiles in places where pipeline transmission and distribution system of these gaseous fuels does not exist, it is required to provide an alternative cost-effective and convenient means of storage, transportation and distribution of these gaseous fuels in these places.
The most commonly perceived way is to store natural gas and its blends under pressures between 3,000 to 5,000 psig. This method of high pressure storage requires use of very heavy and expensive storage cylinders and expensive fuelling equipment. The high pressure gas is also a safety hazard. In the case of an accident, high pressure natural gas and Hythane could explode due to ignition. Therefore, this method of high pressure Natural Gas storage is not acceptable for use in barbecue stoves and indoor burners.

Presently, natural gas is used mainly for fuelling stationery systems such as power plant combustors, industrial boilers, residential and commercial space heaters and domestic appliances. In these applications , natural gas is supplied by gas pipe line technology. Its application in mobile systems is limited since the energy density of stored natural gas is low due to its gaseous nature. For the same reason, it has found little application as a domestic fuel in places where it is not available via pipelines.
Another way of off-line (non-pipeline) transportation of natural gas and its blends is to supply it in liquid form in thermally-insulated tanks. However, this method of natural gas and Hythane storage and distribution is also not a viable option due to the prohibitively high costs involved in liquefaction and refrigeration, and extraordinary safety precautions that must be taken during the transportation and handling of such dangerous cryogenic liquids.
Conventionally, the storage of natural gas is achieved by compression, liquefaction, dissolution, adsorption, clathration and encapsulation.
However, in the storage of natural gas , the compression is the widely used technique. The maximum storage pressure is found to be 20.7 Mpa. At this high pressure at ambient temperatures, the energy of compressed natural gas is only 30% of the energy of an equal volume of petrol. The gas cylinders used are made up of steel or reinforced aluminium. Both, these types of cylinders are however, heavier and more expensive than a petrol tank, moreover, at these high pressures the used cylinders have to be rechecked periodically.
Another method of concentrating natural gas is to liquefy it at a temperature of -164°C. Natural gas is liquefied by a refrigeration cycle and stored in insulated tankers. The natural gas is reduced to about one six-hundredth of its original volume and the non methane components are largely eliminated. This requires, however, that the liquefied natural gas be kept in insulated

containers and stored under refrigeration conditions. This is also not found to be appropriate solution in the circumstances when the storage containers are taken to remote areas. Although liquefied natural gas contains two times more energy per unit volume than compressed natural gas at 2.49mpa, it is not considered to be an economically viable solution due to the higher cost involved in refrigeration and liquefaction compared to its compression. Moreover, the refuelling procedures are more complex and hazardous for liquefied natural gas then for compressed natural gas.
Dissolution of natural gas in a liquid is another option of natural gas storage. The dissolved amount of natural gas is generally low, except when the solvent is ethane or propane. These solvents have, however, high volatiles and as the pressure in the container drops and the natural gas gets depleted, the concentration of ethane or propane increases in the gaseous phase, which modifies the physical characteristics of the fuel mixture. However, this requires more complex and expensive ignition system. The part of solvents are lost and also in case of leak, the higher hydrocarbons tend to settle in low height areas instead of escaping to the atmosphere as is the case with natural gas , thus causing a fire or explosion hazard. Hence, the dissolution of the natural gas in heavier hydrocarbons is also not a viable option.
The other option is to store natural gas by clathration and encapsulation. Clathrates are formed by inclusion of a guest molecule in a cavity made by several host molecules. The components are not held together by primary valence forces, but the guest molecule is necessary for the stability of the host molecules structure. Natural gas hydrates are a kind of clatharate where methane molecules are held in water molecule cages. These natural gas hydrates account for very large natural gas reserves in deep oceans and in the permafrost. The clathration of methane by either water or other compounds has been tried but methane storage is too low to be of any interest.

