阳离子交换树脂+PES制备油酸甲酯

1、 Kinetics of esterication of acidied oil with different alcohols by a cation ion-exchange resin/polyethersulfone hybrid catalytic membraneHonglei Zhang a ,Jincheng Ding a ,Yanli Qiu b ,Zengdian Zhao a ,a School of Chemical Engineering,Shandong University of Technology,Zibo 255049,PR China bGraduate

2、School,Dongbei University of Finance &Economics,Dalian 116025,PR Chinaa r t i c l e i n f o Article history:Received 21October 2011Received in revised form 9February 2012Accepted 21February 2012Available online 3March 2012Keywords:BiodieselCation ion-exchange resin Hybrid catalytic membrane Este

3、rication Kinetic modela b s t r a c tHybrid catalytic membranes consisting of cation ion-exchange resin particles (CERPand polyethersulf-one (PESwere prepared by immersion phase inversion and used as heterogeneous catalysts for the ester-ication of acidied oil with methanol,ethanol,propanol and buta

4、nol.The membranes were characterized by ion exchange capacity and swelling degree tests.The membranes were annealed at dif-ferent temperatures to improve catalytic activity and membranes annealed at 393K had the highest cat-alytic activity.Butanol allowed the highest free fatty acids (FFAsconversion

5、 of 95.28%since it has better miscibility than the other alcohols which strengthened mass and heat transfer.Furthermore,pseudo-homogeneous kinetic models of the esterication of acidied oil with the four alcohols were established according to the experimental data.The kinetic models can well predict

6、the FFA conversion.Ó2012Elsevier Ltd.All rights reserved.1.IntroductionPES is a good candidate as polymeric material for the prepara-tion of catalytic membrane supports since it possesses good mechanical and thermal stability and good chemical resistance to aliphatic hydrocarbons,alcohols and a

7、cids.Moreover,it is gener-ally easy to prepare dried asymmetric membranes by the immer-sion phase inversion method using water as coagulant (Xu and Qusay,2004.Cation ion-exchange resin is widely used in esteri-cation and transesterication processes because it is not corrosive and easy to separate fr

8、om the reaction mixture (Ding et al.,2011;Feng et al.,2010.Conventional cation ion-exchange resins are composed of copolymers of divinylbenzene (DVB,styrene and sul-fonic acid groups (Özbay et al.,2008.Cation ion-exchange resins can offer better selectivity towards the desired product(sandCorre

9、sponding author.Tel.:+865332781225,+86133*;fax:+865332781664.E-mail address:zdz1266 (Z.Zhao.reusability compared to homogeneous acid catalysts(Liu et al., 2006;Feng et al.,2011.Alcohols used in acid-catalyzed esterication mainly included methanol,ethanol,propanol and butanol.Methanol and ethanol are

10、 used most frequently in laboratory research and the biodiesel industry(Demirbas,2003;Fukuda et al.,2001.As one of the clas-sical models for heterogeneous catalysts,the pseudo-homoge-neous(P-Hmodel was applied to study the esterication kinetics to analyze the reaction process and control the reactio

11、n parameters(Lee et al.,2000;Shu et al.,2009.In the present study,a hybrid catalytic membrane consisting of cation ion-exchange resin particles(CERPand polyethersulfone (PESwas prepared by immersion phase inversion and used as a heterogeneous catalyst for the esterication of acidied oil(acid value15

12、2.3mg KOH/gwith methanol,ethanol,propanol and butanol,respectively.Pseudo-homogeneous(P-Hkinetic models of the esterication of acidied oil with the four alcohols by using the CERP/PES hybrid catalytic membranes were also established according to the experimental data.2.MethodsTwenty grams of PES was

13、 dissolved in80g NMP under contin-uous stirring at room temperature for12h to obtain a PES solution, 20g of CERP was added and stirred till a homogeneous solution was obtained.The solution was cast onto a glass plate and a copper wire was used to control membrane thickness.The membrane was immersed

14、into deionized water for phase inversion and washed for 6h to remove the solvents.The membrane was peeled off from the glass plate and allowed to dry in a vacuum oven at323K for24h. The membranes were annealed at353,393,423,473and513K, respectively,for1h in a heating oven and cut into pieces for fur

15、-ther use.IEC indicates the number of milli-equivalents of ions(H+in dry membrane of unit quality.The IEC of the membranes was obtained as follows:about0.1g dry CERP/PES membrane was soaked in 100ml of0.1M sodium chloride for24h.Then the ion-exchanged solution was titrated with0.1mol/L potassium hyd

16、roxide(KOH solution using phenolphthalein as indicator.The IEC value of the membranes was calculated using Eq.(1(Shi et al.,2011:IEC¼C KOHÂV KOHð1Þwhere,IEC is ion exchange capacity value(meq/g,C KOH is the con-centration of KOH(mol/L,V KOH is the volume of KOH used(ml,mis the we

17、ight of the dry membrane(g.The reported values were themean of at leastve measurements and the average estimated errorwas±3%.The swelling degree of the polymers was measured according toCaetanos method(Caetano et al.,2009.The samples were im-mersed in pure methanol,ethanol,propanol and butanol

18、at333Kfor24h.Then,the polymeric samples were removed from the alco-hols,wiped with tissue paper and weighted.The swelling degree,Qwas calculated by Eq.(2:Q¼mÀm0m0ð2Þwhere,m is the mass of swollen sample and m0is the initial mass.The reported values were the mean of at leastve mea

19、surementsand the average estimated error was±5%.Esterication was performed in a three-necked batch reactor(100mlequipped with a reux condenser and mechanical stirrerat atmospheric pressure.The reactor was heated by a heating jack-et and a thermocouple was inserted into the reactor.The catalytic

