JPH0344060B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for separating and recovering methyl ethylbenzene isomers from a _C9 aromatic fraction whose main component is an aromatic compound having 9 carbon atoms. More specifically, the present invention relates to a method for separating and recovering a methylethylbenzene fraction containing methylethylbenzene isomers as a main component from a _C9 aromatic fraction containing methylethylbenzene isomers and trimethylbenzene isomers whose boiling points overlap with each other. (Prior Art) As is well known, the _C9 aromatic fraction is an aromatic compound consisting of nine carbon atoms, namely two types of propylbenzene isomers, three types of methylethylbenzene isomers, and three types of trimethylbenzene. It is a complex mixture consisting mainly of the above nine aromatic compounds of isomers and indane. Moreover, since the boiling points of these nine types of compounds are close to each other, in order to separate and recover each compound individually, an extremely precise fractionation apparatus is required, which is almost impossible in practice.
Furthermore, when classifying these _C9 aromatic compounds into four groups: propylbenzene isomers, methylethylbenzene isomers, trimethylbenzene isomers, and indane, the boiling points are generally propylbenzene isomers < methylethylbenzene isomers < trimethylbenzene The order increases in the order of isomer < indane, but to be exact, the boiling point of 1,3,5-trimethylbenzene (164.7℃) is lower than the boiling point of 1-methyl-2-ethylbenzene (165.2℃), and it is different from the methylethylbenzene isomer. Since the boiling points of the trimethylbenzene isomers overlap, it is also impossible to separate these four groups by distillation. (Problems to be Solved by the Invention) _C9 aromatic compounds contain many industrially useful substances, and even if they cannot be separated and recovered individually, they can be divided into groups, for example, three types of methylethylbenzene isomers. It is also important from an industrial point of view to separate and recover all of these substances in bulk. The recovered methylethylbenzene isomer can be separated into each isomer by precision distillation, but the mixture can also be used as a raw material for subsequent reactions, such as the production of methylstyrene through dehydrogenation. can. The present invention belongs to this group of separation methods, and by removing the trimethylbenzene isomer in the _C9 aromatic fraction by the oligomerization reaction described below, methyl ethylbenzene isomer mainly composed of methylethylbenzene isomer is extracted from the unreacted oil. This is a method of separating and recovering the ethylbenzene fraction. (Means for solving the problem) Formaldehyde oligomerization reaction is effective as a method for selectively reacting trimethylbenzene isomers while minimizing the reaction of methylethylbenzene isomers in the _C9 aromatic fraction. Available. It is a well-known fact that when certain aromatic compounds are reacted with formaldehyde in the presence of an acid catalyst, oligomers (formaldehyde resins) bound by methylene, ether, acetal bonds, etc. are produced (for example, polymer Chemistry, vol. 12, p. 335 (1955)). This reaction has already been studied in detail and is known to be applicable to various methyl substituted products such as benzene and naphthalene. Some findings have been reported regarding the relative reaction rates of various compounds; for example, regarding xylene isomers, the reaction increases in the order of para-xylene < ortho-xylene < meta-xylene, and 1,3,5-trimethyl It is known that benzene is even more reactive than meta-xylene (Koka, Vol. 65,
613 pages (1962)). In addition, formaldehyde resins made from meta-xylene and mesitylene (1,3,5-trimethylbenzene) are called xylene resins and mesitylene resins, and are used as modification agents for phenol resins, paints, adhesives, etc. It is commercially available. The present inventors focused on the high reactivity of 1,3,5-trimethylbenzene and formaldehyde, and conducted an oligomerization reaction between formaldehyde and a _C9 aromatic fraction containing methylethylbenzene isomers and trimethylbenzene isomers. As a result of intensive research, we have arrived at the present invention. That is, the trimethylbenzene isomer exhibits higher reactivity than the methylethylbenzene isomer, and the trimethylbenzene isomer selectively reacts with formaldehyde to produce formaldehyde resin, whereas the reactivity of the methylethylbenzene isomer is It was found that the main component of the unreacted oil was methylethylbenzene isomer. Since the boiling points of unreacted oil and formaldehyde resin differ widely, a methylethylbenzene fraction containing methylethylbenzene isomers as a main component can be separated and recovered by a simple distillation operation.
