Title of Invention

A PROCESS FOR THE EXTRACTION OF AROMATICS FROM AROMATIC RICH PETROLEUM STREAMS

Abstract

A process for the extraction of aromatics from aromatic rich petroleum streams The invention relates to an improved process for the extraction of aromatics from aromatic rich petroleum streams. In this process, aromatics are extracted from aromatic rich petroleum stream such as heavy naphtha, kerosene and gas oil range petroleum fractions using polar organic solvent and further re-extracting the extract phase with C6-C7 paraffinic solvent. Refinery cut light naphtha is used as re-extraction solvent. The unique process of this invention provides feasibility to dearomatize three feedstocks of different boiling range using an eco-friendly solvent N-methyl-pyrrolidone in the same unit using block out operation..

Full Text

The invention particularly relates to the extraction of aromatics from heavy naphtha, kerosene and gas oil range petroleum fractions with the aid of a suitable polar organic solvent and re-extracting the extract phase with a Ce-C/ paraffinic solvent7 Different petroleum fractions obtained in crude distillation unit contain varying concentration of aromatics depending upon crude oil source. These aromatics are required to be removed to produce various end products meeting the specifications with respect to aromatics. For example: Naphtha used as feedstock in petrochemical industry for the production of olefins should not contain more than 5% of aromatics due to refractory nature of aromatics. While in the case of fertiliser industry limitation of aromatics ( naphtha feedstock is due to higher carbon to hydrogen ratio which in turn affects the hydrogen yield. Refining of kerosene fractions is done in order to produce superior kerosene (SK)/ aviation turbine fuel (ATF). These end products should meet BIS specification requirements of smoke point, freezing point (for ATF) and aromatic content on which performance of these products depends. High aromatic content in gas oil fraction results in lowering of cetane number. In order to improve the cetane number the reduction of aromatics is essential. Hydrofming and solvent extraction are the conventional processes for dearomatization. However, severe operating conditions such as high partial pressure of hydrogen and high hydrogen consumption are required for high aromatic feed stocks, which make the process highly capital cost intensive compared to solvent extraction. For example for dearomatisation of kerosene fractions from Assam crude oils, being rich in aromatics solvent extraction is employed. Presently, there are three refineries in the eastern part of our country where kerosene fractions are dearomatized using liquid sulphur dioxide as the solvent (Edeleanu, L. British Patent 11,140 May 22, 1908). Considering present growth in technology development and environment awareness, this is an obsolete process. It has several drawbacks. The main drawbacks are : (1) Liquid sulphur dioxide is highly corrosive in presence of traces of water, therefore, drying of feed and solvent is an important step. (2) There is occasional failure of ATF produced by this process. (3) The number of columns used for solvent recovery from raffinate and extract phases is too large. (4) Extraction temperature is as low as -15°C thus requires refrigeration To overcome the above drawbacks Indian Institute of Petroleum, Dehra Dun, Engineers India Limited, New Delhi and Hindustan Petroleum Corporation Limited, Mumbai have jointly developed a process for refining kerosene fraction (140-240°C) which uses sulpholane as the solvent (Patent No. 170747, 23 Mar 1987) employing conventional extraction route. In this process scheme the recovery of solvent from extract phase is carried out by distillation. This approach is successful for systems constituting feed and solvents having wide difference of boiling points. However, this process consumes significant energy for the recovery of hydrocarbons, due to requirement of stringent operating conditions. Moreover, processing of feeds having wide boiling range e.g. naphtha to gas oil in the same unit using block out operations is not feasible due to over lapping of boiling points with the solvent. For such application solvent extraction in combination