Title of Invention

A PROCESS FOR THE DESULPHURISATION OF HIGH SULPHUR CONTAINING COMMERCIAL DIESEL

Abstract

A process for the desulphurization of high sulphur containing commercial diesel by treating sulphur containing diesel, under magnetic stirring and in the presence of air in ambient conditions, with nitric acid in volume ratio of nitric acid to oil in the range of 0.05 to 0.2 in combination with acetic acid in the volume of oil to acetic acid upto 0.025%, followed by removal of oxidized matter by filtration and solvent extraction with solvent under ambient condition, recovering nitric acid, acetic acid by known methods and separating low sulphur containing diesel.

Full Text

The present invention relates to a process for the desulphurisation of high sulphur containing commercial diesel. The present invention particularly relates to a process for the desulphurisation of high sulphur containing commercial diesel by oxidation and solvent extraction under ambient conditions. This invention more particularly relates to a process for the desulphurisation of diesel into a low sulphur containing diesel by oxidising with nitric acid which oxidises the sulphur containing compounds present in diesel with their enhanced polarity followed by simple extraction with methanol that separates diesel into two fractions i.e. raffinate containing low sulphur and extract phase relatively in small quantity with high sulphur content under ambient conditions together with recovery of oxidant and extractant and also desirably regulated amounts of byproducts such as semi-solid residue, aromatics and sulphur with their recovery potentials. The low sulphur containing diesel has got tremendous utilisation potential in the combustion of fuel in diesel driven transport vehicles and other combustion engines, where it can be burnt in environment friendly manner by minimising the emission of particulates and SOx into the atmosphere. The SOx being one of the main contributors to acid rain causes harmful effects, toxicity to plants, corrosion of building, stonewares and metals and also visibility degradation. Also sulphur compounds in diesel pose corrosion problems in the part of combustion engines and reduce the activity of catalytic converters. Accordingly the reduction of sulphur in diesel is being contemplated by giving due considerations to the present conditions of environmental practices and national and international specification [BIS 1460-1993; CPCB Working Group Meeting Juily 22, 1998, India; Concawe Nos. 5/97 & 6/97-" Motor Fuel Emission Regulations and Fuel Specifications Part-I & II"; UOP Report-" Diesel Fuel Specifications and Demand for 21st Centuary ] under clean air acts [Concawe Report No.-5/97, Part-I; UOP Report; CPCB Working Group Meeting on Fuel Quality for 2005 AD, July 22, 1998, India]. About 45% fuel oil has maximum sulphur content even up to 1.0wt%, hence the sulphur level has been fixed in European Union and other foreign countries. Accordingly, there is interest in low sulphur fuel oil, where market will require to reduce sulphur content about 0.05wt% [Concawe Report No.-6/97, Part-II; Hart's European Fuel News Feb.20, 1998.]. Tlu's is thought to be reduced to this level in India also in future [BIS 1460-1998; CPCB Working Group Meeting July 22, 1998.]. At present the accepted method for reducing sulphur to acceptable level in petroleum derived fuel is catalytic hydrodesulphurisation (HDS) involving high temperature and pressure where sulphur is removed in the form of H2S for which there is necessity of a large number of desulphurisation units and also an unbalanced increase in the demand for meeting additional requirements of units for production of H2 using catalytic reformer in the existing traditional refineries. The limits already fixed on the maximum aromatics content of gasoline also preclude this expansion and compel to go for H2 production from steam reforming of light hydrocarbons or partial oxidation of heavy petroleum components, which will not only incur substantial investment and operating cost but also release large quantity of C02 to the atmosphere. Besides, for deep desulphurisation by HDS, the option of improving catalyst activity at higher temperature is also problematic in respect of cycle length. Hence it is evident that development of a process for reducing sulphur content from liquid fuel under ambient conditions without a recourse to H2 and a catalyst and also without any adverse effect on the quality characteristcs of desulphurised fuel will be highly desirable as a supplement to HDS process. Of the various chemical processes endeavored for removing sulphur, only oxy-desulphurisation process taking the advantage of the oxidation of divalent sulphur of sulphide group to hexavalent sulphur group followed by thermal treatment to eject sulphur in the form of S02is promising [Attar, A. and