JPS63190838A - Production of ethylene glycol - Google Patents

Abstract

PURPOSE:To simply separate ethylene glycol from a catalytic solution and to improve yield economically in obtaining the titled compound useful as a raw material for an anti-freeze, etc., by reacting carbon monoxide with hydrogen by the use of a RH catalyst, by using glycerin and high-boiling polyols firmed as by-products and a high-boiling solvent. CONSTITUTION:In reacting carbon monoxide with hydrogen in the presence of a Rh catalyst, glycerin and high-boiling polyols formed as by-products are subjected to phase separation by using a high-boiling solvent and separated from a catalytic solution to give the aimed compound. To be concrete, a mixed system of a tertiary amine and a polyether, having higher boiling points than the ethylene glycol may be cited as the high-boiling solvent system. Polyethylene glycol dimethyl ethers such as triglyme, etc., may be cited as the polyethers, tri-h-butylamine, etc., may be cited as the tertiary amine and the blending ratio is preferably 1:20-20:1.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is extremely effective in recovering and reusing catalysts when producing ethylene glycol from synthesis gas, that is, a mixture of carbon monoxide and hydrogen. This invention relates to a method for easily separating high-boiling point glycerin and polyols from catalysts.

Ethylene glycol is an extremely important chemical as a raw material for polyester and antifreeze.

[Conventional technology]

Conventionally, ethylene glycol has been produced by the oxidation reaction of ethylene, but in recent years, technology has been developed that uses synthesis gas, which is a cheaper and more plentiful raw material than ethylene, as a raw material. For example, Special Publication No. 53-15047, Special Publication No. 53-3
No. 1122, Special Publication No. 55-5497, Special Publication No. 55-3
No. 3694, Special Publication No. 1983-33697, Special Publication No. 1983-
No. 43821, Special Publication No. 10894, Special Publication No. 1983
-40131, Special Publication No. 5B-40132, Special Publication No. 5
No. o-40698, Japanese Patent Application Publication No. 50-32118, Samurai Dance No. 125203-1983, Special No. i-42808,
JP-A-52-42809, JP-A-53-108889
No., tJ! ! 1 Publication No. 121714/1983 and Japanese Patent Application No. 16415/1983, and U.S. Patent No. 4
, No. 013,700, No. 4,133.776, 4,15
No. 1.192, No. 4,153.523, No. 4,190.5
・No. 98, 4,199.520, 4.199. ．． 51
No. 1, No. 4,211.719, and No. 4.225,53
As described in the specifications of No. 0, a method is often mentioned in which flame oxide and hydrogen are reacted under high temperature and high pressure conditions using a tetradium catalyst.

However, the prior art methods illustrated above use rhodium catalysts in the form of clusters. When considering the production of ethylene glycol on an industrial scale, it is economical to use distillation to separate ethylene glycol and by-products from the catalyst liquid, and it is preferable in terms of ease of process design. The problem of separating living organisms by distillation is extremely difficult, especially for Rh cluster catalysts.

However, Rh clusters are extremely unstable against heating and reduced pressure, and easily lose their carbonyl ligands, become metallized, and precipitate in the separation system. For example, US Pat. No. 4,224,237 g1 describes a process for redissolving the Rh metal solids thus precipitated.

In order to avoid such drawbacks, a method using a Rh catalyst that is less likely to form clusters has also been proposed. For example, the mononuclear rhodium complex RhX(Co)Lx by the present inventors
(L-tertiary phosphine), JP-A-61-12638, characterized in that X is a carboxylic acid anion; Japanese Patent Application No. 1988-7, characterized in that X is an acupoint 4 anion.
No. 2576, and others that produce this complex in-system
No. 1-12637, Japanese Patent Application Laid-Open No. 15850/1982, and Japanese Patent Application No. 72577/1983. These inventions have made it possible to separate ethylene glycol and products with boiling points lower than that by a distillation method without impairing the stability of the iζh@ medium.

[Problem that the invention seeks to solve]

However, it has been found that difficulties arise when trying to separate the glycerin and polyol having 4 or more carbon atoms produced by these inventions by distillation. Glycerin has a boiling point of 290°C, and if it is to be separated from the catalyst liquid at a reduced pressure of 5 cm, which is easy to realize from a practical standpoint, it requires heating to about 154°C. This is stable RhX(C
o) The temperature is severe even for Class L2, and some degree of decomposition is inevitable.

