IMPROVEMENT OF PHYSICO-CHEMICAL PROPERTIES OF TECHNICAL GLYCERIN

ABSTRACT

The article presents the results of research on obtaining glycerin without distillation of technical glycerin obtained from hydrogenated cottonseed oil. Technical glycerin obtained for the study contains 78.5% glycerin, 2.1% moisture and volatile matter, 8.9% ash and 10.5% non-volatile organic residue. After treatment with phosphoric acid, the amount of glycerin is from 78.5 % to 88.3%, moisture and volatile matter increased from 2.1% to 2.4%, ash content from 8.9% to 4.1%, and non-volatile organic residue content from 10.5% to 5.2 decreased to %. After refining with cationite, the glycerin content increased to 98.1%, the mass fraction of moisture and volatile matter decreased to 1.7%, and the amount of ash and non-volatile organic residue decreased to 0.1%. It has been found that refined glycerin can be obtained by refining technical glycerin with phosphoric acid and cationite.

АННОТАЦИЯ

В статье представлены результаты исследований по получению высококачественного глицерина без перегонки технического глицерина, полученного из хлопкового саломаса. Технический глицерин, полученный для исследования, содержит 78,5 % глицерина, 2,1 % влаги и летучих веществ, 8,9 % золы и 10,5 % нелетучего органического остатка. После обработки фосфорной кислотой количество глицерина составляет от 78,5 % до 88,3 % содержание влаги и летучих веществ увеличилось с 2,1% до 2,4%, а содержание нелетучих органических остатков снизилось с 10,5% до 5,2 % и зольность с 8,9% до 4,1%. После очистки катионитом содержание глицерина увеличилось до 98,1 %, массовая доля влаги и летучих веществ снизилась до 1,7 %, а количество золы и нелетучего органического остатка снизилось до 0,1 %. Установлено, что высококачественный глицерин можно получить очисткой технического глицерина фосфорной кислотой и катионитом.

Keywords: glycerin, ash content, distillation, refining, cationite, phosphoric acid.

Ключевые слова: глицерин, зольность, дистилляция, очистка, катионит, фосфорная кислота.

Introduction

Glycerin is a triatomic alcohol that is a colorless liquid with a slightly sweet taste. It is more viscous than water and has a greater density than water. Glycerin is widely used in several industries. Therefore, it is in high demand. Glycerin is produced as a secondary product in soap production, and as a primary product in fat splitting [1-4].

Since natural glycerin is derived from oils and fats, it contains many impurities. These impurities can be fatty acids, triglycerides, mineral and organic salts, coloring agents and fat accompanying substances. The type and amount of impurities in glycerin directly depends on the method and sources of glycerin extraction [5]. Depending on the amount of these substances, glycerin is raw, technical and distilled. In all methods of obtaining glycerin, raw glycerin with a concentration of 10-35% is obtained initially. This glycerin is refined, water content is reduced, and technical glycerin with a concentration of 78-86% is obtained from it. To obtain high-quality glycerin, glycerin is completely refined, and pure glycerin with a concentration of more than 98% is obtained [6-10]. In addition, low purity of technical glycerin its use in industry. The development of processes for the conversion of technical glycerin into other value-added products is being extensively studied, but is currently not widely used in industry.

In Uzbekistan, glycerin is mainly obtained by hydrolysis of fats. This method produces higher quality and more glycerin than by saponification of fats.

Hydrolysis of fats is a chemical process based on the reaction of three glycerides with water. Glycerine and fatty acid are formed.

Hydrolysis or saponification of oil is called oil splitting in industry. Hydrolysis is a stepwise process, with the formation of mono- and di-glycerides.

The glycerin obtained by splitting fat has low quality. Due to its dark and dull color and low concentration, it cannot be widely used. Therefore, glycerin must be refined and turned into a valuable product. There are several different ways to clean glycerin: evaporation, distillation, filtration, adsorption, ion exchange, etc [10]. By choosing several methods high efficiency refining of glycerin is achieved. For example, glycerine obtained by fat splitting is first chemically refined with limewater, filtered, water evaporated, glycerine distilled, adsorption using activated carbon and filtered again [4].

Technical glycerin obtained by evaporation of sweet water is first refined with lime water. Fatty acids, fat and other impurities are separated from the glycerin water. After separating the precipitate by filtration, water with glycerin is evaporated and technical glycerin is obtained. Its concentration is around 78-86%, and it contains traces of fatty acid, soap, alkali metal salts and other impurities of oil. These substances determine the color, ash content, density and clarity of glycerin. To obtain high-quality glycerin, it is necessary to reduce the amount of impurities in technical glycerin. For this, technical glycerin is distilled and bleached in the industry. However, due to the high energy consumption, the price of glycerin increases and the competitiveness of glycerin decreases. Therefore, the development of resource-efficient technologies for glycerin refining is considered urgent.

