CN106220489B - The method for producing M-phthalic acid as raw material using paraxylene raffinate - Google Patents

Abstract

The invention discloses a method for producing isophthalic acid using p-xylene raffinate as a raw material, comprising the following steps: (1) preparing p-xylene containing p-xylene, m-xylene, o-xylene and ethylbenzene The raffinate is rectified to remove o-xylene to obtain a mixture A containing meta-xylene and ethylbenzene; (2) the mixture A is oxidized to generate a mixture B containing isophthalic acid and benzoic acid, and the meta-xylene is separated by crystallization. The crude product of formic acid, the crystallized mother liquor is concentrated by evaporation to obtain benzoic acid; (3) the crude product of isophthalic acid is dissolved to obtain an aqueous solution of isophthalic acid, and the aqueous solution of isophthalic acid is refined by hydrogenation and crystallized to obtain refined isophthalic acid . The method can recover the o-xylene in the p-xylene raffinate and produce high-purity m-xylene, and produce isophthalic acid with the m-xylene, and the production cost is low.

Description

Method for producing isophthalic acid with p-xylene raffinate as raw material

technical field

The invention relates to a method for producing aromatic dicarboxylic acid, in particular to a method for producing isophthalic acid with p-xylene raffinate as raw material.

Background technique

Purified isophthalic acid (PIA) is the raw material of polyester resin, mainly used in the preparation of polyester bottle flakes, fibers, unsaturated resins, and low melting point polyester products. The production method of PIA is to use m-xylene (MX) as raw material, obtain crude isophthalic acid (CIA) through liquid-phase oxidation, and then remove trace impurities in the product through hydrogenation refining to obtain polymer grade PIA. Various oxidation and refining methods are described in detail in the review literature (Process Economics Program Report 9E, Terephthalic Acid and DimethylTerephthalate, SRI Consulting, Menlo Park, California, 94025, January 1997.), and the literature (He Zuoyun, meta-xylene and meta-xylene Phthalic Acid Production Technology, Synthetic Fiber Industry, Vol. 23, No. 2, 41-45, 2000.) further supplemented the domestic research progress. Because the production method of PIA is similar to the process of purified terephthalic acid (PTA) in many aspects, and the production scale is smaller than that of PTA, some companies at home and abroad usually convert small PTA devices to PIA after transformation.

Meta-xylene is the raw material of PIA, and most of the current methods of obtaining MX use mixed xylene as raw material. Fig. 1 is the existing method of producing mixed xylenes with petroleum as raw material, which is also the main source of mixed xylenes at present. Crude oil is often distilled under reduced pressure to obtain naphtha fraction, which is sent to the reforming unit to generate a large amount of aromatics, and the reformed oil is then sent to the aromatics extraction unit to separate aromatics and non-aromatics, and then benzene, toluene and aromatics in aromatics are separated by rectification For heavy aromatics with carbon 9 or more, the final mixture of carbon 8 aromatics contains four components: m-xylene (MX), p-xylene (PX), o-xylene (OX), and ethylbenzene (EB). The approximate content and The physical properties are shown in Table 1.

Table 1 Contents and physical properties of each component of C8 aromatics produced from reformed oil

components MX PX OX EB content(%) 45% 20% 20% 15% Boiling point (°C) 139.1 138.4 144.4 136.2 Melting point (°C) -47.8 13.2 -25.2 -95.0

It can be seen that the boiling points of the four components are very close, and except o-xylene, the other three substances are difficult to separate by rectification. Although the melting points of the four aromatics are significantly different, they can theoretically be separated by cryogenic crystallization, but the system has multiple multi-component eutectic points, making it difficult to separate them by crystallization. This has been reported in many monographs and literature. Therefore, at present, the industry mainly adopts adsorption separation to obtain MX raw materials.

The adsorption separation method is used to adsorb MX with high selectivity, and then the MX is eluted with a desorbent. This method can obtain MX with high purity (MX>99.5%). Patents CN200980125280.6 and CN200610164101.8 respectively disclosed the special adsorbent composition and adsorption conditions of MX, and patent CN200810100400.4 disclosed the structure and adsorption process of MX adsorption device. Patent CN98102372.X and literature (Zhao Yuzhang, Yang Jian, xylene adsorption separation-isomerization combined process to produce high-purity m-xylene, petrochemical industry, volume 29, No. 1, 32-36, 2000.) disclose a A process for the adsorption and separation of MX by gas phase method. The adsorption method is a production method of m-xylene that has been implemented industrially at present. Its advantages are that the obtained MX product has high purity and wide adaptability to raw materials. However, the operation process of the adsorption method is complicated, requiring the use of a large amount of expensive adsorbent, and at the same time, a special desorbent is required to desorb MX, and the desorbed mixture must go through multiple rectification steps to recover the desorbent and purify the MX product. Therefore, the cost of preparing MX by adsorption is high, and the resulting MX is expensive, which limits its market application.

