Title of Invention

AN IMPROVED PROCESSS FOR THE PREPARATION OF METHANOL

Abstract The present invention relates to an improved process for the preparation of methanol by the oxidation of methane, using an oxidant and a solid organotransition metal complex as a catalyst.
Full Text This invention relates to an improved process for the preparation of methanol. More particularly the present invention relates to an improved process for the preparation of methanol by the oxidation of methane, using an oxidant and a solid organotransition metal complex as a catalyst.
Methane conversions are particular interest due to large reserves of natural gas located in remote areas, far from their main centers of consumption. It is expensive to transport the gas to the latter location. It is preferable to convert it into liquids like methanol before transport. Large quantities of methane are also available from the decomposition of biomass, municipal waste, rice fields etc. Methane is one of the major greenhouse gases considered to be the primary cause of global warming. Hence, technologies for the effective conversion of methane to value added fuels or chemicals like methanol are desirable. The direct selective oxidation of methane to methanol is difficult to achieve.
Current technology for methane conversion to methanol is based on steam reforming or partial oxidation to syngas ( CO+H2) followed by methanol synthesis. Considerable research is underway in an attempt to convert methane to methanol directly and bypass the costly reforming step Although well integrated processes have been developed for conventional technology through syngas, there is no escaping the fact that it is first necessary to conduct an energy intensive endothermic steam reforming step
followed by a subsequent catalytic conversion step which has equilibrium limitations. If one could directly convert methane in a single exothermic oxidation step in high yield, this would be more attractive than current trends. One would in effect supplant a two step route having a costly endothermic first step with a direct one-step route which is highly exothermic and cogenerate energy.
Direct non-catalytic methane oxidation gives low yields of methanol. Calculations from gas phase kinetic studies also indicate that obtaining methanol in higher than 5% yield from gas phase radical processes is unlikely. Laboratory studies fall for short of even this limited result. Catalysts have been developed which initiate the formation of radicals which are largely expelled into the gas phase. Under some conditions, methanol yields approaching 5% methanol {70% selectivity at 7% conversion) have been observed but these are far short of commercial viability under most future scenarios. Catalytic oxidation at low temperatures (to avoid CO2 formation) is the only alternative for efficient methane conversion to methanol.
Methane is oxidised to methanol at ambient conditions by certain enzymatic catalyst systems. Certain bacteria have been found which rely exclusively on methane as their source of life-sustaining carbon compounds and energy. The first and most difficult step in the processing of methane by these methane-trophic bacteria is its conversion into methyl alcohol. This
conversion is catalysed by a family of enzymes, the methane monooxygenases . These enzymes use O2, as their oxygen source. Moreover, although methane is the only hydrocarbon known to sustain growth of the bacteria, methane monooxygenases are able to catalyse the oxidation of other hydrocarbons like ethane, propane and butane. Oxidation is accomplished by forming an activated oxygen : enzyme : substrate complex charged with two electrons acquired from a suitable donor such as NADH. The enzymatic systems, however, have practical limitations for industrial use because of the need for low concentrations of substrate, stoichiometric coreductants, narrow windows of temperature and pH etc. Synthetic biomimetic catalysts, dubbed chemzymes can mimic enzymatic catalysis but suffer from similar drawbacks. Recent studies (P.E Ellis and J.E. Lyons; J. Chem. Soc. Chem. Commun. 1989, page 1315) with higher hydrocarbons indicate that it may be possible to mimic some of the characteristics of the biological systems while catalyzing alkane oxidations using only oxygen and no coreductant with catalysts which are robust enough to survive industrial process conditions.
U. S Patent 5,345,011 claims the use of aluminophosphates containing manganese in the structural framework as catalysts for the oxidation of methane to methanol in the vapor phase. However, methane conversion was low, being below 5 %. The selectivity for methanol was in the range 3 0-50 % mole. The use of ruthenium metal complex catalyst containing an end or bridged oxo group with a ligand L and a carboxylato group for the oxidation of
