The Study On Deacidification Of Straight-run Jet Fuel Via Catalytic Esterification

Many refineries have turned their attention to high acid crude oil with the price of crude oil going up in recent years.The acids in crude oil can not only lead to corrosion of storage and transportation equipment,but also shorten service life of the oil refining unit,finally the acids will be transferred to the various distillates.The straight-run jet fuel is one of the important distillates of crude oil,and it is also an important raw material for the production of No.3 jet fuel.No.3 jet fuel is one of fuels with the most strict requirement for its acid number,so the acidic components must be removed from the straight-run jet fuel.The catalytic hydrogenation process is one of the most effective technology used to remove acidic components from various oil products,but its disadvantages of high cost and scarce hydrogen source limit its industrial application.Therefore,it is necessary to develop a new low-cost and non-hydrogenation deacidification process.The physical properties of straight-run jet fuel were measured,it was known that the acid number of straight-run jet fuel was far higher than the requirement of national standard.The composition of petroleum acids in the straight-run jet fuel were identified by means of ESI FT-ICR MS.The analysis results demonstrated that the molecular mass of the acidic components was mainly distributed in the range of220⁴10Da.Most of acidic components were saturated monocarboxylic acid with C₁₆^C₁₈,monocyclic naphthenic acid with C₁₈ and relatively small amount of dibasic saturated carboxylic acid with C₁₉^C₂₄.The concentration of other acidic oxygen-containing compounds was fewer.According to the analysis results by means of ESI FT-ICR MS,the saturated straight chain fatty acid with C₁₈8 was chosen as the model compound of naphthenic acids in straight-run jet fuel.The pertinent thermodynamic data of the esterification reaction of model naphthenic acid compound with methanol,ethanol,propanol,butanol and glycol were assessed by the group contribution method,and these data were used for the thermodynamic analyses of above mentioned esterification reactions.The analysis results indicated that five reactions all could occur spontaneously in the concerned temperature range.Among the above-mentioned five esterification reactions,the equilibrium constant of the reaction with glycol was largest in the concerned temperature range.Based on the previous researchers of our laboratory,M/Al₂O₃ type of catalyst was selected as the esterification deacidification catalyst for straight-run jet fuel.The characterizations of M/Al₂O₃ type catalyst were operated via the methods of XRD and BET.The analytic results indicated that the catalyst had stronger basic sites,larger specific surface area,and it was the mesoporous material.According to thermodynamic analyses results and experimental results of esterification deacidification of straight run jet fuel with different types of alcohols in a stirred batch reactor,glycol was selected as the proper alcohol for the experiments of esterification deacidification in stirred batch reactor and fixed bed reactor.According to the requirement on esterification deacidification of straight-run jet fuel in reactive distillation column,n-butyl alcohol was chosen as the proper alcohol for reactive distillation deacidification experiments of straight-run jet fuel.The stirred batch reactor was used to evaluate the catalytic performance of M/Al₂O₃ type of catalyst,the effects of reaction conditions on esterification deacidification performance were investigated.The evaluation results illustrated that under the higher reaction temperature,the higher mass ratios of glycol to oil,the higher mass ratios of catalyst to oil,and longer reaction time,the deacidification performance would be improved,among the above factors,the mass ratio of catalyst to oil was the most obvious influencing factor.The lab-scale fixed bed reactor was used to evaluate the catalytic activity of M/Al₂O₃ catalyst.The results demonstrated that the higher reaction temperature,the lower space velocity and larger mass ratio of glycol to oil would enhance the deacidification rate of straight-run jet fuel,but while the mass ratio of glycol to oil increased to certain value,the increasing of deacidification rate was not obviously.Therefore,the proper conditions for the deacidification of straight-run jet fuel in fixed-bed reactor were space velocity of 12h^-1,reaction temperature of 120?and mass ratio of glycol to oil of 1.5‰.The long period experimental results in fixed bed reactor demonstrated that the activity of catalyst was kept in a high activity level in the 36h,and decreased subsequently.When the continuous running time was more than 48h,the acid number of straight-run jet fuel at outlet of fixed bed reactor could not meet the acidic value requirement of No.3 jet fuel.The deacidification experiments of straight-run jet fuel by catalytic distillation were carried out in a lab scale reactive distillation column.The temperature and acid number distribution in the tower were measured when the deacidification rate in the reboiler was stable.A long period operation was completed in the lab scale reactive distillation column,the device ran continuously under the condition feedstock temperature of 110?,reboiler temperature of 160?,WHSV of 1h^-1 and mass ratio of n-butyl alcohol to oil of 1.5‰.The experimental results illustrated that the deacidification rate of straight-run jet fuel could be kept in the range of 70%⁷7%within 330h continuous running time,and the acid number of deacidification oil could meet the acidic value requirement of No.3 jet fuel.