Further, encapsulation is another method for the storage of natural gas, which is quite similar to clathration, however, the same is also not found suitable as the storage capacity is low, refuelling requires very high pressure and the release mechanism for natural gas is also very complex.
To overcome the drawbacks associated with all the above referenced techniques involved in the storage of natural gas , there is a need to use a high surface area material which can adsorb large quantities of natural gas at moderate pressures, where the natural gas molecules are adsorbed within the pores of a high surface area solid material using an adequate adsorbent. The adsorbents are used for storing such Natural Gas at low pressures.
Such adsorbents and their compaction and binding technique to fabricate carbon monoliths preferebly from coconut shells have been described in detail in the co-pending Indian Patent Application
The invention relates to a method for loading adsorbent material into a suitable storage container for adsorbing the fuel gas onto it at a pressure of 400 to 600 psig and at ambient temperature (5-50°C), which results in storage of the fuel of about 150 litres of gas per litre of adsorbent.
The storage of this amount of natural gas in the same container without adsorbent is only possible at a very high pressure of about 2000 psi, which is unsafe and expensive for many applications. The adsorbent used are carbon monoliths of high packing density fabricated by binding and compacting microporous carbon particles, prepared from coconut shells, using an inorganic clay material as binder. Natural gas or Hythane so stored in a suitable container can be transported and distributed by conventional or specially made carriers to any place, thus avoiding the need for pipeline system of distribution.

