RU2053215C1 - Method for production of pentaerytritol - Google Patents

Abstract

FIELD: organic chemistry. SUBSTANCE: pentaerytritol is dried at 45-55 C till moisture content and volatile content is 1.0-1.5 %. Then it is ground to particles having size 1-2 mm and is treated by heat. The latter process is carried out within 3-5 s with the help of heat carrier being preliminary heated to 160-180 C and having rate 20-30 m/s. Mass portion of moisture and volatile in desired product is 0.07-0.08. EFFECT: improves efficiency of method. 1 tbl

Description

 The invention relates to the technology of polyhydric alcohols, in particular pentaerythritol, used in paint and varnish and other industries.

 A known method of producing pentaerythritol by reacting formaldehyde with acetaldehyde in the presence of calcium hydroxide. The resulting reaction mass, which contains dissolved pentaerythritol and calcium formate, is treated with soda ash to precipitate a precipitate of calcium carbonate. The liquid phase is filtered, evaporated and pentaerythritol is crystallized by cooling the solution. The precipitate of pentaerythritol is filtered, washed from impurities of sodium formate, further recrystallized in hot water and dried [1] The pentaerythritol obtained in this way has large crystals, which facilitates the processes of filtering, washing and drying.

 The disadvantage of this method is its multi-stage and complexity associated with the need to use in the process of calcium hydroxide in the form of milk of lime, as well as the formation of a little-used by-product of calcium carbonate.

Closest to the proposed is a method for producing pentaerythritol, based on the interaction of acetaldehyde with formaldehyde taken in excess in the presence of sodium hydroxide. The resulting reaction mass, which contains dissolved pentaerythritol, sodium formate, unreacted formaldehyde residue, as well as some by-products, is first subjected to rectification in order to extract the unreacted formaldehyde residue, and then evaporated. Pentaerythritol is crystallized from the evaporated solution by cooling, which is filtered, washed from technological impurities, recrystallized in hot water and the wet product is dried. Drying is carried out in one stage using air heated to 140 ^about C. In the drying process, a small part of the volatile impurities is also removed from the material at the same time [2]
This method is quite simple and is not associated with the formation of underused calcium carbonate.

 The disadvantage of this method is the low efficiency of the drying and removal of volatile impurities. This is due to the fact that during the synthesis of pentaerythritol in the presence of sodium hydroxide, various volatile and non-volatile impurities are formed along with the main product. These impurities partially pass into the composition of the finished product, which causes strong clumping and a decrease in the efficiency of drying and removal of volatile impurities. An increase in the degree of drying and removal of volatile impurities can be achieved by increasing the duration of the process, however, this leads to a deterioration in the quality of the product in terms of color.

The proposed method of producing pentaerythritol, comprising reacting acetaldehyde with formaldehyde in the presence of sodium hydroxide, and evaporation of the rectification of the reaction mass, crystallization, filtration, washing and drying of pentaerythritol, characterized in that the drying process is carried out at 45-55 ^{° C} to a moisture content and volatiles 1 , 5-1,5% of lumps of dried product is isolated and after grinding to a particle size of 1-2 mm additional heat treatment is carried out for 3-5 with the coolant being heated to 160-180 ^{° C} and moving at speed of 20-30 m / s.

 The proposed method allows to intensify the processes of drying and removal of volatile impurities by reducing the lumpiness of pentaerythritol during drying and creating optimal conditions for the removal of volatile impurities. This is achieved by the fact that the drying of pentaerythritol and the removal of volatile impurities are carried out separately in two stages.

In the first step pentaerythritol dried by heating the material to 45-55 ^{° C} to a residual moisture content and volatile products 1.0-1.5%
In the second step of partially lumps the dried isolated pentaerythritol and after grinding to a particle size of 1-2 mm is conducted further for 3-5 momentary heat treatment with a gaseous heating medium heated to 160-180 ^{° C} and moving at a speed of 20-30 m / from.

 The inventive technological mode of the first stage of the process ensures the removal of the main amount of moisture with minimal clumping of material due to slight heating of the material.

Lowering the temperature in the first stage of less than 45 ^about does not provide an additional reduction in clumping, moreover, significantly prolongs the drying time. Increasing the temperature above 55 ^{° C} leads to intensive caking pentaerythritol. This is explained by an increase in the number and strength of phase contacts formed between individual particles during excessively intense evaporation of moisture.

 With an increase in the degree of drying with a corresponding decrease in residual moisture of less than 1.0%, the duration of the process is delayed and the strength of the lumps increases. An increase in the residual moisture of the material of more than 1.5% is also unacceptable, as it leads to clogging of the classification and grinding equipment.

 The inventive technological mode in the second stage ensures the maximum degree of removal of volatile impurities without compromising other indicators of product quality.

 Grinding particles to a particle size of more than 2 mm dramatically reduces the efficiency of the process of removing volatile impurities. Re-grinding with a decrease in particle size less than 1 mm is also impractical, since without providing an additional increase in the efficiency of removing impurities, it promotes strong dust formation and is associated with unjustified energy consumption for the operation of the grinder.

Reducing the coolant temperature below 160 ^{° C} does not provide a high degree of removal of volatile impurities, even when the processing time increase. Increasing the temperature above 180 ^{° C} does not further increase the efficiency of the process, but the final product deteriorates the quality of color indicator.

 With a decrease in the velocity of the gas coolant relative to the surface of the particles of the material less than 20 m / s, the duration of the process of heating the particles is delayed and the quality of the finished product in terms of color is deteriorated. An increase in speed above 30 m / s is also undesirable, since it does not provide an additional reduction in the duration of the heat treatment, causes increased dust content of the spent heat carrier, and makes the process more expensive.

 Reducing the duration of heat treatment less than 3 s reduces the desorption of volatile impurities, and delaying the process for more than 5 s does not give an additional effect, but leads to a deterioration in the color of the finished product.

 The proposed method can be implemented as follows.

The estimated amount of formaldehyde, water and sodium hydroxide is loaded into a reactor with a cooling jacket and stirrer. The mixture was cooled to 12-17 ^{° C} and it is gradually dosed into a calculated amount of acetaldehyde. Due to the heat effect of the reaction the reaction mixture temperature rises to 40-45 ^C. The reaction mixture was neutralized with formic acid to pH 5.5-6.5 and subjected to distillation, for example in the cap a column under overpressure of 2-2.5 kg / cm ² and a temperature of 125-130 ^about With in order to remove excess formaldehyde, and then evaporated under vacuum until a density of 1270-1300 kg / m ³ . The evaporated solution, which contains dissolved pentaerythritol, sodium formate, as well as technological impurities (dipentaerythritol, linear and cyclic formals, etc.), is cooled in crystallizers, which are vertical apparatuses equipped with frame mixers and cooling jackets. The resulting suspension is filtered, washed with water from impurities of sodium formate and recrystallized in hot water. The recrystallized precipitate was dried previously, for example in a drying drum with warm air at 45-55 ^{° C} to a residual moisture and volatile impurities 1.0-1.5% Next lumps formed during drying pentaerythritol separated at screening drum and ground in rotary grinder to size particles 1-2 mm. The shredded material together with a small crystal pentaerythritol subjected to a further short heat treatment during 3-5 with, for example, in an apparatus with a balanced-layer material transported in a stream of hot air heated to 160-180 ^{° C} and at a speed of 20-30 m / s . The finished product after heat treatment, containing not more than 0.07-0.08% moisture and volatile impurities, is fed into the bin of the finished product and then packaged in bags or containers.

PRI me R 1. In the reactor load 5915.7 kg of technical solution of formalin containing 37% formaldehyde, 2700 kg of an aqueous solution of sodium hydroxide containing 20% NaOH and 9914 kg of demineralized water. The resulting mixture was stirred vigorously and cooled ^to 15 ° C, then the reactor over 60 minutes gradually metered technical acetaldehyde in an amount of 540.4 kg. After completion of the reaction mixture (19070.1 kg) was acidified to a pH of 6 using formic acid (75.8 kg) and subjected to distillation under overpressure of 0.25 MPa and a temperature at the column top 130 ^C. in order to remove unreacted portions of formaldehyde.

A solution exiting the bottom of the column in an amount of 12152.4 kg and containing 1322.9 kg of pentaerythritol is mixed with technological solutions containing pentaerythritol and evaporated to a density of 1280 kg / m ³ . The evaporated solution in the amount of 4864.3 kg and containing 1655.9 kg of dissolved pentaerythritol is sent to crystallization of pentaerythritol in crystallizers with stirrers and cooling jackets. The resulting suspension (4864.3 kg) containing 1317.9 kg of pentaerythritol crystals was filtered, the precipitate (1635 kg) was washed with cold water taken in an amount of 500 kg and subjected to recrystallization in hot water (1635 kg), filtered and further washed with cold water (673.5 kg).

The washed precipitate (1132.9 kg) having a humidity of 12% was dried in a drying drum with hot air heated to 140 ° ^C. The dried product (1000 kg), having a temperature of 65 ^{° C,} separated from the formed clumps (200 kg) and packaged in bags or containers. Lumps of pentaerythritol, which are characterized by a high content of moisture and volatile impurities, are returned to recycling by dissolution and crystallization.

EXAMPLE EXAMPLE 2. Conditions similar to Example 1. The difference is that the washed precipitate of pentaerythritol (1132.9 kg) having a humidity of 12% is dried in a tumble dryer preheated air at a temperature of 45 ^{° C} the material to a residual moisture content and volatile impurities 1.5% Next, the dried material is separated from clumps (60 kg), which are crushed to a size of 2 mm and the whole material (1000 kg) was subjected to an additional heat treatment for 3 with the flow of hot coolant gas having a temperature ^of 180 C and a moving at a speed of 20 m / s. The finished product is sent to the hopper of the finished product, and from there it is packed in bags or containers.

 The conditions and results of the method with the other claimed parameters are presented in the table.

 From the analysis of experimental data it follows that the proposed method allows to reduce the duration of the drying and removal of volatile impurities by 1.7-1.9 times while reducing the mass fraction of moisture and volatile impurities in the finished product from 0.3 to 0.07-0, 08% These benefits allow you to increase the productivity of the main technological equipment, increase production and improve the quality of the finished product.

Claims (1)

METHOD FOR PRODUCING PENTAERITRITE, including the interaction of acetaldehyde with formaldehyde in the presence of sodium hydroxide, rectification and evaporation of the reaction mass, crystallization, filtration, washing and drying of pentaerythritol, characterized in that the drying process is carried out at 45 - 55 ^o C to the moisture and volatile products 1, 0 - 1.5%, lumps are isolated from the dried product and, after grinding to a particle size of 1 - 2 mm, additional heat treatment is carried out for 3 - 5 with a heat carrier heated to 160 - 180 ^o С and moving from soon 20 - 30 m / s.

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