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Original Title: Status of Waste Oil Regeneration and Brief Introduction of Its Process Technology Total Cumulative Title 1350 The status of waste oil regeneration and brief introduction of its technology Source: Guangdong Chemical Authors: Yu Yanyan, Yang Xin, Wang Jie Waste oil is a dihedron, which has the dual characteristics of pollution and resource: improper treatment will cause environmental pollution, and recovery and recycling will save energy and alleviate the pressure of resource shortage. According to the provisions of the National List of Hazardous Wastes, waste mineral oil belongs to hazardous waste, numbered HW08. On February 4, 2017, the 2016 edition of the Guidance Catalogue of Key Products and Services for Strategic Emerging Industries, compiled by the National Development and Reform Commission, was officially released, in which the recycling of waste mineral oil was listed in the Guidance Catalogue of Key Products and Services for National Strategic Emerging Industries. However, by 2017, there were 523 enterprises with waste oil recycling and treatment qualification in China, and only 1/3 of the waste oil was treated by these compliant enterprises. A considerable part of the waste mineral oil was basically treated by non-qualified enterprises, and some of them were not properly disposed of, but were often treated by negative means such as disorderly disposal, arbitrary disposal, burning and burying. However, in China, the research on the regeneration process of waste oil was carried out relatively late, and the related investment was relatively small. Only some special petroleum industries could use advanced technology, while most of them were refineries in the form of small workshops, with backward technology, resulting in very low value of finished products. The low price has further limited the development of the industry, and the process has not been improved. In foreign countries, many advanced technologies and processes are becoming mature and have reached the stage of industrial production, such as acid-free process, distillation-hydrogenation and other processes are becoming the mainstream of waste oil treatment in Western countries. However, due to the advancement of these technologies, the complexity of operation, the large one-time investment of regeneration equipment and the need for high-level skilled workers, it is difficult to implement a large number of these technologies in China at this stage, so finding a better solution has become the key to waste oil treatment in China. 1. Current status of waste oil recycling In foreign countries, the regeneration of waste oil started earlier. In the 1960s, some developed countries in Europe and the United States began to study it, and since then they have accumulated valuable experience. Until now, the western countries are in the leading position in the waste oil recycling industry and even in the whole oil industry. The reasons for their success are related to the improvement of policies and government subsidies. It can be seen that relevant government policies, industry standards and market cooperation are prerequisites for achieving a virtuous circle of waste oil regeneration. The 2013-2017 China Waste Oil Market Supply and Demand Analysis and Investment Prospect Research Report released by Booz Data shows that although China's waste oil products have always existed, there has been no effective progress in the effective utilization of waste oil. China's waste oil market is large and will grow with the increase of market demand. However, in China, the reasonable recovery rate of waste oil is not high, which is mainly affected by the relevant policies and regulations of national and local industries, upstream waste oil recovery links, downstream regeneration technology and other restrictions. Expand the full text Although the state and the oil industry have been promoting the formulation and implementation of policies, from the current point of view, although policies and regulations have guiding significance, they are not enforced, there are no severe penalties and certain financial incentives, resulting in many difficulties in operation. Due to the vast land area, the investment and understanding of waste oil recovery and regeneration vary from place to place, and the implementation is different, which leads to many difficulties in the recovery process of waste oil regeneration industry. Except for the special field of petroleum, the recovery of other industries is quite difficult, mainly including the following problems: (1) Unclassified recovery,wiped film distillation, mixed oil varieties are complex, and the performance indicators of waste oil are different. Different types and proportions of waste oil are mixed together, which makes the subsequent regeneration treatment more difficult; (2) Transportation is restricted. The composition of waste oil is complex, containing different pollutants and impurities that may lead to corrosion and scaling of storage tanks, so the transportation equipment should be anticorrosive and explosion-proof at the same time. However, at present, the waste oil recovery mechanism seldom has such special equipment; (3) Disposal of violations.
