What role does solvent play in dewaxing technology?
The solvent dewaxing technology started relatively late. In 1927, the first acetone benzene dewaxing device appeared and began to be put into use. The base oil raw material first passed through a sleeve crystallizer. After wax crystals were generated, the base oil was transported to a spherical solution container using ammonia as a catalyst, and then recycled to transport acetone benzene or other solvents to separate the lubricating oil from the wax. The next step was to send these mixed solutions to the filter to achieve the separation of the solvent solution containing the lubricating oil from the wax crystals. For the separated solvent mixture, distillation can be used to separate the solvent from the lubricating oil.
Although there are various solvent dewaxing technologies for lubricating oil today and their forms may vary greatly, their basic processes and principles have undergone significant changes from the above. The important differences among various solvent dewaxing technologies lie in the selection of solvents, improvement and innovation of crystallization equipment, improvement of filtration equipment, and treatment of solvent recovery. But the basic process of "crystallization, dissolution, filtration, and extraction" has not changed much. In addition, the use of catalysts (such as ammonia mentioned earlier) to improve the efficiency of dewaxing is also a hot topic in this field. As an ancient dewaxing technology in the field of lubricating oil dewaxing, solvent dewaxing technology has undergone multiple improvements and innovations. Whether it is in improving equipment efficiency or exploring the use of solvents and catalysts, its effectiveness has been greatly improved compared to previous solvent dewaxing technologies. Below, the author will explore the current solvent dewaxing technology from four aspects: the use of dewaxing solvents, the selection of catalysts, innovation in solvent dilution methods, and distillation purification of lubricating oil and solvents.
2.1 Selection of solvents
Solvents are mainly used to separate wax and lubricating oil by varying their solubility. When selecting a solvent, both positive and negative factors can be considered. On the one hand, the selected solvent can be well soluble in lubricating oil but poorly soluble in wax. On the other hand, the opposite is true. Solvents have a good solubility effect on wax but are not easily soluble in lubricating oil. On the surface, the latter method appears to be more convenient because it only requires filtration to obtain dewaxed lubricating oil. However, in reality, there are very few solvents that meet the requirements of the latter, and the price is very expensive. Generally, the former is used for industrial refining of lubricating oil.
Some factories do not use a single solvent when blending solvents, but instead use a mixture of multiple solvents to achieve effects that cannot be achieved by a single solvent. This method has actually been used for a long time, such as the combination solvents of acetone, benzene, and toluene commonly used in the early days, as well as the combination liquids of butanone and toluene that later replaced it, and so on. In addition, the rate of change in the volatility, boiling point, and solubility of the selected solution during temperature changes must also be considered when selecting solvents.
2.2 Selection of catalysts
To achieve good results in solvent dewaxing, the selection of dewaxing additives is also very important. The dewaxing agent plays a catalytic role in the solvent dewaxing process. The main purpose of dewaxing lubricating oil is to obtain high-purity lubricating oil, but its by-product paraffin is also an industrial product with high practical value. The use of the dewaxing agent can make the obtained wax crystal particles larger and have lower oil content. The commonly used dewaxing additives currently include methacrylate, fumarate copolymer, chlorinated polymer, and so on. There is not much research on dewaxing additives in China, and imported products are commonly used in industrial production.
2.2 What are the solvent dilution methods?
The base oil that has undergone wax crystallization is not simply mixed into the solvent dilution process. There are still many precautions and measures to be taken in the solvent dilution process. There are currently two commonly used dilution methods in industry, namely multi-point dilution and filtrate comprehensive circulation process. The author will now explain the multi-point dilution process: multi-point dilution refers to adding a solution to the mixture to be diluted in stages and quantities. This segmented placement method produces better dilution effects than a one-time complete injection. Generally speaking, multi-point dilution in industry is mainly carried out for different purposes. The first addition of solvent is to obtain good wax crystallization, the second addition is to reduce the viscosity of the wax mixture, and the third addition is to remove oil from the wax crystallization.
2.3 Distillation
Distillation is the process of using a mixture or solid-liquid system to separate different substances by increasing or decreasing their boiling points, and then gradually evaporating and condensing their different components. In the industrial production process, multi effect evaporation technology is often used to introduce the steam evaporated from one evaporator into the next evaporator, and use the heat released from its condensation to heat the water in the evaporator. Two or more evaporation systems are connected in series to fully utilize heat energy. This method can fully utilize heat and reduce production costs.