Although it is possible to achieve a lower pressure reduction degree industrially, there are economical and equipment constraints for this purpose. Furthermore, it can be said that polyols containing several carbon atoms or more, which are always produced as a by-product, although in a much smaller amount than glycerin, have no ability to be separated by distillation. Therefore, a measure has been considered to keep the accumulated high-boiling products below a certain concentration by constantly purging a part of the catalyst liquid. However, this also results in a part of the usable and expensive Rh catalyst being discharged out of the reaction system9, requiring a great deal of expense to recover and regenerate it.

Thus, in the process for producing ethylene glycol using a Rh catalyst, the requirements for separating glycerin and higher boiling substances from the catalyst liquid by a simple method other than distillation can be easily understood.

[Means for solving problems]

+1) Background leading to the invention Ethylene glycol has a boiling point of 198°C, and in order to separate it from the catalyst system by distillation, a solvent with a boiling point higher than that of ethylene glycol is required. As a result of searching for various solvents that can dissolve the Rh catalyst well, are thermally stable, and are inexpensive, it has been found that polyethers such as triglyme, tetraglyme, pentaglyme, and hexaglyme meet the above requirements well. However, in such a solvent, certain catalyst systems, such as JP-A-60-13
It has been revealed that the ethylene glycol production activity of a catalyst system consisting of Rh and phosphine as seen in Japanese Patent No. 6524 is significantly lower than, for example, the activity of methylpyrrolidone in a more amide-based solvent. This difference is thought to be due to the strong basicity of the amide solvent, but the activity was not significantly improved even in a system in which tertiary amine was added in an amount equivalent to Rh atoms.

However, when considering tertiary amine as a solvent and mixing it with a polyether solvent, it was found that the ethylene glycol production activity and selectivity were significantly improved, reaching a level comparable to that of amide solvents. The effect of this amine is equally seen on both low-boiling point and high-boiling point amines, but when building a process to separate ethylene glycol by distillation, the amine used in large quantities also has the same effect as polyether solvents. A high boiling point is desirable.

Thus, for example, as shown in Example 1, ethylene glycol is synthesized using a solvent system in which N-octylpyrrolidine (boiling point 237°C) is mixed with tetraglyme, and ethylene glycol and lower compounds are synthesized using a vacuum distillation device. When the boiling point product was separated from the jaw fluid, an unexpected f? The facts were discovered.

That is, when a catalyst solution from which ethylene glycol and other substances have been separated is left to stand at room temperature, a solvent-insoluble liquid phase is formed at the bottom, and layers are separated. When this part was analyzed, it was confirmed that it was glycerin containing a small eyelid solvent. Moreover, it was also revealed that this scale contains almost no Rh complex, which is a catalyst.

In other words, some mixed solvents of amine and polyether have low saturated solubility for glycerin and high dissolving power for Rh complexes, so they can be used without losing the catalyst. 4I glycerin can be separated. Prior to this discovery, to remove glycerin and polyols containing more than a few carbon atoms,
It was thought that the only option was to purge a portion of the catalyst liquid out of the system along with the Rh catalyst, or to use a separate extraction process, but this discovery will greatly simplify the separation of glycerin and other substances. Wakasho has arrived at the present invention.

(2) Specific details of the present invention The present invention provides a high-boiling point system that effectively separates glycerin and high-boiling point polyols, which are produced as by-products, into layers when synthesizing ethylene glycol from synthesis gas using Rh and @ medium. This invention relates to a process for separating glycerin and the like from a catalyst liquid using a solvent system.

The Rh catalyst used in the present invention may be any one as long as it mainly produces ethylene glycol, but it is preferable to use a system in combination with a co-catalyst that prevents metalization of Rh. Examples of such catalyst systems include JP-A-60-136524 and JP-A-60-1495.
No. 37, JP-A-61-12637, JP-A-61-12
No. 638, JP-A-61-15850, patent application No. 1988-5
No. 6071, Patent Application No. 1983-131974, Patent Application No. 1983
-72576 and Japanese Patent Application No. 61-72577.

A specific example of a high-boiling point solvent system that substantially separates glycerin and high-boiling point polyols into layers is a mixed solvent system of a tertiary amine having a higher boiling point than ethylene glycol and a polyether.

The polyethers used in this Shima medium system have a boiling point of 2.
Anything above 10°C will do, but some that are qualitatively easy to obtain are triglyme, tetraglyme,
Examples include polyethylene glycol dimethyl ethers such as pentaglyme and hexaglyme. Mixtures of these can also be used without any problem.

