SYNTHESIS OF SUPEROLEOGELS AND IMPROVEMENT OF THEIR ABSORPTION FOR THE PURIFICATION OF ORGANIC SOLVENTS FROM WASTEWATER

ABSTRACT

This research paper describes methods for synthesizing a new type of oleogel capable of effectively working with rubber, acrylic acid, crotonaldehyde, and a crosslinking agent. Effective methods for collecting petroleum products and organic compounds have been developed. The ability of oleogel to absorb dissolved substances, retain them, and return them when necessary has been determined. Preparation of oleogels in various environments depending on temperature, concentration, and composition, as well as the study of their cross-linking, influence on the structure of polymer chains and properties of oleogels, and the production of highly swellable oleogels based on rubbers.

АННОТАЦИЯ

В данной исследовательской работе разработаны методы синтеза нового типа олеогеля, способного эффективно работать с каучуком, акриловой кислотой, кротоновым альдегидом и сшивателем. Разработаны эффективные методы сбора нефтепродуктов и органических соединений.  Определена способность олеогеля поглощать растворенные вещества, удерживать их, возвращать при необходимости. Приготовление олеогелей в различных средах в зависимости от температуры, концентрации и состава, а также изучение их сшивания, влияния на структуру полимерных цепей и свойства олеогелей, а также получение высоконабухающих олеогелей на основе каучуков.

Ключевые слова: Каучук. Олеогель. Абсорбент. Растворитель. Ксилол. Кротоновый альдегид.

Keywords: Rubber. Oleogel. Absorbent. Solvent. Xylene. Crotonaldehyde.

Introduction

Currently, hydrophobic and oleophilic porous materials are considered the most convenient solution for collecting petroleum products and organic solvents. Oleogels are very effective in neutralizing spilled hydrocarbon compounds and oily substances due to their high assimilation capacity and excellent efficiency in processing and returning absorbed petroleum products. However, in practice, synthetic materials such as polyurethane foam, poly(tetrahydrofuran), and porous polydimethylsiloxane materials are used in most cases. The disadvantage of these synthetic sorbents is their high production cost and large amount of waste. Polystyrene is cheap and lightweight, but it is highly flammable and emits toxic gases when burned. Therefore, the synthesis and use of oleogels based on natural rubber (NR) are recognized as the most effective.

Natural rubber (NR) is an important recyclable polymer material with excellent flexibility and mechanical properties. It is easy to produce in the form of foam, which has elasticity, low density, and pronounced hydrophobic properties. Therefore, NR foams are one of the promising candidates for use as oil sorbent materials.

A number of methods for improving the absorption properties of NR foams with respect to petroleum products have been studied, including chemical modifications and the preparation of composite materials.

In this study, maleic anhydride was added to isoprene rubber (IR) for cross-linking to improve its ability to absorb petroleum products, as cross-linking increases the strength of the polymer. In addition, it reduces the hardness of the rubber compared to sulfur, forming a relatively elastic product - oleogel. Another feature is that after a certain amount of cross-linking, the hydrophobic properties improve and the degree of swelling increases without turning into a rubber state. This study investigates the physicochemical properties of oleogel compositions that absorb oil and grease, obtained from various grades of rubber. The elasticity of SKI and the high surface-active stability of maleic anhydride led to good absorption of petroleum products and grease by the composition. To determine the sorption of complex fats on oleogel and the factors affecting it, sorption mechanisms were studied. The results of this comprehensive study are aimed at further developing and improving the rubber industry to protect the environment from harmful waste.

In this research work, isoprene rubber (SKI) and maleic anhydride as a binder were used to obtain a swelling oleogel product in petroleum and oils.

Synthesis process

During the reaction, benzoyl peroxide was used as an initiator to accelerate the process and form an active center. The reaction was carried out in the following sequence: First, a solution of isoprene rubber (SKI) was prepared in 9% toluene, then 0.5% crotonaldehyde was added relative to the rubber to accelerate the start of the reaction when the reaction temperature reached 50 °C, and benzoyl peroxide initiator was used in an amount of 0.1% relative to the rubber to form a radical.

The reaction was carried out at 85°C. The resulting product was first dried at room temperature and then in an oven at 50°C. The finished oleogels swelled in toluene, xylene, and gasoline. It was found that the oleogel product was capable of absorbing up to 100% of toluene, up to 94% of xylene, and 81% of gasoline. The finished oleogels swelled in toluene, xylene, and gasoline.

Oleogel formation is a relatively new approach to cleaning up spilled petroleum products and creating new solid materials without changing the chemical properties of the substances formed. The resulting oleogels are based on the formation of bonds by adding binding agents to the rubber structure.

