JPS6120527B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing mixed xylenes, and particularly to a method for obtaining mixed xylenes having an excellent composition as a chemical raw material. Mixed xylenes have traditionally been industrially separated and purified as a xylene fraction from aromatic fractions such as naphtha catalytic reformed oil and naphtha thermal decomposition byproduct oil by solvent extraction or extractive distillation. Mixed xylene is mainly composed of o-xylene, m-xylene, p-xylene and ethylbenzene, and its industrial uses are broadly divided into solvents and chemical raw materials. When used as a solvent, there are few restrictions on use due to the composition of isomers in mixed xylenes. However, when used as a chemical raw material, the value of p-xylene and o-xylene is particularly important among the isomers. That is, p-xylene is a raw material for producing terephthalic acid, which is in great demand as a raw material for synthetic fibers, and o-xylene is a raw material for phthalic acid, which is a raw material for plasticizers. On the other hand,
m-xylene and ethylbenzene have little value on their own, and m-xylene is converted to p-xylene by isomerization.
Ethylbenzene is converted to xylenes, and ethylbenzene is isomerized to xylenes or dehydrogenated to styrene to increase its value. but,
In the isomerization of m-xylene, the burden of the isomerization step is large, and the ethylbenzene separated from mixed xylene is economically unsuitable as an industrial-scale raw material for styrene. Since each component of mixed xylene has close boiling points as shown in Table 1, it is difficult to isolate each component.

[Table] In general, the industrial method for isolating each component from mixed xylenes is usually carried out by a combination of precision distillation and cryogenic separation. separated by However, it is impossible to separate m-xylene and p-xylene by distillation, which have a small difference in boiling point, and p-xylene is crystallized and separated by cryogenic separation that takes advantage of the difference in melting point. Since both separation steps consume a large amount of energy, a mixed xylene containing a large amount of p-xylene and a small amount of m-xylene and ethylbenzene is desired. The above matters are particularly problematic when aromatic hydrocarbon fractions, which are produced as by-products during thermal decomposition of petroleum hydrocarbons such as naphtha, are used as raw materials for mixed xylene in order to primarily obtain ethylene. . When naphtha is pyrolyzed primarily for the purpose of producing ethylene, the pyrolysis oil produced as a by-product has a high aromatic content and is an important raw material for extracting and refining benzene, toluene, and xylene. Although it is a pyrolysis oil whose main components are aromatics, it also contains small amounts of paraffins and olefins, as well as trace amounts of dienes and acetylenes. Therefore, in normal xylene production, hydrogenation treatment is necessary to avoid various problems caused by the unsaturated components contained, such as blockage of production equipment due to polymerization and quality deterioration due to unsaturated components mixed into the xylene fraction. is being carried out. The disadvantage of this hydrogenation process is that it consumes a large amount of hydrogen, and
Styrene, which is the main unsaturated compound in pyrolysis oil, is converted to ethylbenzene, and therefore the pyrolysis xylene fraction has a high ethylbenzene content of 40 to 50%. Various methods have been proposed to solve this problem. There are methods for removing styrene, which is a precursor of ethylbenzene, at a stage prior to hydrogenation treatment, such as separation by precision distillation of styrene, solvent extractive distillation, and selective adsorption using an adsorbent. However, the economic evaluation of styrene separated by this method is low, and it cannot be said that it is the best method. The present invention solves the above-mentioned problems in xylene fractions containing styrene in addition to xylene. That is, the present invention involves treating a xylene fraction containing p-xylene, o-xylene, m-xylene, and styrene with a mineral acid or solid acid catalyst in a liquid phase at a styrene concentration of 5% by weight or less in the reaction system. In addition, when a mineral acid is used as a catalyst, the xylene is brought into contact at 5°C to 100°C, or at 100°C to 200°C when a solid acid catalyst is used, and an aralkylation reaction between xylene and styrene in the xylene fraction is performed. m in the fraction
The present invention relates to a method for producing mixed xylene characterized by achieving a reduction in xylene and styrene. The objects and effects of the present invention are (1) to remove styrene as an ethylbenzene precursor in the xylene fraction, (2) to reduce m-xylene in the xylene fraction,
(3) To efficiently concentrate o, p-xylene, which is useful as a chemical raw material, and (3) to recover in good yield the xylene-styrene reaction product, which is a useful synthetic oil. Synthetic oil, which is one of the purposes for this purpose, consists of a fraction mainly composed of 1-xylyl-1-phenylethane, which has a boiling point range of 280 to 310℃, and a non-condensed three-ring aromatic oil, which has a boiling point of 370 to 420℃. It is a fraction whose main component is a certain distyrenated xylene. These synthetic oils exhibit excellent performance in compatibility, lubricity, heat resistance, and electrical properties, and are suitable for a wide range of uses, including plasticity, high-boiling point solvents, heat transfer fluids, electrical insulation oils, and hydraulic oils. The present inventors alkylated more of the styrene contained in the pyrolysis oil xylene fraction to m-xylene, and simultaneously removed styrene, which is an ethylbenzene precursor, and simultaneously achieved a reduction in m-xylene. This work has completed a method for recovering unfused polycyclic aromatics, which are synthetic oils useful as xylene reaction products. Furthermore, it has become clear that the composition of xylene modified by the method of the present invention is preferable as an industrial raw material compared to xylene in which ethylbenzene or its precursor styrene is separated and removed by other methods. That is, the present invention was completed by discovering that there is a significant difference in the reaction activity of each xylene isomer toward styrene, and that this brings about favorable results in the composition of modified xylene. Next, it will be explained that the composition of xylene modified by the method of the present invention provides more favorable results than when ethylbenzene and the like are removed by other methods. When a mixture of ethylbenzene and o, m, p-xylene is aralkylated with styrene by the method of the present invention, the reactivity shows the values shown in the table below, where ethylbenzene is taken as 1.