For example, in the automobile repair industry, because there is no qualified unit nearby to deal with the hazardous wastes produced by the automobile repair industry, the compliance unit is far away and the transportation distance is long, resulting in high transportation and disposal costs, so the waste oil is transferred to other oil companies for disposal without going through the transfer formalities, or even sold to waste collectors at will. 2. Domestic and foreign regeneration process Due to the increasing necessity of environmental protection and increasingly stringent environmental legislation, the treatment and recycling of used oil has become very important. Waste oil recycling technology has changed significantly over the past decade. In foreign countries, the regeneration of waste oil is mainly based on hydrogenation refining process, as well as new supercritical technology, membrane separation technology, molecular distillation technology, etc.,wiped film distillation, while in China, it is mainly based on small-scale acid-base refining and adsorption refining. The recovery of used oil can be accomplished by the following different methods: re-cleaning, re-refining, and re-refining. The regeneration and recovery products of used oil are lubricating oil and fuel oil with low quality requirements, respectively, while the re-refining of used oil is to produce base oil with the same quality as crude oil. In general, waste oil refining goes through the following four steps: dehydration and degreasing, deasphalting, fractionation, and finishing. 2.1 Sulfuric acid-clay refining process Sulfuric acid-clay refining process is the first technology to be used in the research of waste oil regeneration process at home and abroad, in which a large amount of sulfuric acid and clay are used to treat waste oil. The used oil is pretreated (pre-flash or vacuum distillation) to separate water and light hydrocarbons. Concentrated sulfuric acid (10% -15%) is added to the dewatered used oil, where foreign matter (impurities such as resins, asphaltenes, oxidation products, etc.) Will form a sludge that will allow it to settle within 16-48 hours and then be separated from the used oil. The filtered oil is distilled to produce a base oil of a fuel oil having various characteristics. Sulfuric acid refining is mainly a chemical reaction, including sulfonation, esterification, polymerization, condensation and neutralization. In addition, there are flocculation by physical and chemical action and dissolution by physical action. Sulfuric acid can react with the non-ideal components present in the waste oil, has a strong ability to remove non-hydrocarbons, and can also remove olefins quite thoroughly. However, the regenerated oil sample treated by sulfuric acid can not achieve the expected effect in terms of quality, use effect and value, so the oil sample treated by sulfuric acid needs to be refined by a large amount of clay, so that the color of the regenerated oil is clearer, and the properties such as stability and viscosity are closer to those of normal diesel oil, and finally the expected qualified oil is obtained. However, in the refining process, this method will produce a lot of acid gases such as sulfur dioxide, which are harmful to human body and pollute the environment, solid wastes such as acid sludge, and liquid harmful substances such as acid water, which are difficult to deal with. In addition, the subsequent clay refining process will still pollute the environment and produce oily saturated clay which is difficult to treat. Under the increasing environmental pressure and the concept that the rapid economic development required by the current modern economic system is gradually turning to economically friendly development and green development, this technology has been banned in most countries, including many developing countries, thin film distillation ,jacketed glass reactor, and it is only a matter of time before the sulfuric acid-clay process is eliminated by the times. 2.2 Solvent extraction refining process Solvent refining process is still one of the mainstream methods to produce diesel oil in industry. The principle of solvent refining is to remove the additives, oxidation products, sludge and other impurities in the waste lubricating oil under certain conditions by using the different solubility of some organic solvents to the hydrocarbons, additives, oxidation products, sludge and other impurities contained in the waste lubricating oil, and then distill and recover the solvent to obtain crude products, which are refined by clay to become reclaimed oil. In foreign countries, solvent refining has gradually changed from propane to N-methyl pyrrolidone and furfural as the solvent of the refining process, among which N-methyl pyrrolidone is widely used because it has the lowest toxicity and can be used at a lower solvent-to-oil ratio, thus saving energy. In China, the mixture of alcohol and ketone (isopropanol, acetone, etc.) [8-10] is mainly studied as a solvent for refining, which can reduce the coking and scaling problems in the subsequent solvent recovery distillation process. Although the solvent refinement process has the above advantages, there are still some problems that can not be solved.