methane to methanol was also claimed in U.S Patent 5,347,057. The catalyst turnover rate for the oxidation reaction, however, was relatively low. In this system, the ligands and the ruthenium metal component are costly components and the recyclability of teh catalysts remains questionable. The gas phase oxidation of natural gas to methanol by molecular oxygen has also been disclosed in U.S Patent 4,618,732. A 13 % conversion of natural gas (composition not mentioned) was claimed at 300-500 °C and 10-100 atmospheres. U.S. Patents 4,918,249 and 5,132,472 used silico-metallates as catalysts for the gas phase oxidation of methane to methanol and CO2 was reported. In all the gas phase oxidations of methane at temperatures above 100 °C, referred to in the above patents, significant amounts of CO2 in excess of 10 % are produced and the selectivity to methanol was low. In addition, large amounts of formaldehyde were also produced.
It is thus evident that there is a need for the development of a process for the low temperature oxidation of methane to methanol in significant yields (at least 10% wt, for example) and using solid, recyclable catalysts and operating at a low enough temperature (below 100 °C, for example) to avoid the production of undesirable byproducts like carbon dioxide.
It is, therefore, an object of the present invention to provide a process for the low temperature oxidation of methane to methanol using a catalyst which would remain in the solid state at the end of the oxidation reaction thereby facilitating the
easy separation, recovery and recycle of the catalyst from the reaction products without having any adverse impact on the environment. Another object of the present invention is to provide an improved process whereby the yield of methanol would be higher than in the prior art processes. Yet another objective of the present invention is to provide an improved process for the oxidation of methane at a temperature below that wherein the production of CO2 is significant.
Phthalocyanines consist of large, planar, conjugated, ring systems which serve as tetradentate ligands. Metalic cations can be easily accommodated at the center of these systems with the four nitrogens as the ligating atoms. Metal containing phthalo-cyanine compounds are known to be useful as chemical reagents of a catalytic nature, more particularly in directing certain oxidative processes. Many known phthalocyanines have been judged to suffer certain drawbacks by being deficient in the combination of properties desired for many candidate uses, such as in the oxidation of alkanes and more particularly in the oxidation of methane. One major drawback of homogeneous phthalocyanine catalysts in industrial oxidation processes is the formation of aggregates in solution which significantly deactivates these catalysts.
Due to our continued research in this area we observed that the organotransition metal complexes used as catalysts are solids insoluble in methane or the reaction products arising from oxidation of methane. Hence they do not undergo aggregation or change
of phase during the oxidation wherein such changes are known to lead to catalyst deactivation problems.
Another drawback of phthalocyanines used in the prior art as catalysts for alkane oxidation is their low oxidative stability which is due to the easy oxidisability of the hydrogen atoms attached to the nucleus of the phthalocyanines.
We have found that the oxidative stability as well as the catalytic activity of the metal phthalocyanines used as catalysts in the oxidation of methane are enhanced by replacing the hydrogens from the pthalocyanines by electron withdrawing groups like the halogens, nitro or cyano groups thereby rendering the metal ions easier to reduce leading to an improved oxidation activity and stability of the catalysts during the reaction.
There are a total of 16 hydrogen atom positions on such phthalocyanine molecules which can in principle, be substituted by other substituents. We have observed that when some or all of the hydrogen atoms of the said phthalocyanines are substituted by one or more electron withdrawing groups such as halogen, nitro or cyano groups or mixtures of such groups there is substantial improvement in selectivity and conversion to methanol.
Accordingly the present invention provides an improved process for the preparation
of methanol which comprises reacting methane with an oxidant such as herein
described, in the presence of a solid catalyst consisting of an organotransition metal
complex wherein some or all of the hydrogen atoms of the said organotransition
metal complex have been substituted by one or more electron withdrawing groups,
and encapsulated with an solid matrix containing an inorganic oxide and an organic
oxide, at a temperature below 100°C , at a pressure in the range of 5 to 1000 psi, in
the presence of solvents and a promoter such as herein described and isolating the
