Title of Invention

AN IMPORVED PROCESS FOR THE PRODUCTION OF CYCLOPENTANE FROM LIGHT PETROLEUM FRACTION

Abstract

The present invention relates to an improved process for the production of cyclopentane from light petroleum fraction. This invention also relates to the separation of cycloaliphatic hydrocarbons (naphthenes) from close boiling paraffinic hydrocarbons (paraffins). Cyclopentasne is separated from close boiling paraffins by extractive distillation using a selective solvent. The feed is optimized so as to minimize the concentration of higher boiling components (2-methyl pentane, 3-methyl pentane, 2,2-dimethyl butane and 2,3-dimethyl butane) and maximize the concentration and recovery of Cyclopentane in the optimized boiling range of the feed.

Full Text

The present invention relates to an improved process for the production of cyclopentane from light petroleum fraction. This invention also relates to the separation of cycloaliphatic hydrocarbons (naphthenes) from close boiling paraffinic hydrocarbons (paraffins).This invention particularly relates to the separation of cyclopentane from close boiling paraffins by extractive distillation using a selective solvent. Cyclopentane (CP) has emerged as the best alternative to CFCs, HCFCs and HFCs for blowing polyurethane used as insulation in refrigeration systems and has been successfully used by all major European refrigerator manufacturers. Its use is now spreading rapidly in both developed and developing countries worldwide. The reasons for the choice of CP for these application are: zero ozone depleting potential, environmental acceptance, reasonably low initial thermal conductivity, appropriate boiling point. These factors outweighed the disadvantage of CP flammability. According to Montreal Protocol, CFCs etc. have to be phased out worldwide by 2010 due to their role in depleting ozone layer and global warming. Accordingly in India an ozone unit has been set up in the Ministry of Environment and Forests to plan the ozone depleting substances (ODS) phase out programme. India had demanded $250 million from multilateral fund under UN environmental programme to cover the loss of dismantling and destruction of existing machinery which produce ODS and the loss of profit. However, India has been finally given $82 million for the purpose. The estimated world demand of CP is reported to be around 85000 t/a. r V _ 7 Indian companies manufacture over 5 million domestic refrigerator units per year/ besides central air conditioners, ice candy machines, deep refrigerators, mobile air conditioners, water coolers, unitary air conditioners etc. The estimated demand of CP in Indian market will be around 4000 t/a besides substantial potential for export. The import price of CP varies from Rs. 50,000 to Rs 90,000 per ton depending on the purity of CP. At present CP in the industry is produced either by catalytic hydrogenation of cyclopentadiene (an intermediate by-product of thermal cracking units) or by synthetic methods. This can also be produced by hydrogenation of cyclopentanone or dehydrogenation of cyclohexane. Extractive distillation is another known technique for separating mixture of components having a relative volatility close to unity (i.e., having nearly equal volatility and having nearly the same boiling point). It is difficult to separate the components of such mixtures by conventional fractional distillation. In an extractive distillation process, an agent (called 'solvent') is added to feed mixture of components to be separated so that the relative volatilities of the components of the mixture are changed to cause effective separation by extractive distillation. The added solvent is usually chosen so as to exhibit high "selectivity" between components to be separated. Selectivity is a relative term related to the change in volatilities of components in the mixture caused by the presence of the solvent. The larger the difference in relative volatility of the components in the mixture, easier the separation of components in a distillation step. Therefore, a solvent should be such that it causes appreciable differences between the relative volatilities of the components in a mixture, and thus allows the separation of components in a mixture with fewer distillation stages. Capacity of the solvent is another important property that affects the solvent rate and total throughput which, in turn, affects efficiency of the column. There should be good compromise between selectivity and capacity of the solvent. The catalytic hydrogenation of diolefins for the production of CP have been employed (Hearn Dennis et.al. US Pat. US6169218, 2001). Extractive distillation method has been tried by different researchers (R.E. Brown and P.M. , US Pat. US4954224, 1990; R.E. Brown et.al., US Pat. US5055162, 1991 and P.M. Lee et.al., US Pat. US5032232, 1991) for separation of cyclopentane from close boiling paraffins using different selective solvents. In these cases synthetic feed mixtures consisting of 2,2-dimethyl butane as typical close boiling paraffin (b.p. 50°C) and CP (b.p.49°C) have been used. US Pat. 4954224 (1990) by R.E. Brown and P.M. Lee reports the use of either N- (p-mercaptoethyl)-2-pyrrolidone (NMEP) or cyclohexanol (CHOL) or N-methyl-pyrrolidone (NMP) or their mixture as solvents for separation of cycloalkane (cyclopentane) and close boiling alkane (2,2-dimethylbutane). R.E. Brown et.al. (US Pat. 5055162, 1991) have further reported use of N-(p-hydroxyethyl)-2-pyrrolidone (HEP) or cyclohexanol (CHOL) or NMP or their mixture as solvent for separation of cycloalkane (cyclopentane) from close boiling paraffins (2,2-dimethyl butane). F.M. Lee et.al. (US Pat. 5032232; 1991) has reported N-methyl-2-thiopyrrolidone (NMTP) as solvent for separation of cyclopentane from 2-dimethyl butane. All the above existing methods either involve hydrogenation step or synthesis or extractive distillation. Hydrogenation and synthesis methods are generally cost intensive approaches involving use of hydrogen, a catalyst and high pressure units. Where as extractive distillation methods developed above are based on synthetic feed mixture consisting of cyclopentane and 2,2-dimethylbutane only. In typical light petroleum streams higher boiling components like 2-methyl pentane (b.p. 60°C), 3-methyl pentane (b.p. 63°C) and 2,3-dimethyl butane (b.p. 58°C) etc., which are more difficult to separate from CP, are also invariably present. Presence of these components affect the final purity and recovery of CP in an extractive distillation step. In the present invention, therefore, actual feedstocks available in the petroleum industry have been investigated wherein different heart cuts have been prepared, analysed (componentwise) and studied in extractive distillation step for production of CP of required purity. The studies revealed that it is difficult to produce required purity of CP in extractive distillation step when these components (2-methyl pentane, 3-methyl pentane, 2,2-dimethyl butane and 2,3- dimethyl butane) are present besides pentanes in appreciable concentrations in the feedstock intended for CP production. The main objective of the present invention is to provide an improved process for production of cyclopentane from light petroleum fraction. Yet another objective of the present invention is to identify and optimise the typical refinery feedstock so as to minimise the concentration of higher boiling components (2-methyl pentane, 3-methyl pentane, 2,2-dimethyl butane and 2,3-dimethyl butane) and maximise the concentration and recovery of CP in the optimised boiling range of the feed. Still another objective of the present invention is to study this optimised feedstock composition to separate CP from close boiling paraffinic hydrocarbons in the extractive distillation step using selective solvent. Yet another object of the present invention is to simulate the results using the mutual solubility data of individual hydrocarbon components with selective solvent. In the present invention, therefore, the cyciopentane is separated from close boiling paraffinic hydrocarbons from optimised light petroleum feedstock by extractive distillation using polar organic solvent like NMP. The flow diagram of the present invention is shown in Figure-1 of the drawing accompanying this specification. According to this process diagram the feed stream is introduced through line (1) in the fractional distillation column (A) where two streams are produced. The bottom stream being rich in heavier impurities is discarded via line (2). The top stream containing light boiling components alongwith maximum CP introduced through line (3) in the extractive distillation column (B) and lean solvent is introduced via line (4) where two streams meet counter currently. The column may be comprised either by packed or plate column. The distillate and bottom phase, thus produced are separately withdrawn through line (5) & (6) respectively. The bottom phase obtained from column (B) is introduced via line (6 in the second distillation column (C) for solvent recovery from where solvent free hydrocarbons are withdrawn through line (7) and recovered solvent is withdrawn through line (8) routed