In addition, 1,3,5-trimethylbenzene, which makes it impossible to separate methylethylbenzene isomers and trimethylbenzene isomers by distillation, is particularly reactive among trimethylbenzene isomers. Even if the conversion rate of 1,3,5-trimethylbenzene is increased to nearly 100%, 1,2,4-trimethylbenzene can remain in the unreacted oil. In this case, by fractionating the unreacted oil, a 1,2,4-trimethylbenzene fraction can be recovered in addition to the methylethylbenzene fraction. 1,2,4-trimethylbenzene is an industrially useful substance as a raw material for trimellitic anhydride and the like. (Function) The C ₉ aromatic fraction according to the present invention has 9 carbon atoms.
There are no particular restrictions on the content of methylethylbenzene isomers or trimethylbenzene isomers, as long as the main component is an aromatic compound consisting of There are no particular restrictions. If impurities such as paraffin and naphthene, which have the same boiling point range as the C ₉ aromatic fraction, are present, the purity of the methylethylbenzene fraction to be separated and recovered will decrease, but there is no problem in practice. Additionally, when olefins, dienes, etc. are present, these unsaturated compounds generally polymerize under formaldehyde resin manufacturing conditions,
Although it reduces the purity of the formaldehyde resin, it does not interfere with the purpose of the present invention. Thus, in general, C ₉ aromatic fractions such as reformed xylene bottom oil, naphtha cracking xylene bottom oil, xylene isomerization by-product oil, etc. can be effectively applied. The formaldehyde resin production technology according to the present invention can be applied to the existing xylene resin production technology as is or with partial modification, but an outline will be described below. The formaldehyde source used in the present invention may be in any form as long as it generates monomeric formaldehyde during the reaction, and commercially available 37% formalin, trioxane, paraformaldehyde, etc. can be used as is. Furthermore, if necessary, monomeric formaldehyde can be separately generated from these formaldehyde sources and used. The catalyst used in this reaction is not particularly limited as long as it produces formaldehyde resin from trimethylbenzene isomer and formaldehyde, and sulfuric acid,
Phosphoric acid, hydrochloric acid, perchloric acid, trichloroacetic acid, para-toluenesulfonic acid, chlorosulfonic acid, aluminum chloride, boron trifluoride, chlorosulfonic acid-antimony pentafluoride, strong acid type ion exchange resin, silica-alumina, various zeolites Acid catalysts such as the following can be used. The formaldehyde resin production apparatus for carrying out this reaction may be of any particular type, such as a conventional batch type or flow type. The conditions for producing formaldehyde resin used in this reaction naturally have optimal conditions depending on the type of catalyst, desired yield of formaldehyde resin, etc., but basically any conditions are sufficient as long as formaldehyde resin is produced. For example, 1 mole of C ₉ aromatic fraction, 37
Using 1 mol of formalin, commercially available 98% sulfuric acid 0.5
When mole is used as a catalyst, formaldehyde resin is produced at a reaction temperature of 60 to 120° C. and a reaction time of 1 to 10 hours with a yield depending on the reaction conditions. The boiling point difference between the formed formaldehyde resin and the unreacted _C9 aromatic fraction is large, so they can be separated by a simple distillation operation, but the composition of the unreacted oil naturally depends on the yield of formaldehyde resin. Therefore, an appropriate method for recovering the methylethylbenzene fraction must be adopted in consideration of the composition of the unreacted oil and the desired purity of the methylethylbenzene fraction. In general, when the formaldehyde resin yield is kept low, almost only 1,3,5-trimethylbenzene is selectively converted into resin, so in addition to methylethylbenzene isomers, 1,3,5-trimethylbenzene and 1, 2,4-trimethylbenzene 1,2,3
-Contains trimethylbenzene. but,
Because it contains almost no 1,3,5-trimethylbenzene, which hinders the fractional distillation of methylethylbenzene isomers and trimethylbenzene isomers,
It can be fractionated into methylethylbenzene isomers and trimethylbenzene isomers (1,3,5-trimethylbenzene is not included). Furthermore, the boiling points of 1,2,4-trimethylbenzene and 1,2,3-trimethylbenzene among these trimethylbenzene isomers are 169.4℃ and 176.1℃, which is a relatively large difference in boiling point. , 4-trimethylbenzene can be separated and recovered by distillation. However, if the yield of formaldehyde resin is increased, an unreacted oil containing almost no trimethylbenzene isomers can be obtained, so simply separating the unreacted oil from the resin using a simple distillation or rotary evaporator will produce methylethylbenzene isomers. A methyl ethylbenzene fraction, which is mainly composed of Of course, a methylethylbenzene fraction of higher purity can be obtained by further performing a distillation operation. Also, part of the methylethylbenzene isomer is converted into resin at the same time as the trimethylbenzene isomer, but among the methylethylbenzene isomers, 1,
Since the reactivity is higher in the order of 4-<1,2-<1,3-methylethylbenzene, the isomer ratio in the recovered methylethylbenzene fraction is different from the isomer ratio of methylethylbenzene in the feedstock oil, and is 1,4. -The proportion of methylethylbenzene increases. Therefore, this reaction can also be effectively applied as a reaction for changing the isomer ratio of methylethylbenzene isomers. The formaldehyde resin produced by this oligomerization reaction has different physical or chemical properties depending on the catalyst used, reaction conditions, etc., but in all cases, about 2 to ₁₀ C9 aromatic nuclei are connected to methylene bonds.