with re-extraction route for solvent recovery is feasible approach. Re-extraction concept for the recovery of aromatics from extract phase is reported to have been used commercially e.g., for the production of pure benzene and toluene by Dimethyl sulphoxide (DMSO) process [Hydrocarbon Processing, 45, (5), 188, 1966]. Handling of low thermal stability solvent is the main drawback of this process. Improvement of cetane number of LCCO [Hydrocarbon Processing, 46, (9), 134, 1967] using Dimethyl formamide (DMF), production of high boiling aromatics by using N-Formyl Morpholine (NFM) [Hydrocarbon Processing, 51, (4), 141,1972], production of pure benzene and toluene from pyrolysis gasoline by using Tetraethyleneglycol [DE 3,409,307 Sept 1985 and ISEC 1971] have also been tried. Re-extraction of aromatics from extract phase of kerosene fractions is also reported by Muller, et. at. [DE 3,207,404; 8 Sept 1983] and Lobov [Nauchn. Osn. Pererab.Negti Gaza Neftekhim., Tezisy Dokl., Vses. Knof. 234-5, 1977]. The solvent tried in the former work was N-Methyl pyrolidinone (NMP) containing 6% water while the reextraction was done by n-hexane, while in the latter work the feed used was kerosene fraction 200-270°C and solvent used was DMF while the re-extraction solvent was n-heptane. In all these processes the lean solvent obtained from bottom of the re-extraction column is directly re-circulated back to the main extraction column without removing the re-extraction solvent. Drawbacks of this process scheme are: - Difficulty in maintaining the extraction solvent composition - Contamination of raffmate phase with re-extraction solvent - Requirement of additional fractionator for removal of re-extraction solvent from raffinate - Requirement of stringent operating conditions in water-solvent fractionator due to higher boiling point of solvents - RE-extraction solvent such as n-hexane & n-heptane being pure hydrocarbons are costly in the present work a modified process scheme has been developed for the extraction of aromatics from petroleum fractions i.e. naphtha, kerosene and gas oil, using re-extraction route for recovery of solvent. The novelty of the present invention lies in: - Proposed invention provides unique feasibility to dearomatize three feed stocks of different boiling range namely Heavy Naphtha, Kerosene and Gas Oil using an eco-friendly solvent such as NMP. - Single plant can be used in blocked out mode of operation to produce additional products such as high octane benzene free stock for gasoline pool, high Cetane Diesel, high aromatic solvent and feedstock for needle coke production. This is the unique feature of the invention as no such process has been reported so far to produce these value-added products from a single unit. - Use of refinery cut light naphtha cut as re-extraction solvent - The invention facilitates the controllability of the severity of extraction while in operation, through manipulating anti-solvent composition depending upon feed characteristics and target product specification. - The invention allows the production; of dearomatised raffinate free of re-extraction solvent. The main object of the present invention is to provide an improved process for the extraction of aromatics from petroleum streams, which obviates the drawbacks as detailed above. Another objective of the present invention is to provide modified process wherein solvent extraction of aromatics from aromatic rich petroleum fractions to obtain the products e.g. high octane aromatic extract for Motor Sprit pool, superior kerosene, high cetane gas oil and speciality solvents for particular end use. Yet another objective of the process is to achieve savings in capital cost by eliminating raffinate-re-extraction solvent fractionator. Still another objective is to reduce operating cost by saving in utilities by using heat integration of hot and cold streams. Yet another objective of the process is to produce superior quality special boiling point solvents. In the present invention therefore, the aromatics are separated from nonaromatics from the feedstocks by extraction using polar organic solvent. The solvent used here is N-Methyl pyrolidinone admixed with water, glycols, sulpholane etc. The flow diagram of the present invention is shown in