1-s2.0-S1385894713010796-main

8/12/2019 1-s2.0-S1385894713010796-main

1/9

Glycerol valorisation as biofuels: Selection of a suitable solvent for aninnovative process for the synthesis of GEA

Rui P.V. Faria, Carla S.M. Pereira , Viviana M.T.M. Silva, Jos M. Loureiro, Alrio E. Rodrigues

Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering of University of Porto, 4200-465 Porto, Portugal

h i g h l i g h t s

Solvent selection for reactiveadsorptive processes: Synthesis ofglycerol acetal.

Acetalization of glycerol over

Amberlyst-15 in the presence of

dimethyl sulfoxide.Kinetic model considering a LHHW

mechanism and diffusion inside the

catalyst.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 30 March 2013

Received in revised form 6 August 2013

Accepted 12 August 2013

Available online 21 August 2013

Keywords:

Glycerol acetal

Acetalization

Amberlyst-15

Solvent selection

SMBR

a b s t r a c t

The study of the production of glycerol ethyl acetal, through the acetalization of glycerol with acetalde-hyde in a simulated moving bed reactor requires the selection of a suitable solvent/desorbent for the pro-cess. The methodology described in this paper, based on reaction, adsorption and environmental

variables, lead to the identification of dimethyl sulfoxide as the solvent that best fitted the specificationsof such reactiveadsorptive processes. Furthermore, a detailed study of the acetalization of glycerol in thepresence of this solvent and using Amberlyst-15 as catalyst, allowed the determination of its reaction

activation energy, 77.7 kJ mol1. The reaction rate was described by a LangmuirHinshelwoodHou-

genWatson model, and was obtained from batch experiments with a complete model considering dif-fusion inside the catalyst particles.2013 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND

license (http://creativecommons.org/licenses/by-nc-nd/3.0/ ).

1. Introduction

For the past few years, biodiesel has been suggested as a reliablerenewable alternative for fossil fuels, mainly due to its reducedtoxicity and exhaust emissions. However, the intensification of

the production of these fatty acid esters [1]lead to an excess ofglycerol in the market, since it is a byproduct obtained in approx-imately 10%, wt/wt, motivating the research and development ofseveral glycerol-based products[24].

Glycerol-acetals have shown interesting results as green oxy-genated fuel additives [3,5,6]. Within this family of compounds,

glycerol ethyl acetal (GEA), has evidenced the potential to reduce

exhaust gases particle emissions [7,8] and control of fuel fluid

properties[913]. However, it must be mentioned that GEA mightnot be a suitable gasoline additive, due to the existence of solubil-ity problems[14]. On the other hand, this problem was not verified

for diesel or biofuels[15,16].Researchers have reported the acetalization of glycerol with

acetaldehyde [1724]and the transacetalization of glycerol with1,1-diethoxyethane (DEE) [8,2528] as the two main reaction

pathways for the synthesis of GEA. In both cases an isomeric mix-ture containing cis-5-hydroxy-2-methyl-1,3-dioxane, trans-5-hy-droxy-2-methyl-1,3-dioxane, cis-4-hydroxymethyl-2- methyl-1,3-dioxolane, and trans-4-hydroxymethyl-2-methyl-1,3- dioxolaneis obtained. However, the direct condensation of glycerol with

http://dx.doi.org/10.1016/j.cej.2013.08.035

1385-8947/2013 The Authors. Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/ ).

Corresponding author. Tel.: +351 22 508 1686; fax: +351 22 508 1674.

E-mail address:[email protected](C.S.M. Pereira).

Chemical Engineering Journal 233 (2013) 159167

Contents lists available at ScienceDirect

Chemical Engineering Journal

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c e j
http://creativecommons.org/licenses/by-nc-nd/3.0/http://dx.doi.org/10.1016/j.cej.2013.08.035http://creativecommons.org/licenses/by-nc-nd/3.0/mailto:[email protected]://dx.doi.org/10.1016/j.cej.2013.08.035http://www.sciencedirect.com/science/journal/13858947http://www.elsevier.com/locate/cejhttp://www.elsevier.com/locate/cejhttp://www.sciencedirect.com/science/journal/13858947http://dx.doi.org/10.1016/j.cej.2013.08.035mailto:[email protected]://creativecommons.org/licenses/by-nc-nd/3.0/http://dx.doi.org/10.1016/j.cej.2013.08.035http://-/?-http://creativecommons.org/licenses/by-nc-nd/3.0/http://-/?-http://-/?-http://-/?-http://crossmark.crossref.org/dialog/?doi=10.1016/j.cej.2013.08.035&domain=pdfhttp://-/?-

8/12/2019 1-s2.0-S1385894713010796-main

2/9

acetaldehyde not only requires a less complex production schemebut it also has a higher mass efficiency and only makes use ofreactants obtained from biomass, presenting itself as a more inter-

esting route for the synthesis of GEA. Nonetheless, this route stillpresents some drawbacks. On one hand, this is a thermodynami-cally limited reaction. On the other hand, as the product is in-tended to be applied as a fuel additive, the water formed as a

secondary product during the synthesis step must only be presentin residual amounts in the final product. Therefore, the assay re-quired for GEA might imply significant separation costs.