20、membranes were cut into small pieces(about3mmÂ3mmtoachieve better contact with reactants and to eliminate the inu-ence of diffusion on esterication.The acidied oil wasrst intro-duced into the reactor and heated to the determined temperature.Then the desired amount of the alcohol and catalytic m

21、embranewere added and the reaction began at the desired conditions.Thereaction conditions(Ding et al.,2011were:acidied oil20g;alco-hol/acidied oil molar ratio29:1;hybrid catalytic membrane/acid-ied oil0.166meq/g;reaction temperature equal to the boilingpoint of every alcohol;reaction time8h.Samples

22、were removedevery hour and treated by decompression distillation with a rota-tional evaporator at353K and0.01MPa to remove unreacted alco-hol and produced water to determinate acid value and FFAsconversion.After completion of the reaction,the mixture waspoured into a separating funnel and allowed to

23、 settle for1h to sep-arate alcohol and biodiesel.The biodiesel was further puried bydecompression distillation to remove alcohol and other impurities.The acid value was determined by titration according to ChinaStandard GB/T5530-2005:animal and vegetable fats and oils-determination of acid value and

24、 acidity(Shi et al.,2011.Briey,about0.2g sample was added to150ml neutral boiling ethanoland dissolved.Phenolphthalein(0.5mlwas used as indicator.The sample was titrated with0.1mol/L KOH solution.The acid va-lue was calculated using Eq.(3:S¼56:1ÂV KOHÂC KOHmð3Þwhere,S is the

25、 acid value(mg KOH/g acidied oil,C KOH is the con-centration of KOH used for titration(mol/L,V KOH is the volume ofKOH employed for titration(ml,m is the weight of the sample ta-ken to be analyzed(g.FFAs conversion is dened as the ratio of acid value variationrate of acidied oil before and after rea

26、ction to the initial acid va-lue.The conversion was calculated according to Eq.(4:FFAs conversion¼S iÀS tS iÂ100%ð4ÞH.Zhang et al./Bioresource Technology112(2012283329where,S i refers to initial acid value(mg KOH/g acidied oiland S t refers to the acid value at pre-determine

27、d reaction time(mg KOH/g acidied oil.The reported values were the mean of at leastve measurements and the average estimated error was±5%.3.Kinetic modelThe esterication reaction of FFAs with alcohols for producing fatty acid esters and water in the presence of catalytic membranes is given as fo

28、llows:RCOOHðFÞþr1OHðaÞ$RCOOR1ðEÞþH2OðWÞThe kinetic model of this work was built on the following assumptions:(1The rate of the non-catalyzed reactions is negligible com-pared with the catalyzed reactions;(2The catalytic activity of all sites on the c

29、atalytic membranesurface is the same.Under these conditions,the reaction was assumed to be pseu-do-homogeneous,second-order in the forward and reverse direc-tion.The reaction rate can be described as:Àd C Fd t¼k1ÂC FÂC AÀk2ÂC EÂC Wð5Þwhere C F,C A,C E and

30、 C W denote the concentration of FFAs,alcohol, fatty acid esters and water,respectively,k1and k2are the kinetic constants for the forward and reverse reactions.C F¼C F0Âð1ÀXÞð6ÞC E¼C W¼C F0ÂXð7ÞX and C F0refer to FFAs conversion and the ini

31、tial concentration of FFAs.Then Eq.(5can be converted to Eq.(8.Àd½C F0ð1ÀXÞd t¼k1ð1ÀXÞC F0C AÀk2C2F0X2ð8ÞEq.(8can be integrated to:lnXþ1þa2þ1pÀaXÀ1þa2þ1pÀa¼À2k2a C F0tð9Þwhere,a

32、88;14:5Kð14:5Kþ2Þp,K¼k12.Reaction rate constants k1and k2were determined by trial and er-ror,using variable K values until a plot of the left-hand side of Eq.(9 consisting of a straight line with a negligible intercept was obtained.The esterication reaction rate relates closely w

33、ith the value of the activation energy,the lower the activation energy,the faster the reaction rate,so the reduction of the activation energy will effec-tively promote the reaction.To consider the effect of reaction tem-perature on the kinetic model,the Arrhenius equation is listed as: k¼A exp&

34、#240;ÀE a=RTÞð10ÞThe reaction rate constants at different temperatures can then be used to get the pre-exponential factor A and activation energy E a with the Eq.(11transformed from Eq.(10ln k¼ÀE a=RTþln Að11Þ4.Results and discussionFig.1shows the FFAs co

35、nversion of acidied oil with different alcohols catalyzed by CERP/PES membranes annealed at different temperatures.Butanol had the highest FFAs conversion followed by methanol,propanol and ethanol in the esterication of acidied oil as also reported by Nye et al.(1983.This is mainly because the highe

36、r miscibility of butanol with acidied oil.Besides,the reac-tion temperature(boiling point of butanol,390K,was higher than that of the other alcohols,so the extent of phase separation de-creased and the rate constant increased,leading to a shorter reac-tion time(Lotero et al.,2005.The order of reacti

37、on speeds for methanol,ethanol and propanol was methanol>propanol>etha-nol,as also found by Johanna et al.(2005.This is probably because methanol has higher reactivity and the catalytic membrane swells better in methanol.Compared with ethanol,propanol is esteried at a higher reaction temperatu

38、re and propanol has better miscibil-ity with acidied oil.The membrane annealed at393K showed the best catalytic activity among the membranes(Fig.1Csince mem-branes annealed at lower temperature contain more water while membranes annealed at higher temperatures have a lower number of sulfonic acid groups which leads to a decrease in catalytic activ-ity.The result is in accordance with