PIA, which is a polyester raw material, is used together with purified terephthalic acid (PTA) as a copolyester component in most cases. For example, as a bottle-grade copolyester, PIA only accounts for 2-3% of PTA, and PIA only accounts for 20-40% of low melting point polyester. Therefore, in order to avoid the difficult problem of separating MX, some patents adopt the method of mixed xylene co-oxidation to obtain the mixed dicarboxylic acid product of PIA and PTA to reduce the cost of preparing PIA. Patent CN200610154821.6 first proposes to use mixed xylene as raw material for liquid-phase co-oxidation to obtain a mixture of terephthalic acid, isophthalic acid, and phthalic acid, and then use phthalic acid and p- and m-carboxylic acids Significant difference in solubility, a mixture of PTA and PIA was obtained by crystallization separation, as a raw material for copolyester. Similar schemes are mentioned many times in subsequent patents. For example, patent CN201210014597.6 proposes to use a mixture of p-xylene (PX) and MX as a raw material, add a part of PX to adjust the composition into a specific ratio, and then oxidize and refine it to produce special raw materials for various copolyesters. Patent CN200980109527.5 proposes to use C8 aromatics containing mixed xylene and ethylbenzene as raw materials, firstly remove ethylbenzene in C8 aromatics through appropriate separation methods, and then remove o-xylene by rectification, and the remaining PX and MX mixture Then liquid-phase oxidation is carried out to obtain the mixture product of PTA and PIA. But this patent does not propose a definite ethylbenzene separation method, nor does it provide specific co-oxidation conditions. The difference between the boiling point of ethylbenzene and p-xylene is only 1.8°C, and they are also very close in nature, so it is difficult to separate them. In view of this, the patent CN200810022473.6 proposes a scheme of co-oxidizing C8 aromatics containing ethylbenzene to obtain a mixture of phenylacetic acid and three dicarboxylic acids. However, in fact, benzoic acid is generally generated after ethylbenzene is oxidized, and it is difficult to generate phenylacetic acid. The proposed scheme is difficult to implement, and the use of the mixed polycarboxylic acid generated is also very limited. Therefore, in order to obtain MX and PIA at low cost, we must find another way and adopt new ideas and methods.

Contents of the invention

The invention provides a method for producing isophthalic acid (PIA) with p-xylene (PX) raffinate as raw material, the method can produce meta-xylene at low cost and reclaim ortho-xylene (OX) simultaneously, through Oxidation of toluene yields isophthalic acid.

A method for producing para-xylene and co-producing meta-xylene, comprising: containing a carbon 8 aromatic hydrocarbon mixture containing para-xylene (PX), meta-xylene (MX), ortho-xylene (OX) and ethylbenzene (EB) Separation of p-xylene by adsorption to obtain a p-xylene raffinate containing p-xylene, m-xylene, o-xylene and ethylbenzene, and part of the p-xylene raffinate is subjected to isomerization reaction and combined with the C 8 aromatic hydrocarbon mixture ; Another part of the xylene raffinate is rectified to remove o-xylene to obtain a mixture containing m-xylene and ethylbenzene.

The isomerization reaction is to convert m-xylene, o-xylene and part of ethylbenzene into mixed xylene containing p-xylene, and at the same time deethylate and remove part of ethylbenzene that is difficult to convert.

A kind of method taking p-xylene raffinate as raw material to produce isophthalic acid comprises the following steps:

(1) The p-xylene raffinate containing p-xylene, m-xylene, o-xylene and ethylbenzene is rectified to remove o-xylene to obtain a mixture A containing m-xylene and ethylbenzene;

(2) Mixture A is oxidized to generate mixture B containing isophthalic acid and benzoic acid, the crude product of isophthalic acid is separated by crystallization, and the crystallized mother liquor is concentrated by evaporation to obtain benzoic acid;

(3) The crude product of isophthalic acid is dissolved to obtain an aqueous solution of isophthalic acid, and the aqueous solution of terephthalic acid is refined by hydrogenation and post-treated to obtain refined isophthalic acid.

In step (1):

The p-xylene raffinate is a C8 aromatic hydrocarbon mixture containing m-xylene, o-xylene, ethylbenzene and a small amount of p-xylene after p-xylene is separated by adsorption.

In terms of mass percent concentration, the p-xylene content in the p-xylene raffinate is less than 1%, the content of m-xylene is 65-70%, the content of o-xylene is 20-30%, and the content of ethylbenzene is 3-10%. Further, the content of p-xylene in the p-xylene raffinate is less than 1%, the content of m-xylene is 65-69%, the content of o-xylene is 25-28%, and the content of ethylbenzene is 5-8%.