methanol formed by conventional methods.
In an embodiment of the present invention the organotransition metal complex may
be selected from phthalocyanines.
In another embodiment of the present invention the transition metal may be
selected from iron, copper or mixtures thereof.
Some non limiting examples of such organo transition metal complex used as
catalysts in the oxidation of methane to methanol are iron halopthalocyanines,
copper, halo pthalocyanines, iron nitro pthalocyanines, copper nitro pthalocyanines,
copper cyano pthalocyanines and iron cyano pthalocyanines.
In yet another embodiment of present invention the electron withdrawing groups
attached to the organotransition metal complex is selected from the halogens like
fluorine, chlorine, bromine or iodine or the nitro or cyano groups.
In a preferred embodiment of the present invention, the oxidation of methane by molecular oxygen may be catalysed by the halogen, cyano or nitro pthalocyanines of the metals iron or copper.
In yet another embodiment of the present invention, the oxidant can be molecular oxygen, alkyl hydroperoxides, dialkyi hydroperoxides, or mixtures thereof.
In yet another embodiment of the present invention, the source of molecular oxygen can be pure oxygen gas, air or a mixture of oxygen and an inert gas diluent like nitrogen.
In yet another embodiment of the present invention, the above mentioned oxidation reaction can be carried out in the presence or absence of solvents. It may be an advantageous option to carry out the said oxidation reaction in the presence of a suitable solvent which would maintain the oxidation products like methanol in the dissolved state during the course of the reaction, thereby facilitating the separation of the said methanol from the solid catalysts. Suitable solvents for such use include acetonitrile, benzonitrile and pyridine. Examples of such solvents which can be used in the process of the present invention include acetonitrile, acetone, benzene or any other organic solvent which is inert under the oxidation reaction conditions .
In one advantageous embodiment of the present invention, the rates of the oxidation of methane to methanol may be significantly enhanced by addition of very small catalytic quantities of a promoter. Examples of such promoters include alkyl hydroperoxide, dialkylperoxides and such compounds. Cyclohexyl hydroperoxide, cumyl peroxide, tertiary butyl hydroperoxide are some of the examples of such promoters which may be present in concentrations not exceeding 1% by weight of methane and more preferably 0.1% by weight of methane.
In yet another advantageous embodiment of the present invention, the organotransition metal complex may be encapsulated in a solid matrix. Due to the greater dispersion of the organotransition metal complex catalyst in solid matrices and the consequent enhanced stability of the structural integrity of the catalyst significant process advantages like greater activity, stability and easy recovery and recyclability of the catalyst are observed. Examples of such solid matrices include inorganic oxide like silica, alumina, molecular sieves, zeolites and the like as well as organic polymeric material.
It is an advantageous feature of the process of the present invention that due to the high activity the catalysts used herein, the oxidation reaction can be carried out at temperatures much below those used in the prior art and preferably below 100°C, thereby leading to much lower yields of undesired side
products like CO2.
The details of the present invention is described in the examples given below which are provided by way of illustration only and therefore should not be construed to limit the scope of the invention.
Example-1
In an autoclave, 50 psi methane, 0.25 g of tertiary butyl
hydroperoxide, 100 ml of acetonitrile and 0.3 g of solid iron
hexa deca chloro phthalocyanine were stirred at 30°C with a
continuous bubbling of air for 8 hrs. At the end of the
reaction, the gas was collected and analysed for unreacted
methane and formaldehyde using a Hewlett Packard 5880 Gas
Chromatograph equipped with a FID detector and a capillary column
(50 m x 0.25 mm crosslinked methyl silicon gum). C02 was
analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from the solid catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 4.8 % mole
Methanol yield : 2.6 % mole
Formaldehyde yield : 2.1 % mole
CO2 : 0.1 % mole
Example-2
In an autoclave, 50 psi methane, 2.25 g of tertiary butyl hydroperoxide, 100 ml of acetonitrile and 0.5 g of solid copper tetra deca chloro phthalocyanine encapsulated in zeolite Na-Y were stirred at 30°C for 18 hrs. At the end of the reaction, the gas was collected and analysed for unreacted methane and formaldehyde using a Hewlett Packard 5880 Gas Chromato-graph equipped with a FID detector and a capillary column (50 ra x 0.25 mm crosslinked methyl silicon gum). C02 was analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from the solid catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum) . The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 5.5 % mole
