RU2843391C1 - Method for gas-phase dehydration of glycerol to acetol - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemistry and chemical production and specifically to a method for gas-phase dehydration of glycerol to acetol. Method involves preparation of catalyst by mixing support in nitrate salt solution, drying the obtained powder in a muffle furnace and carrying out the reaction in continuous mode in a flow gas reactor with a fixed catalyst bed at atmospheric pressure. Catalyst is prepared by adding to zeolite with mordenite structure 2-3 wt. % of silver. Reaction is carried out using glycerine with concentration of 99.3 wt. % through which an inert gas is bubbled at rate of 15-20 ml/min. Obtained mixture of inert gas and glycerin vapour is passed through a quartz reactor at temperature of 150-200 °C.

EFFECT: simple preparation of the catalyst, low power consumption and high conversion of glycerol to 89.6 % and acetol selectivity of up to 76 %.

1 cl, 3 tbl, 7 ex

Description

The invention relates to the field of chemistry and chemical production, namely to a method for gas-phase dehydration of glycerin into acetol (hydroxyacetone), as a method for processing glycerin into products with high added value.

The observed global trend of expanding biofuel production has led to a sharp increase in the production of crude glycerol, the main by-product (about 10 wt.%) of the biodiesel industry. Overproduction of unrefined glycerol reduces its economic value and itself leads to environmental problems. Glycerol can be used to produce various valuable chemicals through dehydration, carboxylation, transesterification and other reactions. Acetol is a chemical reagent used in various organic chemical reactions, widely used in the synthesis of 1,2-propylene glycol, as well as acetone, lactic acid, propionaldehyde. It is a component of the Mannich reaction, a direct asymmetric aldol reaction catalyzed by amino acids. In the pharmaceutical industry, acetol is used in the synthesis of imidazoles. Also, being non-toxic, it is used in the food and cosmetic industries.

State of the art

Industrial production of acetol is not efficient enough. The main disadvantages of traditional methods are high reaction temperature, the need to use expensive reagents compared to the product, and additional costs for wastewater removal and treatment, which together lead to high energy consumption and high cost of the technology.

A method for producing acetol by dehydrating glycerol using a copper-containing catalyst at temperatures from 180 to 400°C and pressures up to 20 bar is known [1], with the help of which it was possible to achieve 92.7% conversion of glycerol at a temperature of 280°C. The disadvantages of the known method include the high temperature and high pressure required for the reaction to occur, as well as low selectivity for acetol, not exceeding 36.4%. Therefore, subsequent studies were aimed at finding a catalyst in which the reaction occurs at lower temperatures and pressures, with higher selectivity.

A method is known [2] for dehydrating glycerol to obtain acetol as the first stage of a two-stage synthesis of 1,2-propanediol (1,2-propylene glycol) from glycerol: catalytic dehydration of glycerol to acetol and its subsequent hydrogenation in the presence of hydrogen. The reactivity was tested at an _H2 pressure of 13.78 bar and a temperature of 200°C using catalysts containing Ru, Pt, Pd, Cu, and Ni. It was shown that copper-containing catalysts demonstrate the greatest efficiency in dehydrating glycerol to obtain acetol. The disadvantages of the known method, despite the high conversion values of glycerol, include the use of expensive metals, as well as labor intensity due to the need to create high pressure and the requirement for further selective purification due to the large number of by-products.

A method is known [3] for producing acetol by mixing glycerol with a water content of less than 50 wt. % with a catalyst. The reaction takes place at a temperature in the range from 170 °C to 270 °C, for up to 24 hours, at a pressure of 0.2 to 25 bar and using hydrogen to remove acetol from the solution. Pd, Ni, Rh, Cu, Zn, Cr and their combinations are used as catalysts. The best results at normal pressure were demonstrated by the Cu/Cr catalyst (5 wt. %): with a reaction time of 1.5 hours at 220 °C and 3 hours at 240 °C, the glycerol conversion was 90.96%, and the selectivity for acetol was 90.62%. However, with a decrease in the catalyst concentration to 0.83 wt. %, with a slight decrease in glycerol conversion (to 86.96%), the selectivity for acetol decreases to 59.76%. A significant disadvantage of this method is the rapid aging of the catalyst and the need for a complex procedure for its regeneration, as well as relatively high temperatures and the need to use hydrogen.