through reboiler (D) and water heater (E) recycled back to extractor (B) via line (4). The distilled water from separator (F) is fed to water heater (E) via line (9). The steam generated in water heater is fed in to the solvent recovery column © through line (10). The reflux ratio (Ratio of the portion of condensed vapour which is returned to the distillation column to the portion of condensed vapour which is withdrawn as distillate) may be employed in the range of 5:1 to about 50:1 (vol/vol). Accordingly the present invention provides an improved process for production of cyclopentane from light petroleum fraction comprises a) Characterized in that prefractionating the light petroleum fraction feed to prepare total boiling point (TBP) cut in the range of 25-55°C, b) contacting the above said feed cut with a polar organic solvent N-methyl-2- pyrrolidone containing 0-25% by weight of water in the extractor-B at a reboiler temperature ranging between of 80-200°C with a solvent to feed ratio in range of 2-20 by weight to obtain an extract phase and a distillate phase, c) distilling the above said extract phase in a column-C at a reboiler temperature in the range of 100-200°C to recover the desired cyclopentane and recovering the extraction solvent for recycle. In an embodiment of the present invention optimised petroleum feed cut boiling is preferably in the range of 25-45°C. In another embodiment of the present invention the extraction solvent used is N-methyl-2-pyrrolidone containing preferably 0-20% of water. In yet another embodiment of the present invention the ratio of solvent to feed is preferably in the range of 5-15 by weight. In still another embodiment of the present invention the bottom temperature of extractor-B is preferably in the range of 100-160°C. The process of invention is illustrated by the use of the following examples, which should not be construed to limit the scope of the invention. EXAMPLE-1 The liquid-liquid equilibrium data were generated with n-pentane-cyclopentane model mixture containing 60.6 wt.% of n-cyclopentane, which was in admixture with an equal weight of NMP at 20°C. The liquid phase under equilibrium were formed. Each phase was separated made solvent free and analyzed. Cyclopentane was reduced to 49.6 wt.% in the raffinate phase. The solvent-free extract obtained contains 16.4 wt.% of cyclopentane. The solubility of the extract hydrocarbons being 23.4 wt.% in the solvent phase. EXAMPLE-2 The n-pentane-cyclopentane model hydrocarbon mixture with small impurities containing 11.9 wt.% cyclopentane was fed into the 10th plate of feed entry point in extractive distillation column at a rate of 0.1925 kgs/hr and solvent (NMP) fed into the 40th plate of the column at a rate of 0.9917kgs/hr. The temperature of reboiler is maintained at 110°C while the temperature of feed entry point and top is maintained at 38°C and 34°C respectively. The resulting distillate phase was withdrawn from the top of the column at a rate of 0.120kgs/hr and bottom phase was withdrawn at a rate of 1.1656kgs/hr. The distillate phase from the extractive distillation column contain 93.3 wt.% of n-pentane, 0.4 wt.% of cyclopentane and 6.3 wt.% of other saturates without NMP. The solvent -free bottom phase from the extractive distillation column contains 34.5 wt.% of cyclopentane, 54.3 wt.% of n-pentane and 11.2 wt.% of other saturates impurities. EXAMPLE-3 The n-pentane-cyclopentane model hydrocarbon mixture with small impurities containing 11.9 wt.% cyclopentane was fed into the 10th plate of feed entry point in extractive distillation column at a rate of 0.1927 kgs/hr and solvent (NMP) fed into the 40th plate of the column at a rate of 0.9297kgs/hr. The temperature of reboiler is maintained at 130°C while the temperature of feed entry point and top is maintained at 50°C and 34°C respectively. The resulting distillate phase was withdrawn from the top of the column at a rate of 0.1331kgs/hr and bottom phase was withdrawn at a rate of 1.0416kgs/hr. The distillate phase from the extractive distillation column contains 93.2 wt.% of n-pentane, 0.2 wt.% of cyclopentane and 6.1 wt.% of other saturates without NMP. The solvent -free bottom phase from the extractive distillation column contains 51.7 wt.% of cyclopentane, 40.3 wt.% of n-pentane and 8.0 wt.% of other saturates impurities. EXAMPLE-4 The n-pentane-cyclopentane model hydrocarbon mixture with small impurities containing 15.7 wt.