Synthesis of Glycerol Carbonate from Glycerol, a By-Product of Biodiesel Production

Transcription

1 INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING Volume Artcle A87 Synthess of Glycerol Carbonate from Glycerol, a By-Product of Bodesel Producton Zsanett Herseczk Tamás Varga Gyula Marton Unversty of Pannona, herseczk@freemal.hu Unverst of Pannona, vargat@fmt.un-pannon.hu Unversty of Pannona, martongy@almos.un-pannon.hu ISSN Copyrght c 009 The Berkeley Electronc Press. All rghts reserved.

2 Synthess of Glycerol Carbonate from Glycerol, a By-Product of Bodesel Producton Zsanett Herseczk, Tamás Varga, and Gyula Marton Abstract Methyl esters of fatty acds (also known as bodesel) made from transesterfcaton of vegetable ols and anmal fats wth methanol, have shown a lot of promse as alternatve desel fuels. Glycerol s the nevtable byproduct of transesterfcaton process. Whle there are exstng markets for glycerol, a sgnfcant ncrease n avalablty of glycerol, resultng from the expanded use of vegetable ols and anmal fats, would destablze the glycerol market. In ths study, the synthess of glycerol carbonate from glycerol and dmethyl carbonate was nvestgated. Glycerol carbonate s a key multfunctonal compound employed as a solvent, addtve, monomer and chemcal ntermedate. The resultng glycerol carbonate was obtaned n almost quanttatve yeld. Accordng to measured data a well-elaborated mathematcal model of the reactor was used for experments can be adequate to assgn parameters of knetc equatons of the assumed reacton mechansm. Component mass balances were bult nto the reactor model and order of reactons was fxed. KEYWORDS: glycerol, bodesel, glycerol carbonate We thank Ms. Béláné Márkus for skllful assstance n the synthetc experments.

3 Herseczk et al.: Synthess of Glycerol Carbonate 1 Intoducton Utlzaton of glycerol has a sgnfcant role on bodesel producton snce large amount of glycerol s obtaned as a by-product of vegetable ol methanolyss. Glycerol holds the potental of beng an extremely versatle buldng block wthn the borefnery. Although many uses have been developed for glycerol, most product markets are currently small and fragmented. However, development of a bodesel market could have a huge mpact on the avalablty and use of glycerol. Snce glycerol s a key coproduct of bodesel manufacture, ncreasng use of bodesel wll lead to much greater glycerol avalablty and lower cost. At lower projected costs, there s a tremendous potental to develop a varety of new processes and product lnes from glycerol, takng advantage of ts unque structure and propertes. As a renewable and cheap raw chemcal, converson processes of glycerol to useful materals have receved ncreasng attentons, and recently several examples have been reported: acd-nduced dehydraton of glycerol to acrolen n supercrtcal water (Ott et al., 006), glycerol oxdaton to dhydroxyacetone and glycerc acd usng carbon-supported gold catalysts (Demrel et al., 007), and 1,3-propanedol producton by metabolc engneerng approach. Glycerol carbonate s a stable and colorless lqud that offers useful applcatons as a novel component of gas separaton membranes, a surfactant component, a new solvent for several types of materals or a nonvolatle solvent n the pant ndustry, a component n coatngs, and a component of detergents. Also glycerol carbonate can be utlzed as a source of new polymerc materals (Km et al., 007). Glycerol carbonate can be obtaned accordng to varous methods, usng epoxy compounds as well as glycerol as raw materals. It was reported that glycerol carbonate can be formed n the reacton of epchlorohydrn wth KHCO 3 carred out at 80 C n the presence of 18-crown ether. Promsng methods of glycerol carbonate preparaton comprse the reacton of glycerol wth CO or carbon monoxde and oxygen n the presence of Cu(I) catalysts (Rokck et al., 005). In our approach, the glycerol carbonate synthess was carred out under mld condtons wthout any solvent, usng glycerol and dmethyl carbonate as envronmentally bengn and renewable reagents. Due to the almost quanttatve reacton yeld there s no need for product purfcaton by dstllaton at hgh temperature and recovery of unreacted glycerol. Publshed by The Berkeley Electronc Press, 009