The concept behind multifunctional reactors, which integrate

reaction and separation processes within a single unit, relies onthe equilibrium displacement promoted by the continuous re-moval of the products from the reaction media, favouring products

formation and, therefore, increasing conversion. These hybrid tech-nologies are able to improve selectivity towards a product and alsohave the potential to reduce capital investment and energy con-sumption. In what concerns acetals production, very satisfactory

results have been obtained with the simulated moving bed reactor(SMBR) [29]. The production of 1,1-dimethoxyethane [30], DEE[3132]and 1,1-dibuthoxyethane[33]was achieved by the direct

acetalization of methanol, ethanol and butanol with acetaldehyde,respectively, in a SMBR where the chromatographic columnswhere packed with Amberlyst-15 that acted both as catalyst andadsorbent. Thus, the SMBR might be a suitable technology for theproduction of GEA from glycerol and acetaldehyde, once it will

be able to shift the reaction thermodynamic equilibrium and,simultaneously, remove the undesired water from the final prod-uct stream as verified for the previous acetalizations in this multi-functional reactor.

In most SMBR applications reported in the open literature, oneof the reactants was used as solvent; however, in the GEA synthesisby direct condensation of glycerol with acetaldehyde, this method-ology cannot be applied. Glycerol, due to its high viscosity would

significantly increase the pressure drop in the operation unit as

well as add a mass transfer resistance to the system. Plus, its highboiling point would represent an increase in the final product

purification costs. Acetaldehyde, on the other hand, in the presenceof an acid catalyst will undergo oligomerization reactions [34],thus in order to decrease the possibility of side-products forma-

tion, acetaldehyde amount must be kept as low as possible. There-fore, another compound must be selected as solvent and particularattention was given to the analysis of parameters related to itsreactivity and physical properties with focus on adsorption. As

far as our knowledge goes, although some systematic solventscreening methodologies have been published, none was specifi-cally focused on SMBR. They are either for generic organicsynthesis processes[3537], for simpler chromatographic systems

[3840] or mainly oriented for the identification of "green"solvents[4143].

Therefore, the work herein reported, presents a first approach

for a simple but expeditious solvent screening methodology forreactiveadsorptive processes, such as the SMBR. A compilationof significant physicalchemical properties of a large list of themost common solvents for chemical processes was performed

and the list was sequentially reduced based on theoretical param-eters related with reactiveadsorptive processes requirements.Miscibility, adsorption and reaction experimental tests were per-

formed with the solvents that presented the best results of the the-oretical screening, allowing the selection of a suitable solvent forthe production of GEA in a SMBR.

Finally, a kinetic model was proposed for the direct condensa-tion of glycerol with acetaldehyde in the presence of the selected

solvent. A parametric study comprising a wide range of operatingconditions was performed in order to determine the kinetic param-eters for this reaction. The results were compared with the solventfree reaction for the synthesis of GEA.

2. Experimental

2.1. Chemicals and catalyst

The chemicals used in the experimental tests wereacetaldehyde (>99%), glycerol (>99%), acetonitrile (>99%) and

Nomenclature

Cb,i molar concentration of compound i in the bulk(mol dm3)

Cp,i molar concentration of compoundi in the intraparticlefluid (mol dm3)

Deff,i compoundi effective diffusion coefficient (cm2 s1)

Ea reaction activation energy (kJ mol1)DG0 standard reaction Gibbs free energy (kJ mol1)DHS,W water enthalpy of adsorption (kJ mol

1)DHS,DMSO dimethyl sulfoxide enthalpy of adsorption (kJ mol

1)Keq reaction equilibrium constant ()kc reaction kinetic constant (dm

6 mol1 g1cats1)

kc0 Arrhenius pre-exponential factor for the reaction kineticconstant (dm6 mol1 g1cats

1)KS,W water adsorption equilibrium constant (dm

3 mol1)KS;W0 Vant Hoff pre-exponential factor for water adsorption

equilibrium constant (dm3 mol1)KS,DMSO dimethyl sulfoxide adsorption equilibrium constant

(dm3 mol1)KS;DMSO0 Vant Hoff pre-exponential factor for dimethyl sulfoxide

adsorption equilibrium constant (dm3 mol1)

NP total number of measurements for a kinetic experiment()

NE number of kinetic experiments performed ()P pressurebarr radial position (cm)

rAcet/Gly reactants initial molar ratio ()qads adsorbed molar amount (mol L

1cat)

R ideal gas constant (J mol1 K1)R2 correlation coefficient ()Rp catalyst particle radius (lm)

R reaction rate based on the local intraparticle composi-tion (mol g1cats

1)T temperature (K)t time (min)wtcat/wt catalyst weight percentage (%)xi molar fraction of compoundi ()Xexp

ij jth point for the conversion measured in experimenti(

)Xmodij jth point for the conversion in experiment predicted by

the model i ()eb bulk porosity ()ep catalyst particle porosity ()mi compoundi stoichiometric coefficient ()qp catalyst particle solid density

AbbreviationsDEE 1,1-diethoxyethaneGEA glycerol ethyl acetalSMBR simulated moving bed reactor

160 R.P.V. Faria et al. / Chemical Engineering Journal 233 (2013) 159167
http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-

8/12/2019 1-s2.