RU2540404C1 - Method and apparatus for isomerisation of c5-c6 hydrocarbons with supply of purified circulating hydrogen stream - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for isomerisation of C₅-C₆ hydrocarbons with supply of circulating hydrogen, which includes loading hydrogen and feedstock containing C₅-C₆ hydrocarbons into an isomerisation zone, products of which are fed into a separator, removing a product stream containing C₄ or heavier hydrocarbons from below the separator into a fractionation unit consisting of at least one fractionation column, and removing from the top of the separator a gas stream consisting of hydrogen and light hydrocarbons, which is subjected to recirculation using a recirculating compressor for combining with the feedstock, into which an additional amount of hydrogen is fed if necessary. The method includes purification of the circulating hydrogen stream from C₅ and C₆ hydrocarbons, which are the end products of the isomerisation process, to a value not greater than presence thereof in the feedstock, and also from components which boil at a temperature higher than the boiling point of isopentane. The fractionation unit consists of a stabiliser, a first and a second fractionation column. The present invention also relates to an apparatus for carrying out said method.

EFFECT: use of the present method enables to obtain an isomerisation product having a high octane number.

16 cl, 2 tbl, 6 dwg

Description

The invention relates to the isomerization of hydrocarbons to obtain a high-octane component of gasoline and can be used in the refining and petrochemical industries.

A known method of isomerization of light paraffin hydrocarbons C ₄ -C ₆ , including mixing them with hydrogen or a hydrogen-containing gas, the molar ratio of H ₂ : hydrocarbons at the inlet of the isomerization reactor is (0.2-7): 1 (patent for the invention RU 2176233 C1 , C07C 5/27, C10G 35/085, 11/27/2001). The disadvantages of this method are:

- the use of a hydrogen-containing gas containing components of 2,2-DMB and isopentanes, which reduce the selectivity of the isomerization process;

- the patent does not specify the cases in which a hydrogen-containing gas may be used or fresh hydrogen should be used.

A known isomerization unit containing catalytic isomerization, stabilization units and a distillation column for extracting normal hexane from the isomerization products of isomerizate returned to the reactor as a recycle (Akhmetov SA Lectures on the technology of deep processing of oil into motor fuels: a training manual. St. Petersburg: St. -Petersburg Medical Publishing House, 2007, p.262). The main disadvantages of the installation are the lack of circulation of a hydrogen-containing gas, leading to a deterioration in the economic characteristics of the process, and low quality fractionation.

Known isomerization unit "Isomalk-2", aimed at obtaining a gasoline fraction and comprising a tube furnace, isomerization reactors, a separator, a desiccant of hydrogen-containing gas, a compressor, a stabilization column (Production of environmentally friendly gasolines. The latest information on the design and construction of isomerization units. Analysis of technological schemes of isomerization . http://nefthim.com/pics/press_cat1_item58_pre.pdf). The disadvantages of this installation are:

- feeding from the top of the separator a circulating hydrogen-containing gas containing components of 2,2-DMB and isopentanes, which reduce the selectivity of the isomerization process directly to the isomerization reactors;

- the stabilizer available on the installation does not provide for the circulation of normal pentane and hexane hydrocarbons returned to isomerization reactors, which reduces the yield of final products.

By technical nature, the closest to the claimed invention is a method for the isomerization of C ₅ -C ₆ hydrocarbons, which includes loading hydrogen and raw materials containing C ₅ -C ₆ hydrocarbons into the isomerization zone, the products of which are sent to a separator, from the bottom of the separator are taken to separation in a fractionation unit consisting of at least one fractionator product stream comprising c ₄ and heavier hydrocarbons, and is withdrawn from the top separator gas stream consisting of hydrogen and light hydrocarbons which podver ayut recirculation using recycle compressor for combining with the feedstock, where additional hydrogen is introduced as necessary (patent RU 2364582 C2, C07C 5/22, C07C 9/16, 20.04.2009). The disadvantages of this method are:

- the use of a circulating hydrogen-containing gas containing components of 2,2-DMB and isopentanes, which reduce the selectivity of the isomerization process;

- the patent does not specify in which cases fresh hydrogen is supplied.

Also known is a C ₅ -C ₆ hydrocarbon isomerization unit with a circulating hydrogen flow supply, including a raw material isomerization reactor, a separator, a fractionation unit consisting of one distillation column with rectification product outlet fittings, refrigerators, riboilers, a compressor, pumps, pipelines that combine technological devices into a single technological scheme (patent for invention RU 2364582 C2, C07C 5/22, C07C 9/16, 04/20/2009). The main disadvantages of the installation are:

1) supply from the top of the separator a circulating hydrogen-containing gas containing components of 2,2-DMB and isopentanes, which reduce the selectivity of the isomerization process directly to the isomerization reactors;

2) one distillation column available at the plant does not provide a clear recovery of the recirculating normal pentane and hexane hydrocarbons returned to the isomerization reactors, since isohexanes enter this stream simultaneously with normal pentane and hexane, which reduces the yield of final products.

3) insufficient depth of extraction of isomerization products associated with the fractionation of isomerization products in one distillation column and the loss of isomerization products into hydrogen containing gas.

