RU2120931C1 - Method of selective hydrogenation of diolefins (versions) - Google Patents

Abstract

FIELD: petrochemical syntheses. SUBSTANCE: diolefins contained in light naphtha are hydrogenated in order to produce tert-amyl methyl ether by feeding the first stream of light naphtha containing diolefins and the second stream containing hydrogen into distillation column- reactor to be brought into contact with hydrogenation catalyst. The latter represents in reactor a structure capable function as catalytic rectification structure producing pentenes and other hydrogenation products in reaction mixture at such operation pressure providing evaporation of a part of reaction mixture and maintaining specified temperature. From this column, liquid vat residue and top vapor fraction together with unreacted hydrogen are taken off. EFFECT: enhanced process efficiency. 15 cl, 4 dwg, 3 tbl

Description

US Pat. No. 5,087,780 relates to hydroisomerization of mixed C ₄ streams and hydrogenation of butadiene.

The present invention relates to the selective hydrogenation of diolefins (dienes) contained in refinery streams containing mainly C ₅ hydrocarbons, especially C ₅ hydrocarbon olefins. More specifically, the invention relates to a method for the selective hydrogenation of dienes using a distillation column containing a hydrogenation catalyst as a reactor, which also acts as a component of the distillation structure. More specifically, the invention relates to the selective hydrogenation of a C ₅ feed stream to produce tert-amyl methyl ether (TAME).

 Mixed refinery streams often contain a wide range of olefin compounds. This is especially true for catalytic or thermal cracking products. These olefin compounds include ethylene, acetylene, propylene, propadiene, methylacetylene, butenes, butadiene, etc. Many of these compounds are valuable substances, especially as starting materials for chemical products. Ethylene is especially distinguished. Additionally, propylene and butenes are valuable. However, olefins containing more than one double bond and acetylene compounds containing a triple bond are harmful to many chemical processes that use compounds with one double bond, for example polymerization.

Oil refinery streams are usually separated by fractional distillation and therefore they often contain compounds very close in boiling point, that is, the separation is not precise. C ₅ streams, for example, may contain C ₄ -C ₈ hydrocarbons. These compounds may be saturated (alkanes), unsaturated (monoolefins) or polyunsaturated (diolefins). Additionally, the components may be any or various versions of the isomers of the individual compounds.

 Hydrogenation is the reaction of hydrogen with a carbon-carbon complex bond, resulting in a “saturated” compound. The reaction is well known and is usually carried out at elevated pressure and moderate temperature in excess of hydrogen over a metal catalyst. Among the metals known as hydrogenation catalysts are the following: platinum, rhenium, cobalt, molybdenum, nickel, tungsten and palladium. Typically, commercial supported catalyst forms are supported oxides of such metals. The oxide is reduced to its active form either before use with a reducing agent, or during the use of raw materials with hydrogen. These metals also catalyze other reactions, most significantly, dehydrogenation at elevated temperatures. They can also promote the reaction of olefin compounds with each other or with other olefins to form dimers or oligomers with an extended residence time.

Selective hydrogenation of hydrocarbons has been known for quite some time. Peterson et al., In their publication, Selective Hydrogenation of Pyrolysis Gasoline, presented to the Petroleum Division of the American Chemical Society in September 1962, discusses the selective hydrogenation of C ₄ and higher diolefins. Buyo et al. In the post "Recent Hydrogenation Catalysts." Hydrocarbon processing, March 1985, provided an overview of the various uses of hydrogenation catalysts, including selective hydrogenation using proprietary bimetal hydrogenation catalysts.

Isomerization can be performed on the same family of catalysts. Typically, the relative reaction rates of various compounds are reduced in the following order:
1) hydrogenation of diolefins
2) isomerization of monoolefins
3) hydrogenation of monoolefins.

 In general, it has been shown that in a stream containing diolefins, the hydrogenation of diolefins proceeds faster than isomerization.