[Table] As is clear from Table 2 above, the reactivity of m-xylene is overwhelmingly high. Therefore, when treated with the method of the present invention, the styrene to be removed is selectively added to m-xylene by aralkylation. As a result, the modified xylene fraction also has a reduced content of m-xylene, which is not used industrially. Therefore, terephthalic acid,
p-xylene and o- are important raw materials for phthalic acid.
The amount of xylene is large, which is very preferable as a mixed xylene as a chemical raw material. O useful as a chemical industrial raw material by the method of the present invention
- Highly concentrated with a total of xylene and p-xylene of 60.0%. A further noteworthy advantage of the present invention is that p, which is a crude raw material for the polyester fiber industry,
- It is possible to recover mixed xylene, which has a very favorable composition for xylene production. Generally, the method of separating each component individually from a mixed xylene is usually carried out by a combination of precision distillation and cryogenic separation. Ethylbenzene and o-xylene, which have different boiling points, are first separated by precision distillation. be done. However, m, p, and xylene, which have a small difference in boiling point, cannot be separated by distillation, and p-xylene is crystallized and separated by cryogenic separation that takes advantage of the difference in melting point. Therefore, the larger the ratio of p-xylene to m-xylene is, the more advantageous and preferable it is. However, in the method of the present invention, m-xylene is converted into heavy oil by selective aralkylation with styrene, so the p/m
The effect of improving the ratio can also be achieved. Here, Table 3 shows the untreated (1), hydrogenated
The compositions of (2), one in which only styrene was separated and removed (3), and one treated by the method of the present invention (4) are shown below. table-
3, the effects of the present invention are clear.