A method [4] of liquid-phase dehydration of glycerol into acetol is known, which takes place in a reactive distillation apparatus in a mixture of glycerol with a concentration of 99.3 wt.% and 5 wt.% of Cu ₂ O catalyst. The process is carried out for 3 hours with constant stirring at a temperature of 180-240°C, a vacuum pressure of 2.9 kPa with nitrogen bubbling. The maximum selectivity for acetol (73.5%) is achieved at 205°C with a glycerol conversion of 87.6%. The disadvantages of this method include the need to regenerate the catalyst after operation to remove resinous deposits, as well as the need to maintain a vacuum.

A method for liquid-phase dehydration of glycerol to acetol is known [5], according to which the production of acetol from glycerol occurs with high (80-100%) selectivity for acetol, in which the initial mixture containing 10-80 wt.% glycerol and a solvent (water, alcohols, preferably aliphatic, individually or in combinations thereof) is heated in the presence of a catalyst in the temperature range of 180-220 °C under atmospheric nitrogen pressure. Cu, Cr, Al, Ba, Zn, Si, Zr, Mg or a combination thereof are used as a catalyst. In particular, a composition of 20% CuCr ₂ O ₄ and 80% SiO ₂ /Al ₂ O ₃ /zeolite H-β is proposed. The disadvantages of this method include the use of solvents, as well as a complex catalyst preparation process, including multi-stage calcination and treatment in a hydrogen stream.

In the known method [6], gas-phase dehydration of glycerol is carried out at 275°C for 7 hours on one of the most popular catalysts - zeolite HZSM-5, treated in an alkaline solution of Na ₂ CO ₃ to create mesoporosity, followed by ion exchange in a solution of NH ₄ NO ₃ to restore acidic properties. The conversion of glycerol after 7 hours of reaction did not exceed 48-68.7% with a selectivity of 15.2-19% for acetol. Despite the clearly defined porous structure, and, consequently, a large surface area, and high thermal stability, this catalyst demonstrates insufficiently high conversion of glycerol and low selectivity for acetol. A large number of by-products formed require further multi-stage processing, which reduces the economic efficiency of the method.

In the known method [7], adopted as a prototype, catalysts containing 10 wt.% of metal were obtained by impregnating Cu and/or Ni supports with γ-Al ₂ O ₃ and TiO ₂ in solutions of nitrate salts. After impregnation, the catalysts were dried at 120°C for 12 h and then reduced at 450°C in a flow of 5% H ₂ /Ar for 3 h, then the catalyst in the form of granules 2-3 mm in size was loaded into the reactor. The catalytic conversion of glycerol was carried out in the gas phase in a flow-through quartz reactor with a fixed catalyst bed at a temperature of 280°C and atmospheric pressure. An aqueous solution of glycerol (5% by volume) was pumped with a flow rate of 5 ml/h into the carrier gas N ₂ , fed into the reactor at a rate of 150 ml/min.

The features of the claimed method that are common with the prototype are the preparation of the catalyst by mixing the carrier in nitric acid solutions, drying the resulting powder in a muffle furnace and carrying out a gas-phase reaction in a flow reactor at atmospheric pressure.

The disadvantages of the prototype include a large number of energy-consuming calcination stages and the labor intensity of the process due to the need for hydrogen reduction during catalyst synthesis, as well as the high temperature of the glycerol conversion process, leading to a decrease in the economic efficiency of the method. The disadvantages of this method also include a low degree of glycerol conversion and low selectivity for acetol - no more than 63% and 55%, respectively.