The boiling point of OX differs from that of MX by 5.3°C. As a preference, a rectification tower is used to separate o-xylene. The operating conditions are: feed from the middle and lower part of the rectification tower, the number of theoretical plates is 70-120, and the top reflux ratio is 10. ~20, the temperature at the top of the tower is 139~141°C, and the temperature at the bottom of the tower is 155~170°C.

Under the above-mentioned operating conditions, obtain the mixture A of MX and EB that OX content is less than 0.3% from the rectifying column top, wherein MX content is greater than 90%, and EB content is less than 10%, as further producing refined isophthalic acid (PIA ) and benzoic acid; the bottom of the rectifying tower obtains the heavy fraction of OX content > 85%, and the heavy fraction can be sent to the isomerization unit to be converted into mixed xylene and C 8 aromatic hydrocarbon mixture and be used for adsorption to prepare PX, and can also Further rectification to produce high-purity OX products.

In step (2):

The separation of EB from C8 aromatics has always been a technical difficulty. The boiling point difference between EB and MX is only 3°C, so it is difficult to cut by rectification. Although the melting points of the two are quite different, cryogenic crystallization is theoretically possible, but the crystallization separation is characterized by a low yield, and a considerable part of MX is still difficult to recover in the mother liquor, and the cost of cryogenic separation is relatively high.

The present invention oxidizes the mixture A containing MX and EB. As a preference, when oxidizing the mixture A, acetic acid is used as a solvent, cobalt salt, manganese salt, and hydrogen bromide are used as catalysts, and the oxidizing agent is an oxygen-containing gas.

Preferably, the cobalt salt is cobalt acetate, and the manganese salt is manganese acetate.

Preferably, the operating conditions of the oxidation mixture A are as follows: the temperature is 180-210° C., the pressure is 1.0-1.5 MPa, the reaction time is 45-90 minutes based on the average residence time of the solvent, and the weight ratio of the feed acetic acid to m-xylene is It is 2-4:1, and the catalyst concentration in terms of atomic concentration is: Co is 200-500ppm, Mn is 200-500ppm, and Br is 400-1000ppm.

Under the above-mentioned oxidation conditions, the two methyl groups on MX are oxidized to corresponding alcohols, aldehydes, acids in turn, and finally converted to isophthalic acid (IA). The conversion rate of MX is greater than 98%, and the yield of crude isophthalic acid Greater than 94%.

Studies have proved that the ethyl group on ethylbenzene is relatively active. Under the above oxidation conditions, the ethyl group will be gradually oxidized into a monocarboxyl group, and ethylbenzene will be converted into benzoic acid (BA). The EB conversion rate is greater than 99%, and the BA yield Greater than 96%.

The solubility of the generated benzoic acid in acetic acid solvent is extremely high, such as greater than 100g/100mL at the oxidation temperature, and the two form a dicarboxylic acid co-solvent, which can promote the oxidation of alkylaromatics and can accelerate oxidation reaction. Therefore, the formation of benzoic acid is a factor that favors the oxidation of m-xylene and ethylbenzene. On the other hand, the solubility of benzoic acid in the solvent acetic acid and water is much greater than that of isophthalic acid, and these two oxidation products are easily separated by crystallization, so that isophthalic acid is enriched in the solid phase and benzoic acid is enriched in the liquid phase, Thereby obtaining two carboxylic acid products respectively.

The above oxidation conditions are similar to the conditions for the oxidation of p-xylene (PX) to terephthalic acid (TA). Therefore, some patents introducing PX oxidation technology claim that their technology is also applicable to the oxidation of MX or other alkyl aromatic hydrocarbons. However, in these patents No distinction was made between MX oxidation and PX. According to the inventor's research, although the overall characteristics of MX oxidation are similar to those of PX oxidation, such as using the same solvent and catalyst, there are two significant differences: one is that the first methyl group of PX is easily oxidized, and the second methyl group is easy to oxidize. It is difficult to oxidize, while the first methyl group of MX is difficult to oxidize and the second methyl group is easier to oxidize. This difference in difficulty leads to a great difference in the depth of reaction and the content of intermediate products, which affects the adjustment of reaction conditions and Subsequent determination of crystallization and separation conditions; second, the solubility of the product IA in the solvent acetic acid and water is more than ten times greater than that of TA, so that the oxidation of MX and the crystallization and separation conditions of the product are significantly different from those of PX. In terms of oxidation, since the oxidation reaction heat is carried out of the reactor by the evaporation of solvent acetic acid, the high solubility of IA in acetic acid leads to low solvent evaporation ability, so that under the same pressure, the oxidation temperature of MX is 7 times higher than that of PX oxidation. ~15°C, resulting in the reaction rate of MX oxidation, catalyst concentration and ratio, heat transfer and energy utilization, rectification and dehydration and other conditions are different from those of PX oxidation, simply apply the PX oxidation conditions to MX oxidation without paying attention The distinction between the two is infeasible. In terms of crystallization, due to the difference in solubility between IA and TA, there are significant differences in the crystallization conditions of the two, but this difference has not been noticed in the current patent. It should be pointed out here that the present invention is different from the previous patents on the oxidation process of MX or PX in two points: one is that the present invention adopts the co-oxidation of MX and EB to generate two products of IA and BA, and does not need to separate EB in the raw material. There is no similar content in the patent; the second is that the present invention rationally arranges the conditions of MX oxidation and crystallization according to the difference between MX oxidation and PX oxidation, and the previous documents and patents have not noticed this difference, basically using PX The oxidation conditions are applied to the MX oxidation process.