4 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A87 Materals and methods Dmethyl carbonate, glycerol, glycerol carbonate and K CO 3 were purchased from Sgma-Aldrch and used wthout further purfcaton. As frst step reactons were carred out n a 500 ml glass flask equpped wth a mechanc strrer, thermometer and Lebg cooler. Glycerol (9 g, 1 mol) and dmethyl carbonate (70 g, 3 mol) were mxed n the flask. When reactor temperature reached 60 C, K CO 3 (4.14 g, 0.03 mol) was added to the mxture as catalyst. In case of lower catalyst concentratons (weght proporton catalyst/glycerol: ), reacton tme was approxmately two tmes longer. Catalyst dssolved n reacton meda wthn 5 mnutes. Dmethyl carbonate (DMC) was used n a molar excess (3:1) (Rokck et al., 005) and methanol was removed contnuously to shft the reacton equlbrum towards the product. Methanol forms a mnmum bolng azeotrop wth DMC (Table 1), so when methanol s removed, DMC leaves the flask, as well. Table 1. Composton of methanol-dmc azeotrope NBP Bolng pont (C ) Molecular weght Bnary azeotrope (70% methanol + 30% DMC) Methanol DMC Reacton was carred out at C n presence of K CO 3 as a catalyst for 5 h, and then unreacted dmethyl carbonate was dstlled off at 40 C under reduced pressure (4-6 kpa). Reacton progress was montored by collectng samples of reacton mxture. As next step reacton was carred out n a Mettler Toledo LabMax Automatc Lab Reactor (Fgure 1). The transparent, double-walled glass reactor allows automatc performance of chemcal syntheses n the temperature range 50 to 0 C (TR). The pressure range vares from vacuum to ambent pressure. The workng volume of the glass reactor s 0.6 lter. Analyss Samples of reacton products were analysed wth a Merck LaChrom HPLC equpped wth an Ultrahydrogel column (I.D. = 7.8 mm, L= 300 mm) and a Merck LaChrom RI detector. Water was used as eluent. Retenton tme of the components n mnutes: glycerol 10.97; unknown component 1.58; glycerol carbonate and DMC

5 Herseczk et al.: Synthess of Glycerol Carbonate 3 Fgure 1. Expermental set-up Results and dscusson We have developed a convenent method for synthess of glycerol carbonate from glycerol and dmethyl carbonate (Fgure ) usng K CO 3 as catalyst. Resultng glycerol carbonate was obtaned n almost quanttatve yeld. Publshed by The Berkeley Electronc Press, 009

6 4 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A87 HO OH OH + O O O OH - MeOH - MeOH HO O O A B C D O HO O O O Fgure. Synthess of glycerol carbonate Between two types of hydroxyl group n glycerol, two prmary alcohols are presumably more reactve than a secondary hydroxyl group. Therefore, ntermedate C mght be formed at the frst step, and subsequently formaton of product D occurs through ntramolecular converson. On the chomatograms t can be seen that there s an unknown peak at retenton tme mn, whch s probably ntermedate C. Table. Influence of tme on reacton of glycerol and dmethyl carbonate Reacton tme (mn) Glycerol (wt%) Glycerol carbonate (wt%) DMC (wt%) Intermedate (area %) Samples were collected from reacton mxtures at 1, 3, 5, 7, 10, 30, 60, 10, 180, 40 and 300 mnutes. Unfortunately the frst three samples were not representatve because durng ths perod there are two phases n the flask (glycerol and dmethyl carbonate) and solublzaton starts when mxture contans enough amount of glycerol carbonate. Table contans composton of samples, amount of ntermedate s gven n area %, other components were factorzed. Reactor model When a reactor s desgned the frst step s to nvestgate the possble reactons take place n reactor, all the mcro and macro processes (e.g. strrng) and operatng condtons whch have some nfluence on them. Reactors are planned and used to make value added compounds, so the most mportant task to know how the cheap raw materals can be converted nto a value added product. The converson pathway can be demonstrated by reacton mechansm. Unfortunately, reacton mechansm does not contan all necessary nformaton whch s needed to