When creating the invention, the task was to increase the output of the high-octane component for compounding marketable gasolines by intensifying the operation of the isomerization reactor and increasing the clarity of the separation of isomerization products.

The solution to this problem is achieved by the fact that in the method of isomerization of C ₅ -C ₆ hydrocarbons with the supply of circulating hydrogen, including the loading of hydrogen and raw materials containing C ₅ -C ₆ hydrocarbons, into the isomerization zone, the products of which are sent to the separator, are taken away from the separator to the separation a fractionation unit consisting of at least one fractionator product stream comprising c ₄ and heavier hydrocarbons, and is removed from the top of the separator the gas stream consisting of hydrogen and light hydrocarbons, the latter d is recycled using recycle compressor for combining with the raw material, if necessary, adding additional hydrogen by purification of the circulating flow of hydrogen from hydrocarbons C ₅ and C _6, which are the end products of the isomerization process, to a value not greater than their presence in the feedstock, and also from components boiling above the boiling point of isopentane, and the fractionation unit consists of a stabilizer, first and second distillation columns.

It is advisable to purify the circulating hydrogen stream by providing absorption with the supply of an external hydrocarbon fraction containing C ₅ or C ₆ hydrocarbons or a mixture thereof, in which up to 0.5% of the mass is absent or present, as an absorbent. end products of the isomerization process.

It is advisable to purify the circulating stream of hydrogen by providing absorption with the supply of pentane or hexane recycles or a mixture thereof obtained on the fractionation unit as absorbent. The use of the pentane fraction recovered from the depentanization or deisopentanization-deptentanization column allows absorption of the final isomerization products in order to prevent their return to the reactor, which will inhibit the main isomerization reaction. Similarly, when the hexane fraction recovered from the deisohexanizer column is used as absorbent, the final isomerization products are selectively removed from the circulating hydrogen stream. Saturated with the end products of isomerization, pentane and hexane recycles are returned back to the corresponding columns. When using a mixture of pentane and hexane recycles as an absorbent, they are enriched with the final products of isomerization. Moreover, in all variants of the use of absorbent, a deep purification of the circulating hydrogen stream is ensured mainly from isomeric hydrocarbons, which contributes to the intensification of the operation of the isomerization reactor. The advantage of this method is the minimal cost of cleaning the circulating hydrogen stream through the use of absorbents of our own production, which eliminates the cleaning of the absorbent from harmful impurities and moisture when using a third-party absorbent, as well as the possibility of using the absorbents necessary for cleaning the circulating hydrogen stream in a wide range of costs.

It is advisable to provide the purification of the circulating hydrogen stream with a membrane method, which makes it possible to efficiently separate hydrogen from gas mixtures containing hydrogen in the range of 40-80%. Using the membrane method, it is possible to produce hydrogen with a purity of at least 98%, which intensifies the operation of the isomerization reactor. In addition, the advantages of the membrane method are the continuity of the process, its simplicity, compactness of the equipment, quick exit to the operating mode. Membrane processes are actively used in the regeneration of purge and waste gases of cyclic processes of oil refining and petrochemicals, they provide highly concentrated hydrogen, which is returned to the process, thereby saving the consumption of fresh hydrogen.

It is also advisable to purify the circulating hydrogen stream by providing short-cycle adsorption both in one purification step and in two steps, while deep removal of the final isomerization products is ensured in full. In the first case, the purification of the circulating stream of hydrogen from hydrocarbons returned to the rectification unit is ensured. In a two-stage purification of the circulating hydrogen stream, normal paraffinic hydrocarbons are recovered from it by CaA zeolites from the first stage, which, after regeneration of the adsorbent by hydrogen, are returned to the isomerization reactor, and in the second stage of purification, isoparaffin hydrocarbons are recovered from the purified circulating hydrogen stream by NaX, which are sent further to the regeneration of the adsorbent fractionation unit. The short-cycle adsorption method is economical and modern; advantages of this method:

- process continuity;

- low consumption of adsorbent;

- cheap adsorbents;

- effective and simple technologies;

- high depth of gas flow purification;

- slight pressure loss of the gas being cleaned.

Note that both membrane and adsorption methods (under conditions of short cycle separation) are molecular-selective processes and do not contain energy costs for phase transitions. These processes are currently quite promising.

It is also advisable to clean the circulating stream of hydrogen to provide low-temperature separation, while the loss of hydrogen is minimal. Hydrogen is extracted from the mixture by cooling the gas mixture to a temperature at which hydrocarbons become liquid and hydrogen remains in the gaseous phase. The separation is based on the difference in partial pressures of hydrogen and hydrocarbons.

The choice of a specific method for purifying a circulating hydrogen stream is determined by the economy and technological features of a particular production.

The considered method of isomerization of C ₅ -C ₆ hydrocarbons can be implemented on a C ₅ -C ₆ hydrocarbon isomerization unit, including a raw material isomerization reactor, a separator, a fractionation unit, consisting of at least one distillation column with rectification product outlet fittings, refrigerators, riboilers, compressor, pumps, pipelines, combining technological devices into a single technological scheme, on the pipeline of the circulating hydrogen flow connecting the compressor with the feed pipe the installation unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons is installed, and the fractionation unit consists of stabilizer pipelines connected in series, a first distillation column and a second distillation column.

The unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons can have a different hardware design.

It is advisable that the unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons include an absorber connected in the upper part by a fitting with a supply pipe as an absorbent of the external hydrocarbon fraction containing C ₅ or C ₆ hydrocarbons or a mixture of them that are absent or are present before 0.5% of the mass. the final products of the isomerization process, and in the lower part the fitting of the outlet of the saturated absorbent connected by a pipeline to the first distillation column. It is also possible to connect the absorber supply pipe at the top of the absorber with a pentane recycling outlet fitting from the first distillation column, or a hexane recycling outlet fitting from the first distillation column, or a fitting for withdrawing a mixture of pentane and hexane recycling from the first distillation column. It is necessary that the absorber ensures the absorption of C ₅ and C ₆ hydrocarbons by the absorbent supplied to the top of the absorber. The absorber is a vertical column apparatus with contact devices in the form of plates or nozzles.

It is advisable that the unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons include a membrane separation apparatus that operates on the principle of different permeability of gas mixture components through polymer membranes, including hydrogen and hydrocarbons, installed on the pipeline of the circulating hydrogen flow. Concentration of hydrogen from a circulating stream of hydrogen to a technologically necessary level makes it possible to return hydrogen back to the installation, thereby increasing the capacity and economic efficiency of production.

It is advisable that the unit for cleaning the circulating stream of hydrogen from C ₅ and C ₆ hydrocarbons includes an adsorber and a stripper operating alternately. The adsorber and desorber are vertical column devices with a fixed adsorbent layer. The flow of circulating hydrogen is supplied to the adsorber at elevated pressure and ambient temperature, the cleaned flow of hydrogen is returned to the pipeline of the circulating flow of hydrogen. In the adsorber, the easily adsorbed components of the flow — hydrocarbons — are absorbed by the adsorbent, while the weakly adsorbed or non-adsorbed (hydrogen) pass through the apparatus, which separates the circulating hydrogen stream into purified hydrogen and adsorbed hydrocarbons. The adsorbent absorbs gas to a state of equilibrium between adsorption and desorption, after which the adsorber switches to the regeneration stage to remove absorbed components from the surface of the adsorbent and becomes a desorber as intended. In this case, the apparatus is connected to the pipelines for the supply of a desorbing agent and the removal of desorption products.

It is advisable that the unit for cleaning the circulating hydrogen flow from C ₅ and C ₆ hydrocarbons includes two stages of adsorption purification, while the stripper of the first purification stage is connected with the inlet fitting to the hydrogen supply pipe as a desorbing agent and the outlet fitting is connected to the raw material input pipe to the installation, and the stripper the second stage of cleaning was connected by an inlet fitting to the pipeline for supplying water vapor as a stripping agent and the outlet nozzle was connected in series with a condenser refrigerator, eparatorom and first distillation column.

It is also advisable that the unit for cleaning the circulating stream of hydrogen from C ₅ and C ₆ hydrocarbons includes a low-temperature separator.

The figure 1 presents according to the prototype method for the isomerization of C ₅ -C ₆ hydrocarbons and the installation scheme that implements this method. Figure 1 contains the following positions:

104 - zone of isomerization,

105 - compressor

108 - a separator of reaction products,

110 - column deisohexanizer,

113 - capacitor

114 - cooling device

119 - isomerizate stripping column,

101-103, 106, 107, 109, 111, 112, 115, 116-118, 120, 121 - pipelines.

The method of isomerization of hydrocarbons according to the prototype is as follows.

Fresh feed is introduced into isomerization zone 104 containing a zeolite isomerization catalyst. Hydrogen is mixed with the feed to the isomerization zone 104. Additional gas may be supplied if necessary.

The reaction products from the isomerization zone enter a reaction product separator 108, in which the reaction products are separated into a product stream containing C ₄ and heavier hydrocarbons and an overhead gas stream consisting of hydrogen and lighter hydrocarbons, including C ₃ and low boiling compounds. The effluent can enter into heat exchange before the reaction products 108 enter the separator. The hydrogen-rich gas stream flows from the reaction product separator 108 and is recycled using a recirculation compressor 105 to combine with the feed.

According to the invention, the product stream is sent to a deisohexanizer column 110, from where a stream containing light gases and butane is discharged from the top. The overhead stream from the deisohexanizer column 110 may be directed to the overhead condenser 113 to form off-gas containing mainly light gases and butane, and a recycle stream containing C ₅ and higher hydrocarbons. The recycle stream is sent to a deisohexanizer column 110. Since a portion of C ₅ and higher hydrocarbons can pass through the upper condenser 113, an optional cooling device 114 may be provided on the upper stream discharged from the condenser to minimize losses of C ₅ and higher hydrocarbons.

