CN1453336A - Catalytic distillation method for selective hydrogenation of C4 hydrocarbon mixture - Google Patents

Abstract

A catalytic distillation method for the selective hydrogenation of C4 hydrocarbon mixtures, C4 raw materials and hydrogen enter the tower from the upper and lower parts of the catalytic distillation tower respectively, and the two are in countercurrent contact on the surface of the catalyst, including hydrogen and dimethyl ether After the gaseous phase impurities go out from the top of the tower and pass through the condenser and reflux tank, hydrogen and most of the low-boiling point impurities leave the device, and the liquid phase flow in the reaction section goes down through the stripping section and enters the reboiler, and a small amount is dissolved in the liquid phase flow. The low-boiling point impurities are distilled out and separated from the top of the tower under the stripping action of hydrogen and the steam generated by the reboiler, while the C4 fraction after the hydrogenation reaction is discharged from the reboiler at the bottom of the tower. Because the selective hydrogenation of butadiene and the distillation and separation of dimethyl ether are carried out simultaneously in one tower, equipment and investment costs are saved; the balance of the hydrogen transfer reaction is constantly shifted to the direction of generating 2-butene due to the distillation, To maximize the conversion of 1-butene in the raw material into 2-butene.

Description

A catalytic distillation method for selective hydrogenation of C4 hydrocarbon mixtures

Technical field

The invention belongs to a catalytic distillation method for selective hydrogenation of C4 hydrocarbon mixtures, more specifically, it is a method for removing butadiene in C4 hydrocarbon mixtures through selective hydrogenation and through column fractionation. Catalytic distillation method for dimethyl ether removal.

Background technique

Alkylation is an important process for the production of high-octane gasoline in the modern refining industry. Under the catalysis of acidic catalyst, the alkylated oil produced by the alkylation of isobutane and butene is a mixture of isoparaffins, with high octane number, low sensitivity, and ideal volatility and clean combustion It is an ideal gasoline blending component. Alkylation feedstock is generally refined and fractionated catalytic cracking gas. In refineries with MTBE units, isobutene can be removed by MTBE units before being used as alkylation raw materials.

In the alkylation process, one mole of diene consumes two moles of isobutane to produce heavier alkane compounds or polymerizes to produce polymers as heavy alkylate and acid regeneration column by-products. At the same time, since the acid consumption accounts for a large proportion of the operating costs, the process must strictly limit the impurities in the raw materials that can increase the acid consumption. The impurities in the alkylation raw material are mainly: water, sulfide, butadiene and dimethyl ether. There are other ways to remove sulfide and water in the raw material. The present invention is only aimed at the removal of butadiene and dimethyl ether, and for the mixed C4 raw materials of the alkylation process, the butadiene content must be less than 300ppm, and the dimethyl ether content must be less than 50ppm. If the C4 raw material comes from the MTBE unit, the content of butadiene and dimethyl ether cannot meet the requirements and must be refined before use. In the alkylation process, the catalytic alkylation of isobutene and butene can produce light alkylated products mainly composed of trimethylpentane, and the alkylated products of different butenes are different. 1-butene reacts to produce 2,3-dimethylhexylpentane, its octane number is very low, the octane number of the research method is 71, 2-butene reacts to produce 2,2,4-, 2,3,4 -, 2,3,3,-Trimethylpentane has a very high octane number, and the octane number of the research method reaches 100-106. Therefore, increasing the content of 2-butene in the selective hydrogenation product can benefit the alkylation reaction.

The research on the selective hydrogenation of C4 components mainly focuses on the two aspects of catalyst and process. Most of the catalysts use noble metals such as platinum and palladium on the alumina carrier, but the active temperature of the noble metal catalyst is 50 ° C ~ 60 ° C, Its sulfur resistance is poor, and the sulfur content is generally required to be less than 20ppm. The traditional process is to first use a fixed bed for selective hydrogenation, and then remove dimethyl ether by distillation. The disadvantages are that the reactor temperature is not easy to control, the process is long, and the investment in equipment is large. In recent years, catalytic distillation and catalytic extractive distillation processes have appeared for selective hydrogenation.

Catalytic distillation technology (Catalytic-Distillation Technology) is a new process technology that combines catalytic reaction and product fractionation in one tower. The catalyst is installed in the middle section of the tower, and the upper and lower parts of the tower are the rectifying section and the stripping section respectively. Since the reaction product is fractionated at any time, it is beneficial to increase the conversion rate of the reaction, and the heat generated by the reaction is directly used for distillation, thus saving energy. Catalytic distillation technology was originally used to produce methyl tert-butyl ether (MTBE), and has now been extended to C4 olefin dimerization, hydrogenation and other processes.

USP5,877,363 discloses a method for removing vinyl acetylene, ethyl acetylene and 1,2-butadiene in the C4 hydrocarbon stream, the reaction section is equipped with platinum, palladium or rhodium noble metal catalysts prepared by distillation structure, and the raw material is from the tower The middle part enters, after the vinyl acetylene and 1,2-butadiene are selectively hydrogenated through the reaction section of the distillation tower, the products are simultaneously discharged from the top and bottom of the tower respectively. However, this method uses a noble metal catalyst, and the hydrogenation is more moderate. Both vinylacetylene and ethylacetylene are converted into 1,3-butadiene, and neither 1,3-butadiene nor dimethyl ether can be removed.

USP6,040,489 discloses a method for separating 1,3-butadiene from a C4 hydrocarbon stream, hydrogen, solvent and C4 hydrocarbon stream enter a catalytic extractive distillation column with a reaction zone, in which a section of acetylene Hydrogenation catalyst, butane and butene are pulled out from the top of the tower because they are insoluble in solvents, and butadiene and acetylene, which are easily soluble in solvents, are brought to the reaction zone with the solvent, and acetylene is hydrogenated in the reaction zone. Hydrogen product, the hydrogenation product and butadiene are separated in the extraction and distillation part of the device; the mixture of solvent and diene enters a solvent extraction tower and is separated by distillation; diene enters the diene fractionation tower to separate 1,3-butadiene Diene and 1,2-butadiene. However, although this method can remove alkynes and dienes in C4, this process requires two towers and the addition of solvents, the process is more complicated, the cost is high, and dimethyl ether cannot be removed.

USP6,072,091 discloses a method for the selective hydrogenation of C3-C10 hydrocarbon fractions. The raw material containing acetylene, diene and hydrogen-rich gas are passed through the distillation section and at least one catalytic hydrogenation reaction bed layer, so that at least part of the acetylene and Dienes are hydrogenated to saturation. This method is suitable for the treatment of catalytic cracking products containing high unsaturation. Due to the wide distillation range and wide temperature range of the processed fractions, the complex equipment is not suitable for processing narrow C4 fractions, and it cannot remove dimethyl ether.

Contents of the invention

The purpose of the present invention is to provide a kind of method for the catalytic distillation of the selective hydrogenation of C4 hydrocarbon mixture on the basis of prior art, make butadiene and 1-butene in C4 hydrocarbon mixture all or partially convert to 2-butene and remove dimethyl ether simultaneously.

The catalytic distillation method for the selective hydrogenation of C4 hydrocarbon mixtures provided by the present invention is as follows: C4 feedstock and hydrogen enter the tower from the upper rectifying section and the lower stripping section of the catalytic distillation/stripping tower respectively, and the two flow countercurrently on the surface of the catalyst Contact, butadiene in the C4 raw material is selectively hydrogenated to form butene, and different butene isomers undergo hydrogen transfer reactions to convert each other, and gas phase impurities including hydrogen and dimethyl ether go out from the top of the tower through the condenser and After the reflux tank, the hydrogen and most of the low-boiling impurities exit the device, and all or part of the liquid phase material in the lower part of the reflux tank returns to the tower, and the liquid phase flow in the reaction section in the middle of the catalytic distillation column goes down through the stripping section and enters the reboiler. A small amount of low-boiling impurities dissolved in the liquid stream are distilled out, and separated from the top of the tower under the stripping action of hydrogen and steam generated by the reboiler, while the C4 fraction after hydrogenation reaction is removed from the bottom of the tower by the reboiler out of the device.