Corcoron, W. H., Desulphurisation of S compounds by selective. oxidation-I, Regenerable and Nonregenerable Oxygen Carriers, hid. Eng. Chem. Prod. Res. Dev., 1978, \7, p. 102; Vasilakos, N. P. et al, Oxidative chlorination of DBT, Eng. Chem. Prod. Res. Dev., 1981, 20, p. 376] and without a recourse to H2but suffers from substantial and undesirable thermal cracking of rest of fuel molecules. Another feature of sulphur atoms to render slightly more polarity than hydrocarbon molecules in which it occurs permits the selective removal of sulphur compounds by solvent treatment. Further oxidised sulphur compounds like sulphones and sulphoxides being more polar than sulphides, a combination method of oxidation and solvent extraction can be effectively applied [Block, E. Reactions of Organosulphur Compounds by Oxidation and Solvent extraction, Acad. Press, NY, 1978 p. 202 ; Zanikos, F. et al, Desulphurisation of Petroleum Fractions by Oxidation and solvent Extraction, Fuel Process. Techno., 1995, 42, p.35; Patrick, S. T. et al, Desulphurisation of Fuel by Oxidation 1. Enhancement of Extraction of Oil Yield, Ind. Eng. Chem. Res. 1990, 29, p.324; Aida, T., Eur. Patent Appl. 563, 324 (Chem. Abstract 1993, 119:253486g) ; Guth E. D.and Diaz, A. F., Method of Recovering S and N in Petroleum Oils, US Patent, 3847,800, 1974; Guth, E. D. et al, Petroleum Oil desulphurisation Process, US Patent, 3,919,402, 1975] with varying degree of successes depending on reaction conditions in lowering sulphur content of petroleum derived fuel in raffinate with added bonus of lower aromatics content by recent specifications [UOP Report-" Diesel Fuel Specifications nad Demand for the 21st Centuary; Mukhopadhyay, P. K., Dr. Hiralal Memorial Lecture-CHEMCON 96 on Recent Developments in Petroleum Refining technology, Chemical Weekly, Jan 28, 1997, p. 147] and concentrating high sulphur compounds and aromatics in the extract phase, which can be subjected to thermal treatment to eject sulphur in the form of SO2 followed by further upgradation by more intensive processes of catalytic cracking or hydrotreating. U.S. Patent No. 3,135,680, 1964 discloses oxidation of a sour petroleum fraction with nitrogen dioxide followed by washing with water and alkali to desulfurise diesel oils and improve cetane number in that the product obtained tends to have an objectionable colour and subsequent sulfuric acid treatment, vacuum distillation or clay treating are necessary for complete removal of materials formed during oxidation. Besides, there is reduction or elimination of the increase in cetane number. Also, due to high Ramsbottom carbon content, the product of this process forms substantial coke upon distillation. A process of desulfurising light petroleum distillates by treatment with nitrogen dioxide followed by alkali wash and water wash is disclosed in U.S. Pat. No. 3,267,027, . But this process is also unsuitable for producing diesel fuels of acceptable stability and carbon residue. The treatment of oil with nitrogen dioxide and washing with aqueous alkali and/or solvent extraction followed by a water wash, for producing diesel fuel of improved cetane number and odour has been described in U.S. Pat. No. 3,164,546, 1965, where nitromethane, dimethylformamide, pyridine, acetonitrile, glycolonitrile, ethylene glycol, ethanol amine and phenol are suitable disclosed solvents. However, Ramsbottom carbon content specifications were found to be the most difficult product specifications together with reduced yield. Thus, the oxidation/extraction methods described above have met with some success in improving petroleum diesel fuels. The known approaches toward oxidation to remove a portion of the original sulfur content as gaseous sulfur oxides, and to convert a portion of the original sulfur content into sulfoxides and/or sulfones followed by extraction with appropriate solvents to achieve a desired low sulfur raffinate have not completely eliminated problems of instability and other characteristics including carbon residue for diesel fuels together with the disadvantage of low yields on extraction with solvent. Therefore, there is a definite need for the development of a process (without recourse to hydrogen and under ambient condition) like oxidation and solvent extraction which is quite effective in removal of sulphur from diesel to the level of nationa/international specifications with appreciable yield and without any adverse effect on the quality/characteristics of diesel. The main object of the present invention is to provide a process for the desulphurization of high sulphur containing commercial diesel, that is to produce a low-sulphur-diesel with an appreciable yield without a recourse to H2 and catalyst by oxidation with nitric acid and solvent extraction with methanol under ambient conditions in an environment friendly manner with no adverse effect on