[Table] The values in (1) in Table 3 are the distillation temperatures from pyrolysis oil.
Among the components of the fraction obtained in the range of 135°C to 150°C, the composition is shown with the sum of xylene ( _C8 aromatic) as 100. In the treatment method in Table 3 above, the composition number 3 shows the value assuming that the styrene to be removed can be ideally removed, so the actual o,
The p-xylene content is believed to be even lower. Next, embodiments of the present invention will be specifically described. As the xylene fraction of the present invention, a mixture of each component as appropriate can be used. A preferable xylene fraction is one obtained by pre-distilling pyrolysis oil and separating a fraction mainly consisting of xylene fraction with an ordinary pressure boiling point of 130 to 160°C, more preferably a fraction of 135 to 150°C. It is. The main components of this fraction are xylenes,
It is styrene and also contains small amounts of toluene, _C9 aromatics, and very small amounts of olefins that have the same boiling point as paraffins. If the amount of styrene in this fraction is small and xylene modification cannot be expected, adding styrene from the outside can
-Concentration of xylene should also be understood as an implementation of the present invention. The method of the present invention requires a liquid phase. Therefore, the processing pressure must be high enough to maintain the xylene fraction in a liquid phase within the reaction temperature range. Although the necessary pressure naturally varies depending on the processing temperature, it is usually within a pressure range of 40 kg/cm ² or less. The catalysts used in the present invention are solid acid catalysts and mineral acids. All of these are known as catalysts for the aralkylation reaction, which is the basic reaction. Metal halides known as Friedel-Crafts catalysts such as aluminum chloride and boron fluoride are also known to have the ability to catalyze aralkylation reactions, but they also promote the polymerization of styrene, resulting in the reaction between styrene and m-xylene. This is not preferable because it is difficult to achieve a reduction in m-xylene. Clay minerals such as acid clay and activated clay are particularly preferred as solid acids, and sulfuric acid is particularly preferred as mineral acids. The treatment temperature in the method of the present invention ranges from 0°C to 200°C and varies depending on the catalyst used. At the lower limit temperature described below, the polymerization reaction rate of styrene in the xylene fraction becomes relatively high, and a polymeric tar-like substance is produced due to the polymerization of styrene, which is not preferable. If the temperature exceeds the upper limit described below, it is not preferable because it causes deterioration of the properties of the by-product heavy oil due to thermal decomposition. Particularly preferred is a temperature range of 100°C to 200°C for solid acids and 5°C to 100°C for mineral acids. In order to selectively react styrene with m-xylene in the xylene fraction, it is necessary to keep the concentration of free styrene in the reaction system at 5% by weight or less. When the styrene concentration in the reaction system is high, the amount of styrene polymer produced increases due to the reaction between styrene molecules, and the selectivity for the reaction with xylenes deteriorates, making it difficult to achieve the purpose of modifying the xylene fraction. I can't. The styrene concentration in the reaction system can be adjusted by recycling the reaction product or by reusing the recovered modified xylene and mixing it with the xylene fraction. The heavy by-product oil obtained in the present invention is mainly an aralkylated product of xylene and styrene, and
Distillation temperature 135~150℃, 180~ under reduced pressure (3mmHg)
There are two types available in the 230℃ range. Distillation temperature 135
The first fraction at ~150°C is styrenated xylene mainly composed of 1-methaxyl-1-phenylethane. It was confirmed by infrared absorption analysis, NMR, and mass spectrometry that the second fraction with a distillation temperature of 180 to 230°C was mainly composed of distyrenated xylene. Example 1 Distillation temperature of 135 xylene fraction from the aromatic-rich cracked by-product oil produced in the naphtha raw material pyrolysis process
The fraction between 148°C and 148°C was separated by distillation. The composition of this xylene fraction is shown below. Non-aromatics 3.7wt% Toluene 0.1 Ethylbenzene 8.8 13.2 o-xylene 18.6 28.0 m-xylene 26.9 40.5 p-xylene 12.2 18.3 Styrene 29.5 100.0 Kyumene 0.2 100.0 Ethylbenzene as a diluent at the initial stage of the reaction
13.2wt%, o-xylene 28.0wt%, m-xylene
A formulated xylene containing 40.5 wt% and 18.3 wt% of p-xylene was used. (The purpose of using prepared xylene in this example is to dilute the styrene at the initial stage of the reaction. Therefore, when repeating the present invention, this purpose can be achieved by using modified recovered xylene.) 400 g of mixed xylene and 200 g of 90% sulfuric acid were placed in a 10-capacity reactor equipped with a stirrer and a thermometer, and the temperature was 5°C.
Cool to Add the xylene fraction while stirring.
Add dropwise at a rate of 100 to 200ml/min, after completion of addition
After stirring for 10 to 15 minutes, the temperature rise due to the reaction heat has stopped, and when the temperature has cooled again to 5 to 7°C, the xylene fraction is further added. In order to prevent the styrene concentration in the system from exceeding 5%, the addition was done as follows: 65g each 5 times, 120g 5 times each, 220g
A total of 7875 g was reacted with 5 times of 410 g, 5 times of 760 g each, and 5 times of 760 g each. In this case, the styrene concentration is
It fluctuates in the range of 2.7-4.1%. After the reaction is completed, the sulfuric acid is separated by precipitation, and the reaction product is neutralized with a 5% aqueous solution of caustic soda. Cleaning liquid is neutral (PH6.8
~7.2Q). Unreacted modified xylene is separated at atmospheric distillation temperature of 150°C, and by-product heavy oil is recovered under reduced pressure. Recovered modified xylene is analyzed by gas chromatography,
The structure of the by-product heavy oil was confirmed by mass spectrometry and IR analysis. The results are shown in Table 4. Example 2 The cracked xylene fraction used in Example 1 was used. The recovered modified xylene obtained in Example 1 was used as a diluent at the initial stage of the reaction. In a reactor with a capacity of 10 equipped with a stirrer and a thermometer, 1000 g of the recovered and modified xylene and 250 g of acid clay are charged and heated to reflux temperature. The cracked xylene fraction was added at a rate of 100 to 200 ml/min, and as in Example 1, 170 g x 5 times and 300 g x 5 were added.
Add in 500g x 5 times and 900g x 2 times. After the reaction is complete, the acid clay is separated and separated by distillation. The results are shown in Table 4. Comparative Example 1 This was carried out in the same manner as in Example 1. However, 300g x 2 so that the styrene concentration in the reaction system exceeds 5%
600g x 2 times, 1000g x 2 times, 1500g x 2 times for a total of 6800g. In this case the styrene concentration varies between 6.1 and 12.6%. The results are in Table 4
Shown below.