% cyclopentane was fed into the 10th plate of feed entry point in extractive distillation column at a rate of 0.1937 kgs/hr and solvent (NMP) fed into the 40th plate of the column at a rate of 0.9297kgs/hr. The temperature of reboiler is maintained at 150°C while the temperature of feed entry point and top is maintained at 82°C and 34°C respectively. The resulting distillate phase was withdrawn from the top of the column at a rate of 0.160kgs/hr and bottom phase was withdrawn at a rate of 0.9255kgs/hr. The distillate phase from the extractive distillation column contains 94.9 wt.% of n-pentane and 5.1 wt.% of other saturates without NMP. The solvent -free bottom phase from the extractive distillation column contains 80.7 wt.% of cyclopentane, 4.4 wt.% of n-pentane and 14.9 wt.% of other saturates impurities. EXAMPLE-5 The n-pentane-cyclopentane model hydrocarbon mixture with small impurities containing 14.0 wt.% cyclopentane was fed into the 10th plate of feed entry point in extractive distillation column at a rate of 0.0927 kgs/hr and solvent (NMP+10% wtaer) fed into the 40th plate of the column at a rate of 0.908kgs/hr. The temperature of reboiler is maintained at 140°C while the temperature of feed entry point and top is maintained at 50°C and 33°C respectively. The resulting distillate phase was withdrawn from the top of the column at a rate of 0.0813kgs/hr and bottom phase was withdrawn at a rate of 0.9194kgs/hr. The distillate phase from the extractive distillation column contains 94.9 wt.% of n-pentane and 5.1 wt.% of other saturates without NMP. The solvent -free bottom phase from the extractive distillation column contains >95.3 wt.% of cyclopentane, 1.8 wt.% of n-pentane and 2.9 wt.% of other saturates impurities. EXAMPLE-6 The IBP-35°C cut of NGL/naphtha containing -1.7-4.1% of cyclopentane was fed into the 10th plate of feed entry point in extractive distillation column at a rate of 8.7 kgs/hr and solvent (NMP) fed into the 40th plate of the column at a rate of 56.0 kgs/hr. The temperature of reboiler is maintained at 145°C while the temperature of feed entry point and top is maintained at 40°C and 25°C respectively. The resulting distillate phase was withdrawn from the top of the column at a rate of 8.9 kgs/hr and bottom phase was withdrawn at a rate of 55.9 kgs/hr. The distillate phase from the extractive distillation column contains 41.6 wt.% of n-pentane, 36.1 % of i-pentane, 22.3 wt.% of other saturates, 6.4 wt.% water and without NMP. The solvent-free bottom phase from the extractive distillation column contains -80 wt.% of cyclopentane, 2.3 wt.% of n-pentane and 17.7 wt.% of other saturates impurities. The main advantages of the present invention are as follows: 1. Selection of proper feedstock and its boiling ranges. 2. Production of required purity of CP used in blowing polyurethane foam. 3. Use of environmentally friendly solvent such as NMP in an admixture with antisolvent such as water. 4. Highly simplified and flexible flowsheet. We Claim: 1. An improved process for production of cyclopentane from light petroleum fraction, said process comprises steps; a) Characterized in that prefractionating the light petroleum fraction feed to prepare total boiling point (TBP) cut in the range of 25-55°C, b) contacting the above said feed cut with a polar organic solvent N-methyl-2- pyrrolidone containing 0-25% by weight of water in the extractor-B at a reboiler temperature ranging between of 80-200°C with a solvent to feed ratio in range of 2-20 by weight to obtain an extract phase and a distillate phase, c) distilling the above said extract phase in a column-C at a reboiler temperature in the range of 100-200°C to recover the desired cyclopentane and recovering the extraction solvent for recycle. 2. A process as claimed in claim 1 wherein the optimized petroleum feed cut boiling is preferably in the range of 25-45°C, 3. A process as claimed in claims 1&2 wherein the extraction solvent used is N- methyl-2-pyrrolidone containing preferably 0-20% of water. 4. A process as claimed in claims 1 to 3 wherein the ratio of solvent to feed is preferably in the range of 5-15 by weight. 5. A process as claimed in claims 1 to 4 wherein reboiler temperature of extractor-B is preferably in the range of 100-160°C. 6. An improved process for the production of cyclopentane from light petroleum fraction substantially as herein described with reference to the examples and drawings accompanying this specification.

Documents:

430-del-2001-abstract.pdf

430-del-2001-claims.pdf

430-del-2001-correspondence-others.pdf

430-del-2001-correspondence-po.pdf

430-del-2001-description (complete).pdf

430-del-2001-drawings.pdf

430-del-2001-form-1.pdf

430-del-2001-form-18.pdf

430-del-2001-form-2.pdf

430-DEL-2001-Form-3.pdf