The oxidation reactor can be a bubble column, a gas-liquid stirred tank and other types of gas-liquid contact and reaction devices.

The mixture B containing isophthalic acid and benzoic acid output from the reaction is sent to the crystallization unit to reduce the temperature under reduced pressure to precipitate solid IA, and at the same time feed a small amount of air or oxygen-containing gas to further oxidize unconverted MX and other intermediates into products IA and BA.

Preferably, multi-stage crystallizers are used during crystallization, and the crystallizers at each stage are gradually reduced in pressure and temperature to separate out isophthalic acid.

The purpose of using multi-stage crystallization is to control the supersaturation of crystallizers at all stages so as to facilitate the growth of crystals.

Preferably, oxygen-containing gas is fed into the first crystallizer to deeply oxidize the remaining reactants in the mixture B.

The temperature of the last crystallizer determines the recovery rate of solid product. For the crystallization process of isophthalic acid, the pressure of the final crystallizer generally needs to be evacuated to form a negative pressure to reduce the temperature and maximize the crystallization and precipitation of IA products.

Preferably, the operating conditions of the last stage crystallizer are: the pressure is -0.05-0.08MPa, the temperature is 80-100°C, and the solid content in the obtained solid slurry is 36-40%.

The solid content rate is the ratio of the mass of solids in the solid slurry to the total mass of the solid slurry.

Because the solubility of benzoic acid in acetic acid is far greater than that of isophthalic acid, the product isophthalic acid is separated out as a solid, and the product benzoic acid is still enriched in the liquid phase, and these two products can be separated by liquid-solid separation.

The output slurry of the above-mentioned last-stage crystallizer is sent to the liquid-solid separation unit, and the solid crude isophthalic acid (CIA) and the mother liquor containing benzoic acid are obtained by filtration, centrifugation, drying or other liquid-solid separation methods. A part of the mother liquor is directly returned to the oxidation reactor, and another part of the mother liquor is sent to the benzoic acid separation unit to evaporate the solvent acetic acid to obtain a solid benzoic acid product, and the solvent evaporated from the benzoic acid separation unit is returned to the oxidation reactor. The mass ratio of stream A used to separate benzoic acid from the oxidation mother liquor to the total mother liquor is 15 to 95%. The higher the ratio of the extracted stream A, the lower the concentration of benzoic acid in the oxidation mother liquor, and the entrainment in the CIA solid The benzoic acid is also lower. The purity of the crude benzoic acid obtained by evaporating the mother liquor is 95% to 98%, and a product with higher purity can be obtained through further vacuum distillation or recrystallization.

The oxidation tail gas is sent to the solvent dehydration tower for rectification to remove the water generated by the reaction, the dehydrated acetic acid at the bottom of the solvent dehydration tower is refluxed into the oxidation reactor, the water vapor containing the inert tail gas at the top of the tower enters the condenser, and part of the condensate is returned to the solvent dehydration tower As reflux water, part of the solvent water extracted as the refining unit in step (3) is sent to the water slurry preparation unit to mix with CIA. The non-condensable gas in the condenser is sent to the tail gas treatment unit for purification and then discharged.

With the oxidation reactor as the core, together with the attached slurry treatment unit, mother liquor treatment unit and gas treatment unit, it constitutes the main flow of the oxidation process. After the raw materials MX and EB enter the process, they form CIA and BA through co-oxidation reaction. CIA can obtain the polymer grade product PIA through the subsequent hydrorefining process.

In step (3):

The crude isophthalic acid (CIA) obtained from the above oxidation process contains a small amount of impurities, mainly incompletely converted oxidized intermediates, trace colored impurities and benzoic acid, etc., which can be refined through a hydrorefining process.

The purpose of the hydrofinishing process is to reduce the colored impurities and intermediates embedded in the isophthalic acid crystals into colorless and water-soluble substances by hydrogenation reduction method, together with the residual traces of benzoic acid, through the crystallization step. Transfer to an aqueous solution, thereby crystallizing to obtain high-purity PIA solid.