The claimed invention is free from the indicated disadvantages and its technical-economic the result is the creation of an effective gas-phase method for processing glycerol into acetol using a zeolite with a mordenite structure modified with silver, which simplifies the preparation of the catalyst by reducing the number of stages and lowering the heat treatment temperature to 150°C, reduces energy costs by lowering the temperature of the glycerol conversion process to 175°C and achieves better process efficiency indicators - an increase in glycerol conversion to 89.6% and selectivity for acetol to 76%(in the prototype these figures are no more than 63% and 55%, respectively).

The distinctive features of the claimed method from the prototype are: the use of a zeolite with a large surface area of 380 ^m2 /g as a support for the catalyst; other conditions for its preparation (at a temperature of 20-25°C in solutions of nitrate salts with stirring for 12-24 hours, after which the filtered and washed with water sample is dried at a temperature of 100°C for 12-20 hours); carrying out the process of gas-phase dehydration of glycerol at a reduced temperature of 150-200°C; the use of a process of bubbling an inert gas through glycerol at a rate of 15-20 ml/min using 99.3 mass glycerol.

The use of the proposed method for converting glycerol into acetol based on a zeolite catalyst modified with silver is capable, as confirmed by numerous laboratory studies, of ensuring efficient and cost-effective utilization of glycerol on an industrial scale.

In the claimed invention, ion-exchange zeolites with a mordenite structure (MOR) containing Ag, Cu, a combination of Ag and Fe are used as a catalyst. The choice of catalyst is determined by a number of factors: transition metal cations are Lewis acid centers, the presence of which is necessary for the spatial coordination of the primary OH group, for the formation of acetol; the zeolite, having a porous structure, provides good access of glycerol molecules to active centers, and the topology of the mordenite zeolite framework and the localization of transition metal cations in the zeolite channels enhance the conversion of glycerol and the selectivity for acetol in the glycerol dehydration reaction.

In addition, the proposed method for converting glycerol into acetol based on a zeolite catalyst ensures efficient and cost-effective utilization of glycerol, since it contributes to: 1) a reduction in energy costs during catalyst preparation due to a reduction in the number of stages and temperature of heat treatment, 2) a reduction in energy costs during the glycerol dehydration process due to a reduction in the process temperature, 3) a reduction in production costs due to the use of high-concentration glycerol, which reduces the requirements for its preliminary preparation.

The specified technical result is achieved by the fact that: 1) for the preparation of the catalyst, a zeolite with a mordenite structure is used as a carrier, which is subjected to an ion-exchange reaction in a solution of nitrate salts of Ag, Cu, Fe at 20-25 ° C with subsequent drying without any additional stages, as a result of which a catalyst with a larger specific surface area is obtained, containing metal cations in an alumina-silica matrix, which are Lewis acid centers necessary for obtaining acetol, 2) the process of gas-phase dehydration of glycerol is carried out in a flow-type reactor at a temperature of 150-200 ° C, containing a fixed catalyst layer 1-2 mm thick, in a flow of a mixture of glycerol vapors and an inert gas at a constant rate of 0.9-1.0 l / h, obtained by saturating the inert gas with glycerol when passing through a bubbler at a rate of 15-20 ml / min at a pressure 1-1.03 bar.

The essence of the claimed method is as follows.

In the preparation of the catalyst, a zeolite with a mordenite structure is used, 0.5 g of which in powder form is mixed in 20-25 ml of an aqueous solution of 0.05N - 0.1N nitrate salt (salts) of Ag, Cu, Fe at 20-25 ° C for 20-24 hours, followed by washing with distilled water, centrifugation (or filtration) and drying at a temperature of 100 ° C for 12-20 hours. The process of gas-phase dehydration of glycerol is carried out in a flow-type reactor containing a fixed catalyst layer 1-2 mm thick, at a temperature of 150-200 ° C in a flow of a mixture of glycerol vapors and an inert gas with a constant volumetric velocity of 0.9-1.0 l / h at a pressure of 1 - 1.03 bar, obtained by saturating the inert gas with glycerol when passing through a bubbler at a speed 15-20 ml/min. The claimed method allows to prepare catalysts of the composition: 2-3 mass. % Ag and 4-5 mass. % Cu, as well as a bimetallic catalyst with 2 mass. % Ag and 0.2 mass. % Fe.

