Study On The Catalytic Esterification For Deacidification Of Different Oils

Petroleum acid is a kind of common corrosive substance in crude oil and the distillate oils.The main component in petroleum acid is naphthenic acid which can be as high as 90%,while monocyclocyclic,dicycloid and tricyclic naphthanoic acid amount is more than 85%in the naphthenic acid.Naphthanoic acid has all the chemical properties of carboxylic acid,so it often causes serious corrosion,which affects the operation and service life of crude oil processing equipment and the equipment using the oil products.With the increasing production of high acid crude oil worldwidely in recent years,the corrosion and product quality problems caused by high acid crude oil and high acid value distillate oils are becoming more and more serious,so it is urgent to develop economical and efficient deacification technology and the processing route.At present,there are many kinds of deacidification processes reported,but almost all the technologies have thiere own advantages and disadvantages.It is reported that the esterification deacidification method can deal with almost all high acid value crude oil and oil products,which can effectively reduce the acid value of oil products and reduce the corrosion of equipment.It provides convenience for the further processing of raw oil,and is a promising deacidification method.In this dissertation,the catalysts with high efficiency,high stability and low preparation cost were developed for the oil catalytic esterification deacidification,and the supported zinc oxide solid acid catalyst was prepared.The activity and reuse performance of the prepared catalyst for esterification deacification of vacuum fraction oil were systematically evaluated.In order to further improve the catalytic esterification deacidification effect of zinc oxide catalyst,Fe₂O₃-Zn O bimetallic composite catalyst was prepared by doping iron oxide to zinc oxide,which improved the catalytic esterification deacidizing efficiency of vacuum fraction oil and showed good catalytic deacidification performance for crude oil either.The main contents are as follows:（1）The therotical analysis of thermodynamic and frontier orbital of the esterification of naphthenic acid has been done.The thermodynamic parameters of methanol,ethanol and ethylene glycol,which are commonly used in the esterification reaction,are calculated by using six naphthenic acid model molecules of single ring,double ring and three-ring,and the thermodynamics is also analyzed.The results show that the single ring naphthenic acid is more prone for spontaneous esterification reaction than the binary ring naphthenic acid and the three-ring naphthenic acid.For example,the cyclohexane acid is more easily esterified with different alcohols than the cyclopentane acid,and the Gibbs free energy of the esterification between cyclohexane acid and the three alcohols is in the order of Methanol<ethanol<ethylene glycol.The selected six kinds of naphthenic acid model molecules respectively reacted with methanol,ethanol,and ethylene glycol,the entropy-variable values of△S were all close to zero,indicating that the reactions were close to the equilibrium state in the selected temperature interval 423.15～563.15 K.The frontier molecular orbital analysis of the thermodynamic results was carried out,and the above laws and conclusions were further verified.According to the endothermic,exothermic and the Gibbs free energy variation results of the esterification reactions based on naphthenic acid model molecular,it showed that the higher reaction temperature is favorable for the esterification of the naphthenic acid.（2）The supported Zn O catalyst was synthesized by impregnation method and its physical and chemical properties were investigated by XRD,TG-DSC,BET,FT-IR and SEM and discussed.The results have shown that the zinc oxide crystal is successfully loaded on the surface of the alumina carrier,and the particle diameter of the zinc oxide crystal is about 40 nm.The preferred preparation parameters include the Zn O loading amount 15%,the calcining temperature of 400℃and the calcining time of 45 min.Under the above condition,the surface acid content of the Zn O catalyst is 0.75mmol·g^-1,the catalyst BET area was 132 m²/g and the blank carrier 174 m²/g.The Zn O/Al₂O₃ catalyst prepared under the condition of the preferred parameters was used for catalytic esterification deacidification of the 4^th vaccum gas oil.The results showed that,the amount of the 4^th vaccum gas oil 40 g,the catalyst amount 2.5 wt%of the raw oil,the glycol amount 4.0 wt%,the reaction temperature and time respectively 250℃and 1 hour,the deacidification rate of the refined oil could be over 95%and the catalytic deacidification rate of 5 times could still reach nearly 94%by the same batch catalyst without any treatment.The refined 4^th vaccum gas oil was characterized by the FT-IR,the results showed that the characteristic absorption peak of carboxyl in the 4^th vaccum gas oil was 1705 cm^-1,which almost disappeared in the refined oil,and the new ester-based characteristic absorption peak at 1740 cm^-1 in the refined oil confirmed the successful esterification deacidification.The ¹³C-NMR spectrum analysis of refined oil showed the ester group atδ174.2 in amd no longer present atδ178.5 in the raw oil.The result from NMR was consistent with the FT-IR spectrumt.The main physical and chemical indexes such as density,viscosity and flash point of the oil before and after the catalytic esterification deacidification changed little,so the esterification deacidification technolgogy didn’t obviously affect the oil qualities.The analysis of reaction mechanism showed that the catalytic esterification by zinc oxide is a typical solid acid catalytic mechanism.（3）In order to further improve the effect of supported Zn O catalyst on the esterification deacidification of distillate oil,iron oxide and cerium oxide were used for its doping modification,and the results illuminated that iron oxide had better doping effect.The catalytic esterification mechanism of bimetallic composite catalyst Fe₂O₃-Zn O was analyzed in combination with literature reports,and the physicochemical properties of the catalyst were analyzed by XRD,BET,SEM,TG-DSC,NH₃-TPD and others,the catalytic esterification activity was also evaluated.The characterization results have shown that the lowest doping amount for the obvious characteristic peak of doped iron oxide should not be less than 3.0 wt%of the support mass;the modified catalyst still belonged to mesoporous material,but the BET surface area before and after doping changed little,the particle diameter of doped catalyst increased to 40～120 nm.The calcining temperature 400°C was reasonable when preparing the catalyst.The total surface acidity of doped catalyst decreased but the weak acid sites was than before,and the increase of weak acid sites was beneficial to the esterification reaction.The deacidification results indicated that under the condition of Fe₂O₃-Zn O catalyst dosage 2.5 wt%,the ethylene glycol amount 4.0 wt%,the reaction temperature and time were respectively 250°C and 1 hour,the esterification deacidification rate of 4^th vaccum gas oil reached up to 97.6%;under the condition of Fe₂O₃-Zn O catalyst dosage 2.5 wt%,the ethylene glycol amount 3.5 wt%,the reaction temperature and time were respectively 250°C and 1 hour,the esterification deacidification rate of the second vaccum gas oil reached up to 97.8%;the catalytic deacidification rate reached to 95.1%for the crude oil when the Fe₂O₃-Zn O catalyst usage of 2.5 wt%,the ethylene glycol amount was 4.5 wt%,the reaction temperature was 250°C and the reaction time was 1 hour.The NMR analysis of the crude oil after catalytic esterification deacidification was carried out,the results proved that the carboxy functional group of naphthenic acid disappeared and new ester compounds were formed.The catalytic esterification is a good deacidification process to realize the refinement of the oils.