Extract part of the condensate in the condenser of the solvent dehydration tower above as a solvent to dissolve solid crude isophthalic acid to obtain an aqueous solution of isophthalic acid. Hydrogenation reduction reaction removes impurities.

Preferably, the hydrogenation reactor during hydrofinishing is a fixed bed filled with catalyst, and the operating conditions for hydrofinishing are as follows: temperature is 220-260°C, pressure is 5.0-8.0MPa, isophthalic acid aqueous solution isophthalic acid The mass ratio of formic acid to water is 35-55%, the residence time of the isophthalic acid aqueous solution is 5-15 minutes, and the catalyst used is palladium catalyst supported by activated carbon particles.

Under these conditions, all or most of the carboxybenzaldehyde and colored impurities in the isophthalic acid aqueous solution are reduced to water-soluble toluic acid and colorless substances.

The hydrogenation reactor is the same as that of purified terephthalic acid (PTA), which has been introduced in many documents and patents. The difference between the present invention and PTA hydrogenation is that the conditions are different, and PIA hydrogenation uses a lower Temperature, pressure and higher concentration of IA solution to adapt to the characteristics of high solubility of IA.

The aqueous solution of isophthalic acid after hydrofining is sent to the isophthalic acid crystallizer unit to evaporate under reduced pressure, and the solid isophthalic acid is precipitated, and the water slurry is further sent to the liquid-solid separation unit to obtain purified isophthalic acid (PIA ) solid products and refined mother liquor wastewater with an organic concentration of 0.3-1.5%.

Preferably, a multistage crystallizer is used for crystallization. The isophthalic acid crystallizer adopts multi-stage crystallizers to depressurize and cool down step by step to increase the particle size of the crystals and reduce the difficulty of subsequent liquid-solid separation. The pressure and temperature of the last stage crystallizer should be close to normal pressure and the boiling point of water in order to Precipitate as much PIA solid as possible.

The liquid-solid separation unit can use filtration, centrifugation, drying and other liquid-solid separation methods to obtain high-purity solid PIA products, and the discharged refined mother liquor contains isophthalic acid and other organic impurities with a total concentration of 0.3-1.5%.

Due to the high solubility of IA in water and the high content of organic matter in the refined mother liquor wastewater, there are problems in both economic and environmental aspects of direct discharge. In the present invention, the refined mother liquor is sent to the solvent dehydration tower, and the isophthalic acid in the refined mother liquor is recycled together with the reacted intermediates and water. The trace impurities and other organic matter in the refined mother liquor enter the oxidation reactor along with the reflux solvent. The converted impurities are finally taken out of the mother liquor with oxidation and enter the benzoic acid separation unit, and are discharged together with the crude benzoic acid stream, and are discharged as residue in the subsequent benzoic acid refining unit.

All the refined mother liquor is sent to the top of the solvent dehydration tower in the oxidation process to replace part of the condensed reflux liquid. Most of the distilled water produced by the top condenser of the solvent dehydration tower is extracted as solvent water in the refining process, and a small part is returned to the solvent dehydration tower as top reflux. liquid. The mass ratio of the condensed reflux liquid to the refined mother liquor in the top reflux liquid of the solvent dehydration tower is 1:2.

In this way, the refined mother liquor can be recovered, waste water discharge can be avoided, and a large amount of deionized water solvent can be saved.

A similar water replacement method has been used in the production process of terephthalic acid. For example, patents CN95191048.5, US8173834B2, and EP0962442A1 have reported that the TA refined mother liquor is used for the reflux water of the solvent dehydration tower in the PX oxidation process, and the solvent dehydration tower distilled water It is used as solvent water in the refining process, but this scheme has not been reported for the production of isophthalic acid. Different from PTA, due to the high solubility of IA in the PIA process, less water is used in the refining process, and the concentration of organic matter in the refined mother liquor is ten times or even dozens of times higher than that in the PTA process, and the amount of water used for solvent dehydration tower replacement is less than that in the PTA process. , In this case, the replacement of water has a greater impact on the operation of the solvent dehydration tower in the oxidation process and the crystallization unit in the refining process than PTA, and special consideration is required.

Compared with the water replacement scheme of the PTA process, the water replacement technology at the top of the rectification tower is more suitable for the production process of isophthalic acid, because the solubility of isophthalic acid is large, and the content of organic matter in the refined mother liquor is high, and the refined mother liquor used for replacement The amount is less than the PTA process. Therefore, the composition of the reflux liquid of the solvent dehydration tower and the operating conditions of the crystallization unit in the refining process are significantly different from those of the PTA process.

