RU2208009C1 - Method for preparing pentaerythritol with content of basic substance above 98 mass % and pentaerythritol enriched with dipentaerythritol in amount 5-20 mass % - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: invention relates to the improved method for preparing pentaerythritol with the content of basic substance above 98 wt. -% and pentaerythritol enriched with dipentaerythritol in the amount 5-20 wt.-% used in paint and varnish and other branches of industry. Method involves condensation of acetaldehyde with formaldehyde in an aqueous alkaline medium, the following neutralizations of reaction mixture, desorption of formaldehyde excess, evaporation, crystallization under vacuum at 45-55 C and density of suspension ρ₅₀ = 1.30-1.35 g/cm³, filtration, washing out the prepared technical pentaerythritol, its the following recrystallization in hot water at 45-55 C and drying resulting to isolation of pentaerythritol with content of basic substance above 98 wt.-%. Then technical pentaerythritol suspension filtrate and filtrate from the stage of recrystallization are combined, evaporated, subjected for crystallization under vacuum at 38-45 C, formed suspension if filtered off, precipitate is washed out, recrystallized again in hot water, precipitate is filtered at 45-55 C and dried to yield pentaerythritol enriched with dipentaerythritol in the amount 5-20 wt.-%. As a rule, the precipitate obtained after stage of crystallization under vacuum at 38-45 C and filtration is carried out with demineralized water and/or filtrate enriched with pentaerythritol taken from the recrystallization stage. Usually, at stages for preparing pentaerythritol with the content of basic substance above 98 wt.-% the latter is isolated in the amount 55-74 wt.-%. Method ensures to improve quality the prepared pentaerythritol, to obtain valuable product additionally, to enhance the total degree of isolation of pentaerythritol and to reduce consumption norms by the main raw species. EFFECT: improved preparing method. 3 cl

Description

The invention relates to the technology of organic synthesis, in particular pentaerythritol, used in paint and varnish and other industries
A known method of producing pentaerythritol by reacting acetaldehyde with formaldehyde in the presence of calcium hydroxide with further processing of the reaction solution with sulfuric acid in order to eliminate excess alkalinity of the medium and the binding of calcium ions. The resulting fine precipitate of calcium sulfate in the form of gypsum is separated by filtration as a by-product. The filtered reaction solution containing pentaerythritol, formic acid and process impurities is concentrated by evaporation and cooled to crystallize pentaerythritol. The resulting pentaerythritol precipitate is filtered, washed with water, recrystallized in hot water and dried [A.S. USSR 585149, 1974].

 The disadvantage of this method is the difficulty of high-quality separation of gypsum from the reaction solution, which complicates the evaporation process and significantly reduces the quality of the finished product.

There is also a method of producing pentaerythritol, based on the interaction of acetaldehyde with formaldehyde taken in excess in the presence of sodium hydroxide. The resulting reaction solution, containing pentaerythritol, sodium formate, formaldehyde and a small amount of technological impurities, is treated with formic acid to eliminate the alkalinity of the medium and subjected to rectification to remove excess formaldehyde. After crystallization, the solution is evaporated and pentaerythritol is crystallized by cooling the evaporated mass from an initial temperature of 100-105 ^o C to a final temperature of 20-25 ^o C. After crystallization, the suspension is filtered, the precipitate is washed from impurities of sodium formate, recrystallized in hot water and dried [US Patent 2951095, 1960].

 The disadvantage of this method is the low efficiency of the processes of cooling the evaporated reaction mass and crystallization of pentaerythritol. This is due to the fact that, as a result of evaporation, the total concentration of dissolved substances, including sodium formate, increases several times. When cooling such a highly concentrated mass, its viscosity sharply increases, which impairs the efficiency of the processes of mixing, cooling and crystallization of pentaerythritol.

In addition, a known method for producing pentaerythritol, including the interaction of acetaldehyde with formaldehyde in the presence of sodium hydroxide, desorption and evaporation of the reaction mass, crystallization during cooling, filtering and drying the finished product, while crystallization of the reaction mass is subjected to pulsation mixing with an amplitude of 0.2- 0.5 m and a frequency of 10-40 vibrations per minute, and cooling is carried out stepwise with a temperature difference of 2-4 ^o C between adjacent steps, and part of the reaction mass in the amount of 10- 20% of its total amount is returned from each subsequent cooling stage to the previous one [RU 2110508, 05/10/98].

 The disadvantage of this method (prototype) is the reduction of the degree of allocation of pentaerythritol (increase in expenditure rates) to ensure the quality of the commercial product by the content of the main substance monopentaerythritol (MPE) of at least 98 wt.%.

 The technical result achieved by the present invention is the possibility of obtaining pentaerythritol (PE) with a content of the main substance monopentaerythritol (MPE) of more than 98% and PE enriched with dipentaerythritol (DPE) in an amount of 5-20 wt.%, Used for the production of alkyd varnishes of high viscosity, increasing the degree of allocation of pentaerythritol and, as a result, a decrease in expenditure rates for the main types of raw materials.

The technical result is achieved by the method of producing pentaerythritol with a basic substance content of more than 98 wt.% And pentaerythritol enriched with dipentaerythritol in an amount of 5-20 wt.%, Which consists in the condensation of acetaldehyde with formaldehyde in an aqueous alkaline medium, followed by neutralization of the reaction mixture, desorption of excess formaldehyde, evaporation, vacuum crystallization at 45-55 ^o C and a suspension density of ρ ₅₀ = 1.30-1.35 g / cm ³ , filtering, washing the obtained technical pentaerythritol, distant by recrystallization in hot water, filtration at 45-55 ^o C and drying to isolate pentaerythritol with a basic substance content of more than 98 wt.%, the filtrate of a suspension of industrial pentaerythritol and the filtrate from the recrystallization step are then combined, evaporated, vacuum-crystallized at 38- 45 ^o C, filter the resulting suspension, the precipitate is washed, recrystallized, filter the precipitate at 45-55 ^o C and dried to obtain pentaerythritol enriched with dipentaerythritol in the amount of 5-20 wt.%.

Washing the precipitate obtained after the stage of vacuum crystallization at 38-45 ^o C and filtering is carried out with demineralized water and / or the filtrate enriched with pentaerythritol taken from the stage of recrystallization.

 At the stages of obtaining pentaerythritol with a basic substance content of more than 98 wt.%, The latter is isolated in an amount of 55-74 wt.%.

 To clarify the foregoing, an example 1 of the implementation of the proposed method in the claimed modes.

Example 1
Sodium hydroxide in the form of a 40% solution in the amount of 2875 kg and acetaldehyde in the amount of 1100 kg are metered in for 60 minutes in an aqueous solution of formaldehyde.

The temperature of the reaction mixture during the synthesis rises from 25-40 to 50-60 ^o C. The molar ratio of the reagents Ac: CH ₂ O: NaOH: H ₂ O-1: 8.5: 1.15: 68.

At the end of the dosing of the reagents, the reaction mixture was incubated for 15 minutes and neutralized with formic acid. The resulting reaction solution is fed to a desorption step to distill off excess formaldehyde. VAT liquid containing 3128 kg of monopentaerythritol (92% of theory), 95 kg of DPE, 1955 kg of sodium formate, water, organic impurities are sent to the evaporation stage, then to the vacuum crystallization stage of technical pentaerythritol with a final crystallization temperature of 50 ^o С and ρ ₅₀ = 1.35 g / cm ³ . The suspension is filtered off, the precipitate of technical petaerythritol is washed with the filtrate from the recrystallization step to remove sodium formate, recrystallized in hot water, filtered at a temperature of 51 ^o C, dried, packaged. Get 2055 kg of marketable product - pentaerythritol, including MPE 2033 kg (98.9 wt.%), DPE 20 kg (1.0% wt.), Organic impurities (balance).

 The degree of MPE release in the first stage is 65%.

Then the filtrate of the suspension of technical pentaerythritol and the filtrate from the recrystallization stage, enriched with PE, are combined and the resulting technical mother liquor containing 1095 kg of MPE, 75 kg of DPE, 1055 kg of sodium formate, water and organic impurities is evaporated and subjected to vacuum crystallization at a final temperature of 40 ^o С , the resulting suspension is filtered, the precipitate is washed with demineralized water to remove sodium formate. The washed precipitate is subjected to recrystallization in hot water, filtration at a temperature of 48 ^o C, drying and packaging. Receive 915 kg of a commercial product - pentaerythritol enriched with dipentaerythritol, including MPE - 845 kg (92.3 wt.%), DPE - 65 kg (7.1 wt.%), Organic impurities (balance).

 The degree of MPE release in the second stage is 27% of the total content in the initial bottoms solution.

 The total degree of MPE release is 92%. The overall process efficiency is 84.6%, which corresponds to an acetaldehyde consumption coefficient of 382 kg / t (in terms of the allocated MPE).

 From the analysis of experimental data it follows that the proposed method allows to obtain pentaerythritol with a content of the main substance monopentaerythritol of more than 98 wt. % and in the second stage pentaerythritol, enriched with dipentaerythritol, in an amount of 5-20 wt.%.

 These advantages allow to obtain non-waste production, improve the quality of the obtained pentaerythritol, get two products at the same time - high-quality pentaerythritol and enriched dipentaerythritol, used to produce high viscosity alkyd varnishes, increase the overall degree of pentaerythritol emission and reduce consumption rates for main types of raw materials by ~ 10 %

Claims (3)

1. The method of producing pentaerythritol with a basic substance content of more than 98 wt.% And pentaerythritol enriched with dipentaerythritol in an amount of 5-20%, which consists in the condensation of acetaldehyde with formaldehyde in an aqueous alkaline medium, followed by neutralization of the reaction mixture, desorption of excess formaldehyde , evaporation, vacuum crystallization at 45-55 ^o C and the suspension density ρ ₅₀ = 1.30-1.35 g / ^cm3, filtration, washing the resulting technical pentaerythritol, its further recrystallisation in hot water, f ltratsiey at 45-55 ^o C and drying with pentaerythritol release the content of the main substance of more than 98 wt.% suspension of technical pentaerythritol filtrate and the filtrate from the recrystallization step is then combined, evaporated and subjected to vacuum crystallization at 38-45 ^o C, filtered the resulting suspension , the precipitate is washed, recrystallized in hot water, the precipitate is filtered at 45-55 ^o C and dried to obtain pentaerythritol enriched with dipentaerythritol in the amount of 5-20 wt.%. 2. The method according to claim 1, characterized in that the washing of the precipitate obtained after the stage of vacuum crystallization at 38-45 ^o C and filtering is carried out with demineralized water and / or filtrate enriched with pentaerythritol taken from the recrystallization stage.  3. The method according to any one of claims 1 and 2, characterized in that at the stages of obtaining pentaerythritol with a basic substance content of more than 98 wt.%, The latter is isolated in an amount of 55-74 wt.%.