 The use of solid ground catalyst as part of a distillation structure in a distillation column reactor combination for various reactions is described in US Pat. NN 4,227,177, 4,307,254, 4,336,407, 4,504,687, 4,918,243 and 4,978,807; (dimerization) 4242530; (hydration) 4982022; (dissociation) 4,447,668; and (aromatic alkylation) 4950834 and 5019669. In addition, US patents NN 4302356 and 4443559 describe the structure of the catalysts used as part of the distillation of the structure.

The C ₅ hydrocarbon fraction is of value as a component in mixing gasoline or as a source of isoamylene in the production of ether by reaction with low alcohols. Tert-amyl methyl ether (TAME) is quickly becoming a valuable product as a result of the recently issued Clean Air Act, which sets new limits on gasoline composition. In particular, the Act requires 1) to include a certain amount of “oxygenated” compounds, such as methyl tert-butyl ether (MTBE), TAME or ethanol, 2) reduce the amount of olefins in gasoline and 3) reduce the vapor pressure (volatility).

C ₅ hydrocarbons serving as raw materials for TAME synthesis plants are contained in a single fraction of Easy Naphtha, which includes C ₅ -C ₈ and higher hydrocarbons. The mixture may contain 150-200 components, which makes identification and separation of substances difficult. Typically, C ₅ hydrocarbons and a small portion of C ₆ hydrocarbons are isolated for use in the synthesis of TAME. However, the inclusion of tertiary C ₆ -C ₈ olefins will make it possible to obtain other valuable essential products. For this reason, TAMEs are not separated from the heavier components, but mixtures are entirely used as octane mixing components.

 Some of the minor components (diolefins) in the feed will slowly react with oxygen during storage to form tar and other undesirable materials. However, these same components also react very quickly in the process for producing TAME with the formation of a yellow, foul-smelling resinous material. Thus, it is desirable to remove these components, regardless of whether the “light naphtha” will be used only as a component in mixing gasoline or also as a raw material for TAME synthesis.

 An advantage of the present hydrogenation method in which diolefins are selectively hydrogenated is that the hydrogenation of monoolefins proceeds slightly or not at all. An additional feature of the method is that part of the monoolefins obtained by selective hydrogenation of diolefins isomerized into the desired products.

 SUMMARY OF THE INVENTION

The present invention provides for the supply of a light naphtha fraction containing a mixture of hydrocarbons together with a hydrogen stream to a distillation column reactor containing a hydrogenation catalyst that is a component of the distillation structure, and the selective hydrogenation of light naphtha diolefins. At the same time, light components, including unreacted hydrogen, are distilled off and separated as the overhead from partially hydrogenated light naphtha. Additionally and simultaneously with selective hydrogenation and distillation, part of the C ₅ - monoolefins isomerized in the feed for the synthesis of TAME. Substantially all diolefins are converted to monoolefins with a very small degree of hydrogenation of monolefins.

In one embodiment, where the raw material is mainly C ₅ - stream, light naphtha of the product is taken from the cube. The overhead is fed to a condenser in which all hydrocarbons capable of condensing are condensed, and some of them are fed to the top of the column as irrigation.

In the second embodiment, where the feed is a C ₅ - C ₈ stream, C ₅ hydrocarbons are separated from the C ₆ components in the lower section of the distillation column reactor. The C ₆ components are given as bottoms, while the boiling C ₅ hydrocarbons reach the upper section of the distillation column reactor with a catalytic distillation structure, where diolefins are selectively hydrogenated. Hydrogenated C ₅ components are taken from the top of the column along with excess hydrogen and sent to a condenser, in which all components capable of condensing are condensed, and then separated from non-condensable components (mainly hydrogen) in the receiver of the irrigating fraction. Part of the liquid from the receiver is returned to the distillation column-reactor as irrigation, and the residue is removed as a product that can be directly sent to the TAME synthesis unit. If necessary, you can apply an additional inert distillation section above the catalytic distillation structure, equipped with a side outlet for the selection of C ₅ -product. An additional section may be useful for separating excess hydrogen and other light components, such as air, water, etc., which may interfere with the downstream TAME synthesis plant.