Methanol yield : 5.0 % mole
Formaldehyde yield : 0.4 % mole
CO2 : 0.05 % mole
Example-3
In an autoclave, 50 psi methane, 0.25 g of tertiary butyl hydroperoxide, 100 ml of acetonitrile and 0.3 g of solid copper tetra deca chloro phthalocyanine were stirred at 0°C with a continuous bubbling of air for 8 hrs. At the end of the reaction, the gas was collected and analysed for unreacted methane and formaldehyde using a Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). C02 was analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from, the solid "catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 11.8 % mole
Methanol yield : 5.75 % mole
Formaldehyde yield : 6.0 % mole
CO2 : 0.025 % mole
Example-4
In an autoclave, 50 psi methane, 0.25 g of tertiary butyl hydroperoxide, 100 ml of acetonitrile and 0.3 g of solid iron hexa deca bromo phthalocyanine were stirred at 30°C with a continuous bubbling of air for 18 hrs. At the end of the reaction," the gas was collected and-analysed for unreacted methane and formaldehyde using a Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). C02 was analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from the solid catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gaa Chromatograph oquippesd with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 7.9 % mole
Methanol yield : 4.1 % mole
Formaldehyde yield : 3.7% mole
CO2 : 0.1 % mole
Example-5
In an autoclave, 50 psi methane, 0.25 g of tertiary butyl hydroperoxide, 100 ml of acetonitrile and 0.3 g of solid iron hexa deca chloro phthalocyanine encapsulated in zeolite Na-X, were stirred at 30°C with a continuous bubbling of air for 8 hrs. At the end of the reaction, the gas was collected and analysed for unreacted methane and formaldehyde using a Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum) . CO2 was analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from the solid catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 3.4 % mole
Methanol yield : 2.9 % mole
Formaldehyde yield : 0.5 % mole
Example-6
In an autoclave, 50 psi methane, 0.25 g of tertiary butyl hydroperoxide, 100 ml of acetonitrile and 0.3 g of solid copper tetra nitro phthalocyanine encapsulated in polystyrene were stirred at 30°C with a continuous bubbling of air for 9 hrs. At the end of the reaction, the gas was collected and analysed for unreacted methane and formaldehyde using a Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). CO2 was analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, "formaldehyde and formic acid) which were then separated from the solid catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 4.6 % mole
Methanol yield : 4.0 % mole
Formaldehyde yield : 0.5 % mole
CO2 : 0.1 % mole
Example-7
In an autoclave, 50 psi methane, 0.25 g of tertiary butyl
hydroperoxide, 100 ml of glacial acetic acid and 0.5 g of solid
copper hexa deca chloro phthalocyanine were stirred at 30°G
with a continuous bubbling of air for 9 hrs. At the end of
the reaction, the gas was collected and analysed for unreacted
methane and formaldehyde using a Hewlett Packard 5880 Gas
Chromatograph equipped with a FID detector and a capillary column
(50 m x 0.25 mm crosslinked methyl silicon gum). CO was
analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of acetone was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from the solid "catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 7.3 % mole
Methanol yield : 5.8 % mole
Formaldehyde yield : 1.4 % mole
CO2 : 0.05 % mole
Example-8
In an autoclave, 50 psi methane, 2.25 g of tertiary butyl hydroperoxide, 100 ml of acetone and 0.5 g of solid iron tetra nitro phthalocyanine encapsulated in polystyrene were stirred at 30°C for 18 hrs. At the end of the reaction, the gas was collected and analysed for unreacted methane and formaldehyde using a Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). CO2 was analysed using a Shimadzu GC- 15A equipped with a TCD detector and a poropak N column. 10 ml of benzene was added to the liquid products (unreacted methane, methanol, formaldehyde and formic acid) which were then separated from the solid catalyst by centrifugation and analysed by gas chromatography Hewlett Packard 5880 Gas Chromatograph equipped with a FID detector and a capillary column (50 m x 0.25 mm crosslinked methyl silicon gum). The identity of the products was further confirmed by GC mass spectroscopy (Shimadzu GCMS-QP 2000A) and also using standard compounds. The results are given below :
Methane conversion : 7.4 % mole
Methanol yield : 7.0 % mole
Formaldehyde yield : 0.3 % mole
CO2 : 0.1 % mole




