RU2446138C1 - Method of producing isoprene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for liquid-phase synthesis of isoprene by reacting formaldehyde with isobutylene or derivatives thereof in the presence of a solid-phase catalyst and subsequent extraction of the end product, characterised by that the catalyst used is phosphates selected from zirconium, niobium or tantalum phosphates, wherein the reaction takes place at temperature 100-200°C, pressure 7-20 atm and molar ratio of isobutylene or derivative thereof to formaldehyde equal to (1-20)/1.

EFFECT: use of the method enables synthesis of isoprene with high output and selectivity.

7 cl, 17 ex, 1 tbl

Description

The present invention relates to a liquid-phase process for the production of isoprene, in particular to the production of isoprene by reacting formaldehyde with derivatives of isobutylene on a heterogeneous catalyst.

Various methods of producing isoprene are used in industry: 1) from isobutylene and formaldehyde, 2) two-stage dehydrogenation of isopentane, 3) dehydrogenation of isoamylenes, 4) dimerization of propylene, 5) extraction of isoprene from the C5 fraction of pyrolysis of oil products, among which the most attractive is condensation of isoprene by condensation isobutylene with formaldehyde due to the fact that both of these reagents are based on the primary products of oil refining and associated gas.

Known methods based on the gas-phase process for the production of isoprene in the presence of various heterogeneous catalysts, for example GB 863330; GB 841746; GB 1025432; US 4014952; US 4000209; US 3437711; US 3,662,016; US 4092372. Phosphoric acid supported on silica gel, phosphates of group IIIB elements (boron, aluminum, gallium) supported on silica gel, chromium, cobalt, calcium, barium, copper, supported on silica gel phosphates, acidic catalysts are used as catalysts in these processes. based on tin oxide and silica gel or silica gel and bismuth, silver deposited on aluminosilicate is also used.

However, the known methods do not completely satisfy the basic requirements for industrial catalysts. Some methods use catalysts that give low conversions or a large number of undesirable by-products. Another part of the methods allows to achieve high degrees of conversion, however, the catalysts used in them are quickly deactivated and have a low inter-regeneration range. In addition, the significant disadvantages of the one-stage gas-phase methods for producing isoprene are the high energy costs associated with the high process temperature, the need to separate and recycle a large amount of isobutylene, and the need to concentrate formaldehyde due to incomplete conversion.

Liquid-phase methods for producing isoprene are deprived of these disadvantages. Most of these methods involve two-stage synthesis of isoprene, in which the by-product of 4,4-dimethyldioxane-1,3 (DMD) is formed in the first stage of the process at a temperature of about 100 ° C and a pressure of 20 atm from isobutylene and formaldehyde in the presence of sulfuric or phosphoric acid. . In the second stage, DMD is decomposed in the gas phase on a heterogeneous phosphate catalyst at temperatures from 370 to 400 ° C. The disadvantages of these methods are two-stage, the use of soluble acid, the presence of which in the system leads to rapid corrosion, the formation of a large number of high boiling point by-products, and the rapid deactivation of the DMD decomposition catalyst.

Known methods for producing isoprene, aimed at creating a closed system of acid circulation (SU 460614, RU 2098398, JP 60-226834), to transfer the process of decomposition of DMD into the liquid phase (RU 2098398, RU 2085552, JP 60-224641, JP 60-226834, JP 58-116428), for the processing of high-boiling by-products (WFP) into isoprene (RU 2134679, RU 2135450, RU 2164909), to search for new additives used in the synthesis of isoprene (JP 60-224641, JP 58-116428), and the use of weaker acids as a catalyst (SU 508050, SU 889653, SU 1743136, SU 1743137).

A known method of one-stage production of isoprene, involving the use of metal chlorides as catalysts (US 3890404).

A one-step method is also known, which involves shifting the equilibrium due to the removal of isoprene from the reaction zone (US 4,511,751). All this leads to an increase in the selectivity of the process, a decrease in the energy intensity of the process and a decrease in the consumption of acids.

However, the known methods do not solve the problems associated with corrosion of equipment, the formation of waste during the neutralization of acids and the formation of high-boiling by-products in the synthesis of isoprene.

The closest in technical essence and the achieved result is a method for producing isoprene, comprising reacting formaldehyde with an isobutylene derivative in the presence of an ion-exchange resin as a catalyst (JP 59-025337, 1984).

The disadvantage of this method is the addition of a water-soluble acid catalyst and the implementation of the process in two temperature zones and, accordingly, the use of two reactors.

The present invention is the development of a liquid-phase method, devoid of the above-mentioned disadvantages and allowing the synthesis of isoprene in high yield in the liquid phase.