Compared with prior art, the beneficial effect of the present invention is:

(1) Select the stream rich in m-xylene (MX) after extracting p-xylene in the existing aromatics complex as raw material, and adopt rectification method to separate and remove o-xylene (OX) to obtain m-xylene rich in The mixture of toluene (more than 90%) and a small amount of ethylbenzene (EB, less than 10%), as the raw material for preparing isophthalic acid, compared with the separation of MX by adsorption, the operation is simple and the cost is low;

(2) Using the m-xylene mixture containing a small amount of ethylbenzene as raw material, benzoic acid and polymer-grade refined isophthalic acid can be obtained through oxidation and refining, so as to realize the high-value utilization of the raffinate produced in the PX production process ;

(3) All the refined mother liquor is sent to the top of the solvent dehydration tower in the oxidation process to replace part of the condensed reflux liquid, and the distilled water produced by the top condenser of the solvent dehydration tower is mostly extracted as solvent water in the refining process, so that the refined mother liquor can be recovered. Avoid waste water discharge, and save a lot of deionized water solvent.

Description of drawings

Fig. 1 is the flow chart of producing mixed xylenes as raw material with crude oil;

Fig. 2 is the flow chart of the present invention taking carbon 8 aromatics as raw material to produce m-xylene;

Fig. 3 is that the present invention takes m-xylene and ethylbenzene as the flow chart of raw material production refined isophthalic acid and benzoic acid.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention, but do not limit it in any way.

1. Production of m-xylene

As shown in Figure 2, a typical PX production unit adopts naphtha reforming method to produce aromatics and adsorption method to separate PX from C8 aromatics. The main process includes two modules: adsorption separation and isomerization. Containing the C 8 aromatics mixture S100 of the composition shown in Table 1 and the equilibrium stream S104 output by the isomerization unit, it is mixed and sent to the PX adsorption unit U101 together, and after adsorption and separation, the PX product with a purity of 99.5% is obtained, which is produced by the stream S101 The output system, the raffinate S102 is sent to the isomerization reactor U102 to convert the raw material S102 into the equilibrium composition S104 containing PX, and at the same time remove part of the ethylbenzene, and then mix with the raw material S100 to adsorb and separate PX, and so on. Complete conversion. In order to obtain MX, the present invention draws a part from the PX raffinate S102, marked as S105, and obtains a stream S107 rich in MX after separation and removal of OX by rectification, as shown in the right half of Figure 2.

The composition of the drawn PX raffinate S105 is as follows:

MX 67%, OX 27.5%, EB 5%, PX 0.5%.

S105 of above-mentioned composition is sent into rectifying tower U103, removes o-xylene OX, rectifying tower condition is:

The number of theoretical trays is 100, the position of the feed tray is the 65th (from top to bottom), the feed temperature is 158°C, the top reflux ratio is 16, the bottom temperature is 167.8°C, the top temperature is 139.2°C, and the top pressure is For normal pressure.

Under the above conditions, every ton of feed S105 can obtain 0.70 tons of overhead fraction S107, 0.3 tons of tower bottom fraction S106, and the compositions of the two fractions are respectively:

S107: MX 91.5%, EB 7.5%, PX 0.7%, OX 0.3%

S106: MX 10.6%, EB 0.01%, PX 0.1%, OX 89.3%

The obtained stream S107 is rich in MX and contains a small amount of EB and traces of PX and OX, which is sent to the oxidation unit as the raw material for co-oxidation.

2. Production of isophthalic acid

Fig. 3 is the flow chart of raw material production refined isophthalic acid and benzoic acid with the m-xylene produced by said method.

The raw material solution S107 obtained by the above method is added to the reactor as the feed stream S200A of the oxidation reactor U201, and the acetic acid solvent S200B, the catalyst S200C, the circulating mother liquor S200D and the oxidation extraction mother liquor S200E are also added at the same time, and the air is blown in at the same time. Liquid-phase oxidation is carried out under certain temperature and pressure to convert MX and EB into isophthalic acid and benzoic acid. The operating conditions of the oxidation reactor are listed in Table 2.

Table 2 Operating conditions of oxidation reactor U201

In the table, MX/HAc represents the mass ratio of MX and acetic acid (HAc) in the feed stream S200, the pressure is the tower top gauge pressure, the solution residence time=mixture volume/solvent acetic acid flow rate, and the tail gas oxygen concentration refers to the dry basis of oxygen in S210 concentration.

Under the above conditions, the reaction results of the oxidation reactor U201 are listed in Table 3.

Table 3 Oxidation Reactor U201 Reaction Results

3-CBA in the table refers to the main reaction intermediate m-carboxybenzaldehyde, which together with the colored impurities is the main impurity that needs to be removed by hydrofining. The output stream S201 is rich in isophthalic acid (IA) and also has a small amount of unoxidized raw materials and intermediate products, and is sent to the crystallization unit U202.

