CN1152017C - Catalyst recycling caprolactam hydrorefining method - Google Patents

Abstract

The present invention relates to a hexanolactam hydrofining process with a circulated catalyst. In the method, in a slurry bed reactor, a caprolactam aqueous solution containing impurities is in contact with hydrogen by the continuous circulation addition of a catalyst to make unsaturated materials in the caprolactam aqueous solution hydrogenated into saturated materials; then the catalyst is separated by a hydrocyclone separation device from hydrogenated reaction effluents and is recycled. The utilization rate of a catalyst is improved by the method, and simultaneously, the problem that a catalyst is separated from a liquid product is effectively solved.

Description

Catalyst recycling caprolactam hydrorefining method

The invention relates to a caprolactam hydrogenation refining method.

In the production process of caprolactam, in addition to caprolactam products, some unsaturated by-products will also be generated. The physical properties of these unsaturated by-products are very close to those of caprolactam, and it is difficult to remove them by extraction and distillation. The existence of these impurities will affect the polymerization process of caprolactam, which is directly related to the quality of nylon-6 products, so these impurities must be removed. Hydrofining of caprolactam is to saturate unsaturated impurities through hydrogenation process in the presence of catalyst, separate its physical properties from caprolactam, and then remove these impurities through extraction and distillation.

The existing caprolactam hydrorefining method uses a slurry bed reactor, with skeleton nickel (Raney nickel, English name is Raney Ni) as a catalyst. The slurry bed reactor requires that the particle size of the catalyst used is generally not greater than 200 μm, preferably not greater than 100 μm, so that the catalyst is evenly suspended in the reaction material. Although the slurry bed basically eliminates the influence of diffusion in the reaction, it can make full use of the effective catalyst. Activity, but it also brings the problem of solid-liquid separation.

At present, in order to solve the problem of solid-liquid separation, the conventional method is to use a filter with a filter medium or a centrifugal filter with a high separation factor. Both of these methods have disadvantages such as high power consumption, large investment, and complicated operation. In the existing slurry bed caprolactam hydrogenation process using Raney Ni as a catalyst, the catalyst is a one-time pass method, and the residence time of the catalyst in the reaction material is only 10 to 30 minutes, and the filtered catalyst is not recycled and used as a waste object processing. The disadvantages of the prior art are poor adaptability to raw materials, low catalyst utilization rate, high equipment cost, complex process and high labor intensity.

The object of the present invention is to provide a caprolactam hydrofinishing method for catalyst circulation to reduce catalyst consumption.

The caprolactam hydrorefining method provided by the invention comprises:

(1) The aqueous solution of caprolactam containing impurities is contacted with hydrogen in the presence of a solid particle hydrogenation catalyst in a slurry bed reactor, at a temperature of 20-200 ° C, a pressure of normal pressure to 10.0 MPa, and a residence time of 1 ～300 minutes, reacting under the condition that the catalyst concentration in the reactor is 0.001～10% by weight;

(2), after the hydrogenation, the caprolactam aqueous solution containing the solid particle catalyst is separated from the solution through a hydrocyclone separation device, so that the caprolactam aqueous solution is substantially free of solid catalyst;

(3) All or part of the separated catalyst is returned to the reactor for recycling, and the used catalyst is taken out according to the activity level of the catalyst, and fresh catalyst is added.

The raw material used in the present invention is caprolactam aqueous solution containing impurities, which can come from different caprolactam synthesis processes, wherein the concentration of caprolactam is 10-95% by weight. If the caprolactam concentration is too low, it will cause the evaporation of a large amount of water in the downstream distillation process and consume energy.

A slurry bed reactor refers to a reaction vessel that suspends a solid particle catalyst in a reaction liquid material well known to those skilled in the art, such as a mechanically stirred tank, a gas stirred tank, and a reactor that suspends a solid catalyst in a reaction vessel by a liquid flow rate. The liquid-phase suspended bed reactor and the slurry bed reactor can be one, or two to four in series or in parallel.

Solid particle hydrogenation catalysts are any catalysts with a certain particle size that are suitable for hydrogenation of unsaturated bonds, such as Raney nickel catalysts, amorphous alloy catalysts with nickel as the main active component, and nickel, palladium or platinum as catalysts. Supported hydrogenation catalyst of the main active component.

According to the method provided by the present invention, the way of adding fresh catalyst and taking out the used catalyst can be discontinuous periodically or instantaneously continuous.

The hydrogenation reaction temperature is related to the activity of the catalyst used, generally 20-200°C, preferably 70-150°C. Too low reaction temperature will reduce the hydrogenation reaction rate, and too high temperature will have adverse effects on the quality of caprolactam.

The reaction pressure is generally from normal pressure to 10.0 MPa, preferably 0.3-5.0 MPa, most preferably 0.4-1.2 MPa. High reaction pressure can improve the refining effect of caprolactam, but the increase of pressure will increase the investment of the device.

The reaction residence time is related to the reaction temperature, reaction pressure and catalyst concentration, and is generally 1 to 300 minutes, preferably 5 to 120 minutes, most preferably 10 to 35 minutes.

Step (2) is to use hydrocyclone separation equipment to separate the solid particle catalyst from the hydrogenated caprolactam aqueous solution, so that the caprolactam aqueous solution basically does not contain solid catalyst, so that conventional filtering equipment can be omitted. The hydrocyclone separation device generally refers to a separation device that is driven by fluid pressure and uses the principle of centrifugal separation to separate solids from solutions through high-speed rotation of fluid. Because it is driven by the pressure of the fluid itself, the pressure of the caprolactam aqueous solution after hydrogenation can be used as the power to realize the separation of the catalyst and the reaction liquid without adding any additional power. It also has the advantages of continuous and simple operation, large processing capacity, Small investment, easy maintenance and so on. In order to improve the efficiency of solid-liquid separation, several stages such as two to four in series or parallel can be used or used in conjunction with other separation equipment.

The basic structure of hydrocyclone separation equipment is shown in Figure 1. It is composed of a cylindrical part a and a conical part b. There is a feed port c in the middle and upper part of the cylinder a, and an overflow port d in the upper part. There is a vortex cone e in the middle, and an underflow port f under the cone. The recommended structural dimensions are shown in Table 1.

After hydrogenation, the caprolactam aqueous solution containing catalyst particles enters in a tangential direction from the feed port of the cylindrical part, and rotates to generate centrifugal force, which is more violent when it descends to the conical part. Catalyst particles in the solution are thrown to the wall by centrifugal force, and flow down the helical line along the wall to the underflow port under the conical part, and the clarified caprolactam aqueous solution rises through the vortex elimination cone and exits from the overflow port of the cylindrical part .

Table 1 Cylindrical part diameter D _c , mm 10～1200 Inlet diameter D _i (0.1～0.33) _Dc Overflow diameter D _o (0.1～0.33) _Dc Underflow orifice diameter D _u (0.02～0.33) _Dc The height difference _Ht between the inlet and the overflow (0.5～1.5) _Dc Vortex elimination cone length H _c (0.2～1.5) _Dc Bottom diameter of vortex elimination cone _De (0.17～0.33) _Dc Vortex elimination cone top diameter D _t (1.5～3.0)D _e The included angle θ of the conical part 5～20

The pressure drop of the inlet and outlet of hydrocyclone separation equipment is an important operating parameter, which is directly related to the separation efficiency of hydrocyclone separation equipment. The recommended pressure difference between the inlet and outlet of the present invention is 0.05-2.0MPa, preferably 0.1-1.2MPa, most preferably 0.15-0.45MPa.

The particle size of the catalyst will also affect the separation efficiency of the hydrocyclone separation equipment. Generally, the larger the particle size and density, the more conducive to the separation of solid and liquid, but too large particle size will bring difficulties in suspension and transportation; too fine The particle size will lead to the difficulty of hydrocyclone separation. A suitable particle size is 5-300 μm, preferably 15-100 μm.

It is hoped that the feed state of the hydrocyclone separation equipment is in the liquid phase. If the hydrogenation reaction is carried out by using dissolved hydrogen, the reaction liquid can directly enter the hydrocyclone separation equipment; if the hydrogen used for the hydrogenation reaction exceeds the dissolved hydrogen, the material enters the hydrocyclone separation equipment. Before, it is better to remove the gas beyond the dissolved hydrogen part.

The hydrocyclone separation device of the present invention has two functions, one is to clarify the caprolactam solution after hydrogenation; the other is to recover the used catalyst so as to realize the recycling of the catalyst.

In step (3), the catalyst is recycled, so the utilization efficiency of the catalyst can be fully improved. In the existing slurry bed caprolactam hydrogenation process using Raney Ni as a catalyst, the catalyst is a one-pass method, and the residence time of the catalyst in the reaction material is only 10 to 30 minutes. We have found that there is not much loss of catalyst activity in such a short time, so it is necessary to recycle it in order to reduce the catalyst consumption of the process. Catalyst recycling can be achieved by:

One of the methods: the hydrocyclone separation equipment is placed above the liquid phase discharge pipeline of the reactor. After the liquid phase material from the reactor enters the hydrocyclone separation equipment, the pressure of the overflow material and the underflow material is reduced to normal pressure. The underflow containing the catalyst is sent back to the reaction system through the pressure pump.

Method 2: The liquid phase material coming out of the reactor is first pumped and then sent to the hydrocyclone separation equipment for separation. The separated underflow material is the catalyst and is directly sent back to the reaction system, while the overflow material is the caprolactam after hydrogenation The solution is sent to the downstream unit under reduced pressure.

When the activity of the catalyst drops to a particularly low level, the spent catalyst is removed and fresh catalyst is replenished at the same time.

According to the caprolactam hydrogenation method for catalyst recycling provided by the present invention, the concentration of the catalyst in the reactor can be adjusted as required. In principle, when the raw material quality is poor or the hydrogenation effect needs to be improved, it is often necessary to increase the concentration of the catalyst, otherwise the concentration of the catalyst needs to be decreased. In the existing slurry bed process, the increase of catalyst concentration can only be realized by increasing the amount of fresh catalyst added, which will lead to a substantial increase in catalyst consumption; while the method of the present invention is realized by changing the circulation amount of catalyst , there is no problem of greatly increasing the amount of fresh catalyst, so it has good operational flexibility and raw material adaptability. The adjustment of the catalyst concentration needs to consider various factors such as the quality of the raw material, the effect of hydrofining, the performance of the catalyst used, the catalyst replacement cycle, and the separation effect of the hydrocyclone separation equipment. 2% by weight, preferably 0.01 to 1.0% by weight.

The method provided by the present invention will be further described below in conjunction with the accompanying drawings.

Accompanying drawing 2 is one of method embodiment provided by the present invention.

The caprolactam aqueous solution containing impurities enters the slurry bed reactor 4 through the pipeline 1 as the raw material, and the circulating catalyst solution also enters the reactor 4 through the pipeline 3, and the hydrogen enters the bottom of the reactor 4 through the pipeline 2 and fully mixes with the materials in the reactor And hydrogenation reaction is carried out, and the remaining gas is discharged from the top of reactor 4 through pipeline 5. The caprolactam aqueous solution after hydrogenation and the catalyst enter hydrocyclone 7 through pipeline 6 by self-pressure, and the clarified liquid enters hydrocyclone 7 from hydrocyclone 7. The overflow port at the top is sent out of the device through the pipeline 8; the solid catalyst and a small amount of liquid material come out from the bottom of the hydrocyclone 7 through the pipeline 9, and are circulated back to the reactor 4 through the pump 12 and the pipeline 3 together with the fresh catalyst supplemented through the pipeline 11 . When the activity of the catalyst drops to a particularly low level, fresh catalyst can be added intermittently or continuously through the pipeline 11, and the catalyst can be taken out intermittently or continuously through the pipeline 10 at the same time, and the concentration of the catalyst in the reactor can be changed by adjusting the circulation amount of the catalyst circulation pump 12 .

Accompanying drawing 3 is the second embodiment of the method provided by the present invention.

The caprolactam aqueous solution containing impurities enters the slurry bed reactor 4 through the pipeline 1 as the raw material, the hydrogen gas enters the reactor 4 through the pipeline 2, fully mixes with the materials in the reactor and undergoes hydrogenation reaction, and the remaining gas passes through the pipeline 5 from the reactor The top of the device 4 is discharged, and the caprolactam aqueous solution after hydrogenation and the catalyst enter the hydrocyclone 7 through the pipeline 13, the pump 12 and the pipeline 6 successively, and the clarified liquid is sent out from the overflow port at the top of the hydrocyclone 7 through the pipeline 8. The solid catalyst and a small amount of liquid material flow back to the reactor 4 through the pipeline 9 from the bottom of the hydrocyclone 7 . When the activity of the catalyst drops to a particularly low level, fresh catalyst can be added intermittently or continuously through the line 11, and the catalyst can be taken out intermittently or continuously through the line 10 at the same time.

The method advantage provided by the invention is:

1. Use hydrocyclone separation equipment to realize the separation of catalyst and caprolactam aqueous solution without adding any additional power, continuous and simple operation, large processing capacity, small investment and convenient maintenance.

2. The catalyst is recycled, so the utilization efficiency of the catalyst can be fully improved and the consumption of the catalyst can be reduced.

3. Because the catalyst is recycled, the adjustment of the hydrogenation reaction effect can be realized by changing the circulation amount of the catalyst, and there is no problem of greatly increasing the amount of fresh catalyst. This method has good operational flexibility and raw material adaptability.

The following examples will further illustrate the method, but the method is not limited thereby.

The grade of the catalyst used in the examples is SRNA-4, produced by Hunan Jianchang Petrochemical Co., Ltd. Amorphous Alloy Hydrogenation Catalyst Factory, and its properties are shown in Table 2. The cyclone model used in the examples is BSDF-150B, produced by Beijing Paleozoic Non-Metal Mining Engineering Equipment Co., Ltd., and its structural dimensions (in mm) are shown in Table 3.

Example 1

This example illustrates the effect of the cyclone used in the present invention on solid-liquid separation.

Put 500g of amorphous alloy catalyst into a 1.5m ³ stirred tank pre-installed with 1000kg of water, suspend the catalyst in the liquid by stirring, pump the suspension into the cyclone, and examine the cyclone by adjusting the flow rate of the pump. The solid-liquid separation effect when the pressure difference between the inlet and outlet of the flow device changes.

The solid-liquid separation effect is judged by sampling and analyzing the nickel content in the overflow and underflow separated by the cyclone. The results are shown in Table 4. It can be seen from Table 4 that the cyclone can separate almost all the solid catalyst in the feed into the underflow within the range of differential pressure tested.

Example 2

This example illustrates the recycling of the catalyst used in the present invention.

Add 1500g of caprolactam aqueous solution (containing 30% by weight of caprolactam, the same below) and 3g of amorphous alloy catalyst in a four-necked flask with a capacity of 2000mL, feed hydrogen under normal pressure, and the flow rate is 50L/h, heated by a heating mantle and After heat preservation at 90°C and stirring for 30 minutes (rotating speed 540r.p.m), only the clear liquid after reaction was taken out to measure the RIC value, and the catalyst was kept in the reaction bottle for repeated use once. Add 1500g caprolactam aqueous solution to the reaction bottle, react with the above conditions, measure the RIC value of the clear liquid after the reaction, the catalyst is used twice, and so on. The results obtained are shown in Table 5. It can be seen from Table 5 that the catalyst still has high hydrogenation activity after 6 repeated uses.

The RIC value is used to characterize the content of redoxable substances in the product, which is the method adopted by the Italian SNIA company. The larger the RIC value, the higher the content of redoxable substances. The determination method is: weigh 10g caprolactam (accurate to _0.01g ) in a 100mL beaker, add 50mL water, adjust the pH value of the solution to 5-6 with 0.1N _H2SO4 , then transfer the solution into a 1000mL volumetric flask, Dilute to the mark with water, put 50mL of the solution into a 100mL beaker, stir while adding 1.0mL 0.002M _KMnO4 , and quickly press the stopwatch, when the reaction time reaches 180 seconds, measure the absorbance value (spectrophotometer, wavelength 410nm) . RIC= _10Rf /w (where _Rf is the RIC coefficient and w is the sample weight).

Table 2 BET specific surface area, m ² /g 145 Pore volume, mL/g 0.11 Average pore size, Angstroms 29.4 Particle size distribution,% ＜200 mesh 0 200～300 mesh 80 ＞300 mesh 20

table 3 D _c D _{i Do} D _{u Ht} H _c D _e D _t θ 200 50 50 8 150 150 40 80 15

Table 4 serial number differential pressure overflow flow underflow flow Catalyst content MPa m ³ /h m ³ /h overflow Underflow 1 0.4 20.3 0.095 4.1ppm 9.6%wt 2 0.2 14.0 0.09 7ppm 7.1%wt 3 0.12 9.0 0.087 12ppm 4.8%wt

table 5 Catalyst reuse times raw material 1 2 3 4 5 6 RIC value 15.58 5.73 7.75 7.7 7.84 7.97 8.57

Claims (14)

1. A caprolactam hydrogenation refining method with catalyst circulation, the caprolactam aqueous solution containing impurities is contacted with hydrogen in the presence of a solid particle hydrogenation catalyst in a slurry bed reactor, at a temperature of 20-200 ° C and a pressure of normal pressure to 10.0MPa, the residence time is 1-300 minutes, and the catalyst concentration in the reactor is 0.001-10% by weight to react under the reaction conditions, it is characterized in that after hydrogenation, the caprolactam aqueous solution containing the solid particle catalyst is separated from the catalyst through the hydrocyclone separation equipment The catalyst is separated from the solution, all or part of the separated catalyst is returned to the reactor for recycling, and the used catalyst is taken out according to the activity level of the catalyst, and fresh catalyst is added. 2. The method according to claim 1, characterized in that said slurry bed reactor is any stirred bed or suspended bed reactor capable of suspending the solid particle catalyst in the reaction mass. 3. The method according to claim 1 or 2, characterized in that said slurry bed reactor can be one, or two to four can be connected in series or in parallel. 4. The method according to claim 1, characterized in that the reaction conditions are: temperature 70-150°C, pressure 0.3-5.0 MPa, residence time 5-120 minutes, catalyst concentration in the reactor 0.005-2 wt. %. 5. The method according to claim 4, characterized in that the reaction conditions are as follows: the pressure is 0.4-1.2 MPa, the residence time is 10-35 minutes, and the catalyst concentration in the reactor is 0.01-1% by weight. 6, according to the method for claim 1, it is characterized in that described hydrocyclone separation equipment is made up of cylindrical part and conical part, there is feeding port in the middle and upper part of cylinder, and overflow port is arranged in the upper part, and in the cylinder part There is a vortex-eliminating cone in the middle, and there is a bottom flow port under the cone. 7. The method according to claim 1 or 6, characterized in that said hydrocyclone separation device can be one, or two to four can be connected in series or in parallel. 8. The method according to claim 1, characterized in that said hydrocyclone is operated under a differential pressure force of 0.05-2.0 MPa. 9. The method according to claim 8, characterized in that said hydrocyclone is operated under a differential pressure force of 0.1-1.2 MPa. 10. The method according to claim 9, characterized in that said hydrocyclone is operated under a differential pressure force of 0.15-0.45 MPa. 11, according to the method for claim 1, it is characterized in that described solid particle catalyst can be Raney nickel catalyst, also can be the amorphous alloy catalyst with nickel as the main active component, can also be based on nickel, palladium or platinum Supported hydrogenation catalyst as the main active component. 12. The method according to claim 1, characterized in that said catalyst particle size is 5-300 µm. 13. The method according to claim 1, characterized in that said caprolactam aqueous solution has a concentration of 10-95% by weight. 14. The method according to claim 1, characterized in that the way of taking out the spent catalyst and replenishing the fresh catalyst can be intermittent periodically or instantaneously continuous.

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