Further, the tertiary amine used in the solvent system refers to a compound having the general formula pJ RI R2Rs and having a boiling point of 210°C or higher. Here, R1 to R3 are an alkyl group, an aryl group, an aralkyl group, and those containing oxygen or 9 atoms in any position other than the α position. Specifically, tri-n-butylamine, tri-l-butylamine, tri-t-butylamine, tri-n-hexylamine, tri-n-octylamine, tri-2-ethylhexylamine, tri-t! J-n-dodecylamine, hexylpyrrolidine, octylpyrrolidine, dodecylpyrrolidine, hexylpiperidine, octylpyrrolidine, dodecylpiperidine, pentylhexamethyleneimine, octylhexamethyleneimine, dodecylhexamethyleneimine, diethylaniline, dibutylaniline, dimethylamino Examples include pyridine, octylpyrrole, dodecylpyrrole, dibutylfurfurylamine, dipylfurfurylamine, dibutylaminotetrahydrofuran, tripropaturamine, and tributanolamine.

Substantially separating the layers of glycerin and high-boiling point polyols means that the saturated solubility of glycerin in the mixed solvent system consisting of the polyether and tertiary amine described above is 10 wt at room temperature, that is, within the range of 0 to 40°C. % or less.

In this solvent system, the mixing ratio of polyether and tertiary amine can be freely varied within the range of 1:999 to 999:1 in terms of volume ratio, preferably within the range of 1:20 to 20:1. In the reaction of synthesizing ethylene glycol from synthesis gas, it has been confirmed that if the amount of glycerin is 10wt1i or less, it hardly affects the activity even if it is present in the solvent system (see Example 1).

When the accumulating glycerin is produced in excess of the saturation solubility of less than 10 wt%, the excess glycerin is separated into the lower layer of solvent. Polyols containing more than a few carbon atoms are not detected by gas chromatographic analysis, but if they are produced, they are thought to behave in the same way as glycerin. When we investigated the Rh4 degree that migrates to this glycerin layer, we found that it hardly exists. Although this degree varies depending on the combination and quantitative ratio of the polyether and tertiary amine used, it can be said that ah does not substantially migrate even if the glycerin layer is separated.

If necessary, the glycerin separated into layers can be rectified to remove the solvent and high-boiling substances to obtain pure glycerin. It is also possible to recover Rh from Weika by treating high-boiling substances. Further, in the glycerin stage, a small amount of Rh in glycerin can be extracted with a polyether-tertiary amine mixed solvent to further reduce the amount of Rh present in the glycerin.

Through the above operations, in the ethylene glycol production process, glycerin and high boiling substances, which are problematic when collecting and recycling the catalyst, can be purged from the catalyst liquid, and f! ij
It can be easily and substantially discharged from the reaction system by a layer separation method without using complicated extraction methods.

〔Example〕

Examples of the present invention are shown below, but the present invention is not limited by the following examples unless it goes beyond the scope of the invention. In addition, the reaction conditions in the following examples are hydrogen/-! ! The reaction was carried out at a sigma carbon molar ratio of 1 and a reaction pressure of so#/dG. Activity is defined as the number of moles of ethylene glycol produced by 1f-atom rhodium per hour (mail/f-atom-
h), selectivity is the number of carbons in ethylene glycol (%) relative to the number of carbons contained in the total liquid product.

Example 1 30 mj of tetraglyme and 2 ml of N-octylpyrrolidine were placed in an autoclave equipped with a stirring device with an internal volume of 200 d.
0d, Rh(COXP-MeO-CsH40XP(tB
u)z(nBu)) as a complex 20 mmoj! Introducing 2
The temperature was raised to 15° C. and the reaction was continued for 10 minutes. When the product was analyzed by gas chromatography, ethylene glycol 56.9
mmol (activity 16.7, concentration 7.49 wtJ
), glycerin 9.5 mmol (111 degrees 1.
The reaction solution containing 85wt4)% and other products? I was attacked. Selectivity of ethylene glycol is 61.2%
Met.

Next, most of the ethylene glycol and other low-boiling substances were removed using a thin film distiller. After replenishing some of the components lost with the product and carrying out a synthesis gas reaction under exactly the same conditions as at the beginning, ethylene glycol: r-h 6
0.3 mmof (activity 17.7, selectivity 61.1%
, strength 7.94 wt4), glycerin 7.8 m
moIl (cumulative 17.3 mmojl, cumulative concentration 3
．． 38Wt4) and its +゛h product were obtained.The reaction solution was homogeneous at room temperature.

Furthermore, this reaction solution was passed through a thin film distiller to remove products below ethylene glycol, the solvent component was replenished, and the synthesis gas reaction was performed again under the same conditions. When the reaction solution was cooled to room temperature, the presence of a slightly separated liquid phase at the bottom was confirmed. As a result of analysis of the upper layer, ethylene glycol 57.6 mmol (activity 16.9, selection 1q60
．． 5%, concentration 7.58 wt4), glycerin 6.0
mmol (cumulative 23.3 mmofi%, cumulative 4.6 wt%) and other products were obtained.

Glycerin seems to have a saturated solubility in this catalyst solution5,2
It can be seen that the activity and selectivity towards ethylene glycol do not change at all even though wt'@ is exceeded.

This reaction solution was subjected to the same operations as removal of low-boiling substances and replenishment of solvent, and a fourth synthesis gas reaction was carried out. After the reaction, the liquid clearly separated into two liquids at room temperature, and when the lower layer was separated and analyzed, it was found to be 9.0 mmoJ of glycerin! (
0.83f). The upper layer contains 52.1 mmoj of ethylene glycol! (Activity 15.3,
Selectivity 61.6%), glycerin cumulative 'iJ 23.3
Contains mmol (cumulative concentration 4.6 wt%)
'It was.

Thus, it was confirmed that under these reaction conditions, the catalyst solution could be used for the Kuripe ethylene glycol synthesis reaction while separating the glycerin of 4.6wt1s or more into layers without deteriorating the activity or selectivity.

Example 2 40vt% of glycerin was added to a solvent in which N-octyl bitetralysine and tetraglyme (TGM) were mixed at a volume ratio of 1/4 or V3, and the mixture was thoroughly stirred at room temperature. When this solution was allowed to stand still, the layers were separated into two liquids. Collect this upper layer,
The saturation concentration of glycerin contained was analyzed. The results are shown in Table 1, &1-3 along with the values in TGM alone solvent.

Obviously, the solubility of glycerin decreases as the number of amine-added dishes increases, and the effectiveness of the amine mixed solvent can be understood.

Comparative Example I N-methylpyrrolidine, triethylamine, NIN, N
:N'-tetramethylhexamethylenediamine as TGM
The solubility of glycerin in this solvent was determined by the same method as in Example 2. The results are shown in Table 1 and Haruka 4-6.

In the case of amines such as methylpyrrolidine and triethylamine, which have a low boiling point and easily mix with many substances, the solubility of glycerin is improved rather than dTGM alone, and its molecular weight 1'lK is unreasonable. is understood. on the other hand,
Tetramethylhexamethylene diamine has a boiling point of approximately 220
℃, but since there are two nitrogen atoms in the molecule, the polarity is strong and it also increases the solubility of glycerin, making it unsuitable for the purpose of the present invention.

Examples 3 to 8 Mixed solvents of various amines and TGM listed in Tables 11.47 to 12 were prepared9, and the solubility of glycerin was determined by the same method as in Example 2.

As can be seen from the results in Table 1, it is understood that all of these tertiary amines reduce the saturation solubility of TGM alone and 4-element glycerin, and are therefore effective in its layer separation.

(Left below) Example 9 Tetraglyme 4 was placed in the autoclave used in Example 1.
0d, N-hexylpiperidine IQag, Rhacac
(Co)z 20 mmojl, P(1Pr)340
mmojl.

20 mmojl of phenol was introduced, the temperature was raised to 230°C, and the mixture was reacted for 4 hours. After the reaction solution was cooled in the room, the products below ethylene glycol were removed using a thin film distiller. At the same time, after supplementing the hexylpiperidine that was slightly scattered and returning to the starting composition, the glycerin content was determined to be 3.09 wt.
%, and the liquid was still homogeneous. This reaction solution was reacted once again under the same conditions to produce ethylene glycol and other compounds.

When this reaction solution was again passed through a thin film distiller to remove products with a boiling point below ethylene glycol, the reaction solution was found to separate into two phases, with a small amount of the lower layer being essentially glycerin. Glycerin in the upper layer again! The draft is 4.8wt1
It was confirmed that in this mixed solvent, glycerin at a concentration higher than this concentration separates into layers.

Example IO The same procedure as in Example 9 was repeated except that N-hexylpiperidine t-N-hequine was replaced with hexamethyleneimine. The glycerin concentration after the first reaction was 4.44 wt%, and the liquid was homogeneous. It was found that the reaction solution after the second reaction was separated into two phases, the lower layer contained glycerin, and the upper layer contained 4.1 wt1 glycerin.

Therefore, it was confirmed that even in this mixed solvent, this glycerin with a temperature of 4 degrees or more undergoes phase separation.

Claims (1)

[Claims] When producing ethylene glycol by reacting carbon monoxide and hydrogen in the presence of a Rh catalyst, it is characterized by the use of a high-boiling point solvent system that substantially separates the by-product glycerin and high-boiling point polyols into layers. Method for producing ethylene glycol.