The problem is solved by the described method of liquid-phase production of isoprene by reacting formaldehyde with isobutylene or its derivatives in the presence of a solid-phase catalyst and subsequent isolation of the target product, characterized in that the catalyst is phosphates selected from phosphates of zirconium, niobium or tantalum, while the interaction is carried out at 100-200 ° C, a pressure of 7-20 atm and a molar ratio of isobutylene or isobutylene derivative to formaldehyde equal to (1-20) / 1.

Preferably, tert-butyl alcohol, methyl tert-butyl ether, ethyl tert-butyl ether or mixtures thereof are used as the isobutylene derivative.

Preferably, after the interaction of formaldehyde with isobutylene or its derivatives, the by-products formed are separated from the target product and recycled to the process head.

It is also possible, after the interaction of formaldehyde with isobutylene or its derivatives and separation of the resulting by-products, to carry out the decomposition of the latter on a solid-phase catalyst containing zirconium, niobium or tantalum phosphates.

The by-products of the interaction of formaldehyde with isobutylene or its derivatives are mainly 4,4-dimethyldioxane-1,3, methyldihydropyranes, 3-methylbutanediol-1,3 or a mixture of the above substances with isobutylene or its derivatives.

As a catalyst, zirconium, niobium or tantalum phosphates supported on an inorganic carrier can be used.

Preferably, the process is carried out under continuous flow conditions in a fixed bed reactor.

The ability to achieve the claimed technical result is due to the selection of the claimed catalysts, previously not used in such processes, and the selection of the conditions for the implementation of the method.

The proposed method in General is as follows. The catalyst is preliminarily prepared by heating it in a stream of inert gas (nitrogen, helium) at 150 ° C for 1 hour. Formalin with isobutylene or isobutylene derivatives (tert-butanol, methyl tert-butyl ether, ethyl tert-butyl ether) is fed to a flow-type reactor with a fixed catalyst bed. The pressure regulator at the outlet of the reactor sets the required pressure. At the outlet of the reactor, the products are condensed upon absorption by cold acetonitrile. The products are analyzed by gas chromatography. The amount of formaldehyde is determined by the sulfite method with titration with hydrochloric acid.

The following specific examples illustrate the implementation of the invention using various claimed catalysts under the stated conditions of interaction and demonstrate the achievement of a technical result. The results and parameters of the method are summarized in table.

Example 1

1 g of niobium phosphate (NbOPO ₄ ) is placed in a flow reactor, flushed with nitrogen at a temperature of 150 ° C for 1 hour, then formalin is fed at a rate of 0.43 g / h (formaldehyde content of 36%) and tertbutanol at a speed of 1.55 g / h at a ratio of 1: 4 and at a pressure of 15 atm. The reaction is carried out for 3 hours. The following main products were found at the reactor outlet: tertbutanol 0.236 g / h, isobutylene 0.77 g / h resulting from the dehydration of part of tertbutanol, isoprene 0.195 g / h, methyldihydropyran (MDHP) 0.055 g / h, 4.4-dimethyldioxane -1.3 (DMD) 0.008 g / h, CO 0.008 g / h. The results obtained correspond to the yield of isoprene on converted formaldehyde 55% at a formaldehyde conversion of 100%. In this case, the yield of isoprene to converted isobutylene derivatives (TBS and isobutylene) is 72%. The results of the experiment are presented in the table.

Example 2

The process is conducted as in example 1, the difference is that the measurement of the process parameters occurs 100 hours after the start of the reaction. The process indicators are shown in the table.

Example 3

The process is carried out as in example 1, the difference is that the reaction by-products (MDHP 0.055 g / h and DMD 0.008 g / h) are separated and recycled by adding 0.43 g / h formaldehyde and 1.55 g tertbutanol to the initial stream / h The reaction is carried out for 3 hours. At the reactor outlet, the following main products were found: tertbutanol 0.34 g / h, isobutylene 0.67 g / h, isoprene 0.24 g / h, MDHP 0.062 g / h, DMD 0.01 g / h. The results obtained correspond to the yield of isoprene on converted formaldehyde 68% at a formaldehyde conversion of 100%. In this case, the yield of isoprene to the converted derivatives of isobutylene (TBS and isobutylene) is 80%. These results show the possibility of recycling the reaction intermediates.

Example 4

The process is carried out as in example 1, the difference is that the reaction by-products (MDHP 0.55 g / h and DMD 0.08 g / h) are separated and 1.685 g / h are added to the tertbutanol stream. The reaction is carried out for 3 hours. The following main products were found at the outlet of the reactor: isobutylene 0.945 g / h, tertbutanol 0.27 g / h, isoprene 0.48 g / h, MDHP 0.11 g / h, DMD 0.016 g / h. The results obtained correspond to the yield of isoprene on the converted intermediates of 70% with the conversion of intermediates of 80%. The yield of isoprene to the converted derivatives of isobutylene (TBS and isobutylene) and the converted intermediates is 90%. These results show the possibility of decomposition of intermediates on the catalyst.

Example 5 (comparative).

The process is carried out as in example 1, the difference is that the ion exchange resin Amberlyst-15 (prototype JP 59-025337) is used as a catalyst. Process indicators are also presented in the table.

Example 6 (comparative).

The process is conducted as in example 4, the difference is that the measurement of the process parameters occurs 100 hours after the start of the reaction. Process indicators are presented in the table.

Analysis of the results shows the advantages of the proposed method for the production of isoprene (pr. 1-4) in comparison with the prototype pr. 5, 6). From the obtained results it follows that when using an ion exchange resin, a high yield of isoprene and the stability of the catalyst are not ensured.

Further, in the examples, the possibility of carrying out processes with all the catalysts indicated in the formula under different conditions of the process is shown.

Example 7

The process is carried out as in example 1, the difference is that tantalum phosphate (TaOPO ₄ ) is used as a catalyst.

Example 8

The process is carried out as in example 1, the difference is that zirconium phosphate supported on a carrier (silica gel) is used as a catalyst.

Example 9

Similar to example 1, the difference is that the process is carried out at 100 ° C.

Example 10. Similar to example 1, the difference is that the process is carried out at 200 ° C.

Example 11

Similar to example 1, the difference is that formalin is supplied at a rate of 0.43 g / h and 0.38 g / h of tertbutanol with a tertbutanol / formaldehyde ratio = 1.

Example 12

Similar to example 1, the difference is that formalin is supplied at a rate of 0.43 g / h and 7.7 g / h of tertbutanol with a tertbutanol / formaldehyde ratio = 20.

Example 13

Similar to example 1, the difference is that they supply formalin at a rate of 0.43 g / h and 1.15 g / h of isobutylene with an isobutylene / formaldehyde ratio = 4.

Example 14

Similar to example 1, the difference is that the process is carried out at a pressure of 7 atm.

Example 15

Similar to example 1, the difference is that the process is carried out at a pressure of 20 atm.

Example 16

Similar to example 1, the difference is that formalin is supplied at a rate of 0.11 g / h and 0.39 g / h of tertbutanol with a tertbutanol / formaldehyde ratio = 4.

Example 17

Similar to example 1, the difference is that formalin is supplied at a rate of 3.3 g / h and 11.7 g / h of tertbutanol with a tertbutanol / formaldehyde ratio = 4.

Examples 9-17 illustrate the possibility of implementing the method of producing isoprene in a wide range of variation of the interaction conditions.

Thus, the presented examples confirm the achievement of a technical result regarding the possibility of achieving a high yield and selectivity of isoprene formation under conditions of liquid-phase reaction in the absence of reagents and catalysts that cause equipment corrosion and a large number of interaction by-products.

Claims (7)

1. The method of liquid-phase production of isoprene by reacting formaldehyde with isobutylene or its derivatives in the presence of a solid phase catalyst and subsequent isolation of the target product, characterized in that the phosphate selected from phosphates of zirconium, niobium or tantalum is used as a catalyst, the reaction is carried out at 100- 200 ° C, a pressure of 7-20 atm and a molar ratio of isobutylene or isobutylene derivative to formaldehyde equal to (1-20) / 1. 2. The method according to claim 1, characterized in that as a derivative of isobutylene use tert-butyl alcohol, methyl tert-butyl ether, ethyl tert-butyl ether or mixtures thereof. 3. The method according to claim 1, characterized in that after the interaction of formaldehyde with isobutylene or its derivatives, the by-products formed are separated from the target product and recycled to the head of the process. 4. The method according to claim 1, characterized in that after the interaction of formaldehyde with isobutylene or its derivatives, the formed by-products are separated and decomposed on a solid-phase catalyst containing zirconium, niobium or tantalum phosphates. 5. The method according to any one of claims 3 or 4, characterized in that the by-products of the interaction of formaldehyde with isobutylene or its derivatives are 4,4-dimethyldioxane-1,3, methyldihydropyranes or a mixture of the above substances with isobutylene or its derivatives. 6. The method according to claim 1, characterized in that the phosphates of zirconium, niobium or tantalum are used supported on an inorganic carrier. 7. The method according to claim 1, characterized in that the process is carried out under continuous flow conditions in a reactor with a fixed catalyst bed.