The present invention can better be understood with reference to the accompanying drawings, which are for illustrative purposes and should not in any way be construed to restrict the scope of the invention keeping in view that certain modifications and improvements are possible without deviating from the scope of the invention.
STATEMENT OF THE INVENTION
According to the present invention there is provided a process for storing the fuel gases such as natural gas and its blends in a container at a pressure of 400 psig to 600 pisg at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent where the said adsorbent is monolithic microporous carbon adsorbent of high packing density comprising:
fabricating said adsorbent from granular microporous coconut shell carbon using a binding agent comprising of mixture of a clay and sodium silicate or mixture of a clay and calcium hydroxide or a clay material alone wherein the clay component is chosen from the group comprising of cationic clays and pillared analogues of cationic clays;
fabricating a purification unit comprising a filter material acting as a guard bed to remove moisture, carbon dioxide and heavier hydrocarbons to get the purified fuel gases;
feeding the said fuel gases or its blends from the natural gas supply line to a compressor unit;
passing the said compressed fuel gases through a pressure control and a metering device to control the pressure of compressed natural gas at desired level;
passing the said compressed fuel gases through the purification unit; and
finally, introducing the said purified gases in a storage container containing the fabricated monolithic adsorbent.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 depicts the block flow diagram showing various unit operations involved in the preparation of high density monolithic microporous carbon adsorbent from coconut shells for use in the safe storage, off-line transportation and distribution of natural gas and Hythane fuels.
Figure 2 depicts the block diagram illustrating a process of storing of natural gas and Hythane with monolithic carbon adsorbent.
DETAILED DESCRIPTION OF THE INVENTION
As illustrated in Figure 1, microporous carbon for binding and consolidation in accordance with the method disclosed in the copending Indian Patent
application No. is prepared from coconut shells by the two-stage
process of carbonization and controlled partial oxidation. The raw coconut shells were crushed to particle size of about 5-10 mm, washed with water and dried at a temperature of about 110°C and then subjected to carbonization by heating to a temperature of about 600°C to about 700°C in an inert atmosphere. The char so produced was crushed, screened to 8-30 mesh size and then submitted to controlled partial oxidation with oxidising agents such as carbon dioxide and water vapour/nitrogen mixture at a temperature of about 700°C to about 850°C. The resultant product was a granular microporous carbon having a surface area in the range 1200 - 1800 m2/g. The source of microporous carbon suited for the storage of natural gas and
Hythane is coconut shells. However, Microporous carbons derived from other sources such as coal, coal coke, petroleum coke, wood and rice husks can also be used for safe storage, transportation and distribution of natural gas and Hythane.
The method comprises :
(a) crushing and milling the granular carbon into a fine powder by
conventional means preferably in a ball mill;
(b) preparing an aqueous dispersion of the binder formulation by adding
the ingredients of the formulation to water (25 mL to 50 mL water per gram of
binder) and thoroughly agitating the mix;
(c) mixing dry or pre-wetted carbon powder of step (a) with the water
dispersion of the binder of step (b) in appropriate proportions to make a slurry
of carbon and binding agent;
(d) drying the carbon-binding agent slurry of step (c) to a desired moisture
content ranging from 80% to 100% by weight based on the weight of carbon
used in step (c), by evaporating water while stirring in any conventional
blending-drying equipment;
(e) consolidating carbon-binder mix of step (d) either by compression, at
ambient temperature, inside a suitable die under a pressure of 8,000 to
16,000 psi using a suitable pelleting press or by extrusion process using a
suitable extruder to provide high density, mechanically strong monoliths of
desired shapes and sizes; and
(f) subjecting the said monoliths to drying in steps at a temperature of
60°C to 70°C and at temperature of 120°C to 140°C in air atmosphere to
provide dried monoliths free of moisture.
The said binding agent is a clay material used alone or as a mixture with sodium silicate or calcium hydroxide, wherein the clay component is chosen from a group of cationic clays which are hydrous layer silicates of the so-called phyllosilicate family consisting of such groups as smectite, vermiculite,
serpentine-kaolin, talc-pyrophylite, mica, brittle mica, chlorite and sepiolite-palygorskite, typical examples being bentonite, atapulgite, hectorite, beidellite, fuller's earth, halloysite, illite kaolin, montmorillonite and mullite or from a group consisting of pillared analogues of cationic clays which are materials in which small cations of cationic clay are replaced by large polyoxocationic species. The most preferred clays for use in the binding agent formulation include bentonite clay, sodium exchanged bentonite clay, pillared analogues of bentonite clay (such as AI-, Fe-, Cr-, Zr- or Ti- pillared bentonite clay) and combinations thereof. In the said binding agent formulation, the clay content is 5% to 15% by weight, sodium silicate content is 0.5% to 1.5% by weight, and calcium hydroxide content is 0.5% to 1.5% by weight, all based on the weight of carbon used in step (c).
In step (d), the moisture content of the carbon-binder paste is controlled in the range from 80% to 100% by weight based on the weight of carbon used in the preparation.
The packing density of the monoliths so prepared is nearly twice as much as that of the starting granular material. The binding agents used in this invention are thermally and chemically stable substances which at no stages of monolith fabrication process release obnoxious gases or vapours of any kind and therefore there is no cause for concern from the viewpoint of environmental pollution or occupational health and safety hazard. Unlike prior art, the method of this invention does not require heating of carbon-binder mix during step (e) of the above-described embodiment, thereby providing substantial processing cost savings. Furthermore, since the method does not involve heating and cooling of the material during step (e) of the above-described embodiment, the said carbon-binder mix or paste can be processed to form monoliths in less than 15 minutes, thereby shortening the processing time.
