RU2811258C1 - Method of producing 4,4-dimethyl-1,3-dioxane - Google Patents

Abstract

FIELD: organic and petrochemical synthesis.

SUBSTANCE: invention relates to the technology of a method of producing 4,4-dimethyl-1,3-dioxane in a flow mode. The method involves the condensation of tert-butanol with formaldehyde in an aqueous solution having a neutral environment in the presence of H-forms of synthetic zeolites as a catalyst and subsequent isolation of the target product from the reaction mass.

EFFECT: increase in the environmental friendliness of the technological process by eliminating the stage of processing the reaction mixture with an alkali solution while maintaining high selectivity.

1 cl, 1 tbl, 3 ex

Description

The invention relates to the field of basic organic and petrochemical synthesis, namely to the technology for producing 4,4-dimethyl-1,3-dioxane from tert-butanol and formaldehyde.

One of the most common industrial methods for producing isoprene is the “dioxane” method through the intermediate synthesis of 4,4-dimethyl-1,3-dioxane (DMD). DMD is obtained by liquid-phase condensation of isobutylene contained in C4 fractions or tert-butanol with formaldehyde used in the form of a 20-40% aqueous solution in the presence of sulfuric acid as a catalyst at a temperature of 85-95 ° C and a pressure of 1.8-2.0 MPa, followed by separation of DMD from the reaction mass [Ogorodnikov S.K., Idlis G.S. Isoprene production. L.: Chemistry, 1973, pp. 48-58]. The fundamental disadvantage of this method is the low selectivity of the process, as well as the presence of wastewater contaminated with salts and high-boiling by-products (HBP). The yield of AFFF is 440-460 kg per 1 ton of isoprene, more than 90% of which is AFFF from the stage of synthesis of 4,4-dimethyl-1,3-dioxane.

There is a known method for producing DMD from isobutylene and formaldehyde at a temperature of 100-110°C in the presence of sulfuric acid. The disadvantage of this method is the high corrosiveness of the reaction medium and the need for additional treatment of the oil layer with an alkali solution [USSR Copyright Certificate No. 361174, IPC C07D 319/06, publ. 12/07/1972].

There are known methods for producing DMD in an aqueous medium from isobutylene and formaldehyde using carboxylic acid as a catalyst [French Patent No. 2490642, IPC C07D 319/06, publ. 03/26/1982], salts of polysulfonic acid and metal of group I or II [French Patent No. 2490643, C07D 319/06, publ. 03.26.1982], oxalic acid [USSR Author's Certificate No. 991715, IPC C07D 319/06, publ. 12/27/1999; RF Patent No. 2255936, IPC C07D 319/06, publ. 07/10/2005].

There is a known method for producing DMD from formaldehyde and isobutylene at a weight ratio of 1.1-1.2 in an aqueous solution at 90-110°C and a pressure of 17-25 atm in the presence of oxalic acid. To increase selectivity for DMD by reducing the formation of by-products and losses of isobutylene, 3-6% of trimethylcarbinol (TMC) calculated on DMD and 5-20% of DMD from the amount received are returned to the reaction zone. According to the authors, the return of TMC to the reaction zone makes it possible to reduce the formation of TMC esters with VPP components and at the same time slow down the DMD hydrolysis reaction with the formation of VPP [RF Patent No. 2062270, IPC C07D 319/06, C07C 31/12, publ. 06/20/1996].

There is a known method for producing DMD by condensation of formaldehyde in the form of an aqueous solution with isobutylene in the form of an isobutane-isobutylene fraction in the presence of an acid catalyst at elevated temperature and pressure. Condensation is carried out by feeding the reagents together from bottom to top into a reactor consisting of separate, located one above the other, three sections connected in series, with a temperature decrease of 1-10 ° C in the second and third sections [RF Patent No. 2458923, IPC C07D 319/ 06, publ. 20.03.12].

There is a known method for producing DMD by condensation of isobutylene-containing fraction C 4, or substances that are their sources with an aqueous solution of formaldehyde in the presence of phosphoric acid, taken as an acid catalyst, at elevated temperature and pressure and subsequent isolation of 4,4-dimethyl-1,3 -dioxane from the reaction mass, while condensation is carried out in the presence of surfactants [RF Patent No. 2330848, IPC C07D 319/06, publ. 08/10/2008]. The disadvantages of the known method are the insufficiently high selectivity for the target DMD due to the formation of runway products, including hydrogenated pyrans, as well as the need for disposal of waste surfactants.

The main disadvantage of the listed methods for producing 4,4-dimethyl-1,3-dioxane is the high corrosiveness of the reaction medium and the need for additional treatment of the oil layer with an alkali solution to remove acid residues in a formaldehyde solution.

The technical problem of the present invention is to develop a method for producing 4,4-dimethyl-1,3-dioxane in a neutral environment.

The technical result of the proposed invention is to increase the environmental friendliness of the technological process by eliminating the stage of processing the reaction mixture with an alkali solution while maintaining high selectivity.

This problem is solved and the technical result is achieved by a method for producing 4,4-dimethyl-1,3-dioxane in a flow mode, including the condensation of tert-butanol with formaldehyde in an aqueous solution having a neutral environment, in the presence of H-forms of synthetic zeolites as a catalyst and subsequent isolation of 4,4-dimethyl-1,3-dioxane from the reaction mass.

The process under consideration is one of the acid-catalyzed heterogeneous liquid-phase reactions. The use of mineral and organic Bronsted acids as a catalyst leads to corrosion and rapid wear of equipment due to contact of the acidic reaction mixture with equipment elements. To solve this problem, the use of H-forms of synthetic zeolites is proposed as an alternative to Brønsted acids.

The synthesis of DMD is carried out as follows. HZSM-5 zeolite is placed in a flow-type reactor. The reactor is brought to a set temperature in the range of 150-155°C and a pressure of nitrogen gas is created equal to 10 atm. A solution of formalin and tert-butanol with a molar ratio of formaldehyde/tert-butanol equal to 2.0:1.0 is fed by a piston pump into the reactor, the products and unreacted reagents are collected in the separator. At the end of the experiment, the reaction mass is unloaded from the separator, and the DMD is isolated by extraction. Then the DMD content is determined chromatographically using the internal standard method. The selectivity of the process was determined by the DMD content in the resulting reaction mixture.

The implementation of the proposed method for obtaining DMD is illustrated by the examples below.

Example 1 (control, for comparison)

25 ml of glass beads with a diameter d = 3 mm are placed in the reactor. Formalin solution with a formaldehyde concentration of 23 wt. % 4.14 g (0.138 mol), 29% 5.18 g (0.07 mol) tert-butanol and 5% phosphoric acid are passed through the reactor. The formaldehyde/tert-butanol molar ratio is 2:1. The reactor is brought to a preset temperature in the range of 150-155°C and a pressure of 10 atm is created with nitrogen gas. Next, the reaction mixture is fed into the reactor using a piston pump with OSPS 1.44 h ^-1 for 1 hour. The reaction products and unreacted reagents are collected in a separator. At the end of the experiment, the reaction mass is unloaded from the separator, and the DMD is isolated by extraction. The selectivity of the process was determined by the DMD content in the resulting reaction mixture.

The selectivity of DMD formation is 67%.

Example 2

The process is carried out similarly to example 1, but with the difference that instead of glass beads, synthetic zeolite brand HZSM-5 was used as a (co)catalyst. The selectivity of DMD formation is 68%.

Example 3

The process is carried out similarly to example 1, but with the difference that instead of glass beads, synthetic zeolite of the HMOR brand was used as a (co)catalyst. The selectivity of DMD formation is 74%.

Table 1. Dependence of the selectivity of DMD formation on the material

Experience no. Porous material Selectivity of DMD formation, % mass 1 None (Glass beads) 67 2 Zeolite grade HZSM-5 68 3 HMOR brand zeolite 74

As can be seen from the examples given (Table 1), the proposed invention allows the process of DMD formation to be carried out with a selectivity in the range of 68-74% in a neutral environment.

Thus, the proposed invention makes it possible to increase the environmental friendliness of the technological process by eliminating the stage of processing the reaction mixture with an alkali solution while maintaining high selectivity.

Claims (1)

A method for producing 4,4-dimethyl-1,3-dioxane in a flow mode, including the condensation of tert-butanol with formaldehyde in an aqueous solution having a neutral environment in the presence of H-forms of synthetic zeolites as a catalyst and the subsequent isolation of 4,4-dimethyl -1,3-dioxane from the reaction mass.