In a broad sense, the present invention is a method for the selective hydrogenation of diolefins located in light naphtha, and provides for the following steps:
a) supplying 1) a first stream comprising light naphtha containing diolefins, and 2) a second stream containing hydrogen to a distillation column reactor in a loading zone;
b) simultaneously in a distillation column reactor:
i) contacting the first and second streams in the distillation reaction zone with a hydrogenation catalyst capable of functioning as a distillation structure in order to carry out the reaction of substantially all diolefins with hydrogen and obtain pentenes and other hydrogenation products in the reaction mixture,
ii) establishing a pressure in the distillation column reactor at which part of the mixture evaporates as a result of the exothermic heat of the reaction;
c) removing part of the liquid of stage b, ii) from the distillation column of the reactor as bottoms;
d) removing the vapors of step b, ii) together with unreacted hydrogen from the distillation column reactor as the overhead.

Hydrogen is supplied as a necessary component for carrying out the reaction, for reducing the oxide and keeping it in the hydride state. The pressure in the distillation column reactor is adjusted so that the reaction mixture boils in the catalyst bed. A “foam state” that improves the efficiency of the catalyst and thereby reduces the required height of the catalyst can be maintained throughout the catalyst bed by adjusting the cube and / or overhead extraction rate. As follows from the assessment, the liquid is in a state of boiling and its physical state is indeed a foam having a higher density than the density in a distillation column with a nozzle, but lower than without boiling vapor. The method is preferably carried out at a pressure in the head of the distillation column reactor 0-250 psig (0-17.58 ati) and a temperature inside the distillation column reactor 100-300 ^° F (37.78-148.89 ^° C), preferably 130 - 270 ^° F (54.44 - 132.22 ^° C).

C ₅ - The feed and hydrogen are preferably fed to the distillation column reactor separately or mixed before being fed. Mixed feeds are fed below the catalyst bed or to the bottom of the bed. Hydrogen is separately introduced below the catalyst bed, and C ₅ —the stream is introduced below the catalyst bed or into the catalyst bed at a level up to the middle of 1/3 of the bed. The best variant of the method is that in which the dienes are held in the catalyst bed and the propylene and lighter components are distilled off the top.

 FIG. 1 is a simplified diagram of a first embodiment of the present invention.

 FIG. 2 is a simplified diagram of a second embodiment of the present invention.

 FIG. 3 is a simplified diagram of a third embodiment of the present invention.

 FIG. 4 is a simplified diagram of a fourth embodiment of the present invention.

Description of Preferred Option
The advantages of using a distillation column reactor in this selective hydrogenation process are a better selectivity of diolefins to olefins, heat preservation and distillation separation, by which it is possible to remove undesirable compounds, for example heavy sulfur-containing impurities, from the feed prior to contacting with the catalyst and concentrate the desired compounds in catalyst zone. C ₅ diolefins - fractions have higher boiling points than other compounds and, therefore, can be concentrated in the catalyst zone, while monoolefins are isomerized and removed to the top of the column. The following reactions of C ₅ hydrocarbons are of interest:
1) the reaction of isoprene (2-methylbut-1,3-diene) with hydrogen, leading to 2-methylbut-1-ene and 2-methylbut-2-ene;
2) the reaction of cis and trans 1,3-pentadienes (cis and trans piperylene) with hydrogen, leading to pent-1-ene or pent-2-ene;
3) 3-methylbut-1-ene to 2-methylbut-2-ene and 2-methylbut-1-ene;
4) 2-methylbut-1-ene to 2-methylbut-2-ene;
5) 2-methylbut-2-ene to 2-methylbut-1-ene;
6) 1,3-butadiene in 1-butene and 2-butene.

 The first two reactions remove unwanted components, while the third reaction provides feed for the TAME synthesis reactor. 3-Methyl-1-butene does not react with methanol to form TAME in the presence of sulfonic acids as a catalyst, while two 2-methylbutenes react.

 The catalytic material used in the hydrogenation process must be shaped to serve as a nozzle during distillation. The catalytic material is a component of the distillation system, acting both as a catalyst and as a nozzle during distillation, that is, the nozzle for the distillation column has both a distillation function and a catalytic function.