The upper side stream from the deisohexanizer column 110 with a high concentration of normal pentane, methylbutane and dimethylbutane is directed to the isomerizate 119 stripping column to remove light fractions. The isomerizate withdrawn from the top of the isomerizate 119 stripping column may combine with a stream containing light gases and butane. A stream containing normal pentane, methylbutane and dimethylbutanes is diverted from the bottom of the isomerizate 119 stripping column.

The lower side stream from the deisohexanizer column 110 containing normal hexane and monomethyl pentanes is returned for recycling to the deisohexanizer column 110.

Heavier hydrocarbons are discharged from the deisohexanizer column 110 as a stream of heavy hydrocarbons.

The installation of isomerization of hydrocarbons according to the prototype operates with the following relationship apparatus.

Isomerization feed is supplied to the plant through a pipeline 101, which is connected to the reactor of the isomerization zone 104, while from the bottom of the isomerization zone 104, the unstable isomerizate pipeline 106 is connected to the nozzle of the reaction product separator 108, from the top of which a loop of a circulating hydrogen stream is connected to the compressor 105, after which pipeline 102 is connected to the feed pipe 101, and a fresh hydrogen supply pipe 103 is connected to the circulating hydrogen flow pipe 102. From the bottom of the product separator of reaction 108, the pipe of the isomerizate 107 is connected to the nozzle of the deisohexanizer column 110. The overhead from the column of the deisohexanizer 110 is discharged via line 111, which is connected to the condenser nozzle 113, from where evaporated vapors, after cooling in the cooling device 114, are discharged by line 112 from the unit, and from the bottom, the condensate pipeline 117 is connected to the nozzle of the deisohexanizer column 110. On the side of the deisohexanizer column 110, above the feed input, pipeline 115 is connected to the nozzle of the stripping column from merizata 119, from the top of which conduit 116 is connected to a conduit 111, and from the bottom of stripping column 119 isomerate stripped isomerate conduit 118 removed from the plant. On the side of the deisohexanizer column 110, below the feed input, the pipe 109 is connected to the feed pipe 101. A portion of the heavy hydrocarbons from the bottom of the deisohexanizer 110 is returned to the column, while the pipe 121 is connected to the nozzle of the deisohexanizer 110, and the remainder is discharged from the installation pipeline 120.

The invention is illustrated in the drawing, where figure 2 shows a schematic diagram of an isomerization unit that implements the implementation of the proposed invention by supplementing it with a purification unit for a circulating hydrogen stream and using an additional stabilizer and a second distillation column.

The scheme of the installation of isomerization with the purification of the circulating stream of hydrogen contains the following positions:

2, 8, 12 - heat exchangers,

4 - tube furnace

6 - isomerization reactor,

10, 43 - separator,

14 - stabilization column,

18 - the first distillation column,

22 - the second distillation column,

28 - compressor

30 - absorber,

35 - block membrane cleaning of a circulating stream of hydrogen,

36 - adsorber,

37 - stripper,

38 - stage I adsorber,

39 - desorber stage I,

40 - adsorber stage II,

41 - desorber II stage,

42 - cooling device

45 - block low temperature separation (NTS),

47 - block isomerization,

1, 3, 5, 7, 9, 11, 13, 15-17, 19-21, 23-27, 29, 31-34, 44, 46 - pipelines.

The inventive method of isomerization of hydrocarbons with the purification of a circulating stream of hydrogen is implemented as follows.

The feedstock with a temperature of 50 ° C containing C ₅ -C ₆ hydrocarbons is heated in a heat exchanger 2 to a temperature of 150 ° C, then it enters a tube furnace 4. The raw material heated to 170 ° C is fed to the isomerization reactor 6. The bottom stream containing C ₄ and heavier hydrocarbons, after the isomerization reactor 6 enters the heat exchanger 8, where it is cooled to 40 ° C and then enters the separator 10, in which the circulating stream of hydrogen from the isomerizate is separated. From the separator 10, the isomerizate enters the heat exchanger 12, where it is heated to 120 ° C, and then fed to the stabilization column 14. Light hydrocarbons are evaporated in the stabilization column 14 and hydrocarbon gas and liquefied petroleum gas are removed from the top. From the bottom of the stabilization column 14, a stable isomerizate is discharged to the first distillation column 18 operating in the deisopentanization or deisopentanization-depentanization mode. The upper stream of the first distillation column 18, containing mainly isopentanes, is discharged from the installation. A recycle stream containing mainly pentanes is directed to mixing with the feed. The lower product of the first distillation column 18, containing hydrocarbons of C ₆ and higher, is sent for separation into the second distillation column 22 operating in the deisohexanization-dehexanization mode. The top product 23, which contains mainly isohexanes, is mixed with the top product of the first distillation column 18 and then removed from the installation. The recycle stream of the second distillation column 22, containing mainly hexanes, is directed to mixing with the feed. From the bottom of the second distillation column 22, heavy hydrocarbons are discharged from the installation.

The upper gas stream, consisting of hydrogen and lighter hydrocarbons, from the separator 10 passes through the compressor 28 and then enters the absorber 30, after which it is sent for recycling and combined with the raw material. If necessary, an additional amount of fresh hydrogen is introduced.

