STUDY OF SOLVENTS CAPACITY FOR EXTRACTION

ABSTRACT

This article investigates the efficiency of extracting aromatic hydrocarbons—primarily benzene—from liquid products derived from pyrolysis and reforming processes through extractive distillation. A model system composed of 35% n-hexane and 65% benzene was used to simulate industrial mixtures. The study evaluates the extraction performance of diethylene glycol (DEG), dimethyl sulfoxide (DMSO), and their binary mixtures at varying compositions and process temperatures. Experimental data revealed that a solvent mixture with a 1:1 mass ratio of DEG and DMSO provides optimal separation performance, achieving a benzene content in the extract of up to 87.8% and in the raffinate as low as 16.6%. The influence of temperature (20°C–60°C) on extraction efficiency was also studied. The findings demonstrate that mixed solvents outperform single-component solvents in terms of benzene extraction, with the most effective results obtained at 40°C.

АННОТАЦИЯ

В данной статье рассматриваются возможности экстракции ароматических углеводородов, в частности бензола, из жидких продуктов, полученных в результате процессов пиролиза и риформинга. В качестве модельного раствора была выбрана смесь, содержащая 35% н-гексана и 65% бензола. Исследовано влияние диэтиленгликоля (ДЭГ), диметилсульфоксида (ДМСО) и их смесей в различных соотношениях на процесс экстракции. Также проанализировано влияние состава растворителя и температуры процесса на эффективность экстракции.

Keywords: diethylene glycol (DEG), dimethyl sulfoxide (DMSO), extraction, n-hexane, benzene, toluene, xylene, pyrolysis condensate.

Ключевые слова: диэтиленгликоль (ДЭГ), диметилсульфоксид (ДМСО), экстракция, н-гексан, бензол, толуол, ксилол, пиролизный конденсат.

Introduction

Aromatic hydrocarbons—such as benzene, toluene, and xylenes (BTX)—are essential building blocks in the petrochemical, pharmaceutical, and fine chemical industries. These compounds serve as raw materials for the production of polymers, synthetic fibers, dyes, detergents, resins, and numerous other value-added chemicals. With increasing demand for BTX compounds, efficient and cost-effective methods for their recovery from complex hydrocarbon mixtures have become a significant focus of industrial and academic research[1].

One promising source of aromatic hydrocarbons is the condensate derived from the pyrolysis of hydrocarbons, which is a byproduct in the production of light olefins such as ethylene and propylene. These condensates typically contain high concentrations of benzene, toluene, and xylenes, making them attractive feedstocks for aromatic recovery. Reformate streams from catalytic reforming units in petroleum refineries also contain substantial amounts of BTX compounds. Therefore, developing efficient separation technologies for recovering aromatics from such mixtures is of practical and economic importance[2].

Among the various separation techniques, extractive distillation has emerged as an effective method for separating aromatics from non-aromatic hydrocarbons. The process relies heavily on the choice of solvent, as well as operating conditions such as temperature and solvent-to-feed ratio. Solvents such as diethylene glycol (DEG) and dimethyl sulfoxide (DMSO) are commonly studied due to their selective affinity for aromatic compounds. The use of mixed solvents offers potential advantages in optimizing selectivity and process performance[3].

Objective of the study

The main objective of this study is to investigate the efficiency of benzene extraction from a model hydrocarbon mixture using extractive distillation, with a particular focus on the performance of diethylene glycol (DEG), dimethyl sulfoxide (DMSO), and their mixtures[4].

Research tasks

To achieve this objective, the study addresses the following key tasks:

To prepare and use a model solution consisting of 35% n-hexane and 65% benzene to simulate pyrolysis condensate.

To evaluate the impact of using DEG, DMSO, and mixed DEG+DMSO solvents (in varying ratios) on benzene extraction efficiency.

To analyze how changes in process temperature (20°C to 60°C) affect the separation performance of individual and mixed solvents.

To determine the composition of the extract and raffinate phases under different experimental conditions.

To identify the most efficient solvent composition and process conditions for maximizing aromatic hydrocarbon recovery.

Materials and methods

To study the patterns involved in the separation of aromatic hydrocarbons from pyrolysis condensate using the extractive distillation method, a series of scientific and practical experiments were conducted using a model solution system composed of n-hexane and benzene. For simulating the pyrolysis condensate extraction process, a mixture of 35% n-hexane and 65% benzene was used.

Single-stage extraction was carried out under the following conditions:

Temperature: 35°C

Solvent-to-feed mass ratio: 1:1

Water content: 5% (by mass)

Mixing duration: 15 minutes

Settling time: 30 minutes

The results of single-stage extraction of benzene from the model system using diethylene glycol (DEG), dimethyl sulfoxide (DMSO), and their mixtures containing 10–90% DMSO are presented in the table. As the DMSO concentration in the DEG-based mixed solvent increased from 10% to 40%, the extraction yield decreased compared to pure DMSO and DEG. However, a further increase in DMSO concentration in the mixture led to a corresponding increase in extraction yield[5].