The advantages of the present invention are: the selective hydrogenation of butadiene, the hydrogen transfer reaction of butene and the distillation separation of dimethyl ether are carried out simultaneously in one tower, which saves equipment and investment costs; the trickle bed is replaced by a catalytic distillation process , so that the reaction temperature is easy to control; due to the distillation, the equilibrium of the hydrogen transfer reaction is constantly moved to the direction of generating 2-butene, so that the 1-butene in the raw material is converted into 2-butene to the maximum.

Description of drawings

The accompanying drawing is a schematic flow chart of the catalytic distillation method for the selective hydrogenation of C4 hydrocarbon mixtures provided by the present invention.

Detailed ways

The method provided by the invention comprises:

The C4 raw material and hydrogen enter the tower from the upper and lower parts of the catalytic distillation tower respectively, and the downward flowing hydrocarbon fraction and the upward flowing hydrogen are in countercurrent contact on the surface of the catalyst. The reaction conditions are hydrogen partial pressure 0.1MPa～2.0MPa (absolute pressure), The temperature in the reaction section is 50°C to 120°C, and the volume space velocity is 1 hour ^-1 to 30 hours ^-1 . After the gas phase material goes out from the top of the tower and passes through the condenser and the reflux tank, the hydrogen gas and most of the low-boiling impurities exit the device, and all or part of the liquid phase material in the lower part of the reflux tank returns to the tower; the liquid phase stream in the reaction section is stripped downward section enters the reboiler, a small amount of low-boiling impurities dissolved in the liquid stream are evaporated, and are separated from the top of the tower under the stripping action of hydrogen and the steam generated by the reboiler; while the C4 product after hydrofinishing Then the material is discharged stably from the bottom of the tower.

The C4 feedstock in the present invention is the mixed C4 fraction separated from the fluid catalytic cracking unit of the refinery, including the C4 mixture discharged from the MTBE unit, and other C4 hydrocarbon mixtures that can be used as alkylation feedstocks. Among the above-mentioned raw materials, the former 1 , 3-butadiene content greater than 300ppm, the latter 1,3-butadiene content greater than 300ppm, dimethyl ether content greater than 50ppm. The concentration of the hydrogen gas entering the catalytic distillation tower is 50%-100%; the volume ratio of the hydrogen gas entering the catalytic distillation tower to the C4 raw material is 1-500:1.

The catalytic distillation/stripping tower used in the present invention consists of a rectifying section, a reaction section and a stripping section. The reaction section is in the middle of the tower, and its height is 5 to 95% of the tower height. The rectifying section is in the upper part of the tower, and its height It is 5-50% of the tower height, and the stripping section is at the lower part of the tower, and its height is the difference between the tower height and the height of the reaction section and the rectification section. The reaction section is equipped with a component composed of packing and catalyst. The upper part of the component is a distributed separation area. The area can be random packing such as Raschig ring, Pall ring, saddle packing, etc., or regular packing such as corrugated plate type , grid type, honeycomb type, etc.; the lower part of the component is the reaction area, and the area is a hydrogenation catalyst such as a catalyst containing nickel or palladium. The relative dimensions of the upper and lower regions of the component can be specifically determined by those skilled in the art according to actual conditions. Components can be piled up randomly or whole. The porosity of the component is 30% to 95%, so the component has good gas-liquid distribution performance and low pressure drop, can provide sufficient places for chemical reactions, and fully exert the activity of the catalyst.

The following is a schematic diagram of the catalytic distillation method for selective hydrogenation of C4 hydrocarbon mixture provided by the present invention in conjunction with the accompanying drawings, but the present invention is not limited thereby.

The method flow is described as follows:

In the catalytic distillation/stripping tower 10 composed of a reaction section and a stripping section, the C4 raw material enters the upper part of the tower through the pipeline 1, and the hydrogen gas enters the lower part of the tower through the pipeline 2, and the two are countercurrently contacted in the tower. The downward flowing C4 mixture reacts with the upward flowing hydrogen on the surface of the catalyst. Butadiene is selectively hydrogenated to butene, and the different isomers of butene are converted to each other, in which cis-2-butene and trans-2-butene are transferred downward under the action of distillation, so that the equilibrium is shifted to The direction to generate 2-butene moves. The gas phase material comprising hydrogen and dimethyl ether enters condenser 4 through line 3. The cooled material enters the reflux tank 7 through the pipeline 5, and the material is divided into two phases of gas and liquid in the reflux tank. The hydrogen and the removed dimethyl ether are drawn out of the device through the pipeline 6. According to the situation, the liquid phase materials can be completely refluxed into the catalytic distillation tower through the pipeline 8, or partly refluxed into the catalytic distillation tower through the pipeline 8, and the other part is used as a product through the pipeline 14 out of the device. The refined C4 mixture passes through the stripping section downwards. During the downward flow, most of the low-boiling impurities dissolved in the petroleum fraction are transferred from the liquid phase to the gas phase due to the stripping effect of the hydrogen entering the bottom of the tower. . The remaining impurities enter the reboiler 12 along with the liquid through the pipeline 9, and are steamed back to the stripping section through the pipeline 11 in the reboiler, and are separated from the top of the tower under the stripping action of hydrogen and the steam generated by the reboiler, as shown in the figure The dotted frame indicates that the reboiler can also be omitted; the refined C4 mixture is taken out as a product through the pipeline 13 and stably leads to the device.

The present invention has the advantages of: the selective hydrogenation of butadiene and the distillation separation of dimethyl ether are carried out simultaneously in one tower, which saves equipment and investment costs; the trickle bed is replaced by a catalytic distillation process, so that the reaction temperature is easy to control, The pressure of the system is low, the reaction materials are contacted in countercurrent, and the carbon deposition of the catalyst can be reduced by using the flushing effect of the hydrocarbon flow; The alkene is the heaviest, and it is continuously removed from the reaction zone under the action of distillation, so that the balance of the hydrogen transfer reaction is continuously moved to the direction of generating 2-butene, so that the 1-butene in the raw material is converted into 2-butene to the maximum extent, and the reaction The content of 2-butene in the product is greatly increased. At the same time, when the catalyst containing non-noble metal Ni is used, it can also adapt to raw materials containing more sulfur.

The following examples will further illustrate the process provided by the present invention, but do not limit the present invention thereby.

The C4 fraction raw material and product compositions used in the embodiment are shown in Table 1. The total height of the reactor is 1700mm, wherein the height of the reaction section is 1000mm, the height of the rectification section is 400mm, the height of the stripping section is 300mm, and the inner diameter of the tower is 32mm. The weight is 90g, and the tower components are bundled with steel wire mesh, with a void ratio of 85%. The catalyst used is a selective hydrogenation catalyst whose active component is nickel, and its trade name is CH-24, produced by Changling Catalyst Factory.

Example 1

Hydrogen and C4 feedstock enter the tower from the upper and lower parts of the catalytic distillation tower at a volume ratio of 18.8 for countercurrent contact, and the downwardly flowing C4 raw material and upwardly flowing hydrogen react on the surface of the catalyst. The reaction conditions are: pressure 0.91MPa (absolute pressure ), the reaction temperature is 70°C, and the volume space velocity is 2.0. The liquid stream is fully refluxed. As can be seen from Table 1, the product does not contain diene, the dimethyl ether content is less than 1ppm, the butadiene conversion rate is 100%, the monoene yield is 82.3%, and 1-butene is isomerized into 2-butene The isomerization rate is 28.5%.

Example 2

The process of this embodiment is basically the same as that of Example 1, and the reaction conditions are: pressure 0.91Mpa (absolute pressure), reaction temperature 70°C, volumetric space velocity 2.0, volume ratio of hydrogen to C4 raw material 11.6. The liquid stream is fully refluxed. As can be seen from Table 1, the product does not contain diene, the dimethyl ether content is less than 1ppm, the butadiene conversion rate is 94.4%, the monoene yield is 103.9%, and 1-butene is isomerized into 2-butene The isomerization rate is 52.7%.

Example 3

The process of this embodiment is basically the same as that of Example 1, and the reaction conditions are: pressure 0.91 MPa (absolute pressure), reaction temperature 70° C., volumetric space velocity 2.5, and volume ratio of hydrogen to C4 raw material 17.4. The liquid stream is fully refluxed. As can be seen from Table 1, the product does not contain diene, the dimethyl ether content is less than 1ppm, the conversion rate of butadiene is 100%, the yield of monoene is 107.6%, and 1-butene is isomerized into 2-butene The isomerization rate is 85.3%.

Table 1 raw material Example 1 Example 2 Example 3 C ₃ H ₈ 0.179 0.058 0 0.008 C ₃ H ₆ 0.009 0 0 0 iC ₄ H ₁₀ 35.700 35.934 31.118 23.733 nC ₄ H ₁₀ 12.763 21.9306 15.754 21.208 1-C ₄ H ₈ 18.200 4.2052 10.714 6.841 iC ₄ H ₈ 1.661 1.5624 1.632 1.432 2-C ₄ H ₈ 30.942 36.194 40.612 46.568 1,3 _{- C4H6} 0.413 0 0 0 nC ₅ H ₁₂ 0.085 0.0579 0.092 0.123 iC ₅ H ₁₂ 0.049 0.063 0.057 0.092 Dimethyl ether 246ppm <1ppm <1ppm <1ppm

Claims (8)

1. A catalytic distillation method for selective hydrogenation of C4 hydrocarbon mixtures, characterized in that C4 feedstock and hydrogen enter the tower from the upper rectifying section and the lower stripping section of the catalytic distillation tower respectively, and the two are on the surface of the catalyst Countercurrent contact, butadiene in the C4 raw material is selectively hydrogenated to form butene, and different butene isomers undergo hydrogen transfer reactions to convert each other, and gas phase impurities including hydrogen and dimethyl ether go out from the top of the tower and pass through the condenser After the reflux tank, the hydrogen and most of the low-boiling impurities leave the device, and all or part of the liquid phase material in the lower part of the reflux tank returns to the tower, and the liquid phase flow in the reaction section in the middle of the catalytic distillation column goes down through the stripping section and enters the reboiler , a small amount of low-boiling impurities dissolved in the liquid phase stream are distilled off, and are separated from the top of the tower under the stripping action of hydrogen and steam generated by the reboiler, while the C4 fraction after the hydrogenation reaction is reboiled from the bottom of the tower output device. 2, according to the method for claim 1, it is characterized in that described raw material comes from the mixed C4 cut that refinery FCC unit separates or the C4 mixture that discharges through MTBE unit, and the former contains the butadiene more than 300ppm and the latter Contains more than 300ppm of butadiene and more than 50ppm of dimethyl ether. 3. The method according to claim 1, characterized in that the concentration of hydrogen entering the catalytic distillation tower is 50% to 100%. 4. The method according to claim 1, characterized in that the reaction conditions are hydrogen partial pressure 0.1MPa～2.0MPa, reaction temperature 40℃～120℃, volume space velocity 1 hour ^-1 ～30 hour ^-1 , hydrogen and C4 raw material The volume ratio is 1-500:1. 5, according to the method for claim 1, it is characterized in that described catalytic distillation tower is made of rectifying section, reaction section and stripping section, and reaction section is in the tower middle part, and its height is 5%～95% of tower height, and refining The distillation section is in the upper part of the tower, and its height is 5% to 50% of the tower height, and the stripping section is in the lower part of the tower, and its height is the difference between the height of the tower and the height of the reaction section and the rectification section. 6. According to the method of claim 1 or 5, it is characterized in that the reaction section of the catalytic distillation tower is equipped with components composed of fillers and catalysts, the components can be piled up randomly, or whole, and the porosity of the components is 30%. ~95%. 7. The method according to claim 6, characterized in that the packing in said member can be random packing or regular packing. 8. A method according to claim 6, characterized in that the catalyst in said member is a catalyst containing nickel or palladium.

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