RU2622294C2 - Device for alkylation of isobutane with olefins on solid catalyst - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the device for alkylating isobutane with olefins on solid catalyst in form of distillation column, containing rectification sections and reaction sections with solid catalyst which have feeding channel and overflow pocket linked with rectification sections. The device is characterised by that it is additionally provided with unit for alternative switching the reaction sections from operating mode to catalyst regeneration mode, wherein the feed channel of reaction sections is connected to upper part of the column and the overflow pocket, connected to rectification section located below the section, providing power to reaction section. The tests carried out on laboratory unit showed, that when using the disclosed method, the total heat costs are 2.4 GJ/ton of alkylate, which is 14% less compared to analog. Also, the method allows reducing the content of relatively heavy C₅+ hydrocarbons in reaction section feed by more than 40%.

EFFECT: allows to reduce pressure in distillation column relative to reactor pressure, which requires installation of pumps and throttling valves on return line of reaction products to the column.

6 cl, 1 dwg

Description

The invention relates to the field of oil refining and petrochemical industries, and in particular to devices for producing high-octane gasoline components.

Alkylation is the reaction of paraffin, usually isoparaffins, with an olefin in the presence of a strong acid, which produces paraffins with a higher octane rating than the starting materials, and which boil in the gas temperature boiling range. At the same time, isobutane alkylation with butenes is one of the most important processes for producing high-quality gasolines in modern oil refining, because unlike the production of gasoline by cracking high molecular weight oil fractions, such as gas oil or residual oil products, the target product of this process, alkylate, has a low saturated vapor pressure, characterized by the absence of sulfur compounds, oxygen, nitrogen. In addition, alkylated gasoline contains a small amount of aromatic component, which is more favorable from an environmental point of view.

The isobutane alkylation process is catalytic. The traditional industrial alkylation process is based on the use of sulfuric or hydrofluoric acids as catalysts. The reaction is carried out in a reactor where hydrocarbon reactants are dispersed in the acid phase (RU 2313991, 2006).

The main disadvantages of using these acids as catalysts are the high specific consumption of ingredients, toxicity, corrosion activity and the formation of difficult to recycle waste with a global scale of alkylate production exceeding 70 million tons / year, the high probability of environmental catastrophes leading to the search for other more reliable options for producing alkylates.

Currently, intensive development of environmentally friendly processes for the alkylation of isobutane with olefins, which are based on the use of solid catalysts (RU 2313991, 2006; RU 2306175, 2007; US 5672798,1997; US 5986158,1999), is underway. Research in the field of solid heterogeneous alkylation catalysts is aimed at finding systems operating in the temperature range of 20-120 ° C that do not contain toxic components whose stability would be comparable to traditional liquid catalysts and the corresponding technological equipment. Promising alkylation catalysts are solid acid catalysts such as zeolites, metal halides in combination with inorganic salts, and Lewis or Brønsted acids supported on inorganic and organic carriers, which also include sulfated metal oxides and perfluorinated polymers.

Thus, the alkylation process using Lewis acids is known - halogens of metals of the 3-B group, deposited on the oxide of an element of the 3-B or 4-A group, modified with nickel (1-5 wt.%) Or a metal of the platinum subgroup (0.1-1 wt. %), additives of alkaline (alkaline earth) metals in an amount of 1-10 wt. % (US 3318820; US 5849977; US 6103947). It is shown that the addition of chloride hydrocarbons to the initial reaction mixture increases the stability and selectivity of the catalyst, and there is a need to purify products from hydrogen chloride and unconverted chloroparaffins.

Widely porous, high-modulus zeolites beta, ZSM, MSM, USY (US 4384161; US 6844479), in particular, treated with rare-earth compounds (La, Ce) and modified with transition metals (Cr, Mo, W, Cu, Zn, are usually used as alkylation catalysts) , Ga, Sn, Pb) or Group 8 metals having a hydrogenation function (US 5705729). The process is carried out at a temperature of 100 ° C, the ratio of isobutane / olefin above 500, and dosing of hydrogen in the feed in an amount of 0.2 / 1 with respect to the olefin, which allowed to achieve stability of more than 30 hours at a feed rate of butylenes of 0.06 hours ^{- 1} L, butylene conversion of about 100% and final C ₈ selectivity of about 65%.

It is known to use wide-porous zeolites modified with Lewis acids (BF ₃ , SbF ₅ , AlCl ₃ ) (US 4384161). The introduction of Lewis acids into zeolites makes it possible to increase zeolite activity and C ₈ selectivity, reduce the isobutane / olefin ratio to 3-20, and also increase the feed rate of butylenes to 2.5-5 g / g _cat ⋅ h

The disadvantages of zeolite alkylation catalysts in addition to low stability are higher process temperatures, the need to use higher isobutane / olefin ratios, and catalyst deactivation caused by coking.

