Ethyl Lactate Synthesis using A15 resin as Catalyst/Adsorbent: Kinetic and Adsorption Studies

Transcription

1 Ethyl Lactate Synthess usng A15 resn as Catalyst/Adsorbent: Knetc and Adsorpton Studes Carla S.M. Perera 1, Smão P. Pnho, Vvana M.T.M. Slva 1, and Alíro E. Rodrgues 1 1 Laboratory of Separaton and Reacton Engneerng (LSRE), Faculdade de Engenhara, Unversdade do Porto, Rua Dr. Roberto Fras s/n, -5 Porto, Portugal. Emal: arodrg@fe.up.pt Laboratory of Separaton and Reacton Engneerng (LSRE), Departamento de Tecnologa Químca e Bológca, Insttuto Poltécnco de Braganc a, Campus de Santa Apolóna, Braganc a, Portugal. ABSTRACT The heterogeneous catalyss of lactc acd ( wt. %) esterfcaton wth ethanol n presence of Amberlyst 15-wet was studed. A smplfed Langmur-Hnshelwood knetc model was used to predct the expermental data. The effect of the catalyst loadng, ntal molar rato between ethanol and lactc acd and reacton temperature on lactc acd converson as functon of tme was studed. Bnary adsorpton experments were performed n the fxed bed n absence of reacton at 9.15 K. The expermental breakthroughs obtaned were used to determne the multcomponent adsorpton equlbrum sotherm of Langmur type. The results obtaned wll be very useful to apply for the desgn and optmzaton of ndustral hybrd reactve separaton process usng Amberlyst 15-wet as catalyst/adsorbent. KEYWORDS: Ethyl lactate, knetcs, esterfcaton, adsorpton, Amberlyst 15, Langmur sotherm.

2 1. INTRODUCTION Petroleum ( black gold ) has been revealed lke one of the bggest economcs and poltcs problems of the actualty. It s a fnte resource and the use of petrochemcal solvents has several mplcatons on the envronment. Therefore, the replacement of tradtonal petroleum derved solvents s a bgg challeng. Ethyl lactate s a green solvent derved, for example, from processng corn, and s a promsng replacement for halogenated petroleum-based solvents n a wde range of applcatons. It can be used as food addtve, perfumery, flavour chemcals and solvent (Tanaka et al., ). The ethyl lactate synthess comprses a lqud-phase reversble reacton between ethanol and lactc acd, wheren water s a sub-product: + H ( Eth) + LactcAcd ( La) EthylLactate( EL) + Water( W) All esterfcaton reactons occur n acd medum, they are self-catalyzed by the acd nvolved n the reacton. But, the knetcs of the self-catalyzed reacton s too slow and the use of homogenous or heterogeneous catalyst s advantageous. The knetcs of ethyl lactate producton has been studed snce 1957 (Troupe and Dmlla, 1957), but lately has deserved more attenton snce t s a green solvent and an alternatve to the tradtonally petroleum derved solvents. Troupe and Dmlla (1957) studed the esterfcaton reacton between lactc acd and ethanol usng sulphurc acd as catalyst. However, ths knd of homogeneous catalysts may orgn a lot of problems, because ther mscblty wth the reacton medum, whch causes separaton problems; n addton, strong acd catalysts leads to corroson of the equpment. The replacement of homogeneous catalysts by heterogeneous catalysts s ganng mportance due to ther ecofrendly nature. Besdes beng non-corrosve and easy to separate from the reacton mxture the heterogeneous catalyst can be used repeatedly over a prolonged perod wthout any dffculty n handlng and storage. In ths case, the chosen catalyst was the sulfonc acd on exchange resn Amberlyst 15-wet (Rohm and Haas). Ths resn s of great nterest for use n reversble reactons, snce t can act as catalyst and as selectve adsorbent (Kawase et al., 199; Mazzott et al., 199; Slva and Rodrgues, ; Gand et al., ). Therefore the producton of Ethyl Lactate n a chromatographc reactor usng ths resn s very attractve. However, t s necessary to have nformaton about the knetcs and also about the adsorpton. So, ths work was undertaken to obtan the knetc model that descrbe the synthess of the ethyl lactate n the lqud phase and to determne the multcomponent adsorpton equlbrum sotherm of Langmur type over the A15 resn. These results wll be very useful to apply n the modellng of some reactve separaton processes, such as a fxed-bed reactor.. EXPERIMENTAL SECTION.1 Chemcals and Catalyst The chemcals used were ethanol (>99.9% pure), lactc acd (>5% pure) and ethyl lactate (>9% pure) from Sgma-Aldrch (U.K.). A commercal strong-acd on-exchange resn named Amberlyst 15-wet (Rohm & Haas) was used as catalyst and adsorbent. Ths resn s a bead-form macroretcular polymer of styrene and dvnylbenzene, wth partcle dameter varyng between.3 to 1. mm, an on exchange capacty of.7 meq H+/g of dry resn and nner surface area of 53 m/g. Snce the water adsorbed on the catalyst surface decreases the reacton knetcs, because t s one of the reacton products, t was necessary to guarantee anhydrous resn. For that, the resn was washed several tmes wth deonsed water and dred at 9 ºC untl the mass remans constant.