In the absorber 30, the circulating hydrogen stream is purified from the C ₅ and C ₆ hydrocarbons using an absorbent. Pentane or hexane recycles or mixtures thereof obtained on the fractionation unit, in this case in the first distillation column 18, are used as absorbent. Fresh absorbent enters the upper part of the absorber 30. The saturated absorbent from the bottom of the absorber 30 is returned to the first distillation column 18.

The hydrocarbon isomerization unit according to the claimed invention operates in the following apparatus relationship.

The feedstock containing C ₅ -C ₆ hydrocarbons, enters the installation through pipeline 1, which is connected to the nozzle of the heat exchanger 2, from which pipe 3 is connected to the coil of the tube furnace 4. The heated raw material after the tube furnace 4 by pipe 5 is connected to the nozzle of the isomerization reactor 6 . The bottoms stream comprising C ₄ and heavier hydrocarbons, isomerization reactor after 6 duct 7 is connected to the heat exchanger fitting 8, then the line 9 is connected with the nozzle separator 10. with the bottom of the separator 10 conduit iso The riser 11 is connected to the nozzle of the heat exchanger 12, where it is heated to 120 ° C, and then the pipe 13 is connected to the stabilization column 14. Light hydrocarbons are evaporated from the top of the stabilization column 14, and hydrocarbon gas is discharged through pipeline 15, and liquefied hydrocarbon gas is discharged through pipeline 16 . The stabilization column 14 is connected by a pipe 17 to the first distillation column 18 operating in the deisopentanization or deisopentanization-depentanization mode. The overhead stream of the first distillation column 18, which contains mainly isopentanes, is discharged from the installation via pipeline 19. The pipeline 20 of the recycle stream, which contains mainly pentanes, is connected to the feed pipe 1. The first distillation column 18 is connected by a pipe 21 to the second distillation column operating in the mode deisohexanization-dehexanization 22. The top product, containing mainly isohexanes, is discharged by a pipe 23, which is connected to a pipe 19, and then removed from the installation about the pipeline 24. The pipeline 25 of the recycle stream, containing mainly hexanes, is connected to the feed pipe 1. Heavy hydrocarbons are discharged from the bottom of the second distillation column 22 through the pipeline 26.

The upper gas stream, consisting of hydrogen and lighter hydrocarbons, is discharged from the separator 10 through a pipe 27, which is connected to the compressor 28, then the pipe 29 is connected to the lower fitting of the absorber 30, after which from the top the pipe 31 is connected to the feed pipe 1, and to a pipeline for a circulating stream of hydrogen 31 is connected to a pipeline for supplying fresh hydrogen 32.

The supply of fresh absorbent to the absorber 30 is carried out using a pipe 33 connecting the nozzle of the first distillation column 18 and the upper nozzle of the absorber 30. The saturated absorbent from the bottom of the absorber 30 is returned to the first distillation column 18 through line 34.

The figure 3 presents the purification unit of the circulating hydrogen stream using a membrane purification method. The membrane cleaning unit of the circulating hydrogen stream 35 consists of a membrane gas separation apparatus. According to the presented scheme, the feedstock through pipeline 5 containing C ₅ -C ₆ hydrocarbons is fed to isomerization unit 47. The lower stream containing C ₄ and heavier hydrocarbons, after isomerization unit 47, through pipeline 17 is diverted to the first distillation column 18 The upper gas stream, consisting of hydrogen and light hydrocarbons, after the isomerization unit 47 through pipeline 29 is sent for cleaning to the membrane cleaning unit of the circulating hydrogen stream 35, after which it is circulated through the cleaned pipe 31 The total flow of hydrogen is recycled and combined with the feed. If necessary, an additional amount of fresh hydrogen is introduced, and the concentrated hydrocarbon gas is discharged to the side. An isopentane fraction is discharged from the top of the first distillation column 18 through a pipeline 19, a pentane fraction is discharged by a lateral stream through a pipeline 20, which is sent for recirculation, and hydrocarbons C ₆ and higher are sent to the bottom to be separated.

The figure 4 presents the purification unit of the circulating stream of hydrogen using short-cycle adsorption. According to the presented scheme, the feedstock through pipeline 5 containing C ₅ -C ₆ hydrocarbons is fed to isomerization unit 47. The lower stream containing C ₄ and heavier hydrocarbons, after isomerization unit 47, through pipeline 17 is diverted to the first distillation column 18 The upper gas stream, consisting of hydrogen and light hydrocarbons, after the isomerization unit through line 29 is sent for cleaning to the adsorber 36, after which it is sent through line 31 for recycling and combined with the feed. If necessary, an additional amount of fresh hydrogen is introduced. In the adsorber 36, a deep purification of the circulating hydrogen stream from hydrocarbons is carried out using an adsorbent, for example, NaX zeolite. After the adsorbent is saturated with hydrocarbons, the adsorber switches to the stage of desorption by the desorbing agent — water vapor. So, according to figure 4, the stripper 37 operates in the desorption mode, while the desorption products with water vapor condense and, after separation from the water, the hydrocarbons are combined with the isomerizate entering through the pipe 17 into the first distillation column 18 and are sent together with it to the first distillation column 18 for further separation.