 The reaction system can be described as heterogeneous, since the catalyst remains a separate element. The catalyst may be palladium oxide, preferably in an amount of 0.1 to 1.0 wt.%, Supported on an appropriate carrier, such as alumina, carbon or silica, preferably in a container, as described in this patent or in the form of a conventional molded nozzle for distillation such as Raschig rings, Poll rings, saddle shapes, and the like.

 It was found that placing the catalyst in many pockets in fabric tapes that are held in a distillation column reactor with stainless steel braided wire with open cells by twisting two (tapes) into a spiral allows the reaction mixture to flow, prevents catalyst loss, allows for catalyst swelling and prevents grinding of extruded forms (catalyst) as a result of mechanical abrasion. The new device of the catalytic system is described in detail in the recognized US patents NN 4242530 and 4443559.

 The fabric may be any material that is not destroyed by hydrocarbon feed or products or catalyst under the reaction conditions. Cotton or linen may be used, but fiberglass or Teflon is preferably used. Preferably, the catalyst system comprises a plurality of closed fabric pockets secured in a distillation column reactor with a wire mesh. As other suitable containers, metal or plastic sieves with suitable mesh sizes in the form of short cylinders closed at each end in which the catalyst is located are used. Many of these catalyst containers are randomly or regularly placed in a bed inside a distillation column reactor. There may be one or more of these layers, depending on the requirements of the process catalyst.

 The crushed catalyst material may be in the form of a powder, irregular pieces or fragments, small balls, etc. The shape of the catalytic material in the container is not critical, as long as a sufficient surface area provides an acceptable reaction rate. The particle size of the catalyst should be such that the catalyst remains inside the container.

The catalyst used in the present method is 0.34 weight. % Pd deposited on spherical alumina (Al ₂ O ₃ ) particles of size 3-8 mesh, designated G-68C and supplied by United Catalists Inc. The catalyst supplied by the manufacturer has typical physical and chemical properties (see table 1).

 It is believed that the catalyst is palladium hydride formed during the process. The rate of hydrogen supply to the reactor must be sufficient to maintain the catalyst in active form, because hydrogen is lost by the catalyst during hydrogenation. The hydrogen rate must be set so as to be sufficient to make up for the loss of hydrogen by the catalyst, but should be lower than the speed causing flooding of the column. Typically, the molar ratio of hydrogen to diolefins in the feed to the fixed bed should be at least 1.0: 1.0, preferably 2.0: 1.0.

 In the present invention, the method is carried out in a column filled with a catalyst, which can be evaluated as containing an ascending vapor phase and a certain amount of liquid phase, as in any distillation. However, since the liquid is kept inside the column in a state of "artificial flooding", it should be understood that the liquid has an increased density relative to the density that exists during simple runoff as a result of normal internal irrigation.

In FIG. 1 shows a simplified flow diagram of a preferred embodiment. A distillation column reactor 10 is shown containing a nozzle of a hydrogenation catalyst as part of the distillation structure 12 housed in a wire mesh as described above. The column may also have a standard distillation design 14. Light naphtha is fed into the distillation column reactor 10 below the catalyst bed via line 1. Hydrogen gas is fed through line 2 to or near the bottom of the catalyst bed. The cube is heated to circulate through the boiler 40 and lines 4 and 13. After the reaction has begun, the heat of the reaction, which is exothermic, causes additional evaporation of the mixture in the layer. Vapors are removed from the top of the column through line 3 and sent to a condenser 20, where all condensable material is condensed at 37.78 ^° C. The overhead is then fed to a reflux fraction collector 30 where condensed material is collected and non-condensable components such as unreacted hydrogen are separated . Part of the condensed material is returned to the top of the column 10 and through line 6. The distilled product, withdrawn through line 9, is suitable as a raw material for the TAME synthesis reactor. Non-condensable material is removed via line 7 from the irrigation fraction collector and, to save, hydrogen can be recycled to a reactor (not shown). A bottoms product containing no C ₅ diolefins is taken along line 8 of the stream and sent as a mixing component to produce stable gasoline. The method has the advantage that the high heat of hydrogenation is absorbed by the evaporation of part of the liquid. Temperature control is carried out by regulating the pressure in the system. All excess hydrogen is stripped from bottoms. In the case of C ₅ hydrocarbons, non-hydrogenated components are less volatile and tend to remain in the reactor for a longer time, which contributes to a more complete reaction.