The surface and high elasticity properties of the sorbent materials were tested in a mixture of water and crude oil, and the wetting of the sorbent materials was compared. Each sorbent exhibited different behavior during absorption. Among the four sorbents (SKI, BSK, SKN, and TK), a drop of water or salt water was more stable on almost all of them (with a hemispherical shape and a surface angle of 124°), i.e., the hydrophobicity on the surface of all sorbents was greater. At the same time, all sorbents also show a tendency toward decreased hydrophilicity, which indicates a reduction in contact angles (74 and 83°, respectively). In addition, water droplets and salt water have become oval in shape. Due to the small difference between the angles of interaction of SKI, BSK, SKN, and TK with water, it can be concluded that the concentration of cross-linking agents added to rubbers corresponds to their concentration. If water or salt water gets between the sorbent macromolecules, the oil absorption angle decreases. If the sorbent macromolecules do not absorb water, it can be seen that the materials of these sorbents absorb crude oil well. During the absorption of highly viscous oils and greases, a large volumetric displacement layer forms on the surface of the sorbent. It can be seen that the distribution of crude oil on the surface of oleogels during absorption leads to the formation of a larger coating on virtually all sorbents compared to all others. This is due to the different morphology of the sorbents. If, during the sorption process, the diffusion oil passes along the length of the fiber, this means that the degree of sorbent cross-linking is high or the hydrophilicity is increased. If the diffusion oil is absorbed on the surface of the sorbents, i.e., penetrates into the macromolecule, then increased hydrophobicity can be observed.

The absorption properties of sorbents for various aqueous media are shown in Fig. 1-a. Two types of petroleum products (diesel and crude oil) were used as representatives of petroleum products. In the oil-water system (Fig. 1a), it can be seen that the absorption capacity of the BUK-based oleogel is higher than that of other oleogels (1.2-1.36 times for diesel and crude oil, respectively). This is due to the fact that the presence of styrene in the BSK-based oleogel creates an increased surface area for sorbent materials, resulting in increased oil absorption in molecules with this structure. Oil absorption also depends on the concentration level of the cross-linking agent. The amount of crosslinker was 0.5%. Adding more than 0.5% of the crosslinker to the BSK-based oleogel reduces the oil absorption capacity, as petroleum products cause dense crosslinking of the sorbent matrix and reduce the absorption of petroleum products. The amount of product absorbed in 60 minutes is shown in the results in Fig. 1.

Figure 1. Ability of oleogels to absorb petroleum products in water-oil and salt water-oil systems

In a saline water-oil system (Fig. 2 (b)), the oil content of sorption materials is slightly (<1.2 times) higher than in a water-oil system, which is due to the influence of salinity, ions, and foreign bodies. The salinity of salt water can increase the double electric layer between the sorbate and sorbent materials, which leads to an increase in the ability to absorb oil. The maximum efficiency of oil product absorption was obtained with a 0.5% crosslinker. Thus, an oleogel sorbent based on 0.5% BUK was selected for further research.

In addition, the ability to absorb oil depends on the density and viscosity of the oil. It can be seen that oil (or diesel) with low viscosity easily spreads over the surface and immediately penetrates into the sorbent, while oil with high viscosity (crude oil) remains on the surface of the sorbent and slows down its penetration into the interior of the oleogel. Therefore, it can be concluded that sorbent materials are absorbed faster in low-viscosity oils than in high-viscosity oils.

The use of these sorbent materials for collecting spilled petroleum products is the main objective of this study. Accordingly, the influence of conditions (temperature and swelling) of the salt water environment on the absorption capacity of various sorbent materials (SKI, BSK, SKN, and TK) to absorb crude oil was studied. The results obtained are shown in Figures 2 With an increase in temperature from 4 to 45 °C and the appearance of rotational movement at a speed of 150 rpm, the absorption capacity of BSK and SKN oleogels increased by 3 and 2.4 times, respectively. However, their absorption capacity reaches a maximum at 45°C, and at higher temperatures (60 and 70°C), this capacity begins to decrease again.

Figure 2. Results obtained

Table 1 compares the absorption capacities of various sorbent materials that absorb petroleum products. Various sorbent materials can be used to extract petroleum products from water. In addition, several researchers have suggested that the addition of cross-linking agents can increase the adsorption capacity of the resulting adsorbent to absorb petroleum products, including in our proposed work. At the same time, the oil absorption capacity of each sorbent material depends on a number of factors, such as the hydrophobic properties of the sorbent material and the properties of the oil.

Table 1.

Comparison of oil absorption capacity of various sorbents that absorb petroleum products

Сonclusion. It can be said that in this study, oleogels obtained on the basis of rubbers were successfully studied as a sorbent for the purification of petroleum products. The ability of synthesized oleogels to absorb petroleum products depending on their structure and composition was studied, and the dependence on various factors, such as oil type and oil properties, was established. The studies showed that the synthesized oleogels absorb on average from 92% to 99% of petroleum products. The ability of synthesized oleogels to absorb petroleum products increases depending on the degree of rubber cross-linking, which is optimal in BUK-based oleogel. It has been established that synthesized oleogels sorb diesel fuel better than raw petroleum products, which increases the distribution of diesel fuel in sorbent materials.  Thus, the BSK-based oleogel presented in this study can be considered a promising alternative petroleum sorbent for petroleum products spilled in field conditions.

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