Fig.1 of the drawing accompanying this specification. The petroleum fraction stream is introduced through line (1) and lean solvent is introduced via line (2) into the extractor-A where the two streams meet countercurrently. The extract phase, thus produced, is introduced via line (4) in the extractor-B, which meets the Ce-C? petroleum fraction (63-69°C cut) countercurrently, entering via line (5). The raffinate phase produced is fed to raffinate wash column-E via line (3) where it is washed with water. The two contact zones may comprise either a packed or a sieve plate column. The top phase which leaves the extractor-B via line (6) is water washed in extract wash column-C and then enters via line (8) in the distillation column-D where it is fractionated to yield aromatic extract which is collected via line (11) and C6-C7 petroleum fraction, which is re-circulated to extractor-B via line (5). The bottom of extractor-B enters to solvent recovery column-F via line (7). Hydrocarbons from the top of solvent recovery column (SRC) are routed to column-D via line (15). One part of water is recycled back to extract wash column-C via line (10). Another part of water is recycled back to raffinate wash column-E routed through water stripper-G via line (14). Washed raffinate is taken from line (12). The lean solvent from the bottom of solvent recovery column-F is re-circulated back to extractor-A via line (2). Water containing the solvent is fed to solvent recovery column-F via lines (9) and (13) used as striping stream. Accordingly the present invention provides a process for the extraction of aromatics from aromatic rich petroleum streams which comprises: a) Characterized in that contacting aromatic rich petroleum streams feed with a polar organic solvent containing 2-20 wt% anti solvent at a temperature in the range of 20 - 80°C in a extractor-A column to obtain a extract phase and a raffinate phase, b) contacting the said extract phase obtained from step (a) with 1-6 vol% of secondary solvent consisting of C6-C7 paraffinic petroleum fraction in the extractor-B column at a temperature in the range of 20-60°C to recover the extract hydrocarbons, c) distilling the bottom stream of extractor-B obtained in step (b) in column-F at reboiler temperature of 90-180°C to recover the extraction solvent for further recycling d) washing the top stream of extractor-B obtained in step (b) with water in column-C at a temperature in the range of 20-60°C, followed by fractionating the resultant hydrocarbons at a temperature in the range of 100-400°C to obtain the extract hydrocarbons and secondary solvent and further recycling the secondary solvent to extractor-B, e) washing the raffinate phase obtained from step (a) in column-E at a temperature in the range of 20-60°C, by conventional method to obtain raffinate hydrocarbons. In an embodiment of the present invention, aromatic rich petroleum stream used is petroleum fraction having boiling temperature in the range of 90-360°C. In another embodiment of the present invention, the aromatics extracted from aromatic rich petroleum streams are benzene, toluene, xylene, alkyl benzene, naphthalenes, alkyl naphthalenes and depends on boiling range of feedstock. In an embodiment of the present invention, wherein the resultant hydrocarbons is a mixture of C6-C7 paraffins, secondary solvent and aromatic hydrocarbons. In another embodiment of the present invention the selective solvent used is N-Methyl pyrolidinone admixed with 2.0 to 15wt % water or sulpholane or glycol. In yet another embodiment of the present invention ratio of solvent mixture to feed is in the range of 1:1 to 5:1wt%. In still another embodiment of the present invention feed and extraction solvent is contacted countercurrently in a extractor-A at a temperature of 30 - 80°C. In still another embodiment of the present invention recovery of aromatics from extract phase is affected countercurrently in a extractor-B using secondary solvent selected from C6-C7 petroleum fraction at a temperature of 30 - 60°C. In still another embodiment of the present invention the ratio of secondary solvent to extract phase is in the range of 1 to 4 by volume. In still another embodiment of the present invention recovery of solvent from top phase of extractor-B and raffinate phase is done by known method such as water washing at a temperature of 30-40°C. In still another embodiment of the present invention recovery of secondary solvent from top of the extractor-B is affected by using conventional method such as distillation at atmospheric pressure at a temperature of 110 - 300 °C In still another embodiment of the present invention recovery of residual hydrocarbons in bottom phase of extractor-B is done by using conventional method such as distillation at reboiler temperature of 100-160°C. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Example-1 For the extraction step the model mixture of propyl benzene-decane with 6.0 wt.% propyl benzene, was admixed with an equal weight of NMP (Pure) at 40°C. Two liquid phases under equilibrium were formed. Each phase was separated, made solvent-free and analysed. The extract phase contained 2.6 wt.% propyl benzene, while its concentration reduced to 4.1 wt.% in the raffinate phase with 89.0 wt.% yield. Example-2 For the extraction step the model mixture of propyl benzene-decane with 6.0 wt.% propyl benzene, was admixed with an equal weight of NMP +20% sulpholane at 40°C. Two liquid phases under equilibrium were formed. Each phase was separated, made solvent-free and analysed. The extract phase contained 2.2 wt.% propyl benzene, while its concentration reduced to 4.8 wt.% in the raffinate phase with 94.5 wt.% yield. Example-3 3.3 kgs/hr of heavy naphtha fraction (100-200°C) from Assam crude, containing 30.2 wt.% aromatic is fed to packed extractor-A. It was counter-currently contacted with the selective solvent (NMP+10% water) at 40°C entering the column at a rate of 7.7 kgs/hr. The extract phase produced at a rate of about 8.6 kgs/hr. 4.1 kgs/hr of extract phase produced as above containing 0.54 kgs/hr of total hydrocarbons is fed to packed extractor-B and counter currently contacted with C6-C7 paraffinic petroleum fraction entering at a rate of 6.1 kgs/hr. Phase produced at a rate of 7.0 kgs/hr from the top of extractor-B contains 0.49 kgs/hr of NMP. The phase is water washed and fractionated yielding 0.55 kgs/hr of naphtha extract containing 77.2 wt% of aromatics. The recovered C6-C7 paraffinic petroleum fraction is circulated back to extractor-B. The bottom of the extractor-B contains 3.15 kgs/hr of lean solvent and 0.011 kgs/hr of naphtha hydrocarbons. 2.3 kgs/hr of the raffinate phase produced from extractor-A contains about 0.133 kgs/hr of NMP was water washed in raffinate wash column -E, yielding 2.16 kgs/hr of dearomatized heavy naphtha with 7.8 wt.% aromatics. Example-4 2.0 kgs/hr of gas oil fraction (240-400°C) from Assam crude, containing 39.2 wt.% aromatic is fed to packed extractor-A. It was counter-currently contacted with the selective solvent (NMP+10% water) at 40°C entering the column at a rate of 7.4 kgs/hr. The extract phase produced at a rate of about 8.2 kgs/hr. 4.7 kgs/hr of extract phase produced as above containing 0.377 kgs/hr of total hydrocarbons is fed to packed extractor-B and counter currently contacted with Ce-C/ paraffinic petroleum fraction entering at a rate of 6.8 kgs/hr. Phase produced at a rate of 7.6 kgs/hr from the top of extractor-B contains 0.56 kgs/hr of NMP. The phase is water washed and fractionated yielding 0.345 kgs/hr of gas oil extract containing 86.9 wt% of aromatics. The recovered Ce-C7 paraffinic petroleum fraction is circulated back to extractor-B. The bottom of the extractor-B contains 4.07 kgs/hr of lean solvent and 0.02 kgs/hr of gas oil hydrocarbons. 1.38 kgs/hr of the raffinate phase produced from extractor-A contains about 0.059 kgs/hr of NMP was water washed in raffinate wash column -E, yielding 1.32 kgs/hr of dearomatized gas oil with 16.2 wt.% aromatics. 10 The main advantages of the present invention are as follows : 1. Use of environmentally friendly solvent such as NMP in an admixure with anti solvents such as water, glycols, sulpholane etc. 2. Use of conventional metallurgy such as carbon steel 3. Highly simplified and flexible flowsheet 4. Lower capital cost 5. High capacity solvent like NMP inspite of its boiling point overlap with that of the feed can be used since the hydrocarbons are recovered from the extract phase by re-extraction route. 