The Construction Of The Interlayer Microreactor And The Performance Of Catalytic Esterification Deacidification

Anionic layered materials have specific advantages of designable and adjustable structures and thus show potential and promising application in catalysis field.Among the various deacidification methods,esterification between naphthenic acids and alcohols has been proved to be an effective method to remove the naphthenic acids in the crude oil,due to its mild reaction conditions and little negative effect on the quality of oil.Layered double hydroxides(LDHs)can be used as esterification catalysts due to the catalityc activity of metals in the brucite-like sheets.In previous work,the ethylene glycol(EG)reactants were intercalated into the interlayer of NiAl LDHs.The cyclohexylcarboxylic(Cyc)can enter the inerlyaer space and react with EG to produce esters under the catalysis of metals in the layer.Due to the interlayer confinement effect,the deacidification performance was siginificantly increased when compared with the nitrate LDHs.In this thesis,a series of EG intercalated NiAl or ZnAl LDHs with various M2+/M3+ratios were preapard and used as interlayer catalytic microreactors for the esterication between naphthenic acids and EG.The properties of LDHs before and after reaction were systemically characterized to explore the interlayer confinement effect on the catalytic performance.The possible reaction process of the interlayer catalytic esterification and the property-activity relationship were deduced,which were compared with those of the conventional bulk catalytic reaction.Furthermore,the EG intercalated NiZn layered double hydroxide salts(LHSs)were prepared and used as interlayer catalytic microreactors.The results are listed as follows.1.EG intercalated LDHs with various metal ratios(M2+/Al3+=2-5)can be synthesized in 30 min by a microwave-assisted ion-exchange method using nitrate LDHs as precursors.The synthesis effiency is improved remarkably,owing to the swelling effect of EG,protonation effect of KOH and the advantages of microwave.It is deduced that EG anions could be accommodated in the interlayer with a tilted bilayer arrangement.2.The esterification performances of EG intercalated NiAl and ZnAl LDHs are considerable higher than those of nitrate LDHs with the same M2+/A13+ratios both in crude oil and in model oil system.3.The activity of EG intercalated LDHs is affected by the Ni or Zn content,the amount of EG in the interlayer and the structure of LDHs.Due to the catalysis effect of the metal sites in layers,the increase of Ni or Zn content favors the acids removal ratio and EG conversion.The amount of EG in the interlayer decreases with the increasing M2+/A13+ratios,resulting in the decrease in activity.At the Zn2+/A13+ratio above 4,the catalytic activity of ZnAl LDHs decreases,because of the formation of ZnO impurity.The highest acids removal ratio is achieved at the M2+/A13+of 4.At the same M2+/Al3+ratios,the catalytic activity of NiAl LDHs is higher than that of ZnAl LDHs.4.The arrangement of EG in the interlayer of ZnAl LDHs could be tuned through adjusting the microwave temperature.EG intercalated ZnAl LDHs with the interlayer spacing from 0.9 nm to 1.2 nm can be synthesised.It is found that the higher interlayer spacing favors the deacidification activity.5.The possible reaction process of the interlayer catalytic esterification was deduced based on the characterizations of LDHs and oil before and after esterification.For the crude oil system,naphthenic acids could diffuse and enter the interlayer to react with the pre-intercalated EG under the catalysis of the metal sites in layers.EG in the interlayer was consumed and CO32-anions derived from air enter the interlayer as the charge-compensating anions.After reaction,the layer structure can be well maintained and the un-converted EG and CO32-co-exist in the interlayer,while the ester products are present in the crude oil.For the model oil system containing Cyc acids and hydrotreated straight run diesel,the reaction process is similar to that occurring in the crude oil system.However,after reaction,a part of Cyc anions could stay in the interlayer as the charge-compensating anions.6.EG intercalated LHSs with various metals mole ratios(Ni2+/Zn2+=1-2.37)can be efficiently synthesized by the above microwave-assisted ion-exchange method using nitrate LHSs as precursors.EG anions in the interlayer are in a monolayered arrangement.It is found that the addition of deionized water(5-15 v%)in EG could swell the layers of LHSs and enhance the solvation,facilitating the intercalation of EG.7.The acids removal ratio and EG conversion of EG intercalated NiZn LHSs are considerable higher than those of nitrate LHSs catalysts with the same Ni2+/Zn2+ratios,indicating the advantage of interlayer esterification.The increasing Ni content favors the acids removal ratio and EG conversion.Although the amount of EG in the interlayer decreases with the increase in Ni2+/Zn2+ratio,LHSs still have the high EG capacity,due to the more excessive positive charges of the layers.Therefore,the EG intercalated LHSs show the highest activity at the Ni2+/Zn2+of2.37.8.The interlayer spacing of EG intercalated NiZn LHSs could be changed through adjusting the amount of water in EG.Two LHSs with the Ni2+/Zn2+of 1 but diffierent interlayer spacings were prepared and they show similar acids removal ratios,indicating the less effect of the interlayer spacing on the catalytic activity of LHSs.9.The acids removal ratio of EG intercalated NiZn LHSs is higher than NiAl LDHs with the same Ni content,owing to the more acid sites caused by higher electronegativity of metal.