The disadvantage of solvent refining technology is the dependence of the quality of the finished product on the quality of the feedstock, because the process is a physical process and does not involve any chemical reactions. At the same time, the ratio of solvent to oil remains high in the refining process, and the extensive use of this toxic solvent will cause serious harm to the environment and equipment. The unstable price fluctuation and high unit price of the promising N-methylpyrrolidone solvent are also one of the reasons that restrict the development of this process. Although the solvent can be recovered and reused, it is difficult to recover, the cost of recovery is high, and the yield of recovered oil is not ideal. Nowadays, people at home and abroad have begun to study how to improve the solvent refining process, in which most of them will involve the addition and use of additives. The simple understanding of additive technology is to add a certain amount of suitable additive in the solvent refining process in order to solve various problems that often occur in the solvent refining process, so as to obtain better refining effect [10]. However, most of the current research on the technology of additives is still limited to the preliminary research in the laboratory, and it is difficult to achieve in the scale-up experiment and industrial use, so the technology of additives still has great research value. 2.3 Hydrogenation regeneration process Hydrorefining reactions aimed at removing foreign elements, hydrogenating olefins and aromatics, and hydroconversion reactions aimed at changing the structure of hydrocarbons through cracking and isomerization. The hydrotreating catalyst consists of an active phase made of molybdenum or tungsten sulphide and cobalt or nickel on an oxidic support. The oil and hydrogen are preheated and the oil is trickled down through a reactor packed with catalyst particles where the hydrogenation takes place. The oil product is separated from the gas phase and then stripped to remove traces of dissolved gases or water. Because hydrofining can reduce the loss of effective substances in oil samples, improve the yield of regenerated waste oil, and will not produce a large number of waste clay and pollute the environment as clay refining process, so hydrofinishing process has gradually replaced clay refining as the last step in the reprocessing process, occupying the main position in the research of waste oil regeneration. Almost all foreign countries adopt the hydrofining process to regenerate the waste oil. Compared with other technologies, the hydrofining process has the following disadvantages: high pressure and high temperature; need for hydrogen supply facilities; high safety standards; high operating costs and capital costs; low operating efficiency; crude oil analysis and pretreatment; catalyst regeneration. In this case, the application of the technology of the pressurization process requires relatively high investment, the hydrogenation process has higher requirements for equipment, and the operating conditions are more stringent, so the unit cost of regenerated oil production is higher. For China, which is still in the ranks of developing countries, there are still many difficulties in promoting the hydrofinishing process in an all-round way. 2.4 Thin film evaporation technology Evaporation that accelerates the evaporation process by forming a thin film of the liquid is called thin-film evaporation. The principle that thin film evaporation can accelerate evaporation is that liquid forms a thin film under reduced pressure. The film has a large vaporization surface area, the heat transfer is fast and uniform, there is no influence of liquid co-pressure, and the material can be better prevented from overheating. In a thin film evaporator for waste oil treatment, the feed is distilled into two parts by a cyclone column, and the light hydrocarbons are easily and rapidly distilled due to the formation of a tangential flow film. The vaporized lighter fraction, consisting of light hydrocarbons (gas, diesel) and water, condenses in the upper part of the chamber, from which it separates. The heavier oil portion of the bottom cycle is heated, reducing heat transfer within the chamber and reducing coke formation. Chemically pretreat the used oil to avoid the precipitation of contaminants that could lead to corrosion and contamination of the equipment. The pretreatment step was carried out at a temperature of 80 to 170 ° C. The chemical treating compound includes sodium hydroxide added in an amount sufficient to achieve a pH of about 6.5 or higher. The pretreated used oil is first distilled to separate water and light hydrocarbons. The water is treated and sent to a wastewater treatment facility, where the light hydrocarbons are used as fuel or sold as a product. Thereafter, the anhydrous oil is distilled in a thin film evaporator under high vacuum to separate diesel fuel, which can be used at the plant or sold as fuel. Heavy materials such as residues, metals, additive degradation products, etc. Are transferred to the heavy asphalt stream.