[Table] Example 3 Modification of pyrolysis oil xylene fraction 100 g of the modified xylene recovered in Example 2 and 100 g of 90% sulfuric acid were charged into a reactor as a diluent in the initial stage of modification, and the same procedure as in Example 2 was carried out. Cool to Temperature 5~
At 10° C., 2000 g of the xylene fraction obtained in Example 1 are added dropwise. The other methods are the same as in Example 1. The results are shown in Table 5. Example 4 Modification of pyrolysis oil xylene fraction 100 g of activated clay (Mizusawa Chemical Industry Co., Ltd. Galeonite-236) was used as a reforming catalyst. 100 g of activated clay and 100 g of xylene modified according to Example 2 are charged into a 3-capacity reactor equipped with a reflux condenser and a stirrer and heated to reflux temperature. Xylene fraction obtained in Example 1 under heating to maintain reflux
Add 2000g dropwise. After the addition is complete, the mixture is cooled, filtered through activated clay, and distilled in the same manner as in Example 2. The results are shown in Table 5.

【table】

Claims (1)

[Claims] 1. A xylene fraction containing p-xylene, o-xylene, m-xylene and styrene is mixed with a mineral acid or a solid acid catalyst in a liquid phase at a styrene concentration of 5% by weight or less in the reaction system. , and in the case of using a mineral acid as a catalyst, at a temperature of 5°C to 100°C, or in the case of using a solid acid catalyst, at a temperature of 100°C to 200°C. A method for producing mixed xylenes, characterized by achieving a reduction in m-xylene and styrene in a xylene fraction. 2. The xylene fraction is a cracked oil that is produced as a by-product when petroleum hydrocarbons are thermally decomposed at 700°C or higher to mainly obtain ethylene, and has a boiling point range of 130°C.
The method for producing mixed xylene according to claim 1, which is a fraction contained in a temperature range of 150°C to 150°C.