Known alkylation methods (US 6,583,330), where heteropoly acids supported on carriers with a developed surface and a large pore volume are used as catalysts, for example, a system comprising phosphormolybdenum or phosphor tungsten acids supported on zirconia, silicates or aluminosilicates modified with platinum subgroup metal. At temperatures up to 200 ° C, butylene feed rates of 0.02-2 g / g _cat ⋅ h and isobutane / olefin ratios of 3 to 50, 15.7 g of _alkylate / g _cat was obtained during one run at a final conversion of olefins of not less than 99.8%. After 95 hours of the process, the alkylate contained 80-90% of the C ₈ fraction with a TMP concentration of at least 80%.

The disadvantage of catalysts based on supported heteropoly acids, in addition to their high cost and manufacturing complexity, is the complexity of regeneration, since their structure is destroyed by prolonged high-temperature heating.

The restoration of the activity of a deactivated solid heterogeneous catalyst is carried out, as a rule, by replacing the feedstock with a reformate supplied with a space velocity of 2-3 h ^-1 at a temperature of 130-150 ° C for 4-6 h and additionally saturated with hydrogen under a pressure of 5 MPa (RU 2384366, 2010; RU 2313991, 2006).

Alkylate obtained using solid catalysts is not inferior in quality to the alkylate obtained in traditional processes. The main difficulty in the widespread industrial use of solid catalysts in the alkylation process is their rapid deactivation, which is associated with the side formation of high molecular weight hydrocarbons that block the porous structure and surface active sites of the catalyst. In addition, in these processes, the catalytic system is not connected with separation systems and the thermal effect of the reaction does not find useful application, although the separation unit of the reaction products carries a significant part of capital and operating costs.

To improve the efficiency of the process, various modifications of reactors and equipment used in the alkylation process are proposed (US No. 3496996; 3839487; 2091917; 2472578). However, the most widely used method of mixing the catalyst and reagents is to use various devices of blades, blades, impellers and the like, which strongly mix and mix the components with each other (US No. 3759318; 4075258; 5785933).

The most promising equipment for this process is equipment for carrying out the process of reactive distillation type [Buchold, N. et al. Lurgi Eurofuel - a new alkylation process. Proceedings of the 17th World Petroleum Congress, Brazil. 2002]. In its implementation, the catalyst is distributed over the plates of a distillation column. In the upper part of the apparatus, the formation of light gases С ₁ -С ₃ ; in the middle part - total butane fractions; the lower product is high octane alkylate.

The disadvantage of the proposed technological scheme is the need to use a less efficient catalyst with high resistance to coking processes, because rapid replacement of the catalyst in such an installation is impossible due to technological limitations of starts and stops of the equipment.

The closest in technical essence to the proposed solution in relation to the device is a device that is a distillation column for chemical reactions (EA 201491445, 2014), which contains a reaction zone, which includes at least two catalytic sections, each section having a feed channel and overflow pocket, which simultaneously serves as a supply channel for the next section, so that fluid from each section enters the overflow pocket of this section and through it enters the bottom part of the next section, and the reaction zone is configured to divert the gaseous products of each section, bypassing the remaining sections, the overflow pocket of the last section along the liquid is open with the possibility of free flow of the liquid phase, and a switchgear is located above the feeding pocket of the first section along the liquid providing the supply of the liquid phase in the first section along the liquid section.

The disadvantage of this apparatus is that the reaction products fall on a plate located below the power supply point of the reactor, which leads to the fact that relatively heavy components of alkylate (C ₅ + hydrocarbons) are trapped on the plates from which power is taken for the reaction section which then enter the catalyst. Since the alkylation of C ₅ + hydrocarbons leads to the formation of heavier components than the alkylation of isobutane, this leads to an increase in the rate of deactivation of the catalyst. In addition, the proposed location of the catalyst inside the distillation column does not allow effective periodic regeneration of the catalyst.

The technical problem solved by the authors was to optimize the operation of the device by increasing the life of the catalyst by ensuring optimal conditions for regeneration.

The technical result is achieved by the fact that the device in the form of a distillation column containing distillation sections and reaction sections with a solid catalyst having a feed channel connected to the upper part of the column and an overflow pocket connected to a distillation section located below the section providing power to the reaction section, additionally equipped with a unit for alternately switching the reaction sections from the operating mode to the catalyst regeneration mode. In this case, the alternating switching unit of the reaction sections consists of a control flow heater, pressure control valves and shutoff valves installed on the line between the upper distillation section of the column and the reactor sections.

Along with the foregoing, the inventive device may further include an alkylate stabilization unit and isolating a mixture mainly containing n-butane.

The optimal embodiment of the device is the removal of the reaction sections from the column body.

The solid catalyst may be placed in a container, for example, in the form of a tube, or other similar device.