6. Flexibility in handing wide range of petroleum fractions (naphtha to gas oil) in the same unit by using block out operation is possible 7. Elimination of energy intensive distillation step of aromatic recovery from extract phase will lead to considerable savings in the utility. 8. Operation of re-extraction column at ambient temperature will result in requirement of lower utilities and minimize solvent degradation. This will also minimize the corrosion problem. 9. Production of good quality aromatic rich extract for various end uses e.g. gasoline blending, insecticide formulation. •10. Feasibility of producing superior quality speciality solvents by incorporation of water stripper 11. Availability of additional extraction column operating parameters (e.g. anti solvent composition and extraction temperature) due to incorporation of solvent recovery column We Claim: 1. A process for the extraction of aromatics from aromatic rich petroleum streams which comprises: a) Characterized in that contacting aromatic rich petroleum streams with a polar organic solvent containing 2-20 wt% anti solvent at a temperature in the range of 20 - 80°C in a extractor-A column to obtain a extract phase and a raffmate phase, b) contacting the said extract phase obtained from step (a) with 1-6 vol% of secondary solvent consisting of C6-C7 paraffinic petroleum fraction in the extractor-B column at a temperature in the range of 20-60°C to recover the extract hydrocarbons, c) distilling the bottom stream of extractor-B obtained in step (b) in column-F at reboiler temperature of 90-180°C to recover the extraction solvent for further recycling d) washing the top stream of extractor-B obtained in step (b) with water in column-C at a temperature in the range of 20-60°C, followed by fractionating the resultant hydrocarbons at a temperature in the range of 100-400 C to obtain the extract hydrocarbons and secondary solvent and further recycling the secondary solvent to extractor-B, e) washing the raffmate phase obtained from step (a) in column-E at a temperature in the range of 20-60°C, by conventional method to obtain raffmate hydrocarbons. 2. A process as claimed in claim 1, wherein aromatic rich petroleum stream used is petroleum fraction selected from heavy naphtha, kerosene, and gas oil having boiling temperature in the range of 90-360°C. 3. A process as claimed in claim 1, wherein the aromatics extracted from aromatic rich petroleum streams are benzene, toluene, xylene, alkyl benzene, naphthalenes, alkyl naphthalenes and depends on boiling range of feedstock. 4. A process as claimed in claim 1 ,wherein the resultant hydrocarbons is a mixture of C6-C7 paraffins, secondary solvent and aromatic hydrocarbons. 5. A process as claimed in claim 1, wherein the polar organic solvent used is N-Methyl pyrolidinone admixed with 2.0 to 15wt% water or sulpholane or glycol. 6. A process as claimed in claim 1, wherein ratio of solvent mixture to aromatic rich petroleum stream is in the range of 1:1 to 5:1 wt%. 7. A process as claimed in claim 1, wherein aromatic rich petroleum stream and extraction solvent is contacted counter currently in a extractor-A at a temperature of 30-80°C, 8. A process as claimed in claim 1, wherein recovery of aromatics from extract phase is affected counter currently in an extractor-B using secondary solvent selected from C6-C7 petroleum fraction at a temperature of 30-60°C. 9. A process as claimed in claim 1, wherein the ratio of secondary solvent to extract phase is in the range of 1 to 4 by volume.

Documents:

372-DEL-2002-Abstract-(10-10-2008).pdf

372-DEL-2002-Abstract-(20-11-2008).pdf

372-del-2002-abstract.pdf

372-DEL-2002-Claims-(10-10-2008).pdf

372-DEL-2002-Claims-(20-11-2008).pdf

372-del-2002-claims.pdf

372-del-2002-correspondence others.pdf

372-del-2002-correspondence po.pdf

372-DEL-2002-Correspondence-Others-(10-10-2008).pdf

372-DEL-2002-Correspondence-Others-(20-11-2008).pdf

372-DEL-2002-Description (Complete)-(10-10-2008).pdf

372-del-2002-description (complete).pdf

372-del-2002-drawing.pdf

372-DEL-2002-Form-1-(20-11-2008).pdf

372-del-2002-form-1.pdf

372-del-2002-form-18.pdf

372-DEL-2002-Form-2-(20-11-2008).pdf

372-del-2002-form-2.pdf

372-DEL-2002-Form-3-(10-10-2008).pdf

372-del-2002-form-3.pdf

372-DEL-2002-Petition-137-(10-10-2008).pdf