RU2854385C1 - Method for extracting ethylene glycol from aqueous solutions of organic compounds of hydrolysis-hydrogenolysis of plant carbohydrate raw materials - Google Patents

Abstract

FIELD: biomass processing processes.

SUBSTANCE: invention relates to a method for extracting ethylene glycol (EG) from aqueous solutions of organic compounds of hydrolysis-hydrogenolysis of plant carbohydrate raw materials, containing organic components with unlimited mutual solubility and close boiling points with ethylene glycol, high-boiling organic components and a homogeneous catalyst. Method comprises feeding the aqueous solution into a first vacuum rectification column for distilling off water and obtaining a concentrated stream of organic compounds together with the homogeneous catalyst and feeding the obtained concentrated stream of organic compounds and catalyst into a second vacuum rectification column for removing high-boiling organic compounds and the homogeneous catalyst, with obtaining a partially regenerated concentrated stream containing at least EG, 1,2-propylene glycol and butanediols. The obtained partially regenerated concentrated stream is fed into a third vacuum azeotropic rectification column for removing components with unlimited mutual solubility and close boiling points with EG. Wherein 3-heptanone is used as the azeotropic agent, and at the outlet of the third column, a heterogeneous azeotrope of purified EG and 3-heptanone is obtained. Then the heterogeneous azeotrope is separated in a settling and separation tank to obtain 3-heptanone and pure EG.

EFFECT: extraction of ultra-pure (over 99.99 mas.%) EG.

4 cl, 3 dwg, 5 tbl

Description

The invention relates to the field of biomass processing, namely to a method for extracting ethylene glycol from real reaction mixtures of hydrolysis-hydrogenolysis of plant carbohydrate raw materials (PCR), which are aqueous solutions of organic compounds together with a homogeneous catalyst of the hydrolysis-hydrogenolysis process, containing high-boiling organic products of the PCR hydrolysis-hydrogenolysis process, organic components with unlimited mutual solubility with water and ethylene glycol, close boiling points with ethylene glycol and forming azeotropic mixtures with ethylene glycol, 1,2-propylene glycol (1,2-PG) and butanediols BD (1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol).

State of the art

Ethylene glycol (EG) is used in the chemical, textile, automotive, and electrical industries. Stable demand for monoethylene glycol (MEG), especially in light of impending production cuts in key consuming industries, is driving market growth. EG is an essential raw material in the production of polyethylene terephthalate (PET), which accounts for 81% of global EG consumption. EG is also used in antifreeze and as a feedstock in complex organic synthesis.

All processes for producing EG are catalytic, and the resulting product is usually a mixture of organic compounds that are in the liquid phase.

Methods for producing EG are known that utilize the catalytic hydrolysis-hydrogenolysis reaction of plant carbohydrate raw materials, including cellulose, hemicelluloses (arabinogalactan, xylan), starch, disaccharides (sucrose), monosaccharides (glucose, fructose), and other carbohydrate-containing raw materials of biological origin, alternative to traditional fossil raw materials (RU 2698724 C2, 29.08.2019; RU 2738931 C2, 18.12.2020). The processes for producing EG from RUS utilize catalytic systems consisting of two components. The first component contains metals selected from elements of groups 8, 9, and 10, with examples of catalysts based on nickel, ruthenium, and copper. This component ensures the reduction of reaction intermediates. The second component, containing compounds and complexes of tungsten, molybdenum, lanthanum, and tin, primarily in the form of oxide compounds, preferably homogeneous ammonium or sodium tungstates, with exceptional examples of tungsten carbides, enables retro-aldol cleavage of the substrate and intermediates. This technology is characterized by low raw material costs, the parallel production of several useful products, and is environmentally friendly.

Separating reaction mixtures from the hydrolysis-hydrogenolysis of RUS and obtaining commercial EG is a difficult technical task. The problem of extracting EG obtained from the hydrolysis-hydrogenolysis of RUS is complicated by the close boiling points of the glycols, as well as possible azeotropes contained in the initial reaction mixture, in particular EG-1,2-BG, which makes the process of simple rectification impossible or difficult to implement (Wang J., Shen R., Cao Y., Li W. The Canadian Journal of Chemical Engineering. - 2023. - V. 101. - P. 4217-4229). Obtaining pure products, including ethylene glycol, by conventional rectification requires a large number of theoretical plates and large capital investments, since the difference in boiling points of ethylene glycol, propylene glycol and 1,2-butanediol is very small (De Haan A. B., Bosch H. Fundamentals of industrial separations. – Walter de Gruyter GmbH & Co KG, 2007).