We claim:
1. An improved process for the preparation of methanol which comprises reacting methane with an oxidant such as herein described, in the presence of a solid catalyst consisting of an organotransition metal complex wherein some or all of the hydrogen atoms of the said organotransition metal complex have been substituted by one or more electron withdrawing groups, and encapsulated with an solid matrix containing an inorganic oxide and an organic oxide, at a temperature below 100°C , at a pressure in the range of 5 to 1000 psi, in the presence of solvents and a promoter such as herein described and isolating the methanol formed by conventional methods.
2. An improved process as claimed in claim 1 wherein the organotransition metal complex is a phthalocyanine.
3. An improved process as claimed in claims 1-2 wherein the transition metal is selected from iron, copper or mixtures thereof.
4. An improved process as claimed in claims 1-3 wherein the said electron withdrawing group is selected from the halogens, the nitro group, the cyano group or mixtures thereof.
5. An improved process as claimed in claims 1-4 wherein the oxidant used is
selected from a group consisting molecular oxygen, alkyl hydroperoxides,
dialkylhydroperoxides, or mixtures thereof.
6. An improved process as claimed in claims 1-5 wherein the source of molecular oxygen is oxygen, air or a mixture of oxygen and an inert gas such as nitrogen.
7. An improved process as claimed in claims 1-6 wherein the oxidation reaction is carried out in the presence of solvents such a acetonitrile, benzonitrile, pyridine, benzene and acetone.
8. An improved process as claimed in to claims 1-7 wherein a promoter such as alkyl hydroperoxide, dialkyl peroxide or mixtures thereof is used in the reaction.
9. An improved process as claimed in claims 1 to 8 wherein the concentration of the promoter in the reaction mixture does not exceed 1% by weight of the methane.
10. An improved process as claimed in claims 1 to 9 wherein the solid matrix used is an inorganic oxide such as silica, alumina, aluminosilicates or molecular sieves.
11.An improved process as claimed in claim 1-10 wherein the solid matrix is an
organic polymer. 12.An improved process for the preparation of methanol substantially as herein
described with reference to the examples.

Documents:

794-del-1997-abstract.pdf

794-del-1997-claims.pdf

794-del-1997-complete specifiction (granted).pdf

794-del-1997-correspondence-others.pdf

794-del-1997-correspondence-po.pdf

794-del-1997-description (complete).pdf

794-del-1997-form-1.pdf

794-del-1997-form-19.pdf

794-del-1997-form-2.pdf

794-del-1997-form-3.pdf


Patent Number 194294
Indian Patent Application Number 794/DEL/1997
PG Journal Number 41/2004
Publication Date 09-Oct-2004
Grant Date 03-Feb-2006
Date of Filing 27-Mar-1997
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 PAUL RATNASAMY NATIONAL CHEMICAL LABORATORY, PUNE MAHARASHTRA, 411 008, INDIA
2 ROBERT RAJA NATIONAL CHEMICAL LABORATORY, PUNE MAHARASHTRA, 411 008, INDIA
PCT International Classification Number C07C 31/045
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA