CN114736137A - Fully mixed flow-plug flow combined cyclohexanone ammoximation process and device - Google Patents

Abstract

The invention discloses a fully mixed flow-plug flow combined cyclohexanone ammoximation process and a device, wherein raw materials comprise cyclohexanone, ammonia and hydrogen peroxide, a titanium-silicon catalyst is adopted, an organic solvent or water is used as a solvent, and the process comprises the following three steps: s1, mixing oximation raw materials with the back oximation thick slurry in the circulation reactor, and converting the mixture into a pre-oximation product in a full-mixing flow mode; s2, completing oximation of the pre-oximation product in a tubular reactor in a plug flow mode, and converting the pre-oximation product into a post-oximation product; s3, the post-oximation product is separated by two stages of sedimentation and membrane filtration, clear liquid is pumped out for purifying cyclohexanone oxime, and the remaining thick slurry is pumped back to the pre-oximation. The method improves the oximation process by optimizing the flow field, shortens the reaction time and improves the yield of the cyclohexanone oxime.

Description

Fully mixed flow-plug flow combined cyclohexanone ammoximation process and device

Technical Field

The invention relates to the field of chemical production, in particular to the field of production of a nylon 6 intermediate cyclohexanone oxime.

Background

Caprolactam is a nylon 6 polymerization monomer, and cyclohexanone oxime is a caprolactam synthesis intermediate.

At present, the mainstream route for producing cyclohexanone oxime adopts a titanium-silicon molecular sieve catalyst, and takes cyclohexanone, hydrogen peroxide and ammonia as raw materials for direct oximation:

the reaction temperature is 60-95 ℃, the pressure is 0.2-0.6MPa, the molar ratio of ammonia to cyclohexanone is 1.2-3.0, and the molar ratio of hydrogen peroxide to cyclohexanone is 1.02-1.12.

Organic solvents such as t-butanol may be added to the reaction; or water can be used as a solvent, and an organic solvent is not added. The oximation process without adding organic solvent omits the distillation process of separating solvent from clear liquid, and has short flow and low energy consumption.

Cyclohexanone oximation mostly adopts a slurry bed stirring kettle, has two forms of built-in filtration and external circulation filtration, and can adopt a single kettle or a plurality of kettles connected in series. CN1234683C example compares oximation data of single kettle and double kettle series, the conversion rate and selectivity of the latter is superior to the former; CN104262196B proposes "a process and equipment for ammoximation reaction and separation coupling", which is further described by "improvement and practice of cyclohexanone ammoximation slurry bed reactor" published by jinhong of the same patent inventor in "he bei industrial science and technology" 2016, volume 33, phase 2, and is called "plug flow-complete mixed flow combined oximation system" (hereinafter referred to as plug flow-complete mixed flow combination). The paper lists a list of oximation industrial devices adopting the technology and introduces the actual operation condition, and the conversion rate of cyclohexanone and the selectivity of cyclohexanone oxime can reach 99.95 percent, which is superior to a slurry bed stirred tank.

The inventors studied articles such as CN104262196B and gold macros systematically and examined industrial devices using this technology. More newly built devices in recent years select the 'plug flow-complete mixed flow combined oximation' technology.

It is known that: for non-zero order reaction, the same conversion rate is achieved, the reaction time of the plug flow reactor is shorter than that of the full mixed flow reactor, and the higher the target conversion rate is, the larger the difference between the target conversion rate and the full mixed flow reactor is. In most cases, plug flow is the preferred reactor. However, for the rapid and strong exothermic reaction, the reaction heat is difficult to be timely removed by the plug flow reactor, the temperature may be out of control, and the full-mixing reactor is only adopted, the carrier quantity for storing the reaction heat is increased by means of the high-power back mixing of the product, and the temperature peak value is reduced. Both stirred tank and loop reactors can provide back mixing, and the loop reactor can totally provide back mixing, but the single-round loop flow from the raw material inlet to the product outlet is a flat push flow, which is beneficial to the reaction.

The back mixing can dilute the reaction heat, reduce the temperature peak value of the reaction system, but also dilute the concentration of reactants and reduce the reaction rate, the retention time of partial reactants is far lower than the average value, and the reactants leave the reactor before the reaction is completed, thereby influencing the conversion rate of the reactants; the residence time of part of the product is much higher than the average value, increasing the possibility of adverse cascade side reactions. For the rapid strong exothermic reaction, the single fully mixed reactor is not the best choice for realizing high conversion rate, the more reasonable proposal is to divide the reaction into two sections, the reaction speed of the front section is high, the heat release is large, and the strong back-mixed reactor is adopted to control the reaction temperature; the reaction speed of the back section is slowed down, the heat release is low, and the conversion efficiency is improved by adopting a plug flow reactor.

Oximation is typically a rapid, strongly exothermic reaction and requires high conversion and high selectivity. The combination of the plug flow and the complete mixed flow is actually a loop reactor with a pipe and a kettle connected in series, the front section of each loop is plug flow, the rear section is complete mixed flow, and the whole body still is complete mixed flow. The reaction rate in the early stage of circulation is high, the heat release is strong, the high circulation ratio is necessary for temperature control, the reaction rate in the later stage of circulation is low, the heat release is weak, and the high circulation ratio is more beneficial. Therefore, there is still much room for improvement in this oximation technology.

Disclosure of Invention

The invention aims to optimize the flow field of the oximation process, shorten the reaction time and improve the yield of the cyclohexanone oxime.

In order to realize the purpose, the invention designs a complete mixed flow-plug flow combined cyclohexanone ammoximation process and a device thereof.

A kind of complete mixed flow-plug flow combined cyclohexanone ammoximation technology, the oximation raw material is cyclohexanone, ammonia, hydrogen peroxide aqueous solution, adopt titanium-silicon molecular sieve catalyst, regard organic solvent or water as the solvent; the mol ratio of ammonia to cyclohexanone is 1.2-3.0, and the mol ratio of hydrogen peroxide to cyclohexanone is 1.05-1.15; the reaction temperature is 60-95 ℃, and the pressure is 0.2-0.6 MPa; the method comprises the following steps:

s1, pre-oximation: the oximation raw material and the reflowed post-oximation thick slurry are mixed and react in a fully mixed flow mode to be converted into a pre-oximation product, and the conversion rate of cyclohexanone is 90-99.5%;

s2, post-oximation: adding hydrogen peroxide water solution into the preoximation product, completing the reaction in a plug flow manner, and converting the product into a post-oximation product, wherein the conversion rate of cyclohexanone is more than or equal to 99.99 percent;

s3, separating clear liquid: and separating clear liquid from the post-oximation product through sedimentation and membrane filtration for purifying cyclohexanone oxime in the next process, and returning the residual thick slurry to S1. The amount of the thick slurry is 0.05-5, preferably 0.2-1 of the amount of the clear liquid.

The raw material hydrogen peroxide is divided into two parts, and is respectively fed into S1 and S2, and the molar ratio of hydrogen peroxide to cyclohexanone in S2 is more than S1.

In order to smoothly implement the oximation process of the invention, the inventor designs a complete mixed flow-plug flow combined cyclohexanone ammoximation device, which comprises a pre-oximation loop reactor, a post-oximation tubular reactor, a settler and a membrane filter which are sequentially connected in series, wherein a booster transfer pump is arranged between the pre-oximation loop reactor and the post-oximation tubular reactor or between the post-oximation tubular reactor and the settler, the settler is matched with a thick slurry reflux pump to pump thick slurry back to the pre-oximation loop reactor, a clear liquid feed pump is matched to send clear liquid with most of catalytic particles removed to the membrane filter, and the membrane filter is matched with a membrane filtration circulating pump and a circulating loop to maintain higher flow velocity of the membrane tube.

The pre-oximation circulation reactor comprises a pre-oximation circulation pump, a cooler, a pre-oximation mixer and a circulation loop, wherein the pre-oximation circulation pump can be a centrifugal pump or an axial flow pump, and preferably an axial flow pump. The flow rate of the preoximation circulating pump is 8 times, preferably 15 times larger than that of the clear liquid; the pre-oximation mixer can adopt a dynamic mixer or a static mixer, and preferably adopts a dynamic mixer; the cooler may be single-stage or multi-stage.

The post-oximation tubular reactor can adopt a straight pipe or a plurality of sections of straight pipes which are turned back at 180 degrees, and the reaction pipe can be internally provided with a cross over disc structure disclosed by the Chinese patent No. CN1490065A, so that the difference of reaction time and temperature history caused by radial velocity gradient and temperature gradient is eliminated.

Drawings

The attached drawing is a schematic flow chart of the cyclohexanone ammoximation process and the device, which is used for helping to understand the invention and is not used for limiting the invention.

FIG. 1 is a schematic flow diagram of a cyclohexanone ammoximation process and apparatus provided by the present invention.

Reference numerals:

s1, a pre-oximation procedure; s2, post-oximation; s3, separating clear liquid;

A. a pre-oximation loop reactor; A1. a pro-oximation circulation pump; A2. a pre-oximation mixer; A3. a cooler;

B. post-oximation of the tubular reactor; B1. a post-oximation mixer; B2. a vertical pipe section; a bend of B3.180 degrees; B4. an interchange disk;

C. a settler; D. a membrane filter;

p1, a booster transfer pump; p2, thick slurry reflux pump; p3, a clarified liquid feed pump; and P4, a membrane filtration circulating pump.

Wherein, the materials of each stage are marked as follows:

(0) oximation raw material: (01) cyclohexanone; (02) ammonia; (03a) adding a pre-oximated aqueous hydrogen peroxide solution; (03b) adding post-oximated aqueous hydrogen peroxide; (04) organic solvent (optionally) is added.

(1) A preoximation reactant;

(2) the product of the preoximation: (2.1) circulating-current preoximation product; (2.2) post-oximation of the reactant;

(3) post-oximation product: (3.1) thick slurry; (3.2) clear solution;

(4) a clarified liquid containing trace amounts of catalyst particles;

(5) the pre-filter is formed by merging the components (4) and (6.2);

(6) the filtered material, wherein (6.1) returns to the settling tower, and (6.2) and (4) are combined into a pre-filtered material (5);

Detailed Description

The process parameters provided in the embodiments of the present invention are only examples and do not limit the scope of the present invention.

Referring to fig. 1, the invention provides a complete mixed flow-plug flow combined cyclohexanone ammoximation process and device, the oximation device comprises a front oximation loop reactor A, a back oximation tube reactor B, a settler C and a membrane filter D which are connected in series in sequence, a booster transfer pump P1 is arranged between the front oximation loop reactor A and the back oximation tube reactor B or between the back oximation tube reactor B and the settler C, the settler C is matched with a thick slurry reflux pump P2 to pump thick slurry (3.1) back to the front oximation loop reactor A and is matched with a clear liquid feed pump P3, clear liquid (4) with most of catalytic particles removed is sent to the membrane filter D, the membrane filter D is matched with a membrane filter circulating pump P4 and a circulating loop, and the high flow rate of the membrane tube is maintained.

The preoximation loop reactor A comprises a preoximation circulating pump A1, a cooler A3 and a preoximation mixer A2, wherein the preoximation circulating pump A1, the cooler A3 and the preoximation mixer A2 are connected in series to form a loop circuit; the pre-oximation circulating pump A1 can be selected from a centrifugal pump or an axial flow pump, and is preferably an axial flow pump. The flow rate of the pre-oximation circulating pump A1 is 8 times, preferably 15 times larger than that of the clear liquid; the pre-oximation mixer A2 can be a dynamic mixer or a static mixer, preferably a dynamic mixer; cooler a3 may be single-stage or multi-stage.

The post-oximation tubular reactor B comprises a post-oximation mixer B1 and a reaction tube which are connected in series, wherein the reaction tube can adopt a straight tube or a structure with multiple straight tubes folded back at 180 degrees, and the structure with multiple straight tubes folded back at 180 degrees shown in figure 1 comprises a plurality of vertical tube sections B2 and 180-degree elbows B3. The reaction tube can be internally provided with a flyover disc structure disclosed in the Chinese patent number ZL03156621.9, so that the difference of reaction time and temperature history caused by radial velocity gradient and temperature gradient is eliminated.

The oximation process comprises three stages: s1 pre-oximation, S2 post-oximation and S3 separation of clear liquid, which are respectively as follows:

s1 preoximation:

feeding cyclohexanone (01), ammonia (02), a preoximation hydrogen peroxide aqueous solution (03a), a solvent (04) and a post-oximation product thick slurry (3.1) refluxed from an S3 settler C into a preoximation loop reactor A, and uniformly mixing a circulating preoximation product (2.1) in a mixer A2 to obtain a preoximation reactant (1); the preoximation circulating pump A1 drives (1) to flow along a circulating loop; under the action of a catalyst, ammoximation is carried out on cyclohexanone to convert the cyclohexanone into a preoximation product (2), and the conversion rate of cyclohexanone is 90-99.5%; the product of pre-oximation (2) is divided into two parts, one of which becomes a product of post-oximation (2.2) and is pumped into the step of post-oximation S2 by a booster pump P1, the other part flows back to the mixer A2 to be mixed with cyclohexanone (01), ammonia (02), aqueous solution of pre-oximation hydrogen peroxide (03a), solvent (04) and thick slurry of post-oximation product (3.1) to become the product of pre-oximation (1), and the product of pre-oximation is driven by the circulating pump A1 to flow down for circulation. The mass flow of the post-oximation reactant (2.2) is the sum of the mass flow of the cyclohexanone (01), the mass flow of the ammonia (02), the mass flow of the aqueous hydrogen peroxide solution (03a) added with the pre-oximation, the mass flow of the organic solvent (04) and the mass flow of the thick slurry (3.1). The mass flow rate of the circulation-flow pre-oximation product (2.1) is the difference between the mass flow rates of the pre-oximation reactant (1) and the post-oximation reactant (2.2). The oximation reaction releases heat, and a cooler A3 removes heat; the reaction heat release, the heat removal of a cooler and the sensible heat change generated by the temperature difference of materials entering and exiting the pre-oximation loop reactor A are balanced, and the temperature of any coordinate point of S1 does not fluctuate along with time; the heat release amount of each round of circulation is attenuated along the way, the heat release of the front section is greater than the heat release, the heat release of the rear section is greater than the heat release, and a temperature inflection point exists in the circulation loop; excessively high temperature peaks can induce side reactions, and excessively low temperature valleys can greatly reduce the reaction rate; the larger the ratio of the flow of the preoximation circulating pump A1 to the flow of the clear liquid (3.2), the smaller the difference between the peak and the valley of the circulating temperature is, but the higher the energy consumption is, the comprehensive consideration is needed.

Cyclohexanone (01), ammonia (02), aqueous hydrogen peroxide solution (03a) added with preoximation, organic solvent (04) and thick slurry (3.1) can respectively enter a preoximation loop reactor A, or two or more of the two or more are mixed and then enter the preoximation loop reactor A together; catalyst is required to be fed in at the initial stage of start-up, and only continuous or intermittent micro-supplement of catalyst is required after stable reflux of the thick slurry (3.1) is established.

S2 post-oximation:

and (3) carrying out S2 post-oximation on the post-oximation reactant (2.2), uniformly mixing the post-oximation reactant with aqueous hydrogen peroxide (03B) in a static mixer B1, and then carrying out post-oximation on the post-oximation tubular reactor B, wherein in order to avoid uneven distribution and even blockage caused by the sedimentation of catalyst particles in the tube, a vertical tube section is selected as far as possible for the reaction tube. In order to reduce the total height of the reactor, a plurality of vertical pipe sections can be connected in series by 180-degree elbows, and the flow velocity of the ascending pipe section is higher than the settling velocity of catalyst particles; the 180-degree elbow can reduce the diameter to prevent the catalyst in the horizontal section from settling. A cross over disc (CN1490065A) can be arranged in the reaction tube, the fluid in the inner peripheral area and the fluid in the central area of the guide tube are transposed, the difference of the retention time of the material caused by the radial velocity gradient is eliminated, and the material keeps ideal flat push flow. The overpass disc can be arranged in a straight pipe section or a 180-degree elbow.

The post-oximation reactant (2.2) flows in a back-oximation tubular reactor B in a horizontal pushing mode, under the action of a catalyst, cyclohexanone is sufficiently ammoximated and converted into a post-oximation product (3), and the conversion rate of the cyclohexanone is more than 99.99%.

Sufficient ammonia was dissolved in (2.2) entering the tubular reactor B, and the post-oximation step was performed without adding ammonia.

The post-oximation has little heat release, can generally digest reaction heat by depending on material temperature rise, and is not provided with a heat exchanger.

S3 separating the clear liquid:

the post oximation product (3) enters a settler C to be separated into thick slurry (3.1) and clear liquid (4), more than 99 percent of catalyst particles follow the thick slurry (3.1) and less than 1 percent of catalyst particles follow the thick slurry (4); the thick slurry reflux pump P2 pumps the thick slurry (3.1) back to the S1 pre-oximation loop reactor A, the clear liquid feed pump P3 pumps the clear liquid (4) containing a trace amount of catalyst particles to a membrane filter D, the clear liquid (4) and the circulating filtered substance (6.2) are combined into a pre-filtered substance (5) and then enter the membrane filter D, the clear liquid (3.2) flows out of a shell pass through a membrane tube and is sent to the next process for separating and purifying cyclohexanone oxime, the filtered substance (6) which is used for extracting the clear liquid (3.2) is driven by a membrane filter circulating pump P4 to flow circularly, and the clear liquid (6.1) returns to C, and the clear liquid (6.2) and the clear liquid (4) are combined into the pre-filtered substance (5) and then flow into D. (6.1) the flow rate is the difference between (4) and (3.2).

The thick slurry (3.1) returns the catalyst particles carried over by the post-oximation reactant (2.2) to the pre-oximation loop reactor a, which is necessary; while also backmixing cyclohexanone oxime back to the pro-oximation loop reactor a, which is disadvantageous. Cyclohexanone oxime in the thick slurry (3.1) should be minimized, but the thick slurry (3.1) pumping or material mixing in the pre-oximation mixer A2 cannot be influenced by too high concentration of catalyst particles, and the flow ratio of the thick slurry (3.1) to the clear liquid (3.2) is 0.05-5, preferably 0.2-1.

Example (b):

raw materials: cyclohexanone, ammonia, aqueous hydrogen peroxide (27.5 wt.%), titanium silicalite catalyst, no organic solvent;

the mol ratio of ammonia to cyclohexanone is 2.0, and the mol ratio of hydrogen peroxide to cyclohexanone is 1.07, wherein 98.6 percent of S1 is added, and 1.4 percent of S2 is added; s1 molar ratio of hydrogen peroxide to cyclohexanone was 1.055, and S2 molar ratio of hydrogen peroxide to cyclohexanone was 1.5.

The sum molar flow of the cyclohexanone and the cyclohexanone oxime in each material is Q, and the conversion rate M of the cyclohexanone is defined as the ratio of the molar number of the cyclohexanone oxime to the sum molar number of the cyclohexanone and the cyclohexanone oxime. The conversion rate of cyclohexanone and the selectivity of cyclohexanone oxime which are post-oximation products are close to 1,

control of Q with P1_2.2＝1.5Q₀₁Then Q is_3.1＝0.5Q₀₁

Control of Q with A1₁＝15Q₀₁Then Q is_2.1＝Q₂-Q_2.2＝13.5Q₀₁

Control M₂＝0.99，M₃0.9999, then

The raw material cyclohexanone enters a pre-oximation loop reactor and is immediately mixed with a loop pre-oximation resultant (2.1) to form a pre-oximation reactant (1), and the conversion rate M of the cyclohexanone₁0.92433, the circulating preoximated product (2.1) is further subjected to a round circulation in a plug flow manner and converted into a preoximated product (2), M₂The temperature is raised to 0.99.

(2.2) proceeding to the post-oximation tubular reactor B, continuing to complete oximation in a plug flow mode, and converting into a post-oximation product (3), M₃Up to 0.9999.

The post-oximation product (3) enters a settler C to be separated into thick slurry (3.1) and clear liquid (4), wherein the concentration of catalytic particles in the (3.1) is only 3 times of that in the (3), the conveying efficiency or the mixing efficiency in A2 is not influenced, the cyclohexanone oxime backmixed back to the pre-oximation is only 0.5 times of that in the clear liquid, and the adverse effect on the reaction is small; the concentration of particles in the clear liquid (4) is lower than 0.01 in the post-oximation product (3), and the membrane filtration condition is improved.

Compared with the prior cyclohexanone ammoximation technology, the fully mixed flow-plug flow combined process and device provided by the invention have the following advantages:

1. the preoximation full-mixing flow effectively controls the difference value of the temperature peak and the valley and inhibits side reaction;

2. the post-oximation flat push flow makes full use of reaction driving force and obviously shortens reaction time;

3. cyclohexanone conversion M in clear liquid₃≥0.9999；

4. The molar ratio of the hydrogen peroxide to the cyclohexanone is S2> S1, so that the decomposition of the hydrogen peroxide in S1 is inhibited, the full conversion of the S2 cyclohexanone is promoted, and the unit consumption of the hydrogen peroxide is reduced;

5. the cyclohexanone oxime backmixed from S3 back to S1 is less, thus being beneficial to oximation;

6. the membrane filtration efficiency is improved, catalyst particles in the clear liquid are completely cut off, and the operation and maintenance are simplified.

Claims (8)

1. A kind of complete mixed flow-plug flow combined cyclohexanone ammoximation technology, the oximation raw material is cyclohexanone, ammonia, hydrogen peroxide, adopt titanium silicon catalyst, regard organic solvent or water as the solvent; the reaction temperature is 60-95 ℃, and the pressure is 0.2-0.6 MPa; the mol ratio of ammonia to cyclohexanone is 1.2-3.0, and the mol ratio of hydrogen peroxide to cyclohexanone is 1.05-1.15; the method is characterized by comprising the following steps:

s1, pre-oximation: the oximation raw material is mixed with the reflowed post-oximation thick slurry, and is ammoximated in a fully mixed flow mode to be converted into a pre-oximation product;

s2, post-oximation: adding hydrogen peroxide into the preoximation product, completing oximation in a plug flow mode, and converting the oximation into a post-oximation product;

s3, separating clear liquid: and separating clear liquid from the post-oximation product through sedimentation and membrane filtration for purifying cyclohexanone oxime in the next procedure, and returning the residual thick slurry to the pre-oximation step.

2. The oximation process according to claim 1, wherein the conversion of the premoximation product cyclohexanone is between 90 and 99.5%.

3. The oximation process according to claim 1, wherein the conversion of post-oximation product cyclohexanone is not less than 99.99%.

4. The oximation process according to claim 1, wherein the post-oximation slurry refluxed until the pre-oximation is in the range of 0.05 to 5% by weight of the supernatant.

5. The oximation process according to any one of claims 1 and 4, wherein the post-oximation slurry refluxed to the pre-oximation is in an amount of 0.2 to 1 by weight based on the weight of the serum.

6. The oximation process of claim 1, wherein the hydrogen peroxide feedstock is divided into two portions, which are separately introduced into the pre-oximation and the post-oximation, wherein the molar ratio of the post-oximation hydrogen peroxide to cyclohexanone is greater than that of the pre-oximation.

7. A fully mixed flow-plug flow combined cyclohexanone ammoximation device for implementing the oximation process of claim 1, which is characterized by comprising a pre-oximation loop reactor, a post-oximation tubular reactor, a settler and a membrane filter which are sequentially connected in series, wherein a booster delivery pump is arranged at the outlet of the pre-oximation loop reactor or the post-oximation tubular reactor, the settler is provided with a thick slurry reflux pump and a clear liquid feed pump, and the membrane filter is provided with a circulation loop and a membrane filtration circulation pump.

8. The oximation apparatus according to claim 7, characterized in that the pro-oximation loop reactor comprises a pro-oximation circulation pump, a cooler, a pro-oximation mixer and a loop circuit.

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