RU2150462C1 - Methylal production process - Google Patents

Abstract

FIELD: industrial organic synthesis. SUBSTANCE: process consists in preliminary acetalization of formaldehyde with methanol in pre-reactor at 45-60 C in presence of 0.001-0.050% of 2-tert-butylphenol or of 2-tert-butyl-4-methylphenol on acid cationite to achieve equilibrium composition, after which pre- acetalized mixture is passed through reaction zone in presence of acid cationite at elevated temperature. EFFECT: increased productivity of process due to increased methylal pick-up from unit volume of catalyst and prolonged lifetime of catalyst. 2 dwg, 7 ex

Description

 The invention relates to the petrochemical industry, in particular to a method for producing methylal, which is used as a solvent, high-octane additive, and also a reagent in the synthesis of antioxidants.

 A known method of producing methylal by the interaction of paraform with methanol in the presence of mineral acid [Weigand-Hilgetag. Experimental methods in organic chemistry. - M.: Chemistry, 1968, p. 354]. The disadvantages of the method is the low yield of the target product - 80%, the formation of acidic effluents, corrosion of equipment.

 Using to protect the Rashig rings to eliminate the corrosive effect of the acid catalyst in the separation zone by applying a rubber coating on them economically increases the cost and technologically complicates the process [A. S. USSR 1442516, MKI C 41/58, publ. 12/07/88, Bull. 45].

 A known method of producing methylal by acetalization of aqueous mixtures of formaldehyde and methanol in the presence of mineral acid as a catalyst in a distillation column with a continuous output from its top of a methylal-methanol azeotrope [Pat. Germany 800399, MKI C 07 C 43-30].

 The disadvantages of the method are the emerging problem of corrosion of the equipment, the limitation of the method of highly concentrated solutions of formaldehyde, the continuous consumption of the catalyst.

 The method for producing methylal using iron chloride as a catalyst is free from the above disadvantages [Pat. VD Deutschland 3147320, MKI C 07 C 43/10, publ. 1.6.83]. However, the methylal obtained by the method contains up to 8 wt.% Methanol and small impurities of chlorine. The latter are excluded by replacing the catalyst with iron sulfate, but the allocation of methylal requires a two-stage distillation, with reduced pressure in the first stage and high - in the second.

 A known method of producing acetals by the interaction of stoichiometric amounts of aldehydes and alcohols in the presence of cation exchangers [Industrial Engineering Chemistry, 38, s.1230]. However, in this batch process only anhydrous formaldehyde and methanol are used, the water formed requires continuous removal from the reaction zone. In addition, the method is applicable only to acetals, the boiling point of which and the initial components of their production is higher than the boiling point of the reaction water. With a continuous method of acetalization of anhydrous aldehyde with alcohol on cation exchangers, only a state of reaction equilibrium is achieved with incomplete conversion of the starting aldehyde [Pat. USA 2840615, 2566559].

 The closest technical solution to the claimed is a method for producing methylal by acetalization of formaldehyde with a stoichiometric amount of methanol in an aqueous medium using a strongly acidic cation exchange resin as a catalyst [Pat. US 3317613, IPC C 07 C 43/30, claimed 02/12/1963, issue 05/02/1967].

The method uses 10-40% aqueous formaldehyde solutions and aqueous methanol solutions, any acidic cation exchange resin is used as a catalyst. The method is carried out in a column type apparatus at a temperature of 90 ^° C. in the lower part and 65 ^° C. in the upper part of the reaction zone, wherein an aqueous mixture of formaldehyde and methanol is supplied over the catalyst in countercurrent to the formed methylal. In order to increase productivity, the method provides for pre-acetalization of an aqueous solution of formaldehyde with methanol at room temperature. However, experience shows that under these conditions (18-25 ^o C) the conversion of formaldehyde to methylal is not more than 1%, i.e. practically there can be no talk of preliminary acetalization, which contributes to the unloading of the reaction zone of the column apparatus. The methylal formed in the reaction zone of the column on cation exchange resin rises to the top of the column, filled with Raschig rings.

Part of the liquid from the bottom of the reaction zone is fed into the lower third of the methylal separation zone. The resulting water is continuously discharged from the bottom of the apparatus - the sludge zone, in which the temperature is maintained at about 100 ^o C. Wastewater does not contain formaldehyde and methanol and does not need to be neutralized. The method provides good results at low and high concentrations of aqueous solutions of formaldehyde and methanol, the final product contains 99.4 wt.% Methylal and 0.6 wt. % water. According to the patent, the spent catalyst cannot be reused.

