Research On The Catalyst And Technology Of Mixed-C₄ Alkylation

Abundant C4 hydrocarbons are produced from petrochemical plants such as catalytic cracking,delayed coking,steam cracking,methanol to hydrocarbon and so on.The gasoline addictive possessing the advantages of no sulfur,no aromatics,no olefins and high-octane number could be produced by C4 alkylation technology.By this way,the increasing demand for clean gasoline could be satisfied and meanwhile the abundant C4 hydrocarbons could be utilized reasonably.Therefore,the researches on the catalyst and technology of mixed-C4 alkylation were carried out comprehensively in this thesis.The comprehensive utilization route of mixed-C4 was put forward:the isobutene in the mixd-C4 were reacted by indirect alkylation to obtain high-quality product and the mixture of isobutane and 1-butene.And then the alkylate oil was produced by direct alkylation with the mixture of isobutane and 1-butene as the feed.In the indirect alkylation,the effect of reaction conditions,acid capacity,the inhibitor and the material composition were researched with macroporous sulfonic acid resin as catalyst and pure isobutene,FCC mixed-C4 and prepared mixed-C4 as feed.Then on basis of density functional theory(DFT),the theoretical research was carried out.In the isobutane/butene direct alkylation,the modified HUSY zeolite and SZ/HUSY composite catalyst were prepared and they exhibited superior alkylate performance.The results showed that when pure isobutene was used as feed,the conversion of isobutene was decreased and the selectivity of C8= was increased with the acid capacity decreasing,reaction temperature decreasing and space velocity increasing.Under the conditions of acid capacity ?2.45 mmol H+/g,temperature of 50? and LHSV of 2h-1,the C8=selectivity was high as 95%,especially when the acid capacity?2.91 mmol H+/g,the content of 2,4,4-TMP= in C8= was almost 100%.When the FCC mixed-C4 was used as feed,the C8=selectivity and the content of TMP= in C8= were improved with the addition of ethanol and tertiary butanol,which was because of their higher polarity.In the ethanol-prepared mixed-C4 dimerization system,the results showed that with the ethanol/isobutene molar ratio increasing,the conversion of isobutene and 1-butene were decreased,the yield of ETBE was increased,the yield of oligomers and 2-butene were decreased,the fraction of C8= in oligomers and that of TMP= in C8= were increased.With the temperature increasing,the 1-butene conversion was increased gradually while the isobutene conversion was increased gradually and then level off,the yield of ETBE was decreased,the yield of oligomers and 2-butene were increased,the effect of temperature on the fraction of C8= in oligomers was different at different ethanol/isobutene molar ratio.The effect of WHS V on the conversion and product distribution was almost similar to that of ethanol/isobutene molar ratio.Finally,on basis of density functional theory,the theoretical research of the dimerization-etherification system was carried out.The results showed that the adsorption order of the reactant was ethanol>isobutene>1-butene.The active energy of etherification reaction was lower than that of isobutene dimerization and the active energy of 1-butene isomerization was lower than co-dimerization between isobutene and 1-butene.The addition of ethanol improved the C8= selectivity,which was due to the decrease of active sites,reduce of the acid strength and decrease the concentration of isobutene for dimerization.In the isobutane/butene direct alkylation,HUSY was modified by NH4F,CA and La3+.The physico-chemical properties of these modified catalysts were characterized and their alkylation reaction performance were evaluated.The results showed that the alkylation performances of catalysts modified under suitable conditions were improved,the highest C8 selectivity over HUSY-5F,HUSY-0.1CA and HUSY-0.2La was 74.5%,72.8%and 71.2%respectively,which was increased by 15.6%,13.9%and 12.3%respectively when compared with HUSY parent.It was indicated that the higher B/L ratio and BS/BT ratio was beneficial to improve the hydrogen transfer reaction and the sufficient amount of medium strong Bronsed acid was important to make the catalyst stable.In addition,the secondary pore created during the modification process was helpful for the diffusion of reactant and products,thus the tendency of polyalkylation was reduced and finally the selectivity of C8 was improved.SZ/HUSY composite catalyst was prepared using in-situ precipitation method.In this process,the effect of ZrO2 loading,sulfuric acid reagent and water-washing on the properties and alkylation performances of catalysts were research.The results showed that the amount of medium strong Bronsed acid was increased by introducing SZ and the C8 selectivity of 5SZ/HUSY was improved to 72.9%,which was increased by 13%when compared with HUSY parent.The initial C8 selectivity of SZ/HUSY-H with sulfuric acid as the sulfuric acid reagent was close to that of SZ/HUSY-N with ammonium sulfate as the sulfuric acid reagent,while the stability of the former was superior to the later.The activity of SZ/HUSY catalyst after water-washing was decreased obviously.The sulfur species was lost during the water-washing process,leading the number of active sites reduced and C8 selectivity decreased.Finally,the preparation methods were compared.It was indicated that performance of the SZ/HUSY catalyst prepared by in-situ precipitation method was superior to mechanical mixing method,which could be mainly due to the difference of distribution of SZ.The reaction conditions including the temperature and WHSV were researched with HUSY-5F as catalyst.The results showed that the relative rate of oligomerization reaction was higher at lower temperature while that of cracking reaction was higher at higher temperature.The catalyst possesses a relative higher C8 selectivity and longer lifetime at the temperature of 80?.The effect of WHSV on the C8 selectivity during the stable stage was negligible,however,the lifetime was greatly affected.When the WHSV was large,the catalyst was deactivated very fast.The catalysts obtained at different TOS were characterized by N2 adsorption-desorption,NH3-TPD,TG,GC-MS and in-situ IR.The results showed that some long-chain alkanes were deposited in the pores and covered on the active sites.Although some pores and acid centers still existed in the deactivated catalyst,the alkylate product cannot be obtained,which was due to the diffusion resistance of reactant and the inaccessibility of other active sites.The deactivated catalyst could be regenerated in air at 520? for 300 min and the activity could be recovered almost completely.It was indicated that the catalyst had excellent regeneration performance.