In addition, two-stage adsorption is possible (Figure 5), while in the first separation stage in the adsorber of stage I 38, the circulating hydrogen stream is cleaned from normal paraffin hydrocarbons using a CaA zeolite adsorbent. After the adsorbent is saturated with hydrocarbons, the adsorber switches to the stage of desorption with a desorbing agent - hydrogen. Desorption products discharged from the stage I stripper, normal paraffins, are combined with the flow of a circulating hydrogen stream after the second stage of adsorption purification. From the top of the stage I adsorber 38, the circulating hydrogen stream purified from normal hydrocarbons is sent to the second stage of adsorption purification to stage II adsorber 40, where isostructure hydrocarbons are extracted using the adsorbent zeolite NaX. After the adsorbent is saturated with hydrocarbons, the adsorber of stage II 40 switches to the desorption stage using water vapor as the desorbing agent. Desorption products discharged from stripper II of stage 41 enter a cooling device 42 and are then sent to a separator 43 for separation from water, after which isostructure hydrocarbons are combined with isomerizate, which is passed through pipeline 17 to the first distillation column 18 and sent together with it to the first distillation column 18 for further separation. An isopentane fraction is discharged from the top of the first distillation column 18 through a pipeline 19, a pentane fraction is discharged by a lateral stream through a pipeline 20, which is sent for recirculation, and hydrocarbons C ₆ and higher are sent to the bottom to be separated.

The figure 6 presents the block cleaning the circulating flow of hydrogen using low temperature separation. According to the presented scheme, the feedstock through pipeline 5 containing C ₅ -C ₆ hydrocarbons is fed to isomerization unit 47. The lower stream containing C ₄ and heavier hydrocarbons, after isomerization unit through pipeline 17, is diverted to the first distillation column 18. Upper the gas stream, consisting of hydrogen and light hydrocarbons, after isomerization unit 47 through line 29 is sent for purification to the low-temperature separation unit 45, after which it is sent for recycling through line 31 and combined with the feed m If necessary, an additional amount of fresh hydrogen is introduced. In the low-temperature separation unit 45, a circulating stream of hydrogen enters the separator, from the top of which the stream is sent to the heat exchangers for cooling. The mixture coming from the water condenser-cooler is separated in a low-temperature (cold) separator. The hydrocarbon condensate separated from water, which consists mainly of gasoline and light kerosene fractions, is heated up in the heat exchanger after leaving the low-temperature separation unit 45 via a pipe 46 and enters the stabilization column in the isomerization unit 47. A purified hydrogen stream leaving the low-temperature separation unit 45 through the pipeline 31 combines with fresh hydrogen. An isopentane fraction is discharged from the top of the first distillation column 18 through a pipeline 19, a pentane fraction is discharged by a lateral stream through a pipeline 20, which is sent for recirculation, and hydrocarbons C ₆ and higher are sent to the bottom to be separated.

Mathematical modeling of a number of variants of a method for purifying a circulating stream of hydrogen according to the prototype and the claimed invention is performed. The calculation results are shown in table 1.

When carrying out the process of isomerization of hydrocarbons according to the prototype, the circulating stream of hydrogen contains components that contribute to the inhibition of the isomerization process. For example, as can be seen from table 1, in a circulating stream of hydrogen, the content of isopentanes reaches 10.16 wt.%, 2,2-DMB 8.10% wt., Which leads to a decrease in the selectivity of the process. In addition, the effective presence of the isomerization process requires the presence of normal pentanes and hexanes in the feed. So, according to the prototype, the content of these components in the circulating stream of hydrogen is very small: normal pentane 4.0% of the mass. and normal hexane 3.7% of the mass. It should be noted that the increased hydrocarbon content to C ₄ in the isomerization feedstock, according to the prototype 10% by mass, reduces the contact time of C ₅ -C ₆ hydrocarbons with the catalyst. The flow rate of the circulating hydrogen stream is 40,000 nm ³ / h, in which the fresh hydrogen content is 1,500 nm ³ / h.

When cleaning the circulating stream of hydrogen according to the claimed invention using pentane absorbent, the content of 2,2-DMB in the circulating stream of hydrogen decreases from 8.10 to 0.16% by mass, in addition, the content of normal pentanes increases by 13 times (by 47% by mass .), the content of isopentanes decreases from 10% to 2% of the mass. Compared with the prototype, the recharge of fresh hydrogen is almost 2 times reduced, which leads to a reduction in the cost of an additional amount of fresh hydrogen. The consumption of pentane recycle used as absorbent is 10 m ³ / h.

When cleaning the circulating stream of hydrogen according to the claimed invention using a hexane absorbent, the content of 2,2-DMB in the circulating stream of hydrogen decreases from 8.10 to 0.11% by weight, in addition, the content of normal hexanes increases by a factor of 10 (by 35, 7% of the mass.), The hydrogen content increases by 6.48% of the mass. In addition, slightly increased compared with the prototype feed with fresh hydrogen from 1500 to 1670 nm ³ / h The hexane recycle used as absorbent is 15 m ³ / h.