Moreover, the subject process does not suffer from any drawback associated with the problem of pore plugging with binder because major ingredient of binder formulation (that is the clay component) is applied as a dispersion in water rather then as a solution wherein size of the clay particulates are too large to penetrate into and occupy the micropores of carbon particles. The method of binding and compaction of microporous carbon powder thus overcomes the difficulties associated with the prior art of pelletization or briquetting of activated carbon powders for use in the storage of natural gas.
The process for the storage of natural gas comprises packing the carbon monoliths prepared from coconut shell by the steps of carbonization and partial oxidation with steam or CO2 activation binded together and consolidated into monoliths of high packing density in a storage container (10) of cylindrical or cuboidal geometry. The natural gas or its blends from the source (1) is fed via compressor (2) passes to flow control and metering device (4), via line (3), which is connected to pressure control and metering device (6) through pipe (5), which in turn is connected through a pipe (7) to a purification unit as guard bed (8) packed with suitable solid adsorbent material, preferably activated carbon, carbon molecular sieve, zeolites or a combination thereof, which removes moisture, carbon dioxide and heavier hydrocarbons (C4 and above) constituents present in small amounts in natural gas and Hythane. The exit stream from the purification unit (8) is then introduced via pipe line (9) into the adsorbent packed storage container (10) allowing adsorptive storage of Natural Gas or Hythane fuel under a pressure of 400 psig to 600 psig .
The present monolithic adsorbent produced from coconut shell microporous carbons by binding and compaction using the binding agents and method disclosed as above when packed in a container show high reversible uptakes of natural gas and Hythane on a volumetric basis, thus providing an efficient means of storage of natural gas and its blends. The method does not require expensive and heavy storage vessels, saves compression costs of high
pressure (3000 -5000 psig) storage, and offers safety because container pressure is limited to between 400 psig and 600 psig.
The adsorbent used in the guard bed are prepared from the coconut shell having a packing density of 0.5g/cm2 and a surface area of about 1200 m2/g.
The process for the preparation of activated carbon from coconut shells for use as guard bed is a two stage process ; comprises:
1 pyrolysis/carbonization of dried coconut shell at 873 K under an inert
atmosphere.
2 Activation of coconut char by partial gasification/controlled oxidation
with CO2 at 1073K.
The coconut shells were cleaned of loose fibers and traces of kernel, crushed to particle size of about 10mm, washed with water and dried at 383K overnight.
In a vessel, crushed and dried coconut shells are loaded , which is purged with N2. The vessel is mounted vertically in a tube furnace and heated at a temperature of 873K for a period of two to four hours and then allowed to cool at room temperature. The char so produced is crushed and screened to 10-30 mesh fraction.
The char so produced is treated with dilute Nitric acid at room temperature for four to six hours. The dilute nitric acid treated char is then washed with distilled water till char is free from acid. The washed char is then dried at 383 K overnight.
The acid treated char is activated by partial gasification with CO2 under well defined conditions. The activated carbon so obtained thus used as guard bed in the purification unit.
The natural gas storage vessel can be filled with the natural gas under two conditions as slow filling and fast filling. When filling is done slowly heat liberated due to adsorption dessipates in the environment, while in case of fast filling , there is very little or no scope of heat dissipation to the environment. As a result, adsorbent bed experiences a substantial rise in temperature. Since, adsorption of natural gas by the adsorbent decreases with increase of temperature, the temperature rise during fast filling causes a lowering of the gas stored by the adsorbent, similarly when the desorption is carried out rapidly, the temperature of the adsorbent bed drops substantially, affecting the discharge of the stored gas.
The phase change materials may optionally be introduced in the storage vessel. These phase change materials absorbs the heat liberated during the adsorption cycle by melting and storing the heat at or slightly above the phase change materials melting temperature and then during the desorption cycle releases the stored heat within the phase change material by freezing in the encapsulant and transfer the heat of fusion back to the adsorbent. The Phase change material thus increases the amount of natural gas stored during fast filling and also increases the amount of natural gas to be retrieved from the adsorbent during a rapid discharge cycle. The phase change material may be selected from the group comprising C20 Paraffin, C18 Paraffin, C17 Paraffin, C15 Paraffin, CaCI2.6H2O
Storage containers can be filled in a central filling station and distributed therefrom. Thus, the transportation and distribution of natural gas and Hythane by the method of this invention is not dependent upon an extensive pipeline distribution infrastructure. Once a storage container becomes empty, due to, for example, usage of stored natural gas as fuel in kitchen stove, barbeque stove and like, it can be brought back to the filling station, refilled and transported back to the user. In this way the same batch of adsorbent placed in the storage container can be used for storage and distribution of natural gas or Hythane over and over again for years.
The subject invention can better be understood with reference to the undermentioned examples, which should not be construed to restrict the scope of the invention.
EXAMPLES:
EXAMPLE 1
Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 8,000 psi while maintaining the die at ambient temperature.
The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature of 600°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 700°C using carbon dioxide as the oxidizing agent.
The binding agents used are bentonite clay mixed with sodium silicate. The said carbon-binder mix was prepared by thoroughly blending the fine powder of microporous carbon with the binding agent formulation dispersed in water, and then partially drying the blend (slurry) by evaporation of water under vigorous stirring until the moisture content of the resultant carbon-binder mix corresponded to the 80% by weight based on the weight of dry carbon powder used in the preparation.
The binder dispersion was prepared by adding in the binder ingredients 25 mL water per gram of the binding agent and vigorously stirring the binder-water mixture.
The clay to carbon ratio in the said carbon binder mix is 0.10g/g, while the ratio of sodium silicate to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.78 g/mL.
The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 44.5 grams and having a total geometric volume 56.8 mL was used.
The natural gas storage capacity of the adsorbent was found to be 155 litres of natural gas per litre of adsorbent (155 v/v), as shown in Table 1.
TABLE 1:

(Table Removed)
EXAMPLE :2
Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 10,000 psi while maintaining the die at ambient temperature.
The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature of 650°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 750°C using water vapour - N2 mixture as oxidising agent.
The binding agents used are Bentonite Clay mixed with Calcium Hydroxide. The said Carbon-binder mix was prepared by the process as explained in example 1.
The binder dispersion was prepared by adding in the binder ingredients 30 ml water per gram of the binding agent and vigorously stirring the binder-water mixture.
The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of calcium hydroxide to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.79 g/mL.
The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 36.6 grams and having a total geometric volume 54.9 mL was used.
The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 2.
TABLE :2

(Table Removed)
EXAMPLE : 3
Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 12,000 psi while maintaining the die at ambient temperature.
The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature at 660°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 720°C using water vapour - N2 mixture as oxidising agent.
The binding agents used are Na-exchanged bentonite clay mixed with calcium hydroxide. The said carbon-binder mix was prepared by the process as explained in example 1.
The binder dispersion was prepared by adding the binder ingredients 35 ml_ water per gram of the binding agent and vigorously stirring the binder-water mixture.
The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of calcium hydroxide to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.79 g/mL.
The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 43.4 grams and having a total geometric volume 54.7 mL was used.
The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 3.
TABLE :3

(Table Removed)
EXAMPLE : 4
Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 11,000 psi while maintaining the die at ambient temperature.
The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature of 670°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 735°C using water vapour - N2 mixture as the oxidizing agent.
The binding agents used are Al-pillared Bentonite Clay mixed with Sodium Silicate.
The binder dispersion was prepared by adding the binder ingredients 40 mL water per gram of the binding agent and vigorously stirring the binder-water mixture.
The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of sodium silicate to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.78 g/mL.
The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 4.
TABLE:4

(Table Removed)
EXAMPLE 5
Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 14,000 psi while maintaining the die at ambient temperature.
The carbon monoliths are prepared from coconut shells by first carbonizing the coconut shells by heating to a temperature at 665°C under inert atmosphere and then subjecting the char so produced to controlled partial oxidation at 755°C using water vapour - N2 mixture as the oxidizing agent
The binding agents used are bentonite clay mixed with sodium silicate.
The binder dispersion was prepared by adding the binder ingredients 42 mL water per gram of the binding agent and vigorously stirring the binder-water mixture.
The clay to carbon ratio in the said carbon mix binder is 0.10g/g, while the ratio of sodium silicate to carbon ratio in carbon-binder mix is 0.010g/g. The packing density of monolith was found to be 0.89 g/mL.
The monoliths were tested for the storage of natural gas under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 36.6 grams and having a total geometric volume 54.9 ml_ was used.
The natural gas storage capacity of the adsorbent was found to be 156 litres of natural gas per litre of adsorbent (156 v/v), as shown in Table 5.
TABLE 5:

(Table Removed)
EXAMPLE : 6
Cylindrical shaped microporous carbon monoliths were fabricated by pressing carbon-binder mix contained in a cylindrical die by means of a hydraulic press at pressures of 16,000 psi while maintaining the die at ambient temperature.
The carbon monoliths are prepared from coconut shells as described in the foregoing examples.
The binding agents used are bentonite clay mixed with sodium silicate.
The binder dispersion was prepared by adding the binder ingredients 50 mL water per gram of the binding agent and vigorously stirring the binder-water mixture.
The clay to carbon ratio in the said carbon binder mix is 0.05g/g, while the ratio of Sodium Silicate to carbon ratio in carbon-binder mix is 0.005g/g. The packing density of monolith was found to be 0.87 g/mL.
The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at temperature of 22 °C. A batch of monoliths weighing 36.6 grams and having a total geometric volume 54.9 ml was used.
The natural gas storage capacity of the adsorbent was found to be 154 litres of natural gas per litre of adsorbent (154 v/v), as shown in Table 6.
TABLE :6

(Table Removed)
In the examples 1-6 , the packing densities of the cylindrical shaped monoliths were ranging from 0.67-0.78, which was determined from their physically measured dimensions and weights. A batch consisting of 5 to 7 monoliths were used in the measurement. The weights were recorded after degassing the monoliths under vacuum at a temperature of 130°C to 150°C. The mechanical strength of the monoliths was tested in an apparatus consisting of a screw-thread type hand press attached to an electronic balance. Monolithic pieces were subjected to a constant compressive
pressure of 5 kg/cm2 (applied load divided by cross-sectional area of the monolith) and if found to remain intact it was concluded that the crushing strength of the particular monolith is at least 5 kg/cm2. Packing density of the granular samples was measured by filling a calibrated cylinder with a known sample weight and tapping the cylinder until a constant volume was obtained. The results are reported in Table A. The surface area of granular carbon samples was determined from nitrogen adsorption isotherm measured at liquid nitrogen temperature using BET equation. Packing density of the granular samples was measured by filling a calibrated cylinder with a known sample weight and tapping the cylinder until a constant volume was obtained. The results are reported in TABLE A

