METHOD FOR IMPROVING REACTION YIELD

Abstract

In a catalytic reaction, after a reaction product leaves a catalyst bed, an inert substance with a low temperature is sprayed, and through heat absorption and vaporization processes of the inert substance, the temperature of the reaction product drops rapidly when staying in a catalyst cushion layer at a discharge end of a fixed bed reactor, or in a space formed by the catalyst cushion layer at the discharge end of the fixed bed reactor and a reactor head, or in a space formed by a tube plate at the discharge end of the fixed bed reactor and the reactor head. The residence time of the reaction product is shortened due to the entrance of the inert substance in a gaseous state.

Claims

1. A method for improving reaction yield, wherein, the method comprises: feeding reaction raw materials into a fixed bed reactor; the reaction raw materials flow through a catalyst bed to obtain reaction products; the reaction products pass through a catalyst cushion at a discharge end of the fixed bed reactor and then pass a space which is formed by the catalyst cushion and a reactor head, thereafter leave the reactor; or the reaction products pass through a space which is formed by a tube sheet at the discharge end of the fixed bed reactor and a fixed bed reactor head, thereafter leave the reactor; at this time, performing at least one of the following operations (i), (ii) and (iii): (i) injecting an inert substance into the catalyst cushion at the discharge end of the fixed bed reactor; (ii) injecting an inert substance into the space which is formed by the catalyst cushion at the discharge end of the fixed bed reactor and the reactor head; (iii) injecting an inert substance into the space which is formed by the tube sheet at the discharge end of the fixed bed reactor and the reactor head.

2. The method according to claim 1, wherein the inert substance is at least one of a gas or a liquid that can be vaporized after being heated.

3. The method according to claim 1, wherein the inert substance is nitrogen, helium, argon, carbon dioxide; water; oxygenated organics with a carbon number less than or equal to 10; nitrogenous organics with a carbon number less than or equal to 10; naphthene with a carbon number less than or equal to 12; alkanes with a carbon number less than or equal to 12; aromatics with a carbon number less than or equal to 10; or a mixture of at least two of them.

4. The method according to claim 3, wherein the inert substance is selected from at least one of the group consisting of nitrogen, helium, argon, carbon dioxide, water, C.sub.6-C.sub.8 alkane, C.sub.6-C.sub.8 aromatic, C.sub.1-C.sub.4 alcohol, C.sub.1-C.sub.4 acid, C.sub.2-C.sub.4 nitrile and C.sub.2-C.sub.4 ester; preferably, the inert substance is selected from at least one of the group consisting of nitrogen, helium, argon, carbon dioxide, hexane, heptane, benzene, toluene, xylene, methanol, ethanol, propionic acid, methyl propionate, acetonitrile and water.

5. The method according to claim 1, wherein the inert substance is injected into the reactor through a nozzle; optionally, the nozzle is provided with nozzle hole(s); the nozzle is arranged in the catalyst cushion at the discharge end of the fixed bed reactor, and/or is arranged in the space which is formed by the catalyst cushion at the discharge end of the fixed bed reactor and the reactor head, or is arranged in the space which is formed by the tube sheet at the discharge end of the fixed bed reactor and the reactor head.

6. The method according to claim 1, wherein the amount of the inert material injected is 0.1-5 times weight of the feed amount of the fixed bed reactor, preferably 0.5-2 times weight.

7. The method according to claim 1, wherein the fixed bed reactor is a tube bundle reactor or a single tube reactor, and the reactor has a head.

8. The method according to claim 1, wherein the reaction products, especially heat-sensitive reaction products, can be ethylenically unsaturated acids and their esters, such as vinyl acetate, acrylic acid, methacrylic acid, acrylate, methacrylate (such as methyl methacrylate) etc; the reaction products can also be ethylenically unsaturated aldehyde, such as acrolein, methacrolein, etc., and also can be the olefins, such as propylene, isobutylene, butadiene and styrene compounds, etc., and the reaction products also can be epoxides, such as ethylene oxide, propylene oxide, etc., and unsaturated acid anhydrides, such as maleic anhydride etc.

9. The method according to claim 1, wherein the reaction raw materials may be raw materials for preparing the above reaction products, comprising at least one of olefins, alkanes, aromatic hydrocarbons, carboxylic acids, carboxylic acid esters, aldehydes, alcohols, etc., specifically comprising at least one of ethylene, propylene, isobutylene, propane, butane, isobutane, acetic acid, propionic acid, methyl acetate, methyl propionate, formaldehyde, vinylaldehyde, acrolein, methacrolein, methanol, butene-1, phenylethanol, ethylbenzene, etc; the reaction raw material gas may be obtained by heating and vaporizing the reaction raw materials through a vaporizer.

10. The method according to claim 1, wherein temperature of the reaction is from 240° C. to 700° C.; after cooled by the inert substance, the temperature of the reaction product flowing out the fixed bed reactor can be reduced to 50° C.-250° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 is a schematic structural diagram of a fixed bed reactor according to the present invention.

[0052] FIG. 2 is a flow chart of the reaction process according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0053] The present invention will be further illustrated with reference to the specific examples below. It should be understood that the following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. In addition, it should also be understood that after reading the contents of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present invention.

[0054] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples can be obtained from commercial sources.

[0055] The analysis of propionic acid, methyl propionate, methanol, methacrylic acid and methyl methacrylate are carried out on the Agilent GC7820 with FID detector, DB-FFAP (30 m×0.53 mm×1 μm) capillary column, n-heptane as internal standard; exhaust gas is analyzed via online mass spectrometry model Extreme MAX300. The analysis of formaldehyde in raw materials and products is carried out by chemical titration; the water in raw materials and products are analyzed by Karl-Fischer method.

Conversion of methyl propionate (mol)=the amount of methyl propionate reacted (mol)/the amount of methyl propionate supplied (mol)×100%

Selectivity of propionic acid (mol %)=the amount of propionic acid produced (mol)/the amount of methyl propionate reacted (mol)×100%

Selectivity of methacrylic acid (ester) (mol %)=the amount of methacrylic acid (ester) produced (mol)/the amount of methyl propionate reacted (mol)×100%

Yield of methacrylic acid (ester) (mol %)=conversion of methyl propionate (mol %)×the selectivity of methacrylic acid (ester) (mol %)

[0056] The raw materials: methyl propionate, formaldehyde, and methanol, wherein, the molar ratio of methyl propionate and formaldehyde is 20:1-1:20. The molar ratio of methanol and formaldehyde is 0.1-1.5:1.

[0057] The catalyst is a supported alkali metal cesium silica gel catalyst, which has a loading of alkali metal cesium of 1-15 wt %; the catalyst has a specific surface area of 100-500 m.sup.2/g, an average pore size of 10-17 nm, a pore volume of about 1 ml/g. The catalyst can be prepared by the following method: mixing and shaking the silica gel with alkali metal solution and modifier (such as 2 g/100 mol zirconium (weight of the metal)), and after immersing for 24 hours, drying to constant weight at 120° C., then calcined at 300-500° C. for 2-6 hours. For example, for the preparation of the catalyst, refers to U.S. Pat. No. 6,544,924.

[0058] The reactor is a single tube fixed bed reactor, the catalyst is packed in the middle of the fixed bed, bulk or granular inert packing such like ceramic, glass or quartz, etc locates above and below the catalyst to form the catalyst cushion.

[0059] Among them, formaldehyde can be formalin; or compounds that can produce formaldehyde by heating, such as paraformaldehyde, trioxane, methylal, etc.

[0060] Among them, the inert gas can also be mixed into the reaction materials, such as nitrogen, argon, helium etc., the dilute solvents such as alkanes, aromatics, etc. Nitrogen is preferred.

[0061] The mixed reaction materials and nitrogen are mixed and enter into the vaporizerto be heated and vaporized, and then enter the fixed bed reactor. The temperature of the vaporizer is 240-700° C., the catalyst bed is heated or removed by the medium outside the tube. In the fixed bed, the temperature is 240-400° C., the pressure is 0.1-1.0 MPag, preferably, the vaporizer temperature is 300° C., the fixed bed temperature is 350° C., the pressure is 0.1-0.5 MPag, the residence time is 1-100 s.

Example 1

[0062] FIG. 1 is a schematic structural diagram of a fixed bed reactor according to the present invention. FIG. 2 is a flow chart of the reaction process according to the present invention. As shown in FIG. 1 and FIG. 2, nitrogen 1 and mixed reactant 2 are mixed and enter into vaporizer 3, heated and vaporized, to obtain the heated mixture gas 4, the heated mixture gas 4 enters the reaction from the upper end of the fixed bed reactor 5, inert substances 6 enter into the catalyst cushion at the discharge end of the fixed bed from the lower part of the fixed bed (or into the space formed between the tube sheet at the discharge end of the fixed bed and the lower head of the fixed bed, or the space formed between the catalyst cushion at the discharge end of the fixed bed and the lower head of the fixed bed), and are sprayed into the fixed bed reactor from the inert substance nozzle 7; the reaction mixture 8 containing inert substances enters into the cooler 9 for cooling, the cooled gas-liquid mixture 10 contains products and unreacted raw materials.

Example 2

[0063] Preparing methyl methacrylate (MMA) by the process shown in Example 1 above

[0064] The methanol solution of formaldehyde: 96% (weight percentage, the same below) of paraformaldehyde and equal weight of methanol are mixed and heated to 100° C., keep warm and stirring for 4 hours, paraformaldehyde are all dissolved, the water content is 1% as measured.

[0065] 15 g of catalyst crushed to 1 mm in size into the fixed bed reactor. 100 ml/min (standard condition) nitrogen is introduced through the vaporizer, which is set at 300° C. After the fixed bed is heated to 350° C., nitrogen is introduced steadily for 30 min. The methanol solution of formaldehyde prepared above is mixed with methyl propionate (the raw material molar ratio: methyl propionate/formaldehyde/methanol/water=58/21/20/1). The duration that the reactant contacts the catalyst is 5 s, twice of the flow rate of the liquid reaction of the toluene is fed from the bottom of the fixed bed. The product is cooled and separated for isolating the liquid product, the gas phase was evacuated after online mass spectrometry analysis.

[0066] After test and calculation, the conversion of methyl propionate is 23%; the prepared MMA has a selectivity of 91%; the selectivity of methyl propionate hydrolysis to propionic acid is 8%.

Example 3

[0067] The operation is the same as Example 2, except modifying the feed amount of the inert substance toluene to one time the volume of liquid reactant feed flow.

[0068] After test and calculation, the conversion of methyl propionate is 23%; the prepared MMA has a selectivity of 89%; and the selectivity of methyl propionate hydrolysis to propionic acid is 7.9%.

Example 4

[0069] The operation is the same as Example 2, except modifying the inert substance to n-heptane, the feed volume is twice the volume of the liquid reactant feed flow.

[0070] After test and calculation, the conversion of methyl propionate is 23%; the prepared MMA has a selectivity of 92.5%; and the selectivity of methyl propionate hydrolysis to propionic acid is 7.4%.

Example 5

[0071] The operation is the same as Example 2, except modifying the inert substance to n-hexane, the feed volume is twice the volume of the liquid reactant feed flow.

[0072] After test and calculation, the conversion of methyl propionate is 23%; the prepared MMA has a selectivity of 92.3%; and the selectivity of methyl propionate hydrolysis to propionic acid is 7.6%.

Example 6

[0073] The operation is the same as Example 2, except modifying the inert substance to xylene, the feed volume is twice the volume of the liquid reactant feed flow.

[0074] After test and calculation, the conversion of methyl propionate is 23%; the prepared MMA has a selectivity of 91.5%; the selectivity of methyl propionate hydrolysis to propionic acid is 8.2%.

Example 7

[0075] The operation is the same as Example 2, except modifying the inert substance to methanol, the feed volume is twice the volume of the liquid reactant feed flow.

[0076] After test and calculation, the conversion rate of methyl propionate is 23%; the prepared MMA has a selectivity of 90.2%; the selectivity of methyl propionate hydrolysis to propionic acid is 8.9%.

Comparative Example 1

[0077] Other operating processes are the same as Example 2, the only difference lies in that the bottom material is not flushed.

[0078] After test and calculation, the conversion of methyl propionate is 23%; the prepared MMA has a selectivity of 78%; the selectivity of methyl propionate hydrolysis to propionic acid is 8%. It is can be seen from the above examples and comparative example, under the same preparation operating conditions, the conversions of methyl propionate are same, but by the inert substances cooling down of the present application, the selectivity of the target product MMA is increased by more than 10%.

[0079] The embodiments of the present invention have been described above. However, this invention is not limited to the above embodiments. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.