Extraction of high-octane components (isoparaffins) from the circulating hydrogen stream using the absorption method allows to increase the degree of conversion of normal pentane to an equilibrium value, and also allows to increase the proportion of normal hexane in the feed.

As follows from table 1, when using the membrane method, a high degree of purification of the circulating hydrogen flow is achieved, while the hydrogen content reaches up to 97.87% by mass, the content of 2,2-DMB is 0.23% by mass. The content of isopentanes and isohexanes is absent in the circulating flow of hydrogen, which leads to an increase in the selectivity of the process. In this method, recharge with fresh hydrogen is 2700 nm ³ / h.

Also, a high degree of purification of the circulating hydrogen stream is achieved using low-temperature separation. So, from table 1 it follows that in the circulating stream of hydrogen, the hydrogen content is 83.31% of the mass. In contrast to the prototype, there is several times a decrease in the content of the following components: isopentane from 10.16 to 1.68 wt%, 2.2-DMB from 8.1 to 0.5 wt%. Fresh hydrogen feed is 2426 nm ³ / h.

From the data of table 1 it follows that the octane number of the isomerizate of the prototype is 88 p., And according to the claimed invention 90 p., Which confirms the advisability of cleaning the circulating stream of hydrogen.

Mathematical modeling of the adsorption purification process of the circulating hydrogen flow was not performed, since the possibility of deep hydrocarbon extraction from gas streams by zeolites is known from the literature, for example, for CaA zeolite in the purification of a hydrogen-containing gas with a hydrogen concentration of 86%, the adsorption capacity of the zeolite is 6 g of paraffins per 100 g of zeolites with pressure of 5 atm. and a temperature of 300 ° C (Keltsev N.V. Fundamentals of adsorption technology. M: Chemistry, 1976, p. 439).

Table 2 shows the characteristics of the flows diverted from the fractionation unit according to the prototype and the claimed invention, as a set of components potentially contained in these flows. The degree of purity of these flows was not considered, because depending on the fractionation mode and the number of plates in distillation columns, the content of other components in the corresponding flows of impurities can be infinitesimal. As follows from table 2, in the stream diverted through the pipeline 12 from the distillation column according to the prototype, only a mixture of isopentane and normal pentane can be contained, which does not allow to obtain sufficiently pure isopentane and return normal pentane to the isomerization reactor, through pipeline 9 it is recycled only normal hexane, and the totality of isohexanes is discharged through line 18. In contrast, the fractionation unit according to the claimed invention allows to obtain the total isomerizate, consisting of zopentana isohexane and projected on compounding through conduit 24 and sufficiently pure normal pentane and normal hexane, are returned as recycle via conduits 20 and 25 to isomerization reactor after mixing with the feedstock. In addition, normal hydrocarbons can be partially used as absorbents in the absorption treatment of a circulating hydrogen stream.

Thus, the presented variants of the method of isomerization of C ₅ -C ₆ hydrocarbons with purification of the circulating hydrogen stream and improvement of the isomerizate fractionation unit indicate the usefulness of the claimed invention for increasing the yield of high-octane component for compounding gasoline when implementing the method of isomerization of hydrocarbons with purification of the circulating hydrogen stream.

Table 1 Methods for purifying a circulating hydrogen stream Prototype Absorption Membrane method Low temperature separation Pentane Recycling Hexane Recycling Productivity, t / h 65 65 65 65 65 Circulating hydrogen flow, nm ³ / h 40,000 40,000 40,000 40,000 40,000 The content of the components of the circulating stream of hydrogen: % of the mass. % vol. kg / h % of the mass. % vol. kg / h % of the mass. % vol. kg / h % of the mass. % vol. kg / h % of the mass. % vol. kg / h No cleaning With cleaning H ₂ 41.24 96.12 3355 37.06 95.15 3352 47.72 97.08 3347 97.87 99.9 3353 83.31 99.22 3353 to C ₄ 13.07 1.24 1063 9.79 1,04 886 10.96 0.93 769 1.90 0.08 65 13.23 0.67 533 iC ₅ 10.16 0.66 827 2.02 0.15 183 1.44 0.08 101 out out out 1.68 0.06 67 nC ₅ 4.05 0.26 329 50.86 3.65 4600 0.27 0.02 19 out out out 0.46 0.02 19 2,2-DMB 8.10 0.44 659 0.16 0.01 fourteen 0.11 0.01 7 0.23 0.01 8 0.52 0.02 21 nC ₆ 3.74 0.21 304 0.01 0.003 0.5 39.44 1.88 2766 out out out 0.10 0.01 four C ₇ and above 0.06 0.003 5 out out out out out out out out out out out out Oc isomerizate 88 90 Fresh hydrogen feed, nm ³ / h 1500 850 1670 2700 2426 Flushing, m ³ / h - 10 fifteen - - Recharge ratio one 1.09 1.24 1.06 1.06

table 2 Components Boiling point, ° C Prototype pipelines Pipelines according to the claimed invention 9 (recycling) 12 eighteen 20 (recycling) 24 25 (recycling) iC ₅ 27.9 - + - - + - nC ₅ 36.1 - + - + - - 2,2-DMB 49.7 - - + - + - 2MP 60.0 - - + - + - 3MP 63.3 - - + - + - nC ₆ 69.0 + - - - - + The presence of a specific hydrocarbon in the corresponding stream is indicated by (+), and its absence (-)

Claims (16)

1. The method of isomerization of C ₅ -C ₆ hydrocarbons with the supply of circulating hydrogen, comprising loading hydrogen and raw materials containing C ₅ -C ₆ hydrocarbons into the isomerization zone, the products of which are sent to the separator, from the bottom of the separator is taken to separation in the fractionation unit, consisting from at least one distillation column, a product stream containing C ₄ and heavier hydrocarbons, and a gas stream consisting of hydrogen and light hydrocarbons is removed from the top of the separator, which is recycled using recirculation a compressor for combining with raw materials, where, if necessary, an additional amount of hydrogen is introduced, characterized in that the circulating stream of hydrogen is purified from C ₅ and C ₆ hydrocarbons, which are the final products of the isomerization process, to a value not exceeding their presence in the feed, and also from components boiling above the boiling point of isopentane, and the fractionation unit consists of a stabilizer, first and second distillation columns. 2. The method according to claim 1, characterized in that the purification of the circulating stream of hydrogen is ensured by absorption with the supply as an absorbent of an external hydrocarbon fraction containing C ₅ or C ₆ hydrocarbons or their mixture, in which up to 0.5% of the mass is absent or present. end products of the isomerization process. 3. The method according to claim 1, characterized in that the purification of the circulating hydrogen stream is ensured by absorption with the supply of pentane or hexane recycles or a mixture thereof obtained on the fractionation unit as absorbent. 4. The method according to claim 1, characterized in that the purification of the circulating stream of hydrogen is provided by a membrane method. 5. The method according to claim 1, characterized in that the purification of the circulating stream of hydrogen is provided by a short-cycle adsorption method. 6. The method according to claim 5, characterized in that the purification of the circulating stream of hydrogen is provided by a two-stage short-cycle adsorption method. 7. The method according to claim 1, characterized in that the purification of the circulating hydrogen stream is provided by a low-temperature separation method. 8. Installation of isomerization of C ₅ -C ₆ hydrocarbons with a circulating stream of hydrogen, including a raw material isomerization reactor, a separator, a fractionation unit, consisting of at least one distillation column with rectification product outlet fittings, refrigerators, riboilers, compressor, pumps, pipelines that combine technological devices into a single technological scheme, characterized in that the piping of the circulating stream of hydrogen connecting the compressor to the feed pipe is additionally installed poured purification unit circulating hydrogen stream from hydrocarbons C ₅ and C _6, and fractionation unit consists of series connected pipeline system stabilizer, first fractionator the second fractionator. 9. Installation according to claim 8, characterized in that the unit for cleaning the circulating stream of hydrogen from C ₅ and C ₆ hydrocarbons includes an absorber connected at the top by a fitting with a supply pipe as an absorbent of an external hydrocarbon fraction containing C ₅ or C ₆ hydrocarbons or their mixture, in which are absent or present up to 0.5% of the mass. the final products of the isomerization process, and in the lower part the fitting of the outlet of the saturated absorbent connected by a pipeline to the first distillation column. 10. Installation according to claim 8, characterized in that the unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons includes an absorber connected in the upper part by a fitting with a supply pipe as an absorbent of a pentane recycle with a fitting for its outlet from the first distillation column, and in the lower part of the outlet fitting of a saturated absorbent connected by a pipeline to the first distillation column. 11. Installation according to claim 8, characterized in that the unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons includes an absorber connected in the upper part by a fitting with a supply pipe as an absorbent of hexane recycling with a fitting for its outlet from the first distillation column, and in the lower part of the outlet fitting of a saturated absorbent connected by a pipeline to the first distillation column. 12. Installation according to claim 8, characterized in that the unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons includes an absorber connected in the upper part by a fitting with a supply pipe as an absorbent of a mixture of pentane and hexane recycles with a fitting for its output from the first distillation unit columns, and in the lower part the fitting of the outlet of a saturated absorbent connected by a pipeline to the first distillation column. 13. Installation according to claim 8, characterized in that the unit for cleaning the circulating stream of hydrogen from C ₅ and C ₆ hydrocarbons includes a membrane separation apparatus. 14. Installation according to claim 8, characterized in that the unit for cleaning the circulating stream of hydrogen from C ₅ and C ₆ hydrocarbons includes an adsorber and a desorber operating alternately. 15. Installation according to 14, characterized in that the unit for cleaning the circulating flow of hydrogen from hydrocarbons C ₅ and C ₆ includes two stages of adsorption treatment, while the stripper of the first cleaning stage is connected by an inlet fitting to a hydrogen supply pipe and an outlet fitting connected to the pipeline input of raw materials to the installation, and the stripper of the second purification stage is connected by an inlet fitting to a water vapor supply pipeline and an outlet nozzle in series with a condenser refrigerator, a separator and a first distillation column . 16. Installation according to claim 8, characterized in that the unit for cleaning the circulating flow of hydrogen from C ₅ and C ₆ hydrocarbons includes a low-temperature separator.

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