Ketonization Reaction Of Carboxylic Acid Over Composite Metal Oxides And Its Reaction Mechanism

In the bio-chemical industry,petrochemical industry and coal chemical industry,the equipment corrosion caused by organic acids was widespread,which posed a serious threat to the continuous and stable operation of the chemical plants.For example,during the process of producing liquid fuels from biomass,the existence of numerous organic acids will cause the severe corrosion issues of equipment amd decrease the energy density of bio-fuels.In the processing of high acid crude oil,petroleum acid will not only corrode the refinery equipments,but also affect the quality of petroleum products.In addition,as the by-product of the methanol to olefins reaction,the small molecule organic acid will also cause the equipment corrosion,which increases both the energy consumption and investment.The catalytic ketonization reaction provides an efficient route for the removal of organic acids.This route is green and pollution-free and can increase the C-C bond lengths.Therefore,it is expected that ketonization reaction can provide new technology for solving the corrosion problems in the industrial production.Although CeO₂-based composite oxides present outstanding ketonization activity and selectivity,whereas high reaction temperature?>400 ??is always required for high conversion and the catalysts are easy to deactivate.More importantly,the catalytic active centers of the composite oxides are still not very clear.The dominating factors affecting the ketonization process are not well understood,which hindered the development of high-efficient CeO₂-based catalysts and their application in ketonization process.To solve the above problems and develop highly active catalysts with good stability,the ketonization reactions of acetic and propionic acid were chosen as model reactions.The formation of active sites and reaction mechanism were studied particularly.The structure-activity relationship of ketonzation reaction over two kinds of CeO₂-based composite oxide catalysts and the Mg-Al hydrotalcites based mixed oxides were systematically investigated from the perspective of structure optimization and active center exploration.Finally,the application research on the deacidification process of highly acidic crude oil and MTO products was carried out.The main work and results are as follows:?1?The Ce_1-xFe_xO_2-? mixed oxides were obtained by Fe doping into CeO₂.The catalysts were characterized by XRD,TEM,Raman,H2-TPR,XPS and CO₂-TPD methods and the key factors affecting the ketonization reaction were revealed.The results showed that Ce0.8Fe0.2O_2-? showed the highest catalytic ketonization activity.The introduction of Fe led the formation of Ce-Fe solid solution.The newly formed Ce-O-Fe species as the active sites can enhance the redox properties of catalysts,weaken the strength of M-0 bonds and increase the number of surface oxygen vacancy and basic sites,thus improving the ketonization activity.Through the investigation of the reaction temperatures together with the characterization of the catalyst before and after the reaction,it is proved that there existed the redox cycle of surface Ce species during the ketonziation process.Therefore,the redox properties were the key factors affecting the ketonization reaction.?2?The ketonization reaction of acetic acid on the Ce_1-xTi_xO_2-? composite oxide catalysts were carried out,and the reasons for the increase of catalytic activity and stability were revealed by XRD,Raman,H2-TPR,XPS and NH3/CO₂-TPD methods.The results showed that Ti-doped catalyst can significantly improve the catalytic activity and Ce0.7Ti0.3O_2-? presented the highest catalytic activity and excellent stability.The introduction of Ti can form the CeO₂ solid solution structure,which improved the redox performance of the catalysts and surface acid-base pairs,and increases the number of surface oxygen vacancy,which can promote the ketonzation carboxylic acids.Moreover,the effect of the calcination temperature on the catalysts was also investigated.The results showed that the redox properties of the catalyst become inferior when the calcined temperature increased,resulting in a decline in the activity.?3?The structure-activity relationship for the ketonization performance of acetic acid on Mg?Al?O catalysts was investigated by XRD,N2 desorption and CO₂-TPD and FTIR methods.The process of ketoization reaction was revealed by TPSR and FTIR methods,and the reaction pathways at different reaction temperatures were proposed.In addition,the DFT method was used to study the structural parameters and adsorption energy of different conformation for the adsorption of acetic acid on the catalysts.The results indicated that the surface ketonization reaction route dominated for Mg?Al?O when the reaction temperature is above 330?.The catalytic activity increased with the ratio of Mg/Al,which was related to the increase of surface basic sites.But when the reaction temperature is below 330 ?,the bulk ketonization route dominated and the decrease of the specific surface area caused the decline of the activity.The DFT calculating results showed that the adsorption energy of acetic acid on Mg?Al?O was between MgO and Al2O3,and the bridging coordination mode is the most stable adsorption structure for carboxylic acid.?4?The ketonization activity of was investigated over Mg?Al?O modified by different amount of Ce.The catalysts were characterized by the catalysts were characterized by SEM,TEM,H2-TPR,CO₂/NH3-TPD and XPS,etc.methods and the reasons for the improvent of catalytic activity and stability were obtained.The Mg3Al0.9Ce0.1 displayed the highest ketonization activity and the reaction activity of the catalysts was related to the location of cerium in Mg-Al hydrotalcite.When the content of dopant was low,the cerium oxide was mainly dispersed as small grains on the voids or surface of the interlayer.The surface Ce3+ content and the number of the basic sites were increase due to the strongl interaction between the Ce species and Mg-Al oxideS,thus improving the ketonization activity.For the excessive doping content,the hydrotalcite structures were destroyed and the CeO₂ particles were easy to agglomerate,which led the decline of reaction activity.The surface ketonization reaction pathway dominated for the Ce-MgAl catalysts.The introduction of Ce enhanced the strength of M-0 bond,which is benifical for stabilizing the catalyst structures.Therefore,the reaction stability of ketonization reaction over Mg3Al0.9Ce0.1 was significantly improved.?5?The application of deacidification process for high acid crude oil and MTO product was investigated.The optimal reaction condition were discussed.When the ratio of catalyst to oil was 0.05 and the reaction temperature was higher than 300 ?,the deacidification rate for Ce-Mg?Al?O catalyst was above 85%and TAN value of the reacted crude acid was<0.5 mgKOH/g,which can meet the industrial requirements.In addition,the used catalyst can be recycled for several times.The reaction condition for high-temperature deacidification of MTO products was optimized.The efficient removal of organic acid could be achieved when the deacidification temperature was 480 ?,the space velocity was 2.3 h-1 and the pressure was 0.2 MpaG.The content of organic acid after deacidification was less than 5 ppm.