7 Herseczk et al.: Synthess of Glycerol Carbonate 5 desgn a reactor because t gathers steps of converson but does not gve any nformaton about the reacton rate. To run a reactor under optmal operaton condtons or to fnd the optmal operatng range t s nevtable to know the rate of ndvdual reacton steps. Many knd of correlaton can be appled to descrbe the rate of a reacton wth dfferent number of unknown parameters. To calculate reacton rates the Arrhenus equaton (eq. 3) was used wth two unknown parameters (pre-exponental factor and actvaton energy). The produced heat durng the reactons s called reacton heat, whch s over 0 f the reacton s endothermc whle t s below zero f the reacton s exothermc. Every reacton has reacton heat whch dffers from 0. Hence, to characterze a reacton, next to the earler mentoned two parameters, the reacton heat must be determned too. It can be performed wth some calormetrc measures. k1 A + B C + E k C 3 k D + E k 4 A: glycerol; B: Dmethyl-carbonate; C: Intermedate; D: Glycerol-carbonate; E: Methanol k = = k,0 exp { 1; ; 3; 4} R ( E R T ) A, (1) () (3) Determnaton of unknown parameters can be acheved by usng well-carred out experments to collect accurate analytcal data, but nowadays dfferent knd of modellng technques can be appled to reduce the number of necessary experments. Accordng to measured data a well-elaborated mathematcal model of the reactor was used for experments can be adequate to assgn parameters of knetc equatons of the assumed reacton mechansm. Structure of the elaborated model of reactor s shown n Fgure whle a detaled descrpton of all model equatons can be found n the appendx. As eq. 1-. show both of the reactons n the assumed reacton mechansm are equlbrum reactons so next to the unknown parameters n knetc equatons t s necessary to have a correlaton between the nsde temperature of reactor and the equlbrum content. Arrhenus-type temperature dependent was used to calculate the reacton equlbrum. To nvestgate the effect of the producng methanol on the performance of synthess the methanol s consdered n back Publshed by The Berkeley Electronc Press, 009

8 6 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A87 reactons, so both of back reactons are second order. The frst reacton (eq. 1) s second order snce n the frst step the glycerol and dmethyl-carbonate must be formed the ntermedate whch s decomposed nto glycerol-carbonate and methanol. On ths level of work based on the ntroduced reacton mechansm component mass balances were bult nto the reactor model and order of reactons was fxed. A heat transport couples the nsde and the jacket of the reactor and the heat conductvty phenomena n the reactor wall was not consder n ths model. Slca ol s crculated n the jacket through a thermostat to keep the temperature of the jacket at desred value so only the heat balance of the reactor nsde was bult nto the model. At the next level n the model herarchy there s the level of phases. Snce the reactons equlbrum s modfed wth the evaporaton of products t s necessary to calculate the content of gas phase. The temperature of the lqud and gas phase s equal so only the mass transport couples these phases. At the bottom of the model structure can be found the level of components. The reactons are consdered at ths level. The reactons takes place only n the lqud phase snce the catalyst doesn t evaporate. To check the assumed reacton mechansm the component balances n the lqud phase were completed wth component sources based on the 1- equatons. The dentfcaton of mssng model parameters was performed by comparng the analytcally determned masses of components and the measured temperature trajectory of reactor nsde wth the calculated ones usng the model. Identfcaton and valdaton of model parameters Some of the mssng model parameters can be determned from the lterature (e.g. all the necessary propertes of components) but there s no nformaton about parameters of knetc and equlbrum expressons so parameter dentfcaton was performed based on the comparson of measured and calculated trajectores of state-varables. The square sum of the dfference was calculated n every sample tme. To fnd the global mnma of ths mult varable optmzaton problem an Evolutonary Algorthm (EA), the Covarant Matrx Adaptaton Evolutonary Strategy (CMA-ES) was appled. The EA s an optmzaton method whch based on the natural selecton and survval of the fttest as t works n the real world. EAs consstently perform well approxmatng solutons to all types of problems because they do not make any assumpton about the underlyng ftness landscape, hence t makes EAs applcable from dfferent felds of engneerng to socal scences (Eben et al., 007). Learnng the covarance matrx n the CMA-ES can mprove the performance on ll-condtoned and/or non-separable problems by orders of magntude. The CMA-ES overcomes typcal problems that are often assocated

