The sulfuric acid-white clay refining process is the first process to be used in the research of waste oil regeneration technology at home and abroad, in which a large amount of sulfuric acid and white clay are used to treat waste oil. The waste oil is pretreated (pre-flash or vacuum distillation) to separate water and light hydrocarbons, and concentrated sulfuric acid (10%~15%) is added to the dehydrated waste oil, such as colloidal, asphaltene, oxidation products. The impurities will form sludge, which can be deposited within 16 to 48 hours and then separated from the waste oil. The filtered oil is distilled to produce a base oil of fuel oil having various characteristics.
When sulfuric acid is refined, it mainly acts as a chemical reaction, including sulfonation, esterification, superposition, and shrinkage neutralization. In addition, there are physicochemical flocculation and physical dissolution. Sulfuric acid reacts with non-ideal components present in the waste oil, has a strong ability to remove non-hydrocarbons, and can be removed fairly thoroughly for olefins. However, the sulfuric acid-treated reclaimed oil sample does not achieve the expected effect in terms of quality or use effect and value. Therefore, the acid-treated oil sample needs to be refined by a large amount of white clay to make the regenerated oil. The color is more clear, stability and viscosity are also closer to the characteristics of normal diesel, and finally get the qualified oil that meets expectations. However, in the refining process, the method generates a lot of acid gas such as sulfur dioxide, which is harmful to the human body, and solid waste such as acid slag, and is accompanied by liquid hazardous substances such as acid water.
In addition, the subsequent white clay refining process will still cause environmental pollution and oil-saturated white clay that is difficult to handle. Under the increasing environmental pressure, under the concept of rapid economic development required by the current modern economic system, which has gradually turned to economic friendly development and green development, this technology has been banned in most countries including many developing countries. – It is only a matter of time before the white clay process is eliminated by the times.
The solvent refining process is still one of the current methods for producing diesel in the mainstream industry. The principle of solvent refining is to use certain organic solvents to distinguish the solubility of hydrocarbons and additives, oxidation products and sludges contained in waste lubricating oils, and to add additives, oxidation products, sludges, etc. in waste oil under certain conditions. The impurities are removed, and then the solvent is distilled off to obtain a crude product, and the crude product is purified by white clay to become a regenerated oil.
In foreign countries, solvent refining has gradually changed from propane to N-methylpyrrolidone and furfural as a solvent for this refining process, in which N-methylpyrrolidone is widely used because it is superior to other solvents because it has the lowest It is toxic and can be used at lower agent to oil ratios, saving energy. Domestically, the study mainly studies the mixture of alcohol and ketone (isopropanol, acetone, etc.) [8-10] as a solvent, which can reduce the coking and scaling problems in the subsequent solvent recovery distillation process.
Although the solvent refinement process has all of the above advantages, there are still some problems that cannot be solved. A disadvantage of solvent refining techniques is the dependence of the quality of the finished oil on the quality of the raw materials, as this process is a physical process and does not involve any chemical reactions. At the same time, the ratio of the agent to the oil in the refining process is high, and the use of such a solvent with a certain toxicity may cause serious damage to the environment and equipment. However, the unstable price fluctuation of N-methylpyrrolidone solvent and the high unit price are also one of the reasons that restrict the development of the process. Although the solvent can be recycled and reused, the recovery is difficult, the recovery cost is also high, and the recovered oil sample yield is not ideal.
Nowadays, domestic and foreign research has begun to study how to improve the solvent refining process. In this regard, most of them involve the addition of additives. A simple understanding of the additive technology is to add a certain amount of suitable additives in the solvent refining process in order to solve various problems that often occur in the solvent refining process, in order to obtain better refining effect  . At present, most of the research on additive technology is still limited to the preliminary research in the laboratory. It is still difficult to realize in the amplification experiment and industrial use. Therefore, the additive technology still has great research value.
The hydrofinishing reaction aims to remove hetero elements, hydrogenated olefins and aromatic compounds, as well as hydroconversion reactions aimed at modifying the hydrocarbon structure by cracking and isomerization. The hydrotreating catalyst consists of an active phase made of molybdenum or tungsten sulfide and on the oxide support from cobalt or nickel. The oil and hydrogen are preheated and the oil is trickled down through a reactor filled with catalyst particles in which hydrogenation occurs. The oil product is separated from the gas phase and then stripped to remove traces of dissolved gases or water. Because hydrorefining can reduce the loss of effective substances in oil samples, increase the yield of reclaimed waste oil, and does not produce a large amount of waste white soil in the process of white clay refining and pollute the environment, so the hydrogen replenishing and refining process has gradually replaced Refined clay is used as the last step in the reprocessing process and plays a major role in the research of waste oil regeneration.
Almost all of the foreign countries use the hydrorefining process to regenerate the waste oil. Compared with other technologies, the hydrogenation process has the following disadvantages: high pressure and high temperature; hydrogen supply facilities are required; high safety standards; high operating costs and capital costs; Operating efficiency; crude oil analysis and pretreatment; catalyst regeneration. Under this circumstance, the technology of applying the pressurization process requires relatively high investment, the hydrogenation process has high requirements on the equipment, and the operating conditions are also relatively strict, so the cost of producing unit regenerative oil is relatively high. For China, which is still in the ranks of developing countries, there are still many difficulties in the comprehensive promotion of the hydrogenation refining process.