The crystallization unit U202 uses four-stage crystallizers to evaporate the solvent step by step under reduced pressure, and simultaneously precipitate solid IA. A small amount of air is fed into the first crystallizer to supplement oxidation, and the liquid-phase reactants that cannot be converted in the oxidation reactor U201 are deeply converted. The operating conditions and results of the four-stage crystallizer are listed in Table 4.

Table 4 Crude isophthalic acid (CIA) four-stage crystallizer operating conditions and results

The slurry output from the fourth-stage crystallizer is sent to the liquid-solid separation unit U203, and the oxidation mother liquor is separated from the solid IA by vacuum filtration. The filter cake is washed with fresh acetic acid, and then dried to remove the solvent to obtain crude isophthalic acid solids. Contain impurity 3-CBA 220ppm in this solid, also have trace colored impurity and benzoic acid simultaneously, will remove these impurities by hydrogenation refining.

The mother liquor output by the liquid-solid separation unit U203 is divided into two streams, 50% of the mother liquor S200D is directly recycled back to the oxidation reactor U201, and the other half of the mother liquor S200E is pumped out and sent to the benzoic acid separation unit U211. In this unit, the solvent in the mother liquor The acetic acid is evaporated, and the acetic acid is returned to the oxidation reactor U201. The concentrated benzoic acid melt is further purified by vacuum rectification to the required purity of the product, and a small amount of high-boiling residue at the bottom of the rectification tower is discharged after recovering the catalyst. Under the condition that 50% of the mother liquor is extracted and evaporated to separate the benzoic acid, the concentration of the liquid phase benzoic acid in the oxidation reactor can be controlled not to exceed 5%.

The tail gas S210 output from the top of the oxidation reactor is sent to the solvent dehydration tower U208 to remove the water generated by the reaction, the dehydrated acetic acid S211 at the bottom of the solvent dehydration tower U208 is refluxed into the oxidation reactor, and the water vapor containing the inert tail gas at the top of the tower enters the condenser U209, Part of the condensate S214 is refluxed to the solvent dehydration tower U208 as reflux water S215, and part of the solvent water S216 is taken out as a refining unit and sent to the water slurry preparation unit U204 to be mixed with CIA. The non-condensable gas in the condenser U209 is sent to the tail gas treatment unit for purification and then discharged. The parameters of the solvent dehydration tower U208 are: 60 theoretical tower plates, the temperature at the bottom of the tower is 196°C, and the temperature at the top of the tower is 180°C. In the reflux liquid S209 of the rectification tower, the ratio of the condensed reflux liquid S215 at the top of the tower to the refined mother liquor reflux liquid S207 is 1 : 2, the content of acetic acid in the discharged non-condensable gas is less than 50ppm, which can be recovered by further condensation.

3. Refining of isophthalic acid

The solid S203 output from the liquid-solid separation unit U203 is sent to the water slurry preparation unit U204, mixed with the part of the condensed water S216 extracted from the top condenser U209 of the solvent dehydration tower U208, and then heated with high-pressure steam to prepare crude oil under the following conditions: Isophthalic acid (CIA) aqueous solution: the temperature is 235°C, the pressure is 6.5MP, and the mass ratio of isophthalic acid (IA) to solvent water is 45%.

Use a slurry pump to pump the above aqueous solution into the hydrogenation reactor U205, and at the same time use a hydrogen compressor to inject a small amount of hydrogen to reduce 3-CBA and colored impurities. Hydrogenation reactor U205 is a fixed bed filled with palladium catalyst supported by activated carbon particles. Control the solution flow rate so that the contact time of the solution passing through the bed is 10 minutes. At this time, the concentration of 3-CBA in the outlet stream S205 is less than 5ppm, and the solution changes from the yellowish color of the inlet stream to the transparent and colorless outlet stream.

The hydrorefined solution S205 is sent to the crystallizer unit U206 for evaporation and crystallization under reduced pressure. U206 is evaporated under reduced pressure step by step in 5-stage crystallizers to control the crystal particle size. The operating conditions of the 5-stage crystallizers are listed in Table 5.

Table 5 Operating Conditions of Stage 5 Crystallizer in Hydrofining Process

The condition of the last crystallizer of U206 is close to normal temperature and pressure, and the weight solid content of the output slurry is 43%. The water slurry is further sent to the liquid-solid separation unit U207, vacuum filtered and dried to obtain refined isophthalic acid. (PIA) solid product S208, the purity index of product PIA is:

PIA 99%, PTA<1%, 3-CBA and other impurities<25ppm.

The refined mother liquor S207 discharged from the liquid-solid separation unit U207 contains 1% PIA and other impurities of hydrogenation reduction, and the temperature is 105°C. Provided by condensate S215, the ratio of S207 to S215 is 2:1. In this way, the refined mother liquor is recovered, waste water discharge is avoided, and a large amount of deionized water solvent is saved.