For the catalyst samples prepared by the proposed method, an analysis of the phase and elemental composition, surface morphology and testing of the catalytic activity in the glycerol dehydration reaction were carried out.

X-ray phase analysis of the samples was carried out at room temperature on a D8 DISCOVER device (Bruker, Germany) with Cu(K _α ) radiation, scanning angle range 2θ=5-50 with a step of 0.02.

The catalyst surface morphology and elemental composition were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) using a Zeiss Merlin microscope equipped with an Oxford Instruments INCAx-act EDX console. The specific surface area was determined by nitrogen adsorption at -196°C on a QuadrasorbSI adsorption analyzer and estimated using the Brunauer-Emmett-Teller (BET) method.

The process of gas-phase dehydration of glycerol was carried out in a flow-through catalytic unit with a U-shaped quartz reactor with a diameter of 0.4-0.5 cm, containing a fixed catalyst bed with a thickness of 1-2 mm, at a temperature of 100-250 °C, at atmospheric pressure (1-1.03 atm.), in a flow of a mixture of glycerol and argon vapors with a constant volumetric velocity of 0.9-1.0 l/h, obtained by saturating an inert gas with glycerol when passing through a bubbler at a rate of 15-20 ml/min. Quantitative assessment of the reaction results was carried out by the absolute calibration method using a Chromatec-Crystal 5000 gas chromatograph and the Chromatec Analyst 2.5 program. The rates of formation of reaction products were measured after reaching a steady state in the system, which was judged by the constancy of the areas of the chromatographic peaks. The experiment was carried out by changing the temperature from 100 to 250°C with a step of 25°C, the temperature was maintained constant with an accuracy of 2°C. The next experiment after high-temperature preliminary treatment in a flow of argon began with the same minimum temperature, repeating the entire course of the previous experiment. This allowed us to judge the reproducibility and stability of the catalyst.

The conversion of glycerol was calculated using the formula:

Where - the amount of glycerol fed into the reactor and unreacted, respectively. Selectivity for acetol was calculated as follows: S = n _acetol × 100%. The error in determining each component did not exceed 5% and consisted of the error in measuring the temperature and the error in measuring the feed rate of the reaction mixture.

The method is characterized by the fact that the dehydration reaction is carried out in an inert gas atmosphere, which ensures high stability of the reaction, while high concentration glycerin can be used as raw material; thus, the requirement for subsequent processing of liquid waste is reduced and energy consumption is significantly reduced, and, as a consequence, the cost of production.

The essence of the invention is illustrated by the following examples (1-7) and tables (1-3).

Example 1 (illustrates the method for preparing a catalyst of the Ag-mordenite composition)

The following reagents were used for preparation: Na-mordenite zeolite with an atomic ratio Si/Al equal to 6.5 and a surface area of 386 ^m2 /g (according to the BET method), silver nitrate _AgNO3 and distilled water.

The catalyst samples were prepared as follows: 0.5 g of the starting zeolite was treated in 25 ml of a 0.1 M aqueous solution of AgNO ₃ by stirring with a magnetic stirrer at 500 rpm at 20°C for 20 hours. The sample was then filtered, washed in 100 ml of distilled water and dried at 100°C for 12 hours. Analysis of the composition revealed the presence of Ag in an amount of 2.8 wt. % with a virtually unchanged specific surface area of 364 m ² /g.