9 Herseczk et al.: Synthess of Glycerol Carbonate 7 wth EAs, e.g. the poor performance on badly scaled and/or hghly non-separable objectve functons (Hansen et al., 000; Hansen et al., 005). Another applcaton of CMA-ES n an engneerng problem can be found n (Varga et al., 007). Table 3. Identfed reactor model parameters k 01 [m -3 mol s -1 ] k 0 [s -1 ] E A1 [J mol -1 ] E A [J mol -1 ] AK 1 [ ] BK 1 [ ] e4 1.84e e4 AK BK H reac,1 H reac, c v [ ] [ ] [J mol -1 ] [J mol -1 ] [W m - ] [kg s -1 bar -1 ] e4-4.97e4-6.43e e The result of the dentfcaton of mssng model parameters s summarzed n Table 3 whle measured and calculated trajectores can be compared n Fgure 3. As t can be seen n Table only seven samples were taken and analyzed. In the dentfcaton process the measured value of state varables were lnearly nterpolated between nearby samples to help searchng algorthm wth ncreasng the number of learnng samples. α RJ Publshed by The Berkeley Electronc Press, 009

10 8 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A m A 50 m B tme [s] 150 tme [s] m D T R [K] tme [s] 80 tme [s] Fgure 3. Calculated(thn) and the measured(thck) trajectores of state-varables (the molar rato of B (dmethyl carbonate) and A (glycerol) components s three) As t can be seen n Fgure 3 there are some dfferences between the measured and calculated trajectores after much of reagents transformed. To mprove the accuracy of the worked out model more experments wth varyng jacket temperature trajectory need to be performed n the reactor but results are promsng. The ntal molar rato of reagents s modfed to valdate the developed model. The comparson of the calculated and the measured trajectores s shown n Fgure 4. and Fgure 5. These fgures show that the obtaned model can be appled to further analyze the nvestgated reacton system.

11 Herseczk et al.: Synthess of Glycerol Carbonate m A m B tme [s] tme [s] m D tme [s] Fgure 4. The molar rato of B (dmethyl carbonate) and A (glycerol) components s two. The calculated(thn) and the measured(crcles) trajectores of statevarables. Publshed by The Berkeley Electronc Press, 009

12 10 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A87 m A tme [s] m B tme [s] 100 m D 50 0 tme [s] Fgure 5. The molar rato of B (dmethyl carbonate) and A (glycerol) components s four. The calculated(thn) and the measured(crcles) trajectores of statevarables. Concluson Synthess of glycerol and dmethyl carbonate was nvestgated. A convenent method has been developed for synthess of glycerol carbonate from glycerol and dmethyl carbonate usng K CO 3 as catalyst. Resultng glycerol carbonate was obtaned n almost quanttatve yeld. A well detaled dynamc model of the reactor where the experments were performed has been worked out. The developed mathematcal model of reactor can be appled to unfold reacton steps of other synthess, but before a fnal concluson can be drawn more experments need to be done. Due to the reactor model other synthess can be performed and analyzed n the reactor system n future. The result of model valdaton shows that obtaned model can be appled to further analyze the nvestgated reacton system.

13 Herseczk et al.: Synthess of Glycerol Carbonate 11 Appendx Dynamc reactor model Based on the model assumptons and the supposed reacton mechansm the followng expressons were appled to calculate states of reactor durng the experment. At frst on components level the component source must be calculated so reacton rate constants are the followng assumng an Arrhenus-type correlaton between reactor temperature and the reacton rate: k k R ( E R T ) [ m mol ] 1 k 01 exp A1 s = (4) R 1 ( E R T ) [ ] k 0 exp A s = (5) R [ m mol s ], where K = exp( AK BK ) k + 1 = k1 K T R [ m mol s ], where K = exp( AK BK ) k + = k K T Rate of reactons and component sources were calculated applyng the followng expressons whch all have the same dmenson [mol m -3 s -1 ]: (6) (7) r 1 k1 c A c B r = (8) k cc = (9) r 1 = k 1 cc c E (10) r = k c D c E (11) R (1) A = r1 + r1 R (13) B = r1 + r1 R (14) C = r1 r1 r + r R (15) D = r r Publshed by The Berkeley Electronc Press, 009