The presence in the reaction mixture of a homogeneous catalyst, which is usually a soluble tungsten compound (ammonium and sodium tungstates, tungsten-containing heteropoly acids, etc.), and high-boiling compounds can lead to non-target polycondensation processes during the separation of raw materials during their heating (in distillation, rectification, etc.), and therefore,to the destruction of EG and the formation of highly viscous resinous by-products, which reduce the quality of the finished product and the equipment is out of order.

The problem of the presence of homogeneous catalysts in separated reaction solutions of ethylene glycol is practically not considered in the known patents.

A known method (RU 2440964 C2, June 12, 2007) involves separating a homogeneous catalyst solution from crude monoethylene glycol (MEG) and purifying the MEG obtained from ethylene oxide. The method includes a catalyst separation section by evaporating the crude monoethylene glycol, a rectification section, a light fractions separation section, and a pasteurization section. All stages are carried out at a subatmospheric pressure of 0.5×105 Nm.^-2or less. The method allows for the process of evaporating the monoethylene glycol stream once, which allows the vapors to be transported from the catalyst separation section to the MEG purification stage without the use of a mechanical pumping device.

However, this method is not applicable to reaction mixtures obtained from RUS, due to the complexity of their composition relative to mixtures obtained as a result of the conversion of ethylene oxide, including the presence of a significant amount of high-boiling impurities, which can complicate the purification procedure.

Also known is a method (RU 2594159, 10.08.2016) for separating a mixture containing ethylene glycol and 1,2-butanediol, in particular a method for isolating and purifying EG from a liquid-phase product obtained by hydrogenating oxalate.Way involves distillation of a mixture with an azeotropic agent having the structural formula:

where R1 is an H atom or an alkyl group containing 1 to 4 carbon atoms, R2 is an H atom or an alkyl group containing 1 to 4 carbon atoms, R3 is an H atom or an alkyl group containing 1 to 8 carbon atoms, and R4 is an H atom or an alkyl group containing 1 to 8 carbon atoms. Preferably, the above-mentioned distillation using an azeotropic agent is carried out using a separation column, and the preferred number of theoretical plates of said separation column is 8 to 30, the operating pressure is 30 to 101.3 kPa based on absolute pressure, the reflux ratio R=0.8 to 5, and the molar ratio of the azeotropic agent to ethylene glycol in the feedstock is 0.1 to 10:1.

The described method is proposed preferably for the extraction of EG from mixtures in which the content of light components of the mixture is less than 1%, which does not correspond to the composition of the liquid product of RUS hydrolysis, and the known solution also does not consider the problem of the presence of a catalyst and high-boiling organic components in the composition of the separated reaction mixtures of ethylene glycol.

Also known is a method for purifying non-petroleum EG selected as a prototype (RU 2818912 C2, 07.05.2024), which comprises the following stages: (i) mixing one or more azeotropes (polyhydric alcohols, ketones, etc.) with ethylene glycol obtained from carbohydrate feedstock to obtain a charge containing an ethylene glycol azeotrope; (ii) boiling the charge containing the ethylene glycol azeotrope with reverse flow in an azeotropic or distillation column at a pressure of 1 to 101 kPa; (iii) obtaining extracted material from the top of the azeotropic or distillation column; (iv) adding water to the extracted material to dissolve ethylene glycol in the azeotrope; separating the water-insoluble azeotrope from the aqueous solution of ethylene glycol; and (vi) obtaining ethylene glycol by dehydrating and purifying the resulting aqueous ethylene glycol solution.

One of the drawbacks of the prior art method is the additional step (v) of separating the azeotropic agent from ethylene glycol. Using water added in step (iv) to separate ethylene glycol from the azeotropic agent requires an additional, energy-intensive step (vi) of ethylene glycol dehydration to obtain a product with the target properties. Furthermore, the prior art method does not address the problem of the presence of a homogeneous catalyst in the purified EG solution obtained by any synthesis method that does not involve the use of petroleum, including from carbohydrate feedstock by catalytic hydrolysis-hydrogenolysis, which can affect the properties of the final product.