A schematic diagram of the installation is shown in FIG. 1, where the following designations of the devices used are introduced:

1 - distillation column;

2, 3 — reaction sections;

4 - refrigerator-condenser;

5 - irrigation capacity;

6 - pump;

7 - heater-evaporator distillation column;

8 - block stabilization of alkylate and the allocation of n-butane;

9, 10 - shutoff valves for switching the reaction / regeneration mode of the reactor 2;

11, 12 - shutoff valves for switching the reaction / regeneration mode of the reactor 3;

13, 14 - pressure control valves in the reactor 3;

15, 16 - pressure control valves in the reactor 2;

17 - regenerative flow heater.

The process in question can be carried out using any solid catalyst that is stable and exhibits the required activity and selectivity in paraffin alkylation reactions with olefins. Examples of catalysts are acid catalysts, including zeolites selected from the group X, Y, ZSM-20, EMT and their combinations with the introduction of multimetal materials, or promoted sulfate-zirconium catalysts.

The reaction sections operate alternately in the "reaction" and "regeneration" mode. At least one reaction section operates in a “reaction” mode, i.e. this section receives a mixture of liquid paraffins and olefins at a temperature of 40-80 ° C and an alkylation reaction occurs.

Sections that are in the “regeneration” mode undergo two-stage regeneration: “moderate” regeneration with dissolved hydrogen in liquid paraffins at a temperature of 90-160 ° C and regeneration with a hydrogen-containing gas at elevated temperatures of 200-250 ° C.

The operating hours of the sections in the stages of the “reaction” and “regeneration” are determined by the resistance of the catalyst to the formation of high molecular weight deposits (coke) on the surface of the catalyst, which block active centers and reduce its activity. So, at the stage of the "reaction" may occur from 5 to 24 hours. The stage of “moderate” regeneration requires from 12 to 48 hours, and the stage of regeneration with a hydrogen-containing gas from 1 to 5 hours.

The device operates as follows. The olefin feed (18) is fed directly to the paraffin feed stream of the reaction sections (19) that are in the “reaction” stage. Paraffin feed (20) is supplied to the distillation column (1) below the plates for returning flows from the reaction sections. In the case of using paraffin raw materials with an isobutane content of more than 90% wt. the paraffin feed stream is fed directly to the feed line of the reaction sections. A mixture of paraffins and olefins (21) is fed into the reaction sections operating in the “reaction” mode. In the FIG. 1, the reactor (3) operates in the “reaction” mode, and the reactor (2) in the “regeneration” mode. It is proposed to use shut-off valves (9-12) to change the operating mode of the reaction sections. So, to operate the reactor (3) in the “reaction” mode, the valve (12) passes a stream through itself, and the valve (10) is in the closed state. Thus, the mixture of paraffins and olefins (21) through the valve (12) enters the power supply line (22) of the reactor (3). When the reactor (2) is in the “reaction” mode, the valve (10) opens and the mixture (21) through line 37 and the valve (10) enters the power supply line (38) of the reactor (2).

In the reactor (3), paraffins are alkylated with olefins to form hydrocarbons with a chain length of more than 5 hydrocarbon atoms, which are subsequently high-octane alkylate components.

The liquid products (23) of the reactor (3) through the level and pressure control valve (14) enter the line for supplying the liquid products of the reaction sections (24) to the distillation column (1). Gaseous products (25) of the reaction section (3) through the pressure control valve (13) enter the supply line of gaseous products of the reaction sections (26) to the distillation column (1).

The gaseous products (26) of the reaction sections are higher than the liquid products of the reaction sections (24), but lower than the point of extraction of the vapor stream (27) from the distillation column (1).

Hydrocarbon vapors (27) leaving the top of the column (1) with a temperature of 40-80 ° C are cooled and almost completely condensed in the refrigerator (4) and the vapor-liquid mixture (28) enters the separator (5), which is the irrigation capacity. Hydrocarbons and hydrogen impurities (29) that are non-condensable under the given conditions (temperature and pressure) are removed from the separator from above and can be directed to the isolation of isobutane, which then must be returned to the process (not shown in the diagram).

The liquid (30) from the separator (5), containing more than 75% of isobutane, is pumped (6) mainly to the paraffin supply line of the reaction sections (31) and partially to the distillation column by flow (32). The pump (6) is also designed to allow the reaction sections (2,3) to work with a pressure higher than in the column (1).

The paraffin feed stream of the reaction sections (31) is a “recycle” of isobutane into the reaction sections, for which it is branched into a stream (33) used to prepare a mixture of paraffins and hydrogen for catalyst regeneration, and a stream (19) used to prepare a mixture of paraffins and olefins for carrying out the alkylation reaction. The ratio of flow rate (19) to flow rate (33) is from 10/1 to 100/1.

