CN103467237A - Method for preparing aromatic hydrocarbons by catalytic decarboxylation of terephthalic acid residues - Google Patents

Abstract

The invention discloses a method for preparing aromatic hydrocarbons by catalytic decarboxylation of terephthalic acid residues, which comprises the following steps: drying, pulverizing and gasifying terephthalic acid residues at 450°C-550°C and 0-2MPa, decarboxylation catalyst Under the action of decarboxylation, the high temperature gasification temperature is at least 350°C; the product obtained by the decarboxylation reaction is cooled to 200°C-240°C, and the separated gas is further cooled to 20°C-80°C through gas-solid separation , and then through gas-liquid separation, gas and aromatics mixed liquid are obtained; the obtained aromatics mixed liquid is rectified to obtain benzene and aromatics mixed liquid except benzene respectively. The invention takes both environmental protection and economic benefits into consideration, and proposes a new direction for the comprehensive utilization of PTA residues. The method can obtain low-boiling-point aromatics such as benzene and toluene, has high economic benefits, and is energy-saving and environment-friendly.

Description

Method for preparing aromatic hydrocarbons by catalytic decarboxylation of terephthalic acid residue

technical field

The invention relates to the field of treatment of terephthalic acid residues, in particular to a method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues.

Background technique

Purified terephthalic acid (PTA) is an important raw material for the textile industry and the plastics industry, mainly used in the production of polyester fibers, coatings, films, etc. The rapid development of terephthalic acid industry has brought serious pollution problems of "three wastes", especially the discharge of terephthalic acid residues. Terephthalic acid residues contain a large amount of organic acids, in addition to terephthalic acid, there are benzoic acid, phthalic acid, isophthalic acid, p-toluic acid, p-carboxybenzaldehyde and cobalt-manganese catalysts and other mechanical Impurities, etc. Terephthalic acid residues have always been a problem for environmental protection, and effective methods are urgently needed to deal with them.

At present, many people in China have done research on the recycling of terephthalic acid residues in the chemical fiber industry. For example, the Chinese patent literature with the publication number CN1126730C discloses a method for the separation and purification of terephthalic acid waste, which comprises 75% to 98% of sulfuric acid and 50% to 95% of nitric acid in a volume ratio of 1:1 to 9:1. Add them into the acid tank and stir to form a mixed acid, then add the solid terephthalic acid waste into the mixed acid; filter the slurry generated in the above process with a filter under negative pressure, and send the filter cake to the washing tank after concentration ; The filter cake separated in the above process is washed with desalted water in the washing tank to generate a terephthalic acid solid wet filter cake and sent to the dryer; dry for 20 to 40 minutes to obtain the terephthalic acid solid product.

The Chinese patent literature with the publication number CN1012954B discloses a method for separating terephthalic acid residues. According to the acid analysis principle of the improved Hengel method, the oxidation residues are firstly washed with water, and then separated under high temperature and weak salt conditions. Carry out selective reaction to separate terephthalic acid and isophthalic acid, and then extract with solvent to separate mixed unit acid from terephthalic acid and isophthalic acid.

The above separation method utilizes the differences in physical and chemical properties of aromatic acids to separate one or several components thereof through unit operations such as extraction, fractionation and centrifugal filtration. Due to the extremely similar chemical and physical properties of dibasic acid isomers, the separation process is complicated, the cost is high, a large amount of waste water is generated during the separation process, and the product purity is difficult to meet industrial requirements.

There are above-mentioned problems in the separation and recovery based on PTA residues, someone proposes the comprehensive utilization of PTA residues, as the Chinese patent literature with the publication number CN1508067A discloses a method for preparing activated carbon from terephthalic acid oxidation residues, and the oxidation residues are prepared by calcification. The oxidation residue calcium salt is formed, and then the oxidation residue calcium salt is carbonized in an air-isolated or oxygen-poor atmosphere to obtain a porous powdery activated carbon 1, which is then washed with acid to remove soluble metal salts (mainly calcium carbonate), dried, and obtained Final powdered activated carbon product.

Another example is that the Chinese patent document whose publication number is CN1508167A discloses a method for preparing unsaturated polyester resins by utilizing dibasic acid waste residues such as terephthalic acid and the like. Industrial waste, especially the waste residue of terephthalic acid produced in the polyester industry, replaces or partially replaces dibasic acids, especially phthalic anhydride and butenedioic acid to produce unsaturated resins. The catalyst for the esterification reaction of unsaturated dibasic acid and dibasic alcohol developed by the invention is stannous oxide, or stannous salt, or other stannous compounds, and its addition amount is the effective amount of the catalyst.