14 1 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A87 R (16) E = r1 r1 + r r On level of phases some dfferental equatons must be used to calculate the change of value of state-varables n tme, so the volume of lqud phase s changed only by the evaporaton: dv dt 3 1 [ m s ] F FG = V (17) snce mass and temperature measurements are appled to follow the experment, the followng correlaton s appled to calculate the volume of lqud phase n the model: V F = = F m { A;B;C;D;E} 3 [ m ] ρ F and the densty of lqud phase s evaluated wth: (18) ρ F = = { A;B;C;D;E} = { A;B;C;D;E} 3 [ kg m ] F F m ρ F m (19) expresson, where the densty of pure components s the functon of temperature F R ρ = f ( T ) and the constants of these correlaton were collected from database of ASPEN. The reactor s operated as a batch reactor so there s no reagent feed durng the process and the evaporaton couples the lqud and gas phases. Based on these assumptons the followng dfferental equatons used to calculate the mass of lqud and gas phase: dm dt dm dt 1 [ kg s ] F F FG = V R M m (0) G FG kond, 1 [ kg s ] = m m (1) To calculate the temperature of reactor t s necessary to know the heat of vaporzaton of each component(source: database of ASPEN) and heat of reactons(source: dentfcaton):

15 Herseczk et al.: Synthess of Glycerol Carbonate 13 dt dt R = 1 RJ r ( ΔH, ) j + m R R F j reac j Q ρ c p V j= { 14} = FG { A; B; C; D; E} FG ( ΔH ) evap, () where the heat flux between the reactor and the jacket s: j RJ Q R J 1 ( T T ) [K s ] RJ RJ = A α (3) The next module of reactor model calculates the mass flux from lqud to gas phase. The vapour pressure of pure components was calculated wth Antoneequaton applyng constants found n ASPEN. The gas phase s treated as an deal gas so the component mass of gas phase: = n G { A;B;C;D;E} = G p V R T R G [ mol] (4) where the component mass of each component s calculated wth Raoult-Dalton s law: n G 0 x p G = n [ mol] G (5) p = { A;B;C;D;E} The evaporated lqud s removed from the gas phase through a Lebg cooler, whch s treated as a valve wth a valve constant (c v ): = m G { A;B;C;D;E} = c V p G G A 1 ( p p ) [ kg s ] (6) where p G and p A represent the pressure of gas phase and the ambent n bar. Publshed by The Berkeley Electronc Press, 009

16 14 Internatonal Journal of Chemcal Reactor Engneerng Vol. 7 [009], Artcle A87 References Demrel S., K. Lehnert, M. Lucas and P. Claus, Use of renewables for the producton of chemcals: Glycerol oxdaton over carbon supported gold catalysts, Appled Catalyss B: Envronmental, 007, 70, 1-4, Eben A.E. and J.E. Smth, 007, Introducton to Evolutonary Computng, ( nd prntng), Sprnger. Hansen N., Invarance, self-adaptaton and correlated mutatons n evoluton strateges, Proceedngs of the 6th Internatonal Conference on Parallel Problem Solvng from Nature, 000, Hansen N., References to CMA-ES applcatons, user/nko/cmaapplcatons.pdf, 005. Km S. C., Yong H. Km, H. Lee, D. Y. Yoon and B. K. Song, Lpase-catalyzed synthess of glycerol carbonate from renewable glycerol and dmethyl carbonate through transesterfcaton, Journal of Molecular Catalyss B: Enzymatc, 007, 49, Ott L., M. Bcker and H. Vogel, Catalytc dehydraton of glycerol n sub- and supercrtcal water: a new chemcal process for acrolen producton, Green Chem., 006, 8, 14. Rokck G., P. Rakoczy, P. Parzuchowsk and M. Sobeck, Hyperbranched alphatc polyethers obtaned from envronmentally bengn monomer: glycerol carbonate, Green Chemstry, 005, 7, Varga T., F. Szefert, J. Abony, Evolutonary strategy for feedng trajectory optmzaton of fed-batch reactors, Acta Polytechnca Hungarca, 007, 4, 4,