The evaporation which accelerates the evaporation process by forming a liquid into a film is called film evaporation. The principle that film evaporation can accelerate evaporation is that the liquid forms a film under reduced pressure. The film has a large vaporized surface area, and the heat is spread quickly and evenly. Without the influence of liquid co-pressure, the material can be prevented from overheating. In a thin film evaporator for waste oil treatment, the feed is distilled into two parts by a cyclone column, and light hydrocarbons are easily and rapidly distilled due to the formation of a tangential flow film. The lighter vaporized portion consisting of light hydrocarbons (gas, diesel) and water condenses in the upper part of the chamber and separates therefrom. The heavier oil portion that circulates at the bottom is heated, thereby reducing heat transfer in the chamber and reducing coke formation.
Chemically pretreats waste oil to prevent the precipitation of contaminants that may cause corrosion and contamination of the equipment. The pretreatment step is carried out at a temperature of 80 to 170 °C. The chemically treated compound includes sodium hydroxide in an amount sufficient to bring the pH to about 6.5 or higher. The pretreated waste oil is first distilled to separate water and light hydrocarbons. The water is treated and sent to a wastewater treatment facility where light hydrocarbons are used as fuel or sold as products. Thereafter, the anhydrous oil is distilled in a thin film evaporator under high vacuum to separate the diesel fuel, which may be used at the factory or sold as a fuel. Heavy materials such as residues, metals, additive degradation products are transferred to the heavy asphalt stream.
The Vaxon and EcoHuile (Sotulub) processes are based on vacuum distillation of oil fractions in thin film evaporators to reduce coking caused by hydrocarbon and oil impurity cracking at elevated temperatures. Both processes pretreat the alkaline waste oil, which requires the elimination of synthetic and vegetable oils in the feed. The Vaxon process has additional solvent extraction equipment that produces higher quality product oils compared to Ecohuile products. Despite this, the product quality is worse than the solvent extraction process described above. In order to produce high quality base oils, post-processing steps are added to the thin film evaporation technology and used in conjunction with other technologies, but these modifications will increase operational and capital costs, making this less economically attractive.
The basic principle of membrane separation technology is that under the action of some external driving force, various substances with different properties in the raw material liquid can selectively pass through the membrane, thereby effectively separating the substances of different components and Targeted purification of substances]. Membrane separation technology is a new energy-saving separation technology. Its advantages are mainly environmental protection, high separation efficiency, simple operation, high safety and easy industrial use. On the other hand, the application of membrane separation technology can be improved. The waste oil regeneration rate reduces the unnecessary loss of raw materials, and can reduce the amount of white clay used in the subsequent white clay refining process, which not only reduces the generation of solid waste residue, but also makes the economic accounting of the process more reasonable, and is a large-scale industrial production. Provide the basis.
Mynin et al. use an inorganic film based on graphite and ceramics to regenerate waste industrial lubricants, transformer lubricants, and engine oils. The results show that the quality of industrial lubricating oil and transformer lubricating oil can be reused after being filtered by inorganic ceramic membrane. The physical and chemical properties of engine oil can also be improved to some extent. YuheCao and other three hollow fiber polymeric membranes (PES, PVDF, PAN) are used to treat the regenerated waste lubricating oil, which not only effectively removes metal particles and dust, but also greatly improves the viscosity and flash point of the reclaimed oil.
At present, membrane separation technology has been widely used. Experts and scholars at home and abroad have done a lot of research on membrane technology to treat oily wastewater, and have achieved good results, but it is still difficult to apply in waste oil regeneration treatment. . Because the waste lubricating oil has complex components, high impurity content, and high viscosity, the membrane separation and regeneration of the waste lubricating oil has problems of small membrane permeation flux and serious membrane fouling. Concentration polarization and membrane fouling can significantly reduce the membrane permeation flux and shorten the service life of the membrane, which is the main factor that restricts the application and development of the membrane process.
Sulfuric acid-soil treatment is the first petroleum regeneration process used, but has been gradually replaced by new technologies such as solvent extraction and hydrotreating. Most solvent extraction techniques currently use propane and isopropanol as solvents, but they have lower selectivity for non-ideal components and require a high agent-to-oil ratio, which increases energy consumption. Hydrorefining can reduce the loss of effective substances in oil samples, increase the yield of regenerated waste oil, and does not produce a large amount of waste white soil in the process of white clay refining and pollute the environment. Therefore, the hydrogen replenishing and refining process has gradually replaced the white clay. Refined, but because hydrotreating requires excessive capital investment and operational restrictions, it can no longer be widely used in SMEs.
The post-processing steps are added to the thin film evaporation technology and need to be combined with other technologies, but these modifications will increase operational and capital costs, making this less economically attractive. Most processes use different technologies such as solvent extraction and hydrofining, thin film evaporation and different refining processes and hydrotreating. However, from the current analysis of the status quo of domestic waste oil regeneration, the most attractive method for re-refining waste oil can be a combination of solvent extraction and membrane separation, which should be explored in the best solvent and solve the problems in membrane treatment. Increase research efforts.