Study Of The Catalytic Methyl Esterification Of Colophony And The Kinetics Over ZnO/FC3R With Subcritical CO₂

Colophony is one of the advantageous resources of our country and the main component of colophony are abietic and pimaric type of resin acid.The esterification products are widely used in chemical industry,such as colophony methyl esters catalyzed by colophony and methanol.Super/subcritical CO2 is a new green solvent and catalyst,and it is widely used in hydrogenation,hydrolysis,and esterification reactions for the advantages of non-toxic,cheap,and renewable.In this paper,the waste FCC catalyst activated by high temperature(FC3R)was used as the carrier,a heterogeneous catalyst—FC3R loaded zinc oxide partiles(ZnO/FC3R)catalyst was prepared by wet impregnation,and applied to the optimization of colophony methyl esterification and the reaction kinetics with subcritical CO2.The main research contents are as follows:Using FC3R as a carrier,a ZnO/FC3R heterogeneous colophony methyl esterification catalyst was prepared by equal volume impregnation.Taking the conversion of colophony methyl esters as the evaluation index,and the effect of zinc oxide loading,calcination temperature and time on the colophony methyl esterification was investigated.The results showed that the optimal reaction conditions for the preparation of the catalyst were as follows:a ZnO loading of 25%,a calcination temperature of 450 ℃ and a calcination time of 4.0 h.The catalyst morphology,surface area,the group structure,acid type and the ZnO loading was characterized by SEM,BET,XRD,FT-IR,Py-IR and.ICP-AES.It can be seen from the SEM analysis that large quantities of ZnO crystallites with a particular cuboid structure were observed in the pores of FC3R carriers;BET analysis indicated that the ZnO/FC3R has a larger specific surface area and greater pore size,due to the highly dispersed ZnO particles inside the catalyst;XRD analysis indicated that the structure of FC3R was ZSM-5,Y molecular sieve and Al2O3,and the ZnO active component showed wurtzite structure;Py-IR analysis indicated that both the Lewis and Bronsted acidities of the ZnO/FC3R were greater than those of the FC3R,which tend to greatly promote the esterification reaction;FT-IR analysis showed that there was a characteristic absorption peak of zinc oxide at 472 cm-1;ICP-AES analysis indicated that the actual ZnO loading was determined to be 20.85%,which was slightly lower than the theoretical value.Research of the stability of the supported catalysts was investigated,which showed that ZnO/FC3R catalyst remained had high catalytic activity after repeated use for 6 times.Using the self-made ZnO/FC3R catalyst,colophony and methanol as raw materials,and the subcritical CO2 as an auxiliary catalyst to catalyze the synthesis of colophony methyl esters in a stainless steel reactor.Taking the conversion of colophony methyl esters and the viscosity of products as the evaluation index,and the effect of CO2 partial pressure,the catalyst amount,the methanol:colophony molar ratio,the reaction temperature and time on the colophony methyl esterification was investigated.The pH value of the reaction system within the range of the estimated experimental conditions was 3.91 to 3.54 by van Walsum equation,indicating that CO2 dissolved in water to form carbonic acid can assist in the catalytic esterification reaction.Based on the single factor experiments,a response surface design(BBD)method was used to optimize the reaction,and the factors of CO2 partial pressure,reaction temperature and methanol:colophony molar ratio was optimized.The results of optimum reactions were as follows:the reaction pressure of CO2 was 3.50 MPa,the reaction time was 5 h,the reaction temperature was 224 ℃,the catalyst dosage was 6.4 g and the molar ratio of methanol to rosin was 1.51:1.Under the optimum conditions,the conversion rate of colophony was 97.09%,with the viscosity of 3780 m Pa s,both of which are in accordance with the ASTM standard(ASTM D465-82 and ASTM D1824-66).Through FT-IR and ICP-AES analysis,the colophony could be transferred to rosin esters completely with a short time,besides,it possesses a low mental ion residue.The kinetics of colophony and methanol was studied by special thermal insulation on-line high-pressure test device under the condition of 190-220 ℃and a CO2 pressure of 3.5 MPa.The relationship of concentration change of each component was obtained by high-performance liquid chromatography(HPLC)method.The kinetic parameters were estimated by the Levenberg-Marquart non-linear least-squares method using the MATLAB program,and the activation energies for the isomerizations of neoabietic and palustric acids and for the methyl esterification of neoabietic,abietic,palustric and dehydroabietic acids were found to be 107.09,113.95,68.99,49.85,75.43 and 59.20 kJ mol’1,respectively.An F-test was performed at a confidence interval of 95%to assess the accuracy of the model results,and the results show that the kinetic model is significant at the 95%confidence level,and results from the kinetic model were in good agreement with experimental values.