(Table Removed)
The binding and consolidation with the bentonite clay based binding agents result in an increase in the packing density of the microporous carbons prepared by using different oxidizing agents and having different surface areas, thus making these materials suitable for the storage, transportation and distribution of gaseous fuels such as natural gas and Hythane, as illustrated in the Table A. The mechanical strength of the carbon monoliths was found to be greater than 5 kg/cm2 which is adequate for most applications.
EXAMPLE :7
The polyvinyl alcohol based binder was also tried to be used in the fabrication of carbon monoliths, where Carbon used was a mixture of two coconut shell carbons (surface area ~ 1100 m2 and ~ 1600 m2/g) in the ratio 80 : 20. The binder was a mixture of 0.06 gram of polyvinyl alcohol (mol. wt. ~ 115,000), 0.004 gram of urea and 0.002 gram of ethylene glycol per gram of carbon. A slurry of carbon and binder ingredients in water was prepared, which was
then partially evaporated to obtain a semi-dried mass with a moisture content of 40% by wt. (based on the total wt. of carbon used). Cylindrical shaped carbon monoliths of 20 mm diameter and 15mm thickness were fabricated by pressing the semi-dried mass contained in a cylindrical die by means of a hydraulic press at a pressure of 50,000 psi while slowly heating the die to a temperature of 250°C and holding at that temperature for 1 hour. The average packing density of dried (moisture free) monoliths was 0.84 g/mL
The monoliths were tested for the storage of natural gas fuel under a pressure of 500 psig and at ambient temperature (22°C - 25°C). A batch of pellets weighing 44.7 grams and having a total geometric volume of 53.0 mL was used in the test. The natural gas storage capacity of the adsorbent was measured.
The natural gas storage capacity of the adsorbent was found to be 155 litres of gas per litre of adsorbent(155v/v), as shown in Table 7.
TABLE 7
Natural Gas Storage by Monolithic Microporous Coconut Carbon Monoliths fabricated using Polyvinyl Alcohol based Binder at 500 psig Pressure and Ambient Temperature

(Table Removed)
EXAMPLE : 8
Microporous carbon particles, prepared from coconut shells by carbonization and partial oxidation with water vapour - N2 mixture and having surface area of about 1240 m2/g, were binded together and consolidated into cylindrical monoliths having 20 mm diameter and 40 mm thickness using a mixture of bentonite clay and sodium silicate as binding agent in the amounts of 0.10 gram of bentonite clay and 0.010 gram of sodium silicate per gram of carbon. The average density of carbon monoliths was 0.79 g/mL.
The monoliths were tested for the storage of Hythane fuel (composition : 90 volume percent natural gas and 10 volume percent hydrogen) under a pressure of 550 psig and at ambient temperature 25°C. A batch of monoliths weighing 44.5 grams and having a total geometric volume 56.5 ml was used in the test. The fuel storage capacity of the adsorbent was measured.
The Hythane storage capacity of the adsorbent was found to be 154 litres of Hythane per litre of adsorbent (154 v/v), as shown in Table 8.
TABLE :8
Hythane Storage by Monolithic Microporous Coconut Carbon at 550 psig Pressure and Ambient Temperature.
(Table Removed)
Examples 1-6, which deal with the monolithic carbon adsorbent fabricated using clay-based binders according to the method of this invention, clearly illustrate that the concentrated storage of natural gas at low pressures can be achieved by the method and adsorbent materials of this invention, thus avoiding the high pressures needed for storage as compressed gas (CNG) or cryogenic temperatures needed for storage as liquefied natural gas (LNG).
Example 7, deals with the monolithic carbon adsorbent monoliths fabricated using PVA-based binder. It is evident from the above mentioned table that PVA-based procedure is not only time-consuming, cumbersome and energy intensive but does not offer any advantages also. The natural gas storage capacity of the adsorbent fabricated using clay-based binders according to
this invention, is similar to that of the adsorbent fabricated using PVA-based binder. On the other hand, the clay-based fabrication method has a number of advantages: it is simple and easy-to-practice ; fabrication process does not require costly heating ; and there is no risk of releasing obnoxious gases or vapours. Example 8 illustrates that the method and adsorbent material of this invention is also well suited for low pressure adsorptive storage of Hythane fuel.
The natural gas and Hythane stored in portable containers by the method and adsorbent materials of this invention can be safely transported and distributed by conventional transport system. Storage containers can be fuelled in a central filling station. Once the natural gas or Hythane stored in a container is exhausted due to usage as fuel in the desired application, the container can be brought back to the filling station, refilled and transported back to the user. In this way, the same batch of adsorbent can be used for storage and distribution of natural gas or Hythane over and over again for years.
While the invention has been described and illustrated herein by references to various specific materials, procedures and examples, it is understood that the invention is not restricted to the particular materials and procedures selected for that purpose. Numerous variations of such details can be employed, as will be appreciated by those skilled in the art without deviating from the scope of the invention.