Contents of the invention

The invention provides a method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues, and proposes a new direction for the comprehensive utilization of PTA residues. The method can obtain aromatics with low boiling points such as benzene and toluene, and has high economic benefits, energy saving and environmental protection.

A method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues, comprising the following steps:

1) After the terephthalic acid residue is dried, pulverized, and gasified at high temperature, decarboxylation reaction is carried out under the action of a decarboxylation catalyst at 450°C-550°C and 0-2MPa, and the high-temperature gasification temperature is at least 350°C;

2) Cool the product obtained from the decarboxylation reaction to 200°C to 240°C, undergo gas-solid separation, further cool the separated gas to 20°C to 80°C, and then undergo gas-liquid separation to obtain a mixed liquid of gas and aromatics;

3) The mixed liquid of aromatics obtained in step 2) is rectified to obtain benzene and mixed liquid of aromatics other than benzene respectively.

The rising temperature of benzoic acid (100°C) is relatively low, which is quite different from other dibasic aromatic acids. Higher purity benzoic acid can be recovered by refining after distillation.

As preferably, when the content of benzoic acid in the described terephthalic acid residue exceeds 5wt.%, the terephthalic acid residue is firstly distilled, heated and gasified, and then condensed to obtain a thick benzoic acid product. The gasification temperature is 260°C-270°C; the remaining ungasified residue is then carried out according to steps 1)-3). The distillation treatment of the terephthalic acid residue is carried out in a batch rectification tower.

Preferably, the high-temperature gasification residue in step 1) contains inorganic salts of cobalt and manganese, which are dissolved in acid, filtered, and sodium bicarbonate is precipitated, and then recovered by separation and drying to obtain a cobalt-manganese catalyst.

Preferably, the decarboxylation catalyst in step 1) includes an active component and a carrier, the active component is ZnO, the carrier is Al ₂ O ₃ , and the mass ratio of ZnO to Al ₂ O ₃ is 0.1-5. ZnO is an alkaline semiconductor oxide with low lattice energy. Aromatic acids can be chemically adsorbed on the surface of ZnO to form carboxylate complexes, and carboxylates are further decomposed to generate aromatic hydrocarbons.

Under the action of the above-mentioned decarboxylation catalyst, the terephthalic acid residue undergoes a decarboxylation reaction under high temperature conditions to generate aromatic hydrocarbons such as benzene, toluene, biphenyl and benzoic acid.

Preferably, the mass space velocity of the reactants in the decarboxylation reaction in step 1) is 0.1/h-2/h, more preferably 0.1/h-0.6/h. In the decarboxylation reaction, an appropriate amount of inert gas should be introduced to adjust the contact time between the terephthalic acid residue and the decarboxylation catalyst to prevent the formation of carbon deposits due to excessive residence time. Under the same residence time, the higher the weight hourly space velocity, the lower the conversion rate of aromatic acid. When the mass space velocity is 2/h, the PTA residue can still maintain a conversion rate of more than 60%.

The reaction product obtained through the decarboxylation reaction in step 1) mainly contains benzene, toluene, carbon dioxide, benzoic acid and biphenyl, etc., and benzoic acid and unreacted benzene dibasic acid are separated from the gas during the cooling process; the remaining gas The components are further cooled to 20°C to 80°C, and the carbon dioxide and aromatics are separated by a gas-liquid separator.

The solid separated from gas and solid in step 2) is again distilled, heated to gasify, and condensed to obtain crude benzoic acid product. The heating gasification temperature is 260°C to 270°C; the remaining ungasified residue is then followed by step 1 ) ~ 3) to further improve the utilization of terephthalic acid residues.

In step 1), the terephthalic acid residue is gasified at high temperature by a high-temperature gasifier, and decarboxylated by a decarboxylation reaction device; in step 2), it is cooled by a circulating water heat exchanger, and gas-solid separation is performed by a gas-solid separator. As a preference, the gasifier, batch rectification tower, decarboxylation reaction unit, heat exchanger, and gas-solid separator involved in the process of catalytic decarboxylation of terephthalic acid residues to aromatics are all equipped with spare units to facilitate regular cleaning of each device. Solid residues, to avoid solid substances blocking process devices or pipelines, so that the decarboxylation process can continue to operate normally.

Preferably, the rectification of the aromatics mixture in step 3) is carried out in a rectification tower, and the separation conditions are: the temperature at the bottom of the tower is 100°C to 150°C, and the temperature at the top of the tower is 80°C to 90°C. After separation, relatively pure benzene can be obtained from the top of the tower, and other mixed liquids of aromatic hydrocarbons can be obtained from the bottom of the tower.

Preferably, the product obtained from the decarboxylation reaction in step 2) is cooled by a heat exchanger, and after the heat exchanger is used as a cooling medium to complete heat exchange, it is used again as a heating medium for the distillation column of aromatic hydrocarbons, which can reduce energy consumption and improve energy utilization efficiency.

The invention provides a method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues, which can be used to prepare aromatics products and recover benzoic acid through decarboxylation of terephthalic acid residues. Compared with prior art, the present invention has following advantage:

The present invention proposes a new direction for the comprehensive utilization of terephthalic acid residues, and realizes the high value-added utilization of terephthalic acid residues. Compared with other recycling methods of terephthalic acid residues, the present invention does not need to use a large amount of Solvent and acid-base washing will not produce a large amount of waste liquid, which is safe and environmentally friendly; the catalyst and product are easily separated by using heterogeneous decarboxylation reaction, which greatly simplifies the post-treatment process and reduces energy consumption and capital investment.

The invention is a brand-new method for recycling terephthalic acid residues, which can obtain aromatic products and recover benzoic acid through reasonable process configuration, and has better economic benefits and broad application prospects.

The invention has low selectivity to raw materials, is suitable for components prepared by different production processes and terephthalic acid residues with different contents, and can obtain low-boiling point aromatics such as benzene, toluene and biphenyl through the method of the invention. Taking into account both environmental protection and economic benefits, it has the advantages of high reaction yield, less side reactions, stable product quality, and less pollution generated by the reaction.

Description of drawings

Fig. 1 is the schematic flow chart of the method for preparing aromatics by catalytic decarboxylation of terephthalic acid residue in Example 1;

Fig. 2 is a schematic flow chart of the method for preparing aromatics by catalytic decarboxylation of terephthalic acid residue in Example 3.

Detailed ways

Example 1

components Oxidation residue Terephthalic acid 30.3% Isophthalic acid 35.4% Phthalate 0.66% benzoic acid 30.5% p-toluic acid 1.07% p-Tolualdehyde 0.32% Alkali insoluble matter 1.01% Ash 0.74%

1) Heat the dried terephthalic acid oxidation residue to about 260°C to vaporize benzoic acid. The content of each component of the PTA oxidation residue is shown in the above table. The gasified product is condensed to obtain a crude benzoic acid product. Recovering and obtaining benzoic acid in the PTA residue is 26.47wt.%;

2) The non-gasified substances or other materials obtained in step 1) are dried and pulverized, and transported to a high-temperature gasifier through a solid feeder for gasification at a temperature above 350°C. The residue in the gasifier mainly contains inorganic salts such as cobalt and manganese and ash, which is dissolved with acid, filtered, and precipitated by sodium bicarbonate, and then separated and dried to recover the cobalt-manganese catalyst;

3) Pass the vaporized product obtained in step 2) into a reactor filled with a decarboxylation catalyst (30wt.%ZnO, 5wt.%Cr ₂ O ₃ , 65wt.%Al ₂ O ₃ ), and the mass space velocity of the reaction raw material gas is 0.5 /h, decarboxylation reaction at 500°C and normal pressure.

4) The reacted product in step 3) is cooled to 200°C, and the gas and solid are separated after passing through the gas-solid separator. The PTA residue was almost completely converted, with only a small amount of solid benzoic acid isolated.

5) The gas obtained in step 4) is further cooled to 30°C and passed through a gas-liquid separator to separate gas and aromatics.

Except for benzene, aromatic hydrocarbons only contain a small amount of toluene and biphenyl, etc., which can be directly sold as products without refining. The purity of benzene in the liquid phase product reaches over 95%, and the yield of benzene is close to 70%.

Example 2

Using terephthalic acid oxidation residue with the same composition and content as in Example 1, the decarboxylation reaction conditions are: temperature 550° C., pressure 2 MPa, and other process conditions remain unchanged.

26.47wt.% of benzoic acid was recovered from the PTA residue, and the product after the decarboxylation reaction was cooled to 200°C, and the gas and solid were separated after passing through the gas-solid separator. The remaining PTA residue was 89% converted, and a solid mixture of benzoic acid and benzenedibasic acid was isolated, of which benzoic acid contained about 16%. Recover the benzoic acid in the solid mixture.

Except for benzene, aromatic hydrocarbons only contain a small amount of toluene and biphenyl, etc. The purity of benzene is over 95%, and the yield of benzene is close to 57%.

Example 3

components washing residue Terephthalic acid 76.6% Isophthalic acid 0.01% Phthalate 0.01% benzoic acid 0.85% p-toluic acid 20.52% p-Tolualdehyde 0.46% Alkali insoluble matter 0.75% Ash 0.80%

1) Dry and pulverize the dried terephthalic acid washing residue. The content of each component of the PTA oxidation residue is shown in the table above, and transport it to a high-temperature gasifier through a solid feeder for gasification at a temperature above 350°C. The residue in the gasifier mainly contains inorganic salts such as cobalt and manganese and ash, which is dissolved with acid, filtered, and precipitated by sodium bicarbonate, and then separated and dried to recover the cobalt-manganese catalyst;

2) Pass the vaporized product obtained in step 1) into the reactor filled with decarboxylation catalyst (30wt.%ZnO, 5wt.%Cr ₂ O ₃ , 65wt.%Al ₂ O ₃ ), and the mass space velocity of the reaction raw material gas is 0.6/h, decarboxylation reaction at 500°C and normal pressure.

3) The reacted product in step 2) is cooled to 240°C, and the gas and solid are separated after passing through the gas-solid separator. PTA residue conversion rate is 95.3%, contains 32wt.% benzoic acid in the solid, returns to the process of step 1);

4) The gas obtained in step 3) is further cooled to 60°C and passed through a gas-liquid separator to separate gas and aromatics. Aromatics are further separated through a rectification tower, and relatively pure benzene can be obtained at the top of the tower, and crude toluene can be obtained at the bottom of the tower. Wherein the yield of benzene is 63.4%, and the yield of crude toluene is 83.4%.

Claims (7)

1. a method for preparing aromatics by catalytic decarboxylation of terephthalic acid residue, is characterized in that, comprises the following steps: 1) After the terephthalic acid residue is dried, pulverized, and gasified at high temperature, decarboxylation reaction is carried out under the action of a decarboxylation catalyst at 450°C-550°C and 0-2MPa, and the high-temperature gasification temperature is at least 350°C; 2) Cool the product obtained from the decarboxylation reaction to 200°C to 240°C, undergo gas-solid separation, further cool the separated gas to 20°C to 80°C, and then undergo gas-liquid separation to obtain a mixed liquid of gas and aromatics; 3) The mixed liquid of aromatics obtained in step 2) is rectified to obtain benzene and mixed liquid of aromatics other than benzene respectively. 2. the method for preparing aromatics by catalytic decarboxylation of terephthalic acid residue according to claim 1, is characterized in that, when the content of benzoic acid exceeds 5wt.% in the described terephthalic acid residue, the terephthalic acid residue first undergoes The crude benzoic acid product is obtained after distillation, heating and gasification, and condensation. The heating and gasification temperature is 260° C. to 270° C.; and the remaining ungasified residue is carried out according to steps 1) to 3). 3. The method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues according to claim 1 or 2, characterized in that the high-temperature gasification residue in step 1) contains inorganic salts of cobalt and manganese, which are dissolved and filtered by acid , alkali precipitation, and then separated and dried to obtain cobalt-manganese catalyst. 4. The method for preparing aromatics by catalytic decarboxylation of terephthalic acid residue according to claim 1 or 2, characterized in that the decarboxylation catalyst in step 1) includes an active component and a carrier, the active component is ZnO, and the carrier is _Al2 The mass ratio of O ₃ , ZnO and Al ₂ O ₃ is 0.1-5. 5. The method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues according to claim 1 or 2, characterized in that the mass space velocity of reactants in the decarboxylation reaction in step 1) is 0.1/h-2/h. 6. The method for preparing aromatic hydrocarbons by catalytic decarboxylation of terephthalic acid residues according to claim 1 or 2, characterized in that the solids separated from gas and solid in step 2) are firstly distilled, heated and gasified, and then condensed To obtain the crude benzoic acid product, the heating and gasification temperature is 260°C-270°C; the remaining ungasified residue is then carried out according to steps 1)-3). 7. The method for preparing aromatics by catalytic decarboxylation of terephthalic acid residues according to claim 1 or 2, characterized in that the rectification of the aromatics mixture in step 3) is carried out in a rectification tower, and the separation conditions are: tower still The temperature is 100°C to 150°C, and the temperature at the top of the tower is 80°C to 90°C.