This example describes in detail how to use PX raffinate as a raw material to prepare the whole process of refined isophthalic acid. This process includes three steps: the first step is to obtain PX raffinate from large-scale PX production equipment, Distillation to obtain a raw material solution rich in MX and containing a small amount of EB; the second step is to generate IA and BA through liquid phase co-oxidation of MX and EB, and the two are separated by crystallization; the third step is to prepare CIA into a water slurry and pass Hydrofining and multi-step crystallization are used to obtain polymer grade isophthalic acid products, and the refined wastewater is replaced with the condensed return water of the dehydration tower in the oxidation process to recover the water and organic matter in the refined mother liquor.

The embodiments described above have described the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. All within the scope of the principles of the present invention Any modifications, supplements and equivalent replacements should be included within the protection scope of the present invention.

Claims (8)

1. a kind of method for producing M-phthalic acid as raw material using paraxylene raffinate, which comprises the following steps:

(1) the paraxylene raffinate containing paraxylene, meta-xylene, ortho-xylene and ethylbenzene is subjected to rectifying removal neighbour two Toluene obtains the mixture A containing meta-xylene and ethylbenzene；

In the mixture A, meta-xylene content is greater than 90%, and less than 0.3%, ethyl-benzene level is less than ortho-xylene content 10%；

(2) mixture A is aoxidized and generates the mixture B containing M-phthalic acid and benzoic acid, isophthalic two is gone out by Crystallization Separation Formic acid crude product, crystalline mother solution obtain benzoic acid by being concentrated by evaporation；

The operating condition of oxidation mixture A are as follows: temperature is 180~210 DEG C, and pressure is 1.0~1.5MPa, is stopped with being averaged for solvent Staying meter reaction time time is 45~90 minutes, and the weight ratio for feeding acetic acid and meta-xylene is 2~4:1, in terms of atomic concentration Catalyst concn are as follows: Co is 200~500ppm, and Mn is 200~500ppm, and Br is 400~1000ppm；

(3) M-phthalic acid crude product is dissolved to obtain M-phthalic acid aqueous solution, to M-phthalic acid aqueous solution hydrofinishing And crystallized, obtain smart M-phthalic acid；

Refinement mother liquor after hydrofinishing, crystallization is all sent into what solvent dehydration column overhead was generated as recirculation water, condenser Aqueous solvent of the partial condensation water as dissolution M-phthalic acid crude product in step (3).

2. the method for production M-phthalic acid according to claim 1, which is characterized in that two in paraxylene raffinate Toluene level less than 1%, meta-xylene content be 65~70%, ortho-xylene content be 20~30%, ethyl-benzene level be 3~ 10%.

3. the method for production M-phthalic acid according to claim 1, which is characterized in that in step (1), using rectifying column Rectifying separates ortho-xylene, operating condition are as follows: feeds from rectifying column middle and lower part, theoretical cam curve is 70~120, overhead reflux ratio 10~20,139~141 DEG C of tower top temperature, 155~170 DEG C of column bottom temperature.

4. the method for production M-phthalic acid according to claim 1, which is characterized in that in step (2), oxidation mixture When A, using acetic acid as solvent, cobalt salt, manganese salt, hydrogen bromide are catalyst, and oxidant is oxygen-containing gas.

5. the method for production M-phthalic acid according to claim 1, which is characterized in that in step (2), when crystallization is used Multistage crystallizer, crystallizer decompression step by step coolings at different levels are to be precipitated M-phthalic acid.

6. the method for production M-phthalic acid according to claim 5, which is characterized in that in multistage crystallizer, finally The operating condition of first degree crystalline device are as follows: pressure is -0.05~-0.08MPa, and temperature is 80~100 DEG C, in obtained slurry of solids Solid holdup is 36~40%.

7. the method for production M-phthalic acid according to claim 1, which is characterized in that in step (3), when hydrofinishing Hydrogenator be the fixed bed filled with catalyst, the operating condition of hydrofinishing are as follows: temperature be 220~260 DEG C, pressure For 5.0~8.0MPa, the mass ratio of M-phthalic acid and water is 35~55% in M-phthalic acid aqueous solution, M-phthalic acid water 5~15 minutes residence times of solution, used catalyst are the palladium catalyst of active carbon particle load.

8. the method for production M-phthalic acid according to claim 1, which is characterized in that in step (2), by oxidized tail gas It is sent into the water that solvent dehydration tower rectifying elimination reaction generates, the dehydration acetate of solvent dehydration tower tower bottom flows back into oxidation mixture The oxidation reactor of A, the vapor of tower top tail gas containing inertia enter condenser, condensate liquid partial reflux to solvent dehydration tower conduct Recirculation water.