Disclosure of the essence of the invention

The technical problem requiring a solution in the present invention is to provide a method for isolating EG from aqueous solutions of organic compounds (reaction mixture) - a mixture of RUS hydrolysis-hydrogenolysis products, which necessarily contains a homogeneous catalyst - in which non-target processes involving the catalyst are excluded, for example, polycondensation, when heating the mixture in distillation and rectification processes, and, consequently, the formation of highly viscous resinous by-products. Moreover, the said reaction mixture contains organic components with unlimited mutual solubility and boiling points close to ethylene glycol, in particular, EG, 1,2-PG and BD, as well as high-boiling organic compounds, which may include glucose, fructose, sorbitol, glycerol, glycolic acid, lactic acid, erythritol, isosorbide, hydroxyacetone, and the homogeneous catalyst is soluble tungsten compounds (ammonium and sodium tungstates, tungsten-containing heteropoly acids, etc.).

The technical objective of the claimed solution is the extraction of highly pure (over 99.99 wt.%) ethylene glycol from solutions of RUS hydrolysis-hydrogenolysis products containing organic components and a homogeneous catalyst.

The technical result achieved by the solution consists in extracting highly pure (over 99.99 wt.%) ethylene glycol from a solution obtained by hydrolysis-hydrogenolysis of RUS and containing at least 1,2-PG and BD, high-boiling organic compounds, as well as a homogeneous catalyst.

The essence of the solution is that at the stage of EG purification from high-boiling organic components, these components and the homogeneous catalyst are removed jointly from the dehydrated reaction mixture under vacuum, and at the next stage stages – isolation of pure EG using the azeotropic agent 3-heptanone to carry out azeotropic rectification, which allows for the extraction of ethylene glycol from a mixture of organic compounds containing 1,2PG and BD, with a purity of >99.99%, regardless of the organic compounds contained in the actual product technical solution and the initial content of ethylene glycol in the flow.

In one aspect of the claimed solution, a method is disclosed for extracting ethylene glycol from reaction mixtures of hydrolysis-hydrogenolysis products of plant carbohydrate raw materials, which are aqueous solutions of organic compounds together with a homogeneous catalyst, containing high-boiling organic products of the RUS hydrolysis-hydrogenolysis process, organic components with unlimited mutual solubility with water and ethylene glycol, close boiling points with ethylene glycol and forming azeotropic mixtures with ethylene glycol, includes:

(1) feeding said aqueous solution into a first vacuum distillation column to distill off water and obtain a concentrated stream of organic compounds containing a suspended homogeneous catalyst;

(2) feeding said concentrated stream of organic compounds containing at least a mixture of EG, 1,2-PG and BD, as well as high-boiling organic compounds that may include glucose, fructose, sorbitol, glycerol, glycolic acid, lactic acid, erythritol, isosorbide, hydroxyacetone, wherein the stream necessarily contains a homogeneous catalyst, which is soluble tungsten compounds (ammonium tungstates, sodium tungstates, tungsten-containing heteropoly acids, etc.), into a second vacuum rectification column for distilling off high-boiling organic compounds, separating the catalyst and obtaining a partially regenerated concentrated stream containing at least EG, 1,2-PG and BD;

(3) feeding said partially regenerated concentrated stream into a third vacuum distillation column for azeotropic distillation, wherein the azeotropic agent is 3-heptanone, and at the outlet of the third column a stream of a heterogeneous azeotrope of ethylene glycol and the azeotropic agent 3-heptanone is obtained;

(4) obtaining ethylene glycol by layering the heterogeneous azeotrope stream and separating the bottom layer, which is a stream of regenerated ethylene glycol.

Thus, the proposed method, firstly, reduces the total volume of the liquid phase in distillation columns 2 and 3, secondly, allows the separation of the catalyst from the final product EG (and return it for recycling, if necessary), as well as avoiding non-target processes involving the catalyst, and thirdly, eliminates the additional stage of aqueous separation of EG and the azeotropic agent, as proposed in the prototype patent.