 The disadvantages of the method is the low productivity of the process, the removal of methylal per unit volume of the catalyst is 0.07-0.52 g / ml cat. in hour. In practice, it was found that after 400 hours of catalyst operation, methylal production is reduced by 20-30%, and after 450 hours - 70-80%. The catalyst needs either replacement or regeneration, which at its cost economically increases the cost of the process in the first case and technologically complicates it in the second.

The aim of the invention is to increase the productivity of the process by increasing the removal of methylal per unit volume of the catalyst and extending the life of the catalyst by increasing its activity. This goal is achieved by pre-acetalization of an aqueous mixture of stoichiometric amounts of formaldehyde and methanol in a prereactor at a temperature of 45-60 ^o C for 0.5 to 1.0 hours in the presence of 0.001 - 0.050 wt.% 2-tert-butylphenol or 2-tert-butyl-4-methylphenol on acidic cation exchange resin until an equilibrium composition is reached. The conversion of formaldehyde to methylal is 68-80%, and then the equilibrium reaction mixture is fed into the reaction-distillation column to replenish the reagents.

The reaction-distillation column has three zones: the middle reaction part is filled with a catalyst - acid cation exchanger, the upper and lower zones of the column are filled with a nozzle - Rashig rings. The equilibrium mixture from the prereactor is introduced into the upper catalyst layer countercurrent to the vapors of the resulting methylal. The temperature in the upper part of the reaction zone is 65 ^o C, and the lower one is 90 ^o C. To destroy the azeotrope of methylal with methanol, part of the water is supplied from the cube of the column to the upper zone of methylal, and the rest is continuously withdrawn. The temperature in the bottom of the column is maintained at about 100 ^° C. The formaldehyde conversion is complete, the final product does not contain methanol.

 It was unexpectedly found that the introduction of such small amounts of alkyl phenols into the reaction mixture is sufficient to increase the activity of cation exchanger and increase the removal of methylal per unit of cation exchanger. Apparently, this is explained by the fact that with increasing acid strength in the surface catalyst layer, because alkyl phenolic compounds have acidic properties.

 With a decrease in the concentration of alkyl phenols in the reaction mixture below 0.001 wt.%, The removal of methylal from a unit of cation exchanger decreases.

 When the concentration of alkyl phenols in the reaction mixture is above 0.05 wt.%, There is no further increase in methylal removal from a unit of cation exchanger.

In practice, the process is as follows. A mixture of an aqueous solution of formaldehyde and methanol containing 0.001-0.050 wt.% 2-tert-butyl-4-methylphenol or 2-tert-butylphenol is fed in a stoichiometric ratio to the prereactor (1) (see drawing) filled with acidic cation exchanger. In the prereactor at a temperature of 45-60 ^° C, acetalization proceeds to equilibrium.

 The equilibrium mixture enters the reaction-distillation column (2) on the upper catalyst layer.

 As the catalyst, macroporous cation exchanger KU-23 or KSM-2 with a SOE of at least 1.1 mEq N / 1 ml of catalyst is used.

The temperature in the lower part of the reaction zone is 95 ^o C, in the upper - 65 ^o C. In the reaction part of the column, formaldehyde and methanol are exhausted.

The resulting methylal in the form of vapors rises to the top of the column — a precipitation zone filled with Raschig rings. Water enters the cube of the column (2), where the temperature is maintained at about 100 ^° C. A part of this water is sent to the methylal separation zone, feeding slightly above the input of the reaction mixture. The mass ratio of methylal - methanol azeatrop: water 10: 1-2.

To implement the method, the starting reagents must meet the following requirements:
- methanol - GOST 2222 - 78;
- formalin - GOST 1625 - 89;
- cation exchange resin - KU-23 - GOST 20298 - 74: cation exchange resin KSM - 2-TU 95.981-91
-2-tert-butyl-4-methylphenol is obtained by dealkylation of 2,6-di-tert-butyl-4-methylphenol (ionol) at t 150-160 ^o C in the presence of 0.2 wt.% P-toluenesulfonic acid. After neutralization with alkali from the reaction mass by distillation, 2-tert-butyl-4-methylphenol with a concentration of 98 wt.% And _mp 54 ^° C is isolated.

 -2-tert-butylphenol-STP 38.2112 - 94 g.

 The essence of the proposed method is confirmed in the examples below.

 Example 1 (prototype).

 The preparation of methylal was carried out according to the scheme, including the prereactor (1) and the reaction-distillation apparatus (2) (see drawing).

 The prereactor is a hollow apparatus with a heating jacket with a height of 50 cm and an inner diameter of 5.0 cm. 700 ml of KU-23 grade cation exchange resin are placed in the prereactor in hydrogen form. The static exchange capacity (SOE) of cation exchanger, characterizing the activity of cation exchanger, is 1.15 mEq. N / ml

The reaction-distillation apparatus (2) has a height of 600 cm and a diameter of 5.0 cm. The apparatus is divided into zones: the middle part — the reaction zone is filled with the same cation exchanger — KU-23 — in an amount of 2000 ml. The upper part (separation zone) is filled with Rashig rings with a diameter of 4 mm, in the lower part (sludge zone) there is a heater that provides heating of the cube to 100 ^o C.

1200 g / h of mixture (1), consisting of 21 wt.% Formaldehyde (8.4 mol), 44.8 wt.% Methanol (16.8 mol), are fed to the unheated prereactor (t = 21.5 ^° C.) and 34.2 wt.% Water.

Coming out of the prereactor mixture (II) of the composition: 20.45 wt.% Formaldehyde, 43.69 wt.% Methanol, 1.4 wt.% Methylal and 34.53 wt.% Water are fed at a rate of 20 g / min into the reaction distillation apparatus (2) above the catalyst bed. The temperature in the lower part of the reaction zone is 90 ^o C, in the upper - 65 ^o C.

 From the cube of the reaction column (2), water (III) is continuously withdrawn that does not contain organic impurities, 60 grams of which is fed to the top in the lower third of the separation zone (above the feed of the reaction mixture) to destroy the methylal: aethanol azeotrope. From the top of the apparatus (2) after cooling in the apparatus (3) and condensation in the condenser (4), 642.2 g of a product containing 99.4 wt.% Methylal and 0.6 wt.% Water are removed. The yield of pure methylal was 638.4 g.

 The removal of methylal per unit volume of cation exchanger is 0.236 g / ml cat. hour.

 After 400 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger decreases to 0.13 g / ml cat.h.

 Example 2

 The process is carried out according to the scheme described in example 1.

12000 g / h of mixture (1), consisting of 21 wt.% Formaldehyde (84 mol), 44.8 wt.% Methanol (168 mol) containing 1.2 g (0.01 wt. % per reaction mass) of 2-tert-butyl-4-methylphenol, and 34.2 wt.% water, and heated to a temperature of 55 ^° C. The equilibrium mixture (II) leaving the prereactor of the composition: 5.25 wt.% (21 mol) of formaldehyde, 11.20 wt.% methanol (42 mol), 39.9 wt.% methylal (63 mol) and 43.65 wt.% water are fed at a rate of 200 g / min to the reaction-distillation apparatus (2) above the catalyst bed to replenish the reagents.

The temperature in the lower part of the reaction zone is 90 ^o C, in the upper - 65 ^o C.

 From the bottom of the reaction column (2), 1277 g of water / hour (III) is fed up to the methylal separation zone. Water is introduced slightly higher than the place of introduction of the reaction mixture from the prereactor (1) - in the middle of the methylal zone.

 From the top of the column (2) after cooling in the apparatus (3) and condensation in the condenser (4), 6422.5 g of product containing 99.4 wt. % methylal and 0.6 wt.% water. Water is continuously discharged from the bottom of the column (2). Water does not contain impurities and does not need to be purified.

 The yield of pure methylal is 6383.9 g.

 The removal of methylal per unit volume of cation exchanger is 2.36 g / ml cat.h.

 After 4200 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger is 2.0 g / ml cat.h.

 Example 3

 The process is carried out according to the scheme described in example 1.

 In the prereactor (1), 700 ml of KSM-2 brand cation exchanger with 1.25 mEq of cation exchanger are loaded. N / ml, and in the rectifier-rectifier (2) - 2000 ml of the same catalyst.

12000 g / h of mixture (1), consisting of 10.4 wt.% (41.6 mol) of formaldehyde, 22.19 wt.% (83.2 mol) of methanol containing 6.0 g, are fed to the prereactor (1) (0.05 wt.% Per reaction mass) of 2-tert-butyl-4-methylphenol, and 67.4 wt.% Water and heated to a temperature of 60 ^o C.

Coming out of the prereactor equilibrium mixture (II) of the composition: 2.07 wt.% (8.28 mol) of formaldehyde, 4.42 wt. % (16.56 mol) of methanol, 21.1 wt.% (33.32 mol) of methylal and 72.43 wt.% Of water are fed at a rate of 200 g / min into the reaction-distillation apparatus (2) above the catalyst bed for exhaustion of reagents. The temperature in the lower part of the reaction zone is 90 ^o C, in the upper - 65 ^o C.

 From the bottom of the reaction column (2), 500 g of water / hour (III) is supplied to destroy the azeotrope. From the top of the apparatus (2), after cooling in the apparatus (3) and condensation in the condenser (4), 3180.7 g of a product containing 99.4 wt.% Methylal and 0.6 wt.% Water is removed within an hour. The yield of pure methyl 3161.6 g.

 Water from the cube of the column (2) is discharged into the ChZK. Water does not contain organic impurities and does not require additional purification.

 The removal of methylal per unit volume of cation exchanger is 1.17 g / ml cat. hour.

 After 4200 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger is 0.84 g / ml cat.h.

 Example 4

 In the prereactor (1) with a height of 100 cm and a diameter of 5 cm, 1300 ml of KSM-2 brand cation exchanger with a SOE of 1.25 mEq cation exchanger are loaded. N / ml, and in the rectification reactor (2) - 1400 ml of the same cation exchange resin.

12000 g / h of mixture (1), consisting of 30.8 wt.% (123.2 mol) of formaldehyde, 65.70 wt.% (246.4 mol) of methanol containing 6.0 g, are fed to the prereactor (1) (0.05 wt.% From the reaction mass) of 2-tert-butyl-4-methylphenol, and 3.5 wt.% Water and heated to a temperature of 45 ^o C.

 Coming out of the prereactor equilibrium mixture (II) of the composition: 9.64 wt.% (38.56 mol) of formaldehyde, 20.57 wt.% (77.17 mol) of methanol, 53.6 wt.% (84.64 mol) methylal and 16.19 wt.% water, is fed at a rate of 200 g / min into the reaction-distillation apparatus (2), operating in the mode of example 1.

 From the top of the apparatus (2), after cooling in the apparatus (3) and condensation in the condenser (4), 9419.7 g of a product containing 99.4 wt.% Methylal and 0.6 wt.% Water is removed within an hour. The yield of pure methyl 9363.2 g.

 Water from the cube of the column (2) is discharged into the ChZK. Water does not contain organic impurities and does not require additional purification.

 The removal of methylal per unit volume of cation exchanger is 3.47 g / ml cat.h.

 After 4200 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger is 2.17 g / ml cat.h.

 Example 5

 The process is carried out according to the scheme described in example 1.

12000 g / h of mixture (1), consisting of 21 wt.% Formaldehyde (84 mol), 44.8 wt.% Methanol (168 mol) containing 1.2 g (0.01 wt. % of the reaction mass) 2 - tert-butyl-phenol, and 34.2 wt.% water. The temperature in the prereactor is 55 ^o C.

The equilibrium mixture (II) emerging from the prereactor composition: 5.25 wt.% (21 mol) of formaldehyde, 11.20 wt.% Methanol (42 mol), 39.9 wt.% Methylal (63 mol) and 43.65 wt. .% water is fed at a rate of 200 g / min into the reaction-distillation apparatus (2) above the catalyst bed to replenish the reagents. The temperature in the lower part of the reaction zone is 90 ^o C, in the upper - 65 ^o C.

 From the bottom of the reaction column (2), 1277 g of water / hour (III) is fed up to the methylal separation zone. Water is introduced slightly higher than the place of introduction of the reaction mixture from the prereactor (1) - in the middle of the methylal zone.

 From the top of the apparatus (2) after cooling in the apparatus (3) and condensation in the condenser (4), 6422.5 g of a product containing 99.4 wt.% Methylal and 0.6 wt.% Water is removed within an hour. The yield of pure methylal is 6383.9 g.

 The removal of methylal per unit volume of cation exchanger is 2.36 g / ml cat.h.

 After 4200 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger is 2.0 g / ml cat. hour.

 Example 6

 The process is carried out according to the scheme described in example 1.

 700 ml of KSM-2 brand cation exchanger with a SOE of 1.25 mEq are loaded into the prereactor (1). N / ml, and in the rectifier-rectifier (2) - 2000 ml of the same catalyst.

12000 g / h of mixture (1), consisting of 10.4 wt.% (41.6 mol) of formaldehyde, 22.19 wt.% (83.2 mol) of methanol containing 6.0 g, are fed to the prereactor (1) (0.05 wt.% From the reaction mass) of 2-tert-butylphenol and 67.4 wt.% Water. The temperature in the pre-reactor is 60 ^o C.

Coming out of the prereactor equilibrium mixture (II) of the composition: 2.07 wt.% (8.28 mol) of formaldehyde, 4.42 wt. % (16.56 mol) of methanol 21.1 wt.% (33.32 mol) of methylal and 72.43 wt.% Of water are fed at a rate of 200 g / min into the reaction-distillation apparatus (2) above the catalyst bed for exhaustion reagents. The temperature in the lower part of the reaction zone is 90 ^o C, in the upper - 65 ^o C.

 From the bottom of the reaction column (2), 500 g of water / hour (III) is supplied to destroy the azeotrope. From the top of the apparatus (2), after cooling in the apparatus (3) and condensation in the condenser (4), 3180.7 g of a product containing 99.4 wt.% Methylal and 0.6 wt.% Water is removed within an hour. The yield of pure methyl 3161.6 g.

 Water from the cube of the column (2) is discharged into the ChZK. Water does not contain organic impurities and does not require additional purification.

 The removal of methylal per unit volume of cation exchanger is 1.17 g / ml cat.h.

 After 4200 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger is 0.84 g / ml cat.h.

 Example 7

 1300 ml of KSM-2 brand cation exchange resin with a SOE of 1.25 mEq are loaded into the prereactor (1) with a height of 100 cm and a diameter of 5 cm. N / ml, and in the rectification reactor (2) - 1400 ml of the same cation exchange resin.

 In the prereactor (1) serves 12000 g / hour of the mixture (1), consisting of 30.8 wt.% (123.2 mol) of formaldehyde, 65.70 wt.% (246.4 mol) of methanol containing 6.0 g (0.05 wt.% From the reaction mass) of 2-tert-butylphenol, and 3.5 wt.% Water.

The temperature in the pre-reactor is 45 ^o C.

 Coming out of the prereactor equilibrium mixture (II) of the composition: 9.64 wt.% (38.56 mol) of formaldehyde, 20.57 wt.% (77.17 mol) of methanol, 53.6 wt.% (84.64 mol) methylal and 16.19 wt.% water, is fed at a speed of 200 g / min into the reaction-distillation apparatus (2), operating in the mode of example 1.

 From the top of the apparatus (2), after cooling in the apparatus (3) and condensation in the condenser (4), 9419.7 g of a product containing 99.4 wt.% Methylal and 0.6 wt.% Water is removed within an hour. The yield of pure methyl 9363.2 g.

 Water from the cube of the column (2) is discharged into the ChZK. Water does not contain organic impurities and does not require additional purification.

 The removal of methylal per unit volume of cation exchanger is 3.47 g / ml cat.h.

 After 4200 hours of catalyst operation, the removal of methylal per unit volume of cation exchanger is 2.17 g / ml cat. hour.

Lowering the temperature of pre-acetalization below the lower limit of 45 ^o C leads to a decrease in the removal of methylal per unit of cation exchanger, an increase in the temperature of pre-acetalization above 60 ^o C is not economically feasible, since the equilibrium composition of the mixture remains practically unchanged.

Analysis of the results of the practical implementation of the process of producing methylal by acetalization of formaldehyde with methanol in an aqueous medium according to the known and claimed methods shows that the preliminary acetalization at a temperature of 45-60 ^o C for 0.5 to 1.0 hours. in the presence of 0.001-0.050 wt.% 2-tert-butylphenol or 2-tert-butyl-4-methylphenol in the present method allows to increase the productivity of the process by 5-10 times, removal of methylal per unit volume of cation exchanger from 0.24 to 0.84 - 3.47 g / ml cat.hour and extend the life of the catalyst up to 4000 hours compared with 400 hours in the known method.

Claims (1)

A method for producing methylal by acetalization of formaldehyde with a stoichiometric amount of methanol, including pre-acetalization of formaldehyde and methanol in an aqueous medium in a pre-reaction zone on acid cation exchange resin and subsequent passage of the pre-acetalized mixture through the reaction zone in the presence of acid cation exchange resin while continuously removing methyl vapors from the top at an elevated temperature counter-flowing to and the resulting water from the bottom of the reaction column, characterized in that pre-acetalization ormaldegida methanol is carried out at a temperature of 45 - 60 ^o C in the presence of 0.001 - 0.050 wt% 2-tert-butylphenol or 2-tert-butyl-4-methylphenol..