Research On Process Optimization And Corrosion Prevention Of Benzol-ketone Dewaxing In Lubricating Oil Production

With the continuous expansion of the world's refinery capacity,the competition in the refining industry becomes increasingly fierce.The rapid rise of new energy vehicles has further impacted the fuel demand of the global market.Combined with the continuous decline in gasoline and diesel prices in recent years,refining enterprise earnings are under great pressure,and the survivals of such enterprises are facing difficulties.On the other hand,though the global market's demand for high grade lubricants is increasing,domestic production capacity is facing problems,such as backward processing technology and insufficient production capacity etc.Therefore,by adjusting unit structure and improving the process of currently used equipment to produce high-grade lubricants,it is an ideal way for established oil refineries to increase efficiency and profit.Based on the research of lubricating oil industry at home and abroad,it can be concluded that being able to produce high-quality lubricant base oil is the key to gain profit and maintain sustainable development of refineries.Through structural adjustment and process optimization of the keto-benzene dewaxing unit in a domestic refinery,the quality and production of base oil are both improved.Production experience shows that the base oil yield can be effectively improved by ceasing the addition of pre-dilution solvent and by adjusting the solvent dilution ratios in each dewaxing stage.As to the commonly found corrosion leakage problems in the solvent recovery system in the keto-benzene dewaxing unit,preliminary analysis of the recurring corrosion sites was performed based on the technical process.A heat exchanger and a ketone desorption tower in the unit were taken as typical corrosion sites,and qualitative as well as quantitative analysis of the service fluids were performed by various analytical instrument.It is found that the gradual accumulation of trace organic acids,acetic acids and naphthenic acids in the circulating solvent is the fundamental cause of frequent corrosion leakage.Since 20 carbon steel and 304 stainless steel are commonly used in the keto-benzene dewaxing units,rotating-hanging plate corrosion tests were carried out in air and in low-pressure oxygen-free environment,and their corrosion rates in different service fluids were compared.The product morphologies and components of 20 carbon steel after corrosion tests in heat exchanger shell fluids were made.A transition of corrosion rate was found,and it was induced by the structure change of corrosion products,which changed from loose non-uniform structure to dense uniform ones.The corrosion rate of 20 carbon steel in different working media is hundreds of times that of 304 stainless steel.The corrosion mechanism in the solvent recovery system includes oxidation,hydrogen evolution corrosion,micro-cell corrosion and pore corrosion etc.The occurrence of corrosion induced leakage can be effectively reduced by upgrading the equipment material from 20 carbon steel to 304 stainless steel,strictly controlling the amount of dissolved oxygen in the solvent and injecting proper amount of alkali into the solvent recovery system.