the quality parameters of diesel. Another object of the present invention from economic consideration is to find out the recovery potentials of the reactants (oxidant and extractant) and byproducts such as semisolid residue and aromatics. Accordingly, the present invention provides a process for the desulphurization of high sulphur containing commercial diesel which comprises treating sulphur containing diesel, under magnetic stirring and in the presence of air in ambient conditions, with nitric acid in volume ratio of nitric acid to diesel in the range of 0.05 to 0.2 in combination with acetic acid in the volume of diesel to acetic acid upto 0.025%, followed by removal of oxidized matter by filtration and solvent extraction with water or methenol under ambient condition, recovering nitric acid, acetic acid by known methods and separating low sulphur containing diesel. In an embodiment of the present invention, the rate of air below upto 2.5 litres/minute. In another embodiment of the present invention, the magnetic stirring may be upto 1000rpm. In yet another embodiment of the present invention, the ratio of diesel to solvent may be in the range of 1:2 to 1:5. In still another embodiment of the present invention, the solvent used may be methanol, water. In still another embodiment of the present invention, the reaction time for oxidation is upto three hours. The inventive step of the process of the present invention resides in the step of treating sulphur containing commercial diesel with a combination of nitric acid and trace amount of acetic acid. The broad features of this invention consists of the following steps: a) Oxidation of an appropriate quantity of commercial diesel with nitric acid alone and in combination with acetic acid with and without temperature control for certain period is carried out with constant stirring in a flat round bottom flask equipped with the facility of temperature measurement and ejection of nitric acid vapour (N02) through a water condenser along with air blown from out side in the condenser with dual purpose of pushing nitric acid vapour into the water container and its ultimate conversion to nitric acid in the presence of air and water. b) Thus the obtained diesel after oxidation is filtered and the semi-solid residue formed during oxidation is separated and from the filtrate immiscible acetic acid is separated and the diesel is further extracted with methanol in certain known volumes followed by separation into rafFinate with low sulphur content and extract phase (relatively in small quantity) with high-sulphur content and aromatics in methanol. Then from extract phase, raffinate is separated and methanol is distilled and recovered after stripping aromatics with n-hexane/heptane/ or water, which on distillation gives recovery of stripping solvent and aromatics as residue. The novel features of this invention are as follows: (i) The process can be operated under ambient conditions and effective in removal of sulphur up to 93%, i. e. to the level of 0.05wt%S. (ii) The process is without a recource to hydrogen.and catalyst. (iii) The process is effective in removal of sulphur, nitrogen and aromatics with no adverse effect on the quality of desulphurised diesel and rather appreciable and technologically desired improvement in respect of H/C atomic ratio, N-content, calorific value, CCR, diesel index., specific gravity, pore point etc. (iv) Yield of desulphurised oil enhanced (percent yield loss low) as compared to control process of solvent extraction with methanol and oxidation alone with oxidant. (v) Acetic acid taken in small quantity with nitric acid not only acts as a dispersant for semi-solid residue to enhance more of nitric acid effectiveness but also as a selective extractant for oxidised sulphur compounds and hence less requirement of extractant as well as oxidant as compared to both simple extraction with methanol alone and extraction after nitric acid oxidation, (vi) Recovery potential of methanol, nitric acid and acetic acid can make the process more cost effective, (vii) Small fraction of diesel in the form of extract phase is required to go for thermal treatment to eject sulphur in the form of SO2 with subsequent recovery by refinery process and further upgradation by more intense catalytic cracking or hydrotreating. (viii) The process is environment friendly. The process is explained by means of the following example which should not, however, construed to limit the scope of the present investigation. Example -1 500 ml of the commercial diesel is magnetically stirred at up to 1000 rpm maximum, with 100 ml of 70% nitric acid (LR grade, acid to oil volume ratio 0.2) in a flat round botton flask of two litre size equipped with a facility of temperature measurement ( maximum rise in temperature up to 55°C) and emitting vapour of nitric acid (NO2) is allowed to pass