In FIG. 2 shows a second embodiment of the invention in which light naphtha is fed into the column 10 above the catalytic distillation structure 12 along line 1. The rest of the device is identical to that shown in FIG. 1. In FIG. 3 depicts a third embodiment in which the column is further provided with a conventional distillation structure 216 above the catalytic distillation structure 12 to separate any C ₄ hydrocarbons, lighter components and hydrogen from C ₅ hydrocarbons selected as side stream along line 209.

 Example 1

The one shown in FIG. 4 steel column 310 with a diameter of 7.62 cm and a height of 9.144 m, equipped with a boiler 340, a condenser 320 and an irrigation system 330 and 306. The average 4.57 m is filled with a catalytic distillation structure 312, which is 0.34 wt.% Palladium on spherical aluminum oxide 0.32 cm catalyst and located in pockets of fiberglass tape wrapped in stainless steel wire mesh. The column is purged with nitrogen and a pressure of 1.4 ati is set in it. Light naphtha, which is pre-fractionated to remove most of the C ₆₊ material, is introduced into the column through line 301 at a speed of 22.68 kg / h. When the liquid in the column reaches the desired level, turn on the outlet line 308 from the cube and circulate through the boiler along lines 304 and 313. Heat is supplied from the boiler 340 until the vapors are detected on the top of the column, indicating a uniform temperature of 54.44 ^° C in the entire column. A stream of hydrogen is introduced into the cube of the column along line 302 at a rate of 0.227-0.283 m ³ / h. The column pressure is then adjusted to maintain a cube temperature of 160 ^° C and a temperature in the catalyst bed of 126.67 ^° C. Thus, the pressure in the column head is maintained at about 14 atm. The overhead is taken to line 303 and partially condensed in a condenser 320 and all condensable components are collected in an irrigation fraction collector 330 and returned to the top of the column as irrigation along line 306. The condensable components are removed from the collector along line 307. The bottled liquid is taken to line 308 The results are shown in table. 2, comparing the analysis data of raw materials and cube.

 Example 2

 During the experiment, the pressure in the head of the column is adjusted to change the temperature of the catalyst bed. At lower temperatures, the conversion of diolefins is lower, but the main difference is that the effect on 3-methyl-1-butene isomerization is much greater. In the table. 3 compares the conversion of diolefins and 3-methyl-1-butene at certain operating temperatures.

Claims (15)

