CS250774B1 - Method of terphenyls preparation - Google Patents

Abstract

Solutions falling within the technology field organic matter refers to the method of preparation terphenyls by dehydrogenation condensation benzene. The essence of the solution is that it is benzene was heated in the reactor for 2 to 5 hours 10 seconds to 760-850 ° C. benzene it may contain biphenyl as an additive 0.01 to 60% by weight, or a stabilizer as carbon disulphide or thiophene in an amount of 0.05 % to 5 wt.

Description

The invention relates to a process for the preparation of terphenyls by dehydrogenation by condensation of benzene.

Terphenyls, polycondensed aromatic hydrocarbon derivatives, are formed as by-products in the process of benzene pyrolysis. They exist in the form of three isomers, the so-called. meta-, ortho- and para-terphenyl. Their formation can be described by the following equations:

it

In the production of biphenyl, terphenyls are undesirable by-products that reduce the selectivity of biphenyl formation by pyrolysis (dehydrogenation condensation) of benzene.

The reaction is usually carried out in a tubular reactor, heated by resistance. In addition to terphenyls, higher polycondensed aromatic hydrocarbons are formed in small amounts, the formation of which ultimately leads to coke formation. For these reasons, the reactor must occasionally be regenerated. Regeneration consists in burning the resulting coke by air purging.

However, the mixture of terphenyls or the individual isomers may not always be an undesirable but not merely an undesirable waste. It is known in the literature that a mixture of terphenyls is used as a coolant for a nuclear reactor and a moderator. (Werkstoffe umd Korosion 16/5/412 (1965)). It is also known that p-terphenyl can be used with a radioactive radiation sensitizer (Plasticheskije ma'si 60, 2, 48-52 (1960) and Japan pat. No. 149,069 of Feb 29, 1960 to Matsuhita El. Works Ltd.).

Also described is the use of terphenyls in the function of PVC bleaching agents (U.S. Pat

894 923 of June 14, 1959).

From other applications in industry, respectively. the research describes the use of terphenyls in laser technology as a so-called " terphenyl laser. (Chow W., Boicher H. Applied Physicte 13, 3, 267-269)

The process for preparing terphenyls according to the invention is characterized in that the benzene is heated in the reactor for 2 to 10 seconds at a temperature of 760 to 850 ° C.

The benzene may contain biphenyl in an amount of 0.01 to 60% by weight, or a stabilizer such as carbon disulphide or thiophene in an amount of 0.05 to 5% by weight.

Accordingly, the present invention is based on the dehytrogenation condensation of benzene in such a way that terphenyls are preferably formed.

This effect can be achieved in essentially two ways.

Firstly, in a reactor in which the production of biphenyl is overheated, it is necessary to increase the reaction temperature and to prolong the realization time.

Secondly, it is possible to enrich benzene, which is used as feedstock, with a certain amount of biphenyl. Thus, reactions 4, 5 and 6 are preferred, since biphenyl will not only be formed during the reaction, but will already be present in the feedstock.

It will be understood that both methods can also be combined by using an increased biphenyl content in the feed while increasing the temperature and prolonging the reaction time.

In all terephenyl formation processes, there is an increased possibility of reactor coke formation compared to biphenyl production, so it is necessary to burn the reactor more frequently. Similar to other sulfur derivatives (eg thiophene) in the feedstock to reduce coke formation.

the addition of biphenyl to benzene can be in the range of 0.01 to 60% by weight, but at the upper limit (about 50% / oj), there are already very undesirable products such as tetra-, penta-condensed phenyls to coke, which reduces efficient production.

By the described methods of benzene dehydrogenation condensation (or mixtures thereof with biphenyl), it is possible to achieve preferential terphenyl formation at the expense of mainly biphenyl, which in connection with the recycling of unreacted benzene and unreacted or reacted biphenyl, .

The advantages of this process are, in particular, that they make it possible to obtain, with relatively high selectivity, a mixture of terphenyls, usually difficult to obtain by other processes.

The invention is illustrated by the following examples from both industrial and laboratory practice.

Example 1

In a tubular reactor composed of stainless steel tubes with a total length of 79 meters and an internal diameter of 8.5 cm, benzene dehydrogenation condensation is carried out. At the beginning of the reactor the temperature is about 400 ^° C and at the end 766 ° C. The benzene flow rate is 170 dm ³ .s ^-1 . The reaction time is 3.1 seconds. Under these conditions, the composition of the outgoing gases is by mass. % as follow:

89.7% benzene,

6.8% biphenyl and 3.34% terphenyl.

The individual components are obtained by rectification.

Example 2

In the reactor of Example 1, dehydrogenation condensation of benzene is performed under the conditions of:

temperature at the beginning of the reactor 400 ° C, temperature at the end of the reactor 775 ° C, benzene flow 155 dm ³ .s ^-1 . reaction time is 3.4 seconds.

A gas mixture having the following composition is exited from the reactor under these conditions:

benzene 85.4% by weight,

8.5% biphenyl and

6.1% wt. terphenyls with quaternophenyl contents below 0.01 wt. %, Example 3

In a laboratory tube quartz glass reactor with a total length of 53.8 cm and an internal diameter of 1.8 to 2 cm, filled with a ceramic charge, dehydrogenation condensation of benzene containing biphenyl is added. The reaction is carried out in a pyrolysis furnace, the heated part of the reactor being 30 cm.

The free volume of the reactor per reaction portion is 59.1 µm ³ . The temperature at the end of the reactor is 805 ° C. The biphenyl content of benzene is 20% by weight. The raw material flow is 60 cm ³ . . hr ^-1 , dosed by a linear pump, which represents a reaction time of 4.1 seconds. Under these conditions, the conversion of benzene to products is 18.5% by weight, the resulting product comprising:

61.5 wt. % benzene,

16.0 wt. biphenyl,

21.9 wt. terphenyl and

0.7 wt. higher polyphenyls.

Example 4

Under conditions as in Example 3, only the temperature at the end of the reactor was 820 ° C, dehydrogenation condensation of the mixture containing 45 wt. biphenyl and 0.2% CS2 carbon disulfide as a stabilizer in benzene. The feed rate was 60 cm ³ per hour. Reaction time 4.7 seconds. In the resulting mixture was 27.2 wt. terphenyls, but the tetra- and polyphenyls content determined by chromatography increased to 6.5 wt. After 5 hours of pyrolysis, the reactor ceramic charge was observably coked.

Claims (3)

SUBJECT Process for the preparation of terphenyls by dehydrogenation of benzene, characterized in that the benzene is heated in the reactor for a period of 2 to 10 seconds to a temperature of 760 to 850 degrees C. 2. A process for preparing terphenyls by dehydrogenating condensation of benzene according to point INVENTION 1, characterized in that the benzene contains biphenyl in an amount of 0.01 to 60% by weight. 3. A process for the preparation of terphenyls by dehydrogenation of benzene according to items 1 and 2, characterized in that the benzene contains from 0.05 to 5% by weight of benzene. a stabilizer such as carbon disulfide, thiophene.