It is a resin bound by ether bonds, acetal bonds, etc., and basically has a similar structure to commercially available xylene resins, so it can be used for almost the same purposes. (Example) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Example 1 Four-necked flask with stirring blade and condenser (inner volume: 1
), 120g of _C9 aromatic fraction of raw material (composition is shown in Table 1)
), 140 g of commercially available 37% formalin, and 50 g of sulfuric acid were charged, and the mixture was reacted at a reaction temperature of 90° C. for 4 hours. After the reaction, sulfuric acid and unreacted formaldehyde were removed by washing with water, and distilled under reduced pressure to obtain 49 g of unreacted oil and 76 g of formaldehyde resin. The composition of the obtained unreacted oil is shown in Table 1. Example 2 Using the same equipment as in Example 1, 120 g of the same raw material oil,
37% formalin 82g, para-toluenesulfonic acid 19g
After the catalyst was removed, 95 g of unreacted oil and 19 g of formaldehyde resin were obtained by distillation. The composition of the obtained unreacted oil is shown in Table 1. Example 3 Using the same equipment as in Example 1, 180 g of the same raw material oil,
30 g of trioxane and 50 g of a strongly acidic ion exchange resin (Amberlyst 15) were reacted at 80° C. for 4 hours, and after removing the catalyst, 89 g of unreacted oil and 93 g of formaldehyde resin were obtained by distillation. The composition of the obtained unreacted oil is shown in Table 1.
Shown below. Example 4 Using the same equipment as Example 1, 180 g of the same raw material oil,
30 g of paraformaldehyde and 50 g of a strongly acidic ion exchange resin (Amberlyst 15) were reacted at 80° C. for 4 hours, and after removing the catalyst, 106 g of unreacted oil and 77 g of formaldehyde resin were obtained by distillation. Table 1 shows the composition of the unreacted oil obtained. Example 5 The unreacted oil obtained in Example 1 was subjected to theoretical stage 15~
Distillation was performed using a 17-stage atmospheric distillation apparatus. boiling point range
The purity of the methylethylbenzene fraction separated and collected at 161.0 to 163.5°C was 80.2% by weight. Comparative Example 1 The raw material oil used in Example 1 was distilled using an atmospheric distillation apparatus having 50 to 60 theoretical plates. boiling point range
The purity of the methylethylbenzene fraction separated and collected at 161.0 to 163.5°C was 77.7% by weight.

[Table] Chilbenzene

[Table] (Effect of the invention) As is clear from the results in Table 1, the unreacted oils obtained in Examples 1 to 4 of the present invention were all enriched in methylethylbenzene isomers, and 1, which overlapped the boiling point range and prevented distillation separation of the methylethylbenzene fraction.
The content of 3,5-trimethylbenzene has decreased significantly. Therefore, in order to separate and recover methyl ethylbenzene from these unreacted oils, the number of theoretical plates conventionally required from 50 to 100 as in Comparative Example 1 is required.
Methyl ethylbenzene of the same purity can be recovered by using a precision distillation column with 15 to 30 theoretical plates as in Example 5, without using a precision distillation column with plates.

Claims (1)

[Claims] 1. In a method for separating and recovering a methyl ethylbenzene fraction from an aromatic hydrocarbon fraction, most of which consists of 9 carbon atoms, the raw aromatic hydrocarbon fraction is first reacted with formaldehyde to produce formaldehyde resin, and then A method for separating and recovering methylethylbenzene fraction by separating methylethylbenzene from reaction oil by distillation.