Glycerin can also be refined by ion exchange [3]. The researchers tested the use of cations for the refining of glycerin and studied the effectiveness of the cations. These results indicated that impurities such as inorganic salts and free ions were removed when the ion exchange method was used.

Materials and methods

Technical glycerin obtained from JSC ‘Urganch’ by hydrolysis of hydrogenated cottonseed oil was used for the experiments. Cationite KU-2-8 was used for refining of glycerin by ion exchange method. An 85% solution of phosphoric acid was used in mineral acid treatment processes.

Determination of the mass fraction of glycerol.

Any concentration or relative amount of glycerin in a solution can be determined by the relative density of the solution and the refractive index. The density of glycerin was determined using a densimeter (DURAN) and the refractive index was determined using a refractometer (Refracto 30GS) [11,12].

Determination of ash content.

The mass fraction of ash characterizes the presence of mineral and mineral-organic compounds in glycerin. The method is based on the removal of water and glycerin from the product, making ash of the non-volatile residue and ash recovery [11,12].

Determination of the mass fraction of non-volatile organic residues.

The difference between the amount of ash and the amount of ash remaining after removing water, glycerin and other volatile substances from the analyzed product under certain conditions is taken as the index [11,12].

Determination of mass fraction of moisture and volatile substances.

The mass fraction of moisture and volatile substances in glycerin was determined by drying to a constant mass in a drying oven [11,12].

Results

Ion exchange technology was used to refine glycerin without distillation. For this, technical glycerin is treated with phosphoric acid and refined of its impurities. Then, metal salts contained in glycerin are separated with cationite.

The technical glycerin was refined with mineral acid. For this, technical glycerin put into the flask. The flask was then stirred and heated using a magnetic stirrer. Phosphoric acid was added to the flask and stirred at a constant speed of 200 rpm for 1 hour. The mixture separated into layers of free fatty acid, glycerin and inorganic salt. The first layer containing fatty acids was separated by decantation and the salt precipitate was removed by filtration. NaOH was added to the middle layer containing glycerin and neutralized. After that, obtained salts were separated.

The influence of technological parameters on the processing of technical glycerin with phosphoric acid was studied. In this case, the pH value was 2-6, the process temperature was 30-70 °C, and the reaction duration was 20-60 minutes. The obtained results are presented in Figure 1.

Figure 1. Effect of process parameters on the change of glycerin concentration during the treatment of glycerin with phosphoric acid

From the data in Figure 1, it can be seen that the pH significantly affects the acid treatment process and the quality of the obtained product. The highest values were achieved at a pH value of 2, a temperature of 70 °C and a process duration exceeding 40 minutes.

Conclusion

In the following experiments, the glycerin obtained under these conditions was refined by using a cationite. For this, KU-2-8 brand cationite was placed in a glass tube with a volume of 300 ml. The acid-treated glycerin was passed through the column (25 °C). Glycerin delivery rate was 20-60 ml/min and cation content were 20-60 g. The obtained results are given in Figure 2.

Figure 2. Effect of process parameters on the change of glycerin concentration during the treatment of acid-treated glycerin with cationite

From the data in Figure 2, it can be seen that the degree of purity of the obtained glycerin is inversely proportional to the flow rate of glycerin and directly proportional to the amount of cationite. Purity of glycerin increased from 89% to 98% when cation content increased from 20 g to 60 g. However, this increase value varied depending on the glycerin flow rate. When the glycerin flow rate increased from 25 mL/min to 75 mL/min (20 g of cationite), the purity of the obtained glycerin decreased from 89% to 87%. In summary, the optimum amount of cationite in the process of refining glycerin was 40 g and the glycerin flow rate was 25 ml/min.

In order to evaluate the effectiveness of the conducted experiments, the physico-chemical properties of raw glycerin, acid-treated and cationite-treated glycerins were analyzed and compared (Table 1).

Table 1.

Physico-chemical properties of technical, acid-treated and cationite-treated glycerin

It can be seen from Table 1 that technical glycerin contains 78.5% glycerin, but the ash content, water content and non-volatile organic residues are high. This glycerin corresponds to 3^rd grade 2^nd brand glycerin according to GOST 6823. After treatment with phosphoric acid, the glycerin content increased from 78.5% to 88.3% and the water content increased from 2.1% to 2.4%, the ash content increased from 8.9% to 4.1% and non-volatile the amount of organic residue decreased from 10.5% to 5.2%. Physical and chemical characteristics/properties of glycerin were further improved after cleaning with cationite. In particular, the amount of glycerin increased to 98.1%, the water content decreased to 1.7%, and the amount of ash and non-volatile organic residues decreased to 0.1%. According to these indicators, it corresponds to the control glycerin. It can even be seen that it outperforms distilled glycerin in terms of color and clarity.

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