 1. A method for selectively hydrogenating diolefins contained in light naphtha by feeding a first stream of light naphtha containing diolefins and a second stream containing hydrogen for contacting in the presence of a hydrogenation catalyst, characterized in that the contacting is carried out in a distillation reactor column in which the specified catalyst is located, forming a structure capable of functioning as a catalytic distillation structure, resulting in the interaction of basically all diolefino in hydrogen with pentenes and other hydrogenation products in the reaction mixture and at the same time in the specified column, the working pressure is set at which part of the reaction mixture is evaporated due to the heat of the exothermic reaction and the specified temperature in the reaction-distillation zone is maintained, with the formation of liquid from the specified reactor column parts as a cube and vapors together with unreacted hydrogen as a head fraction.  2. The method according to p. 1, characterized in that the said head fraction is cooled to condense the components contained therein, the condensed components are separated from unreacted hydrogen and returned to the top of the reactor column as irrigation. 3. The method according to claim 2, characterized in that said vapors contain substantially all C ₅ hydrocarbons and more low boiling hydrocarbons, the liquid part contains substantially all C ₆ hydrocarbons and higher boiling hydrocarbons, and the condensing components contain C ₅ hydrocarbons .  4. The method according to p. 3, characterized in that a part of the condensed components is withdrawn as a product.  5. The method according to p. 2, characterized in that the separated unreacted hydrogen is recycled to the specified column reactor.  6. The method according to p. 1, characterized in that the hydrogenation catalyst contains 0.34 wt.% Palladium oxide deposited on spheres of aluminum oxide with a size of 0.32 cm, and the hydrogenation catalyst is placed in pockets of fabric tape wrapped in distillation wire, with the formation of the specified designs.  7. The method according to p. 1, characterized in that the hydrogen is contained in the second stream in an amount providing a molar ratio of hydrogen to said diolefins of 1: 1 to 2: 1.  8. The method according to claim 1, characterized in that the pressure in the upper part of the distillation column reactor is 0-17.58 atm. 9. The method according to p. 8, characterized in that the temperature inside the distillation reaction zone is in the range of 37.78-148.89 ^o C.  10. The method of claim 9, wherein said pentenes include 3-methyl-1-butene and 2-methyl-2-butene, and a portion of said 3-methyl-1-butene isomerized to 2-methyl-2-butene. 11. The method according to p. 1, characterized in that the side shoulder strap is taken from the point located between the top of the specified column and the catalytic distillation structure, which contains C ₅ -hydrocarbons, and divert it as a product. 12. A method for selectively hydrogenating diolefins contained in light naphtha by feeding a first stream of light naphtha containing diolefins and a second stream containing hydrogen for contacting in the presence of a hydrogenation catalyst, characterized in that the first stream contains 3-methyl-1-butene , 2-methyl-1-butene, 2-methyl-2-butene, 2-methyl-1,3-butadiene, cis-1,3-pentadiene and trans-1,3-pentadiene, contacting is carried out in a distillation column reactor in which the specified catalyst is located, forming a structure capable of functionally as a catalytic distillation structure, resulting from the interaction of basically all 2-methyl-butadiene, cis- and trans-1,3-pentadienes with hydrogen pentenes in the reaction mixture with isomerization of a part of 3-methyl-1-butene to 2-methyl -2-butene and at the same time a pressure of about 14 atm is established in the said column, at which the temperature in the reaction-distillation zone is 121.11-132.22 ^o C and part of the reaction mixture is evaporated due to the heat of the exothermic reaction, with the selection of the liquid part from the specified columns as a cube and steam together with unreacted hydrogen as a head fraction.  13. The method according to p. 12, characterized in that the head fraction is cooled to condense the condensable components contained therein and the condensed components are separated from unreacted hydrogen and returned to the top of said reactor column as irrigation.  14. The method according to p. 13, characterized in that the separated unreacted hydrogen is recycled to the specified column reactor. 15. A method for selectively hydrogenating diolefins contained in light naphtha by feeding a first stream of light naphtha containing diolefins and a second stream containing hydrogen for contacting in the presence of a hydrogenation catalyst, characterized in that the contacting is carried out in a distillation reactor column in which the specified hydrogenation catalyst containing palladium oxide deposited on particles of aluminum oxide is located, and this catalyst is located in the pockets of a fabric tape wrapped in distillation a wire forming a structure capable of functioning as a catalytic distillation structure, resulting in the interaction of basically all diolefins with hydrogen of pentenes and other hydrogenation products in the reaction mixture and at the same time set the pressure in the upper part of the said reactor column in the range of 9.14-14, 77 atm, so that the temperature in the reaction-distillation zone is 110.00 - 132.22 ^o C, with the evaporation of part of the reaction mixture due to the heat of the exothermic reaction, with the selection of the first part the resulting liquid as a cube, the second part of the resulting liquid as a side stream and vapor recovery together with unreacted hydrogen as a head fraction, the head fraction is cooled to condense all components that condense at a temperature to which they are cooled and a pressure between 9.14 - 14.77 atm, the condensed components are separated from the non-condensed components of the head fraction and the first part of the condensed components is returned to the specified column of the reactor as Ocean, a second portion is taken as product, and the unreacted hydrogen contained in neskondensiruyuschemsya component is recycled to the distillation column reactor.

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