The Vaxon and EcoHuile (Sotulub) processes are based on the vacuum distillation of oil fractions in a thin film evaporator, which reduces coking caused by cracking of hydrocarbons and oil impurities at high temperatures. Both processes pretreat the alkaline waste oil, which requires the elimination of synthetic and vegetable oils from the feedstock. The Vaxon process has additional solvent extraction processing equipment to produce a higher quality product oil than the Ecohuile product. Despite this, the product quality is worse than the solvent extraction process described above. To produce high quality base oils, thin film evaporation technology needs to be combined with other technologies to add post-treatment steps, but these modifications will increase operating and capital costs, making it economically less attractive. 2.5 Membrane treatment The basic principle of membrane separation technology is that under the action of an external driving force, various substances with different properties in the raw material liquid can selectively pass through the membrane, so as to effectively separate substances with different components and purify certain substances. Membrane separation technology is a new separation technology with high efficiency and energy saving. Its main advantages are green environmental protection, high separation efficiency, simple operation, high safety and easy industrial use. On the other hand, the application of membrane separation technology can also improve the regeneration rate of waste oil, reduce unnecessary loss of raw materials, and reduce the amount of clay used in the subsequent clay supplementary refining process. It not only reduces the production of solid waste residue, but also makes the economic accounting of the process more reasonable, and provides a basis for large-scale industrial production. Mynin et al. Used inorganic membranes based on graphite and ceramics to regenerate waste industrial lubricating oil, transformer lubricating oil, engine oil, etc. The results show that the quality of industrial lubricating oil and transformer lubricating oil can meet the requirements of reuse after inorganic ceramic membrane filtration, and the physical and chemical properties of engine oil can also be improved to a certain extent. Yuhe Cao et al. Used three kinds of hollow fiber polymeric membranes (PES, PVDF, PAN) to treat the regenerated waste lubricating oil, which not only effectively removed metal particles and dust, but also greatly improved the viscosity and flash point of the regenerated oil. At present, membrane separation technology has been widely used, domestic and foreign experts and scholars have done a lot of research on the treatment of oily wastewater by membrane technology, and have achieved good results, but it is difficult to be applied in the regeneration of waste oil in practice. Because of the complex composition, high impurity content and high viscosity of waste lubricating oil, there are two problems in membrane separation and regeneration of waste lubricating oil, namely, small membrane permeation flux and serious membrane pollution. Concentration polarization and membrane fouling can significantly reduce the permeation flux and shorten the service life of the membrane, which are the main factors restricting the application and development of the membrane process. 3. Conclusion The state has begun to pay attention to the progress of waste oil recycling industry, which is a cause beneficial to the country and the people, and vigorously develop waste oil recycling from the perspective of saving petroleum resources and environmental protection. The sources of waste oil in our country are scattered, the varieties are many and the waste oil is not classified and recycled, the phenomenon of illegal disposal is everywhere, and the supply of raw materials for recycling enterprises is very difficult. Therefore, it is difficult to establish large-scale centralized treatment plants, and only small and medium-sized intermittent production methods can be adopted. Because of this, some foreign advanced technologies are not suitable for use in our country. If these small and medium-sized enterprises want to succeed, they must control the production and recovery of waste oil from the upstream, establish a waste oil recovery system, provide sufficient raw materials for the follow-up regeneration treatment, and then eliminate backward technology and use acid-free technology in line with international standards. Sulfuric acid-clay treatment was the first petroleum regeneration process to be used, but it has been gradually replaced by new technologies such as solvent extraction and hydrotreating. Most of the current solvent extraction technologies use propane and isopropanol as solvents, but it has a low selectivity for non-ideal components and requires a high solvent-to-oil ratio, which increases energy consumption.
Hydrofining can reduce the loss of effective substances in oil samples, improve the yield of regenerated waste oil, and will not produce a large number of waste clay and pollute the environment as in the clay refining process, so the hydrofinishing process has gradually replaced the clay refining, but because hydrofining requires excessive capital investment and operational constraints, So that it can no longer be widely used in small and medium-sized enterprises. Thin-film evaporation technology requires the addition of post-treatment steps and the combination with other technologies, but these modifications will increase operating and capital costs, making it less economically attractive. Most of the processes use a combination of different technologies, such as solvent extraction and hydrofining, thin film evaporation and different refining processes and hydrotreating. However,nutsche filter dryer, from the analysis of the current situation of domestic waste oil regeneration, the most attractive method for re-refining waste oil can be the combination of solvent extraction and membrane separation, and more research efforts should be made to explore the best solvent and solve the problems arising from membrane treatment. Return to Sohu to see more Responsible Editor:. toptiontech.com