WE CLAIM:
1 A process for storing the fuel gases such as natural gas and its blends
in a container at a pressure of 400 psig to 600 psig at ambient temperature
resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent,
comprising:
feeding the said fuel gases or its blends from the source of supply to a compressor unit;
passing the said compressed fuel gases through a pressure control and metering device to control the pressure of compressed natural gas at desired level;
passing the said compressed pressure controlled fuel gases through a purification unit comprising adsorbent material preferably activated carbon prepared from coconut shells acting as guard bed to remove moisture, carbon dioxide and heavier hydrocarbons to get the purified fuel gases, and
finally introducing the said purified gases in a storage container containing adsorbent of microporous carbon particles prepared from coconut shells by means of carbonization and partial oxidation to form the monoliths of high packing density in a container.
2 A process as claimed in claim 1, wherein the said adsorbent acting as
guard bed in the said purification unit is prepared from the coconut shell by
the process comprising -
cleaning the coconut shells of loose fibers and traces of kernel, crushing the said cleaned coconut shell to particle size of 8-12mm, washing the said crushed coconut shell with water drying the said washed coconut shell at a temperature of 370-385 K
overnight
loading the said dried coconut shells in a vessel purged with N2 mounting the said vessel containing said dried coconut shell vertically
in a tube furnace and heating the same at a temperature of 870-880K for a
period of two to four hours ;
cooling the said vessel containing said dried coconut shell at room temperature
crushing and screening the said cooled coconut shell to obtain char having mesh size of 10-30 mesh fraction.
treating the said crushed char with dilute Nitric acid at room temperature for four to six hours
washing the said dilute nitric acid treated char with distilled water till char is free from acid;
drying the said washed char at 375-385 K overnight.
activation of said acid treated char by partial gasification with CO2 under controlled conditions to obtain activated carbon to be used as guard bed in the purification unit.
3 A process for storing the fuel gases such as natural gas and its blends in a container at a pressure of 400 psig to 600 psig at ambient temperature resulting in the storage of 130 litres to 160 litres of fuel per litre of adsorbent substantially as herein described with reference to accompanying drawings.

Documents:

558-del-2000-abstract.pdf

558-del-2000-claims.pdf

558-del-2000-correspondence-others.pdf

558-del-2000-correspondence-po.pdf

558-del-2000-description (complete).pdf

558-del-2000-drawings.pdf

558-del-2000-form-1.pdf

558-del-2000-form-13.pdf

558-del-2000-form-19.pdf

558-del-2000-form-2.pdf

558-del-2000-form-26.pdf

558-del-2000-form-3.pdf

558-del-2000-petition-137.pdf

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Patent Number

226283

Indian Patent Application Number

558/DEL/2000

PG Journal Number

01/2009

Publication Date

02-Jan-2009

Grant Date

16-Dec-2008

Date of Filing

06-Jun-2000

Name of Patentee

CHEMISAR LABORATORIES INC.

Applicant Address

248, SILVERCREEK PARKWAY N., GUEIPH, ONTARIO, CANADA N1H 1E7.

Inventors:

#	Inventor's Name	Inventor's Address
1	ASHUTOSH RASTOGI	GAS AUTHORITY OF INDIA LIMITED 16,BHIKAJI CAME PLACE, R.K.PURAM, NEW DELHI - 110 066, INDIA.
2	PARIVESH CHUGH	GAS AUTHORITY OF INDIA LIMITED 16,BHIKAJI CAME PLACE, R.K.PURAM, NEW DELHI - 110 066, INDIA.
3	SHAMSUDDIN AHMED	247 COLE ROAD, GURLPH, ONTARIO, CANADA, N1G.
4	RAJ NARAIN PANDEY	34 OLD COLONY TRAIL, GUE1PH, ONTARIO, CANADA,N1G 4A9,
5	RUPESH NARAIN PANDEY	34 OLD COLONY TRAIL, GUE1PH, ONTARIO, CANADA, NIG 4A9.

PCT International Classification Number

F17C 5/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA