CN103467224B - A kind of Aromatic carboxylic acid decarboxylastion - Google Patents

Abstract

The invention discloses a method for decarboxylation of aromatic carboxylic acid. The aromatic carboxylic acid is passed into a reactor, and the heterogeneous decarboxylation reaction is carried out under the action of a reaction temperature of 300°C-600°C, a pressure of 0-2Mpa and a solid decarboxylation catalyst; The aromatic carboxylic acid has the following structural formula: Wherein, the groups R ₁ -R ₅ are COOH, H, halogen or C ₁ -C ₅ alkyl, and the groups R ₁ -R ₅ are the same or different. The method has a wide range of applications, has no special requirements on the structure of the aromatic carboxylic acid, and has the advantages of less solvent consumption, short reaction time, high reactivity, and easy separation, recovery and regeneration of the catalyst from the reaction product; the method can realize With continuous operation, the yield of aromatic compounds is high and the quality is stable. The method can be used to treat PTA residues, and realize high value-added utilization of PTA residues.

Description

A kind of aromatic carboxylic acid decarboxylation method

technical field

The invention relates to the field of preparing aromatic compounds from aromatic carboxylic acids, in particular to a method for decarboxylation of aromatic carboxylic acids.

Background technique

Decarboxylation reaction is widely used in chemical industry, biology, medicine, food and other fields. Through decarboxylation reaction, waste carboxyl-containing compounds can be used with high added value, which is beneficial to resource recovery and environmental protection. At present, the decarboxylation of aromatic carboxylic acids mainly occurs in a homogeneous system, and the removal of single or multiple carboxyl groups is achieved through the combined effects of light, electricity, organic amines, and heavy metal salts.

For example, the Chinese patent document with publication number CN1138023A discloses a method for preparing aromatic compounds by decarboxylation of aromatic carboxylic acids, especially a method for preparing fluorinated aromatic hydrocarbons by removing part or carboxyl groups from fluorinated aromatic carboxylic acids. Aromatic carboxylic acids dissolved in water are mixed with water-insoluble amines that are inert under reaction conditions, and then reacted with decarboxylation catalysts in water-insoluble solvents for a long period of time at a pH of 3 to 9 and a temperature of 70 to 210°C time, the reacted mixture is purified by extraction, crystallization, drying and other steps to obtain the target product. This reaction is carried out in a homogeneous system, requiring a large amount of strong acid, strong alkali aqueous solution and organic solvent, the reaction speed is slow, and the production cycle is long.

The Chinese patent document with publication number CN101225016A discloses a method for preparing pentafluorobenzene by non-catalytic decarboxylation of pentafluorobenzoic acid in high-temperature liquid water. Add deionized water and pentafluorobenzoic acid into the autoclave, the mass ratio of deionized water to pentafluorobenzoic acid is 2:1~8:1, heat up to 150~250°C for decarboxylation for 5~45min; decarboxylate product is cooled and filtered The pentafluorobenzoic acid remaining in the reaction is recovered, the filtrate is allowed to stand, and the liquid-liquid layer is separated to obtain an organic phase, and the organic phase is subjected to rectification and activated carbon decolorization to obtain pentafluorobenzene. Although there is no need to add a catalyst in this reaction, this method is only applicable to aromatic acids containing multiple halogens, and its application range is narrow.

The decarboxylation reaction disclosed in the above-mentioned patent documents is carried out in a homogeneous system, which requires the use of a large amount of solvent, and the catalyst is difficult to separate, recover and regenerate after the reaction.

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 PTA industry has brought about serious "three wastes" pollution problems, especially the discharge of PTA residues. PTA residues contain a large amount of organic acids, including benzoic acid, phthalic acid, isophthalic acid, p-toluic acid, p-carboxybenzaldehyde, cobalt-manganese catalysts and other mechanical impurities in addition to terephthalic acid. At present, the treatment of PTA residues is mainly divided into three methods: incineration, separation and recovery, and comprehensive utilization. Comprehensive utilization can realize the high value-added utilization of PTA residues.

Contents of the invention

The invention provides a method for decarboxylation of aromatic carboxylic acids. The method has a wide range of applications, has no special requirements on the structure of aromatic carboxylic acids, and has the advantages of less solvent consumption, short reaction time, high reactivity, and the catalyst is easy to mix with the reaction products. The advantages of material separation, recovery and regeneration; this method can realize continuous operation, and the yield of aromatic compounds is high and the quality is stable; this method can be used to treat PTA residues and realize high value-added utilization of PTA residues.

The invention discloses a method for decarboxylation of aromatic carboxylic acid. The aromatic carboxylic acid is passed into a reactor, and the heterogeneous decarboxylation reaction is carried out under the action of a reaction temperature of 300°C-600°C, a pressure of 0-2Mpa and a solid decarboxylation catalyst; The aromatic carboxylic acid has the following structural formula:

Wherein, the groups R ₁ -R ₅ are COOH, H, halogen or C ₁ -C ₅ alkyl, and the groups R ₁ -R ₅ are the same or different.

Preferably, the groups R ₁ to R ₅ are H or halogen.

Preferably, the decarboxylation catalyst 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 carboxylic acids can be chemically adsorbed on the surface of the catalyst to form carboxylate complexes, and carboxylates are further decomposed to generate aromatic hydrocarbons. Especially when the benzene ring contains an electron-withdrawing group, the acidity of the aromatic carboxylic acid is enhanced, and it is easier to adsorb on the surface of the catalyst to form a corresponding carboxylate complex, and the reaction is easier to proceed.

Additives can improve the dispersion of active components, the electron cloud distribution around the active components, and the thermal stability of the catalyst, which is beneficial to improve the activity and stability of the catalyst. Preferably, the decarboxylation catalyst also includes a promoter, which is one or more of the oxides of Mn, Fe, Co, Mo, Cr, Cu and Ni, and the quality of the promoter is 0.1wt.%~ of the mass of the decarboxylation catalyst. 10wt.%.

Preferably, the aromatic carboxylic acid is first dissolved in a solvent, and then passed into the reactor.

The solvent needs to meet the characteristics of high stability at high temperature, high solubility to aromatic carboxylic acid, no side reaction with aromatic carboxylic acid, and easy separation from the target product. The solvent is one or more of water, pyridine, toluene and xylene, and the solvent may be selected from but not limited to the above-listed.

Preferably, the aromatic carboxylic acid and the decarboxylation catalyst are contacted under the protection of an inert gas, and the contact time between the aromatic carboxylic acid and the decarboxylation catalyst can be adjusted by using an inert gas, so as to prevent the formation of carbon deposits caused by excessive residence time .

Preferably, the molar ratio of the inert gas to the aromatic carboxylic acid is 1-30.

Suitable inert gas should not hinder the generation of target product, and described inert gas can be one or more in nitrogen, helium, methane, carbon monoxide, hydrogen, steam, and described inert gas can be selected from but not limited to those listed above. Preferably, the inert gas is nitrogen, helium or water vapor.

Preferably, the weight hourly space velocity of the reactants in the decarboxylation reaction is 0.01h ^-1 ~ 20h ^-1 , more preferably, the conditions of the decarboxylation reaction are as follows: temperature 450°C ~ 550°C, pressure 0.1 ~ 0.8Mpa, weight hourly space velocity 0.2 h ^-1 ~ 10h ^-1 . The decarboxylation reaction is mainly affected by factors such as temperature, pressure, and space velocity. According to the decarboxylation reaction process of aromatic carboxylic acid, since the thermal decomposition of aromatic carboxylate in an inert gas atmosphere needs to be carried out at a certain temperature, the higher the temperature, the more favorable the decarboxylation reaction. The pyrolysis temperature of different aromatic carboxylates is mostly above 400°C, too high a reaction temperature will increase energy consumption, so the temperature should be controlled within a reasonable range. Since the decarboxylation reaction products are mainly aromatic hydrocarbons and carbon dioxide, the increase in system pressure is not conducive to the positive direction of the decarboxylation reaction, that is, with the increase of pressure, the conversion rate of aromatic carboxylic acids tends to decline. Under the same residence time, the higher the weight hourly space velocity, the lower the conversion rate of aromatic carboxylic acid.

The product after the decarboxylation reaction is a mixture of various aromatic compounds. In the present invention, in order to obtain a high-purity single product, further distillation or rectification can be performed. This step is also carried out in an inert gas such as nitrogen.

Compared with prior art, the present invention has following advantage:

After the aromatic carboxylic acid is gasified, the decarboxylation reaction is carried out under the action of high temperature and solid decarboxylation catalyst, without using a large amount of solvent, the residence time is extremely short below 2s, the catalytic activity is high, and continuous operation can be realized. The method is carried out in a heterogeneous system, the reaction product is easily separated from the catalyst, and the post-treatment steps are obviously simplified.

The invention has a wide range of applications and can use aromatic carboxylic acids containing different substituents as raw materials. Applying this method to the catalytic decarboxylation of PTA residues can produce aromatics, taking into account environmental protection and economic benefits, and has the advantages of high reaction yield, less side reactions, stable product quality, and less pollution generated by the reaction, and realizes high addition of PTA residues. value utilization.

Detailed ways

The following examples are intended to illustrate the process according to the present invention for the decarboxylation of aromatic carboxylic acids without limiting the scope of the following embodiments.

Example 1

The decarboxylation catalyst was placed in an electric heating tube with an inner diameter of 2.0 cm and a height of 1 m. The electric heating tube has three stages of temperature control, the upper two stages are used for the gasification of aromatic carboxylic acids, and the third stage is used for filling catalysts. The catalyst bed portion of the tube was filled with about 10 g of catalyst. This section is contained between two layers of glass beads, which are 20 cm below and 40 cm above the catalyst bed, respectively. The diameter of the glass beads is 20-30 mesh. The temperature measuring thermocouple is located in the center of the catalyst layer. The decarboxylation catalyst is Zn-Fe-Al (30wt.%ZnO, 4wt.%Fe ₂ O ₃ , 66wt.%Al ₂ O ₃ ).

Dissolve 40.0 g of terephthalic acid in 250 ml of pyridine to form a 0.08 g/ml solution and place it in a storage tank. Pump the terephthalic acid solution into the reaction tube at a rate of 1ml/min, the nitrogen flow rate is 600ml/min, the temperature of the three sections of the reaction tube is set to 500°C, and the reaction time is 1h, and the terephthalic acid is converted into benzene and carbon dioxide wait. After the catalytic bed, the reaction product is cooled by circulating water and a gas-liquid separator, and the tail gas is washed with water and vented.

Three methods were used to analyze the above reaction products: GC-TCD analysis of carbon dioxide content in the gas phase product, GC-FID analysis of the content of benzene and other aromatics in the liquid phase product, TG analysis of the carbon deposition of the catalyst. The analytical results of the product are as follows:

Benzene: 40.59wt.%, biphenyl: 0.69wt.%, benzophenone: 0.09wt.%, carbon dioxide: 50.99wt.%, others: 0.50wt.%, carbon: 7.14wt.%.

From the above results, it can be seen that the method for decarboxylation of aromatic carboxylic acids provided by the present invention can efficiently convert aromatic carboxylic acids into corresponding aromatic compounds.

Example 2

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%

The composition, consumption and filling method of embodiment 2 decarboxylation catalyst are the same as embodiment 1.

Dissolve 30.0g of PTA oxidation residue in 250ml of pyridine, remove insoluble matter by filtration, and place the filtrate in a liquid storage tank. The content of each component of the PTA oxidation residue is shown in the table above. The PTA oxidation residue solution was pumped into the reaction tube at a rate of 1ml/min, the nitrogen flow rate was 600ml/min, the temperature of the three sections of the reaction tube was set at 550°C, and the reaction time was 1h. The PTA oxidation residue was converted into benzene and carbon dioxide. After the catalytic bed, the reaction product is cooled by circulating water and a gas-liquid separator, and the tail gas is washed with water and vented.

The analysis method is the same as in Example 1, the analysis results of the product: benzene: 37.36wt.%, toluene: 0.61wt.%, biphenyl: 0.72wt.%, benzophenone: 0.29wt.%, carbon dioxide: 48.23wt.% , Others: 3.67wt.%, Carbon: 9.12wt.%.

It can be seen that the present invention can be applied to recover organic acid resources in PTA residues, and decarboxylation to produce aromatic compounds takes into account both environmental protection and economic benefits.

Example 3

Embodiment 3 decarboxylation catalyst consumption and packing method are identical with embodiment 1. The catalyst components are 60wt.% ZnO, 5wt.% CuO, 35wt.% Al ₂ O ₃ .

15g of 2,3,4,5-tetrafluorobenzoic acid was dissolved in 35ml of deionized water, and the configured solution was placed in a liquid storage tank, and the solution was pumped into the reaction tube at a rate of 0.5ml/min, nitrogen gas The flow rate is 200ml/min, and the temperature of the three sections of the reaction tube is set to 450°C. 2,3,4,5-tetrafluorobenzoic acid is converted into 1,2,3,4-tetrafluorobenzene and carbon dioxide. The reaction product is cooled by circulating water and a gas-liquid separator, and the tail gas is washed with water and emptied. The collected liquid was extracted with dichloromethane, the organic phase was separated, dried over magnesium sulfate and filtered to obtain 10.7 g of crude 1,2,3,4-tetrafluorobenzene.

Claims (1)

1. A method for decarboxylation of aromatic carboxylic acids, characterized in that, The decarboxylation catalyst is placed in an electric heating tube with an inner diameter of 2.0 cm and a height of 1 m. The electric heating tube has three stages of temperature control. The upper two stages are used for the gasification of aromatic carboxylic acids, and the third stage is used for filling the catalyst. The catalyst bed part of the tube is filled with about 10 g of catalyst, this part is contained between two layers of glass beads, these two parts are respectively 20 cm below and 40 cm above the catalyst bed; The diameter of the glass beads is 20-30 mesh, and the temperature measuring thermocouple is located in the center of the catalyst layer; The decarboxylation catalyst is Zn-Fe-Al, the composition is 30wt.% ZnO, 4wt.% _Fe2O3 , _66wt .% _{Al2O3 ;} Dissolve 40.0g of terephthalic acid in 250ml of pyridine to form a solution of 0.08g/ml in the liquid storage tank, pump the terephthalic acid solution into the reaction tube at a rate of 1ml/min, and the nitrogen flow rate is 600ml/ min, the temperature of the three sections of the reaction tube is set to 500°C, the reaction time is 1h, terephthalic acid is converted into benzene and carbon dioxide, etc. After the catalytic bed, the reaction product is cooled by circulating water and a gas-liquid separator, and the tail gas is washed with water and vented ; Three methods were used to analyze the above reaction products: GC-TCD analysis of carbon dioxide content in the gas phase product, GC-FID analysis of the content of benzene and other aromatics in the liquid phase product, TG analysis of the carbon deposition of the catalyst; the analysis results of the product are as follows: Benzene: 40.59wt.%, biphenyl: 0.69wt.%, benzophenone: 0.09wt.%, carbon dioxide: 50.99wt.%, others: 0.50wt.%, carbon: 7.14wt.%.