through a glass tube connected with a blower to blow air up to 2.5 Itr./min. maximum inside towards the other end of Leby's condenser connected with another tube dipped in water container. This is carried out for about a period of three hours or before that when the nitric acid vapour apparently stops coming out. The semi-solid residue formed during oxidation of diesel is filtered and remaining acid, if any, is separated by a separating funnel followed by extraction of separated diesel with methanol (volume ratio to oil, 1:2 and 1:5) for half an hour. Then the raffinate is separated from extract phase and washed successively with aqueous dilute sodium hydroxide (about 0.5%) solution and excess of water by magnetic stirring till free from acid and subsequent separation and drying in a desicator containing anhydrous calcium chloride. The high sulphur containing diesel is separated from extract phase by n-hexane/heptane stripping or water. The methanol and stripping solvent are separated from remaining extract phase by distillation/evaporation and residue obtained is aromatics. The typical process conditions and results are given in Table-I and analysis of raw and desulphurised diesel is shown in Table-II: Table-I Typical Process Conditions and Results (Table Removed) Table-II Typical Analysis of raw and desulphurised diesel (Table Removed) Figures in parenthesis: Kinematic viscosity Cst at room temperature (20°C). In the process of the present invention there provides a simple process for the desulphurisation of commercial diesel to an appreciable extent without any adverse effect on the characteristics of the desulphurised diesel rather than some improvement in its characteristics together with the recovery potential of process reagents such as nitric acid and also acetic acid with their recirculation potentiality in environment friendly manner, where the byproduct such as semi-solid residue can be used for the production of various chemical byproducts and from high sulphur containing extract phase, appreciable recovery of aromatics by stripping with n-hexane/heptane/or water and subsequent distillation followed by thermal treatment of high -S content diesel obtained from extract phase to eject sulphur in the form of sulphur dioxide and subsequent upgradation of remaining diesel by more intensive processes of catalytic cracking or hydrotreating can be made. The main advantages of the present process are : 1. The desulphurisation of diesel oil is to the tune of 67 to 93% i.e; to the level of 0.05wr%sulphur. 2. The yield of desulphurised oil is about 60 to 78% and its effectiveness factor is 2-3.2 3. The temperature risen during oxidation is about 60 degree Celsius maximum or less up to 30 degree Celsius under ambient pressure. 4. The recovery of methanol, acetic acid and nitric acid is about 75 to about 95%. 5. The characteristic parameters of desulphurised are either without any appreciable adverse effect or with some technologically desired improvement i.e; increase in respect of H/C atomic ratio, calorific value, CCR, diesel index ( cetane number), specific gravity, viscosity, pore point and decrease in CCR, N-content and aromatics etc. 6. The process environment friendly with no traces of NO2 in the desulphurised diesel and cost effective with recovery potential of reactant and by-products. 7. No sediment formation could be observed in the desulphurised diesel even after a span of one year of desulphurisation. We claim : 1. A process for the desulphurization of high sulphur containing commercial diesel which comprises treating sulphur containing diesel, under magnetic stirring and in the presence of air in ambient conditions, with nitric acid in volume ratio of nitric acid to diesel in the range of 0.05 to 0.2 in combination with acetic acid in the volume of diesel to acetic acid upto 0.025%, followed by removal of oxidized matter by filtration and solvent extraction with water or methanol under ambient condition, recovering nitric acid, acetic acid by known methods and separating low sulphur containing diesel. 2. A process as claimed in claim 1 wherein the ratio of diesel to solvent is in the range of 1:2 to 1:5. 3. A process as claimed in claims 1-2 wherein the magnetic stirring is upto 1000 rpm. 4. A process as claimed in claims 1-3 wherein the rate of air below is upto 2.5 liters/min. 5. A process as claimed in claims 1-5 wherein the reaction time for oxidation is upto 3 hours. 6. A process for the desulphurization of high sulphur containing commercial diesel substantially as herein described with reference to the example.

Documents:

1203-del-2000-abstract.pdf

1203-del-2000-claims.pdf

1203-del-2000-correspondence-others.pdf

1203-del-2000-correspondence-po.pdf

1203-del-2000-description (complete).pdf

1203-del-2000-form-1.pdf

1203-del-2000-form-19.pdf

1203-del-2000-form-2.pdf

1203-del-2000-form-3.pdf