In additional aspects it is disclosed that the distillation of water occurs at a vacuum of 0.01 to 0.6 bar, preferably 0.1 to 0.5 bar; the removal of high-boiling organic impurities and a homogeneous catalyst occurs at a vacuum of 0.01 to 0.6 bar, preferably 0.1 to 0.5 bar; the production of a heterogeneous azeotrope is carried out from a mixture containing 1,2-PG and BD; the production of a heterogeneous azeotrope is carried out using an azeotropic agent 3-heptanone in a ratio of 1/1-5/1 to the weight content of ethylene glycol, preferably in a ratio of 1/1-2/1, with a number of theoretical plates of 30; the production of a heterogeneous azeotrope is carried out at a vacuum of 0.01 to 0.6 bar, preferably 0.1 to 0.5 bar; the original The aqueous solution is obtained by catalytic hydrolysis-hydrogenolysis of RUS and contains EG, 1,2-PG and BD, high-boiling organic compounds that may include glucose, fructose, sorbitol, glycerol, glycolic acid, lactic acid, erythritol, isosorbide, hydroxyacetone, and also necessarily contains a homogeneous catalyst, which is soluble tungsten compounds (ammonium and sodium tungstates, tungsten-containing heteropoly acids, etc.).

Brief description of the drawings

Fig. 1 shows a basic diagram of the implementation of the claimed method, in which:

Az – flow of azeotropic agent 3-heptanone;

D_1 – flow of separated water;

D_2 – partially regenerated ethylene glycol stream containing predominantly ethylene glycol, to a lesser extent 1,2-PG and BD;

D_3 – a heterogeneous azeotrope flow, the lower phase of which is a flow of ethylene glycol regenerated to over 99% of its mass;

F_1 – input for feeding an aqueous solution of RUS hydrolysis-hydrogenolysis products with a homogeneous catalyst;

HL (EG) – stream of purified ethylene glycol;

LL(3HEPT) – flow of spent azeotropic agent;

Q – heat flows;

T-1 – 1st vacuum rectification column for evaporating water and obtaining a concentrated stream of organic compounds with a catalyst;

T-2 – 2nd vacuum rectification column for removing high-boiling organic compounds with T _{boiling point} >200 °C and catalyst;

T-3 – 3rd azeotropic distillation column;

V-100 – tank for settling and separating ethylene glycol and azeotropic agent;

W_1 – concentrated dehydrated flow of organic compounds and catalyst;

W_2 – removed mixture of high-boiling organic compounds and catalyst;

W_3 – flow of separated mixture of 1,2-PG and BD.

Fig. 2 shows the GLC chromatogram of the reaction mixture before separation, Fig. 3 shows the GLC chromatogram of the reaction mixture after separation.

Implementation of the invention

The study utilized a reaction solution obtained during the hydrogenolysis of RUS, the composition of which is shown in Table 1. It contained 10 wt.% EG and 1,2-PG and BD as impurities, high-boiling organic compounds including sorbitol, glycerol, glycolic acid, lactic acid, erythritol, isosorbide, and hydroxyacetone, as well as a homogeneous catalyst selected as an example from the list of soluble tungsten compounds, namely, ammonium tungstate. The reaction solution was placed in a standard 1-liter round-bottomed flask with a reflux condenser, and water was distilled off under vacuum (0.08 bar) at a temperature of 43°C. This resulted in a so-called concentrated dehydrated stream of organic compounds.

The removal of high-boiling organic compounds, including sorbitol, glycerol, glycolic acid, lactic acid, erythritol, isosorbide, hydroxyacetone, and a homogeneous catalyst (ammonium tungstate), was performed using a laboratory batch distillation column. The column was a hollow glass Pyrex tube with an internal diameter of 20-25 mm and an efficiency of 25 tons. The column was packed with SPN-2 stainless steel spiral-prismatic packing. The concentrated stream obtained after water removal was loaded into the still (~50 g), a vacuum was applied (0.08 bar), and the heating was turned on (heating mantle power 280 W). The column was then switched to "flooding" mode, which resulted in wetting of the packing. The column was then brought into operating mode, and the 98-110°C fraction containing EG, 1,2-PG, and BD was collected. This yielded what is known as a partially regenerated concentrated ethylene glycol stream.

The isolation of EG by azeotropic distillation was carried out on a laboratory batch distillation column with an efficiency of 30 tons of fuel and packed with SPN-3 loose spiral-prismatic packing. The column bottom was loaded with a glycol fraction obtained by removing high-boiling compounds and a homogeneous catalyst (a stream of partially regenerated ethylene glycol), and an azeotropic agent, 3-heptanone. The mixture to azeotropic agent ratio was 1:1 by weight. The experiment was conducted at atmospheric pressure (1 bar) and a heterogeneous azeotrope temperature of 147°C. The column bottom and jacket heating were turned on. With the distillate withdrawal valve closed, the column heating mode was set to the operating mode. The column was then switched to the "flooding" mode and brought up to the operating mode. A heterogeneous azeotrope was collected at the top of the column; upon condensation, it separated into two phases: the EG phase (lower) and the 3-heptanone phase (upper). The 3-heptanone phase was continuously returned to the distillation column.

The initial reaction mixture and the resulting EG were analyzed by gas chromatography (Fig. 2 and Fig. 3, respectively). The gas chromatography method showed that the resulting EG had a purity of greater than 99.99.

Based on the obtained experimental data, the calculation of the proposed method for extracting EG from RUS using the proposed azeotropic distillation method was performed, and a separation scheme was proposed (described above and shown in the scheme of Fig. 1, with the initial parameters of the mixture according to Table 2, where TT is the number of theoretical plates, Rwork is the working reflux ratio, Rwork, AA is the azeotropic agent). The column calculations were performed using the NRTL and UNIQUAK modeling packages. To determine the binary coefficients of the EG-1,2BG components, the UNIFAC theoretical method of group contributions was also used. The calculated material balance and flow compositions are presented in Tables 3 and 4, the heat flows are presented in Table 5. The calculations showed that the most optimal ratio is EG/3-heptanone 1/2.6. The calculations indicate that, using this invention, EG with a purity of 99.995% is achieved.

Table 1. Content of components in the reaction mixture of hydrogenolysis of RUS

Component Component content, g/l EG 102.4 1,2-PG 10.7 Glycerol 6.5 Hydroxyacetone 0.9 Sorbitol 0.9 Glycolic acid 5.4 Lactic acid 0.2 2,3-Butanediol 0.3 1,3-Butanediol 0.9 1,2-Butanediol 7.5 1,4-Butanediol 1.5 Isosorbide 0.3 Erythritol 3.0 ammonium tungstate 2.8

Table 2. Main parameters of columns

Parameter/column T-1 T-2 T-3 TT 20 20 30 Rslav 1 1 2 Food plate 10 10 15 Model NRTL NRTL UNIQUAK AA feed, plate - - 25

Table 3. Material flows

Table 4. Composition of material flows

Table 5. Heat flows

Claims (8)

1. A method for extracting ethylene glycol (EG) from aqueous solutions of organic compounds from the hydrolysis-hydrogenolysis of plant carbohydrate raw materials, containing organic components with unlimited mutual solubility and boiling points close to ethylene glycol, high-boiling organic components and a homogeneous catalyst, including: (1) feeding said aqueous solution into a first vacuum distillation column to distill off water and obtain a concentrated stream of organic compounds together with a homogeneous catalyst; (2) feeding said concentrated stream of organic compounds and catalyst to a second vacuum distillation column to remove high-boiling organic compounds and homogeneous catalyst and obtain a partially regenerated concentrated stream containing at least EG, 1,2-propylene glycol (1,2-PG) and butanediols (BD); (3) feeding said partially regenerated concentrated stream into a third vacuum azeotropic distillation column to remove components with unlimited mutual solubility and close boiling points with ethylene glycol, wherein the azeotropic agent is 3-heptanone, and obtaining at the outlet of the third column a heterogeneous azeotrope of purified ethylene glycol and the azeotropic agent 3-heptanone; (4) separating the resulting heterogeneous azeotrope of purified ethylene glycol and the azeotropic agent 3-heptanone in a settling and stratification tank to obtain 3-heptanone and pure ethylene glycol. 2. The method according to claim 1, wherein the organic components with unlimited mutual solubility and close boiling points with ethylene glycol include at least 1,2-propylene glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol. 3. The method according to claim 1, wherein the high-boiling organic compounds include at least glucose, fructose, sorbitol, glycerol, glycolic acid, lactic acid, erythritol, isosorbide, hydroxyacetone. 4. The method according to claim 1, wherein the homogeneous catalyst is a soluble tungsten compound, for example ammonium tungstate, sodium tungstate, tungsten-containing heteropoly acids.