Example 2 (illustrates the efficiency of the glycerol dehydration process with Ag-mordenite catalyst)

The process of gas-phase dehydration of glycerol was carried out in a flow-through catalytic unit with a U-shaped quartz reactor with a diameter of 0.4 - 0.5 cm. For this purpose, 100 mg of Cu-mordenite in a layer 1-2 mm thick was placed on the bottom of the reactor. Glycerol (99.3%) was filled into a bubbler, through which an inert gas (argon) was passed at a rate of 15 - 20 ml/min. A mixture of inert gas with glycerol vapor was passed through the catalytic reactor at a constant volumetric velocity of 0.9 - 1.0 l/h. The pressure in the reactor corresponded to atmospheric pressure - 1.03 bar. Rapid heating to 100 °C was carried out, after which a steady state was achieved in the system at a constant temperature, as evidenced by the constancy of the composition of the gas mixture at the outlet of the reactor, determined chromatographically. Then the temperature was raised in 25°C increments to 250°C, each time recording the composition of the gas mixture upon reaching a steady state. The results of calculating the glycerol conversion and acetol selectivity are presented in Table 1. The maximum acetol selectivity of 76.0% with a glycerol conversion of 89.6% was achieved at a temperature of 175°C.

Table 1. Dependence of glycerol conversion and acetol selectivity using Ag-mordenite catalyst

T, °C Glycerol conversion, % Selectivity for acetol, % 100 83.9 71.5 125 86.9 73.9 150 87.8 75.8 175 89.6 76.0 200 90.5 75.9 225 90.6 75.6 250 90.6 75.7

Example 3 (illustrates the stability of the Ag-mordenite catalyst)

The repeated process of gas-phase dehydration of glycerol in the presence of the Ag-mordenite catalyst was carried out without additional regeneration of the catalyst under the same conditions as in Example 2 - at a temperature of 100 - 250 °C and an atmospheric pressure of 1.01 bar. The results showed that the conversion decreased by no more than 0.1%, and the selectivity remained at the same level.

In addition, studies were conducted on the process of glycerol dehydration with a copper catalyst and a bimetallic catalyst with silver and iron, which also showed the efficiency of the process for obtaining acetol, although with lower values of the degree of conversion and selectivity for acetol, which is illustrated in Examples 4 - 7.

Example 4 (illustrates the method for preparing a catalyst of the Cu-mordenite composition)

The following reagents were used for preparation: Na-mordenite zeolite with an atomic ratio Si/Al equal to 6.5 and a surface area of 386 ^m2 /g (according to the BET method), copper nitrate Cu( _NO3 ) ₂ and distilled water.

The catalyst sample preparation method was as follows: 0.5 g of the starting zeolite was treated in 20 ml of 0.05 M aqueous Cu( _NO3 ) ₂ solution by stirring with a magnetic stirrer at 500 rpm at 25°C for 24 hours. The sample was then filtered, washed in 100 ml of distilled water and dried at 100°C for 20 hours. Analysis of the composition revealed the presence of copper in an amount of 4.6 wt. % and a slightly changed specific surface area of 362 ^m2 /g.

Example 5 (illustrates the efficiency of the glycerol dehydration process with Cu-mordenite catalyst)

The process of gas-phase dehydration of glycerol in the presence of Cu-mordenite catalyst was carried out in the same way as in Example 2 at a temperature of 100-250°C and a pressure of 1 bar. The results are presented in Table 2.

Table 2. Dependence of glycerol conversion and acetol selectivity using Cu-mordenite catalyst

T, °C Glycerol conversion, % Selectivity for acetol, % 100 53.0 17.5 125 59.6 20.6 150 63.6 23.0 175 66.3 25.0 200 70.4 28.7 225 72.2 30.2 250 72.9 31.4

Example 6 (illustrates the method for preparing a catalyst of the AgFe-mordenite composition)

The following reagents were used for preparation: Na-mordenite zeolite with an atomic ratio Si/Al equal to 6.5 and a surface area of 386 ^m2 /g (according to the BET method), _AgNO3 and Fe( _NO3 ) ₃ salts, and distilled water.

The method for preparing the catalyst samples was as follows: 0.5 g of the original zeolite was treated in 25 ml of 0.1 M aqueous solution of AgNO ₃ and 25 ml of 0.1 M aqueous solution of Fe(NO ₃ ) ₃ by stirring with a magnetic stirrer at 500 rpm at 24°C for 24 hours. After that, the sample was centrifuged, washed in 100 ml of distilled water and dried at 100°C for 12 hours. Analysis of the composition established the presence of Ag and Fe in an amount of 2.3 wt. % and 0.2 wt. %, respectively, and a virtually unchanged value of the specific surface area - 378 m ² /g.

Example 7 (illustrates the efficiency of the glycerol dehydration process with an AgFe-mordenite catalyst)

The process of gas-phase dehydration of glycerol in the presence of the AgFe-mordenite catalyst was carried out in the same way as in Example 2 at a temperature of 100-250°C and an atmospheric pressure of 1.01 bar. The results are presented in Table 3.

Table 3. Dependence of glycerol conversion and acetol selectivity using AgFe-mordenite catalyst

T, °C Glycerol conversion, % Selectivity for acetol, % 100 65.0 45.6 125 67.6 48.5 150 72.7 53.9 175 73.8 55.3 200 74.4 56.1 225 75.7 58.1 250 76.4 60.5

The above examples confirm the efficiency of using the claimed method for producing acetol in the glycerol dehydration reaction using catalysts that are mordenite modified with Ag or Cu, or Ag and Fe. The best result is provided by the Ag-mordenite catalyst, which allows achieving a conversion of 90% and a selectivity of acetol formation of 76% at 175°C.

The use of the proposed gas-phase method for the conversion of glycerol using a catalyst based on a modified Ag zeolite with a mordenite structure can ensure, as shown by the above examples based on the results of laboratory studies, an efficient and less energy-consuming utilization of glycerol.

The use of the claimed invention is possible at enterprises processing biomass into biodiesel fuel, such as Oil-Prom LLC, as well as at enterprises processing glycerin waste, for example, ECOTERMINAL LLC.

List of sources used

1. Patent WO1993005006A1. 1992. Fleckenstein T. Göbel, G. Haberlandt, K. Process for making acetol.

2. Dasari M.A., Kiatsimkul P.P., Sutterlin W.R., Suppes G.J. Low-pressure hydrogenolysis of glycerol to propylene glycol // Applied Catalysis A: General. 2005. Vol. 281, no. 1-2. P. 225-231.

3. Patent EP1727875B1 USA. 2015. Suppes G.J., Sutterlin W.R., Dasari M.A. Process for producing acetol from glycerol.

4. Patent RU 2 828859. 2023. Zlobin S.Yu., Lunina D.M., Esipovich A.L. Method for liquid-phase conversion of glycerol to acetol using a copper-containing catalyst.

5. Patent US8809593B2. USA 2014. Chandrasshekhar Vasant Rode, Amol Mahalingappa Hengne, Ajay Ashok Ghalwadkar, Rasika Bharat Mane, Pravinkumar Hansraj Mohite, Hari Shankar Potdar. Process for preparation of hydroxyacetone or propylene glycol.

6. Lago C.D., Decolatti H.P., Tonutti L.G., Dalla Costa B.O., Querini C.A. Gas Phase Glycerol Dehydration over H-ZSM-5 Zeolite Modified by Alkaline Treatment with Na₂CO₃// Journal of Catalysis. 2018. Vol. 366. P.16-27.

7. Morales B.C.M., Quesada B.A.O. Conversion of glycerol to hydroxyacetone over Cu and Ni catalysts // Catalysis Today. 2021. Vol. 372, pp. 115-125. (Prototype).

Claims (1)

A method for the gas-phase dehydration of glycerol into acetol, comprising preparing a catalyst by mixing a carrier in a nitric acid solution of a salt, drying the resulting powder in a muffle furnace and carrying out the reaction in a continuous mode in a flow-through gas reactor with a fixed catalyst bed at atmospheric pressure, characterized in that the catalyst is prepared by introducing 2–3 wt. % silver into a zeolite with a mordenite structure, glycerol with a concentration of 99.3 wt. % is used to carry out the reaction, through which an inert gas is bubbled at a rate of 15–20 ml/min, the resulting mixture of inert gas and glycerol vapor is passed through a quartz reactor at a temperature of 150–200 °C.