The paraffin stream (33), containing predominantly isobutane, is mixed with a hydrogen-containing gas so that the mass concentration of hydrogen is more than 0.5%. A mixture of liquid isobutane and hydrogen (35) is heated in a heater (17) to a temperature of 90-250 ° C to carry out the catalyst regeneration process. In the considered circuit diagram, the reactor (2) operates in the “regeneration” mode, therefore, the valve (9) is open and the valve (11) is closed. Thus, the heated stream (36) enters through the valve (9) into the power supply line (38) of the reactor (2). When the reactor (3) is in the “regeneration” mode, the valve (11) opens and the mixture (36) passes through the line (39) and the valve (11) enters the power supply line (22) of the reactor (2).

During the regeneration process in the reaction sections, hydrocracking of high molecular weight compounds adsorbed on the surface of the catalyst occurs, with the formation of predominantly paraffinic hydrocarbons C ₅ + and light hydrocarbon gases C ₁ -C ₃ .

The liquid products (40) of the reaction section (2) through the level and pressure control valve (16) enter the supply line of the liquid products of the reaction sections (24) to the distillation column (1). Gaseous products (41) of the reaction section (2) through the pressure control valve (15) enter the supply line of gaseous products of the reaction sections (26) to the distillation column (1).

At the bottom of the distillation column (1), hydrocarbons C ₅ + and n-butane are predominantly concentrated. The bottom liquid (42) is mainly sent for evaporation (43) in the evaporator (7) and partially removed from the distillation process by a stream (44). The evaporator (7) is designed to create an upward flow of hydrocarbon vapors through the column (1), thus, the heated and partially or completely vaporized stream (45) from the evaporator (7) enters the distillation column (1).

Stream (44) is an unstable alkylate and contains not more than 35% n-butane and not more than 5% by weight of isobutane. To stabilize the alkylate and the corresponding separation of the components of C ₄ -C ₅ stream (44) can be directed to the stage of stabilization of the alkylate (8), which is carried out by distillation. At the stage (8), a mixture (46) is released, which contains mainly n-butane, and commodity alkylate (47), which is the target alkylation product.

Tests in a laboratory setup showed that when using the proposed method, the total heat consumption is 2.4 GJ per ton of alkylate, which is 14% less compared to the reaction-distillation method, where the reaction sections are located inside the column between the plates or nozzle sections. Also, the method allows to reduce the content of relatively heavy C ₅ + hydrocarbons in the feed of the reaction section by more than 40%.

The octane number of the alkylate (MOC) is 91.5; the saturated vapor pressure is 850 mm Hg.

Chemical transformations in the reaction sections are preferably carried out in a liquid. The temperature of the alkylation reaction is 40-100 ° C, more preferably 60-80 ° C. The pressure required for the hydrocarbons to be in the liquid phase, preferably 600-1500 kPa. The olefin space velocity is from 0.2 to 10 grams of olefin per gram of catalyst per hour. The paraffin / olefin ratio in the reactor feed stream is from 5/1 to 100/1, preferably from 10/1 to 15/1.

The raw material for this method is an olefin feed containing more than 20% of the mass. olefins C ₃ -C ₅ , preferably butenes, and isobutane feedstock containing more than 50% of the mass. isobutane.

A distillation column serves to isolate a mixture of C4 hydrocarbons from the products of the alkylation reaction and its subsequent supply to the reaction sections. C ₅ + hydrocarbons are predominantly concentrated in the cube of the column, and the content of n-butane is not more than 35% wt., Isobutane not more than 5% wt.

Another advantage of the external reaction sections is the ability to reduce the pressure in the distillation column relative to the pressure in the reactor, which will require the installation of pumps and throttling valves on the return line of the reaction products to the column.

Claims (6)

1. A device for the alkylation of isobutane with olefins on a solid catalyst in the form of a distillation column, containing distillation sections and solid catalyst reaction sections that have a feed channel and an overflow pocket connected to the distillation sections, characterized in that it is additionally equipped with an alternating switching unit for the reaction sections from operating mode in the regeneration mode of the catalyst, and the feed channel of the reaction sections is connected with the upper part of the column, and an overflow pocket associated with distillation section located below the section that provides power to the reaction section. 2. The device according to claim 1, characterized in that the alternating switching unit of the reaction sections consists of a control flow heater, pressure control valves and shutoff valves installed on the line between the upper distillation section of the column and the reactor sections. 3. The device according to claim 1, characterized in that the device further includes an alkylate stabilization unit and a unit for isolating the mixture, mainly containing n-butane. 4. The device according to claim 1, characterized in that the reaction sections are removed from the column body. 5. The device according to claim 1, characterized in that the solid catalyst is placed in a container. 6. The device according to p. 5, characterized in that the solid catalyst is placed in a container in the form of a tube.

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