The increase in raffinate yield was studied in relation to changes in dimethyl sulfoxide concentration in the mixed solvent within the 10–90% range. The extraction process carried out using a mixed solvent consisting of 50% DMSO and 50% DEG showed the highest raffinate yield (Table-1).

Table 1.

Experimental Results of Single-Stage Extraction of Benzene from the Model Solution

A graph illustrating the dependence of benzene extraction efficiency from a model mixture of n-hexane and benzene on the variation of DMSO concentration in a DEG-based mixed solvent is presented in the figure.

The addition of 10% DMSO to the DEG solvent did not lead to a significant change in the degree of benzene separation from the model mixture. However, adding 20% DMSO resulted in a slight increase in extraction efficiency. The highest benzene separation efficiency was observed when using a DEG+DMSO mixed solvent containing 40–50% DMSO for extracting the model mixture. Further increases in DMSO concentration led to a decrease in the benzene content within the extract.

The degree of benzene extraction from the model solution was found to be higher when using DEG compared to DMSO alone. However, experiments showed that extraction based on the DEG+DMSO mixed solvent yielded even better results than using either solvent individually (Figure-1).

Figure 1. Graph of the Dependence of Benzene Separation Efficiency from the Model Solution on the Composition of the Mixed Solvent 

To evaluate the quality of the obtained raffinate and extract products, the benzene content in each was determined. The figure presents a graph showing the dependence of benzene content in the raffinate and extract on the DMSO concentration in the mixed solvent.

When extraction was carried out with mixed solvents containing 40–50% and 70% DMSO, low benzene content was observed in the raffinate. As the DMSO concentration in the mixed solvent increased from 70% to 100%, extracts with lower benzene concentrations were obtained from the model solution. The extract with the highest benzene content was obtained using a mixed solvent containing 50% DMSO.

Thus, the lowest benzene content in the raffinate was recorded at 16.6%, while the initial model mixture contained 50% benzene, and the highest benzene content in the extract reached 83.7%.

Among all the conducted experiments, the extraction process using a mixed solvent of 50% DMSO and 50% DEG demonstrated the highest efficiency for benzene separation from the model solution. 

Figure 2. Graph Showing the Effect of DMSO Concentration in the Mixed Solvent on Benzene Content in Raffinate and Extract During Benzene Separation from the Model Solution

In order to determine the patterns of variation in the extraction properties of individual and mixed solvents depending on extraction conditions, several experiments were conducted using a model mixture consisting of 35% n-hexane and 65% benzene as the feedstock. The effect of temperature on the degree of benzene separation from the model mixture, its content in the extract and raffinate, and the yield of both extract and raffinate was studied under the following conditions: extraction duration – 45 minutes, feedstock-to-solvent mass ratio – 1:1, and water content in the solvent – 5%.

Results and discussion

The results of single-stage extraction conducted at temperatures ranging from 20°C to 60°C are presented in the table. An increase in temperature led to a higher extract yield in the DMSO solvent environment. Similarly, in DEG and mixed solvent systems, a positive effect on extract yield was observed within the 20°C to 50°C range.

The graph in Table-2 shows the dependence of benzene separation efficiency from a benzene–n-hexane mixture on the extraction process temperature (20°C–60°C). In all individual and mixed solvent systems, the degree of benzene separation from the model solution increased in the 20°C–40°C range. When the temperature was raised up to 60°C, a decrease in benzene separation efficiency was observed in the DEG solvent environment, whereas in the DMSO environment, it continued to increase.   

Table 2.

Results of Single-Stage Benzene Extraction from the Model Solution at Various Temperatures

The graph clearly shows that, when the extraction process temperature is increased from 40°C to 60°C, the degree of benzene separation from the model solution remains relatively unchanged in the mixed solvent, but is higher compared to the results obtained with individual solvents.

Conclusion

The effect of increasing the extraction temperature on the benzene content in the raffinate is illustrated in the graph. Experimental results showed that as the extraction temperature increased during the process using a mixed solvent, the benzene content in the resulting raffinate decreased. The influence of dimethyl sulfoxide concentration in its mixture with diethylene glycol on the degree of dearomatization of pyrolysis distillate was also studied. The composition of the mixed solvent that enabled the production of raffinate with low aromatic compound content was determined. Experimental results revealed that, for extracting aromatic hydrocarbons from pyrolysis distillate via extractive distillation, the most optimal mixed solvent was one with a DEG:DMSO mass ratio of 1:1.

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