3 . Expermental set-up..1 Batch Reactor set-up (knetc studes) The experments were carred out n a glassjacketed 1 dm 3 autoclave (Büch, Swtzerland), operatng n a batch mode, mechancally strred at rpm, equpped wth pressure and temperature sensors and wth a blow-off valve. The temperature was controlled by thermostated ethylene glycol/water soluton (Lauda, Germany) that flows through the jacket of the reactor and feed vessel. To mantan the reactng mxture n lqud phase over the whole temperature range, the pressure was set at.mpa wth helum... Fxed Bed set-up (Adsorpton studes) The experments were performed n a laboratory-scale jacketed glass column that was mantaned at constant temperature (93.15 K), through a thermostatc bath; at atmospherc pressure. The column was packed wth the resn Amberlyst 15-wet (Rohm and Haas). It has an on exchange capacty of.7 eq H + /kg of dry resn and nner surface area of 53 m /g..3 Analytcal method All the samples were analysed n a gas chromatograph (Chrompack 91, Netherlands) usng a fused slca capllary column (Chrompack CP-Wax 57 CB, 5 m x.53 mm ID, df =. µm) to separate the compounds and a thermal conductvty detector (TCD 93 A) to quantfy t. The column temperature was programmed wth a 1.5 mn ntal hold at 11 ºC, followed by a 5 ºC/mn ramp up to 19 ºC and held for.5 mn. The njector and detector temperature was mantaned at ºC and 3 ºC, respectvely. Helum N5 was used as the carrer gas wth flowrate 1.5 ml/mn. 3. Knetc Studes The expermental results of the reacton knetcs of the esterfcaton of lactc acd and ethanol catalyzed by the A15 resn are presented n ths secton. The effect of the catalyst loadng, ntal molar rato between ethanol and lactc acd and reacton temperature on lactc acd converson as functon of tme s studed. Ths study was performed n absence of mass transfer lmtatons and catalyst deactvaton. A three-parameter model (see Equaton 1) based on a Langmur- Hnshelwood rate expresson; usng actvty coeffcents from the UNIQUAC method s proposed (Perera et al., ). Wth: aelaw aethala r = k K (1) K c c ( 1+ K s, EthaEth + K s, W aw ) ( / T ( K )) 7 =.7 1 exp () ( 1.1/ T( )) K W = exp K (3) ( 359.3/ T( )) K Eth = 1.exp K () Where, a s the actvty for spece, k c s the knetc constant, K, s the adsorpton constant s for speces and K s the equlbrum reacton constant. In Fgures 1, and 3 expermental and smulated results are shown. It can be seen that the proposed knetc law predcts well the tme evoluton of the lactc acd converson for dfferent masses of catalyst (A15), for dfferent ntal molar rato of reactants and for dfferent temperatures. 3

4 converson tme (mn) 1. wt.%. wt.% 3.9 wt.% L-H model Fgure 1- Effect of catalyst loadng on the converson of lactc acd hstory for a molar rato of ethanol to lactc acd of 1. at K. converson REth/La = 1.1 REth/La = 1. L-H model tme (mn) Fgure - Effect of ntal molar rato of ethanol to lactc acd on the converson of lactc acd hstory at 353. K. converson.... T = 3.1 K T = K T = 3.5 K T = 353. K L-H model tme (mn) Fgure 3- Effect of the reacton temperature on the converson of lactc acd hstory for a molar rato of ethanol to lactc acd of 1... Adsorpton Results As the resn A15 acts smultaneously as adsorbent and as catalyst, n order to have nformaton on the adsorptve equlbrum alone t s necessary to perform experments wth non reactve bnary mxtures. So, the breakthrough curves of ethanol, lactc acd, ethyl lactate and water were measured n the absence of reacton. The resn was saturated wth a certan component A and then the feed concentraton of component B was changed stepwse. The possble bnary mxtures to run the breakthrough experments n absence of reacton are ethanol / water, ethyl lactate / ethanol and lactc acd / water. The experments were performed at K and the concentraton hstores of the dfferent pars are presented n Fgures, 5 and.

5 (a) Water 1 1 (b) Water Theoetcal Fgure - Breakthrough experments: outlet concentraton of ethanol and water as a functon of tme; Q= 5 ml / mn; T = K; (a) water dsplacng ethanol; Bottom up flow drecton; (b) ethanol dsplacng water; Top-down flow drecton. 5

6 (a) Ethyl lactate (b) Ethyl lactate 1 Fgure 5- Breakthrough experments: outlet concentraton of ethanol and ethyl lactate as a functon of tme; Q = 5 ml / mn; T = K; (a) ethyl lactate dsplacng ethanol; Bottom up flow drecton (b) ethanol dsplacng ethyl lactate; Top-down flow drecton.

7 5 3 1 Water Lactc acd 1 Fgure - Breakthrough experments: outlet concentraton of water and lactc acd as a functon of tme; Q = 5 ml / mn; T = K; Lactc acd dsplacng water; Bottom up flow drecton. The adsorpton parameters of the multcomponent adsorpton equlbrum sotherm of Langmur type (Equaton 5) were optmzed by mnmzng the dfference between expermental and theoretcal number of moles adsorbed/desorbed for all the adsorpton experments and they are presented n Table 1. Langmur Adsorpton equlbrum sotherm to component : q = n 1+ Q K j= 1 K C j p, C p, j (5) Where Q, and K represent the total molar capacty per unt volume of resn and the equlbrum constant for component, respectvely, and n the total number of components. Table 1- Adsorpton parameters over A15 resn at 9.15 K. Component Q (mol/l real sold ) K (l/mol) Lactc acd Ethyl lactate Water The preferentally adsorbed component by the resn A15 s water and the weakest adsorbed one s ethyl lactate. Ths could be seen analyzng the concentraton front of ethanol n Fgures 7a and 7b. In the frst case t has a dspersve character and n the second one the ethanol concentraton front s self-sharpenng. 7

8 (a) (b) Fgure 7- Outlet concentraton of ethanol as a functon of tme; Q = 5 ml/mn; T = K; top-down drecton flow; a) ethanol dsplacng water; b) ethanol dsplacng ethyl lactate. 5. Conclusons A three-parameter model based on a Langmur- Hnshelwood rate expresson was proposed to descrbe the expermental knetc results: r = kc aetha La a ELaW K (1 + K Etha Eth + KW a ; and the model parameters are 7 =.7 1 exp / T ( K ), ( ) ) / W K c ( ) K W = exp( 1.1/ T( K) ) and K Eth = 1.exp( 359.3/ T( K) ). The agreement between expermental and smulated results was good for the followng operatng condtons: catalyst loadng from 1. wt. % to 3.9 wt. %, ntal molar rato of reactants from 1.1 to 1. and temperature from 5 ºC to ºC. Adsorpton experments n absence of reacton at ºC were performed and used to obtan the adsorpton parameters, by mnmzng the dfference between expermental and theoretcal number of moles adsorbed/desorbed. It was observed that the preferentally adsorbed component by the resn A15 s water and the weakest adsorbed one s ethyl lactate.. References Gand, G. K.; Slva, V. M. T. M.; Rodrgues, A. E. Synthess of 1,1-dmethoxyethane n a fxed bed adsorptve reactor. Industral and Eng.g Chem. Res., v. 5, p. 3-39,. Kawase, M.; Suzuk, T. B.; Inoue, K.; Yoshmoto, K.; Hashmoto, K. Increased esterfcaton converson by applcaton of the smulated movng-bed reactor. Chem. Eng. Sc., v. 51, p , 199. Mazzott, M.; Kruglov, A.; Ner, B.; Gelosa, D.; Morbdell, M. A contnuous chromatographc reactor: SMBR. Chem. Eng. Sc., v. 51, p , 199. Perera, C. S. M.; Pnho, S. P.; Slva, V. M. T. M.; Rodrgues, A. E. Thermodynamc Equlbrum and Reacton Knetcs for the Esterfcaton of Lactc Acd wth Catalyzed by acd on exchange resn. Ind. Eng. Chem. Res., v. 7, p ,. Slva, V. M. T. M.; Rodrgues, A. E. Dynamcs of a fxed-bed adsorptve reactor for synthess of dethylacetal. AIChE Journ., v., p. 5-3,.

9 Tanaka, K.; Yoshkawa, R.; Yng, C.; Kta, H.; Okamoto, K.-. Applcaton of zeolte T membrane to vapor-permeaton-aded esterfcaton of lactc acd wth ethanol. Chem. Eng. Sc. v. 57, p ,. Troupe, R.A. and Dmlla E. Knetcs of the Ethyl Alcohol-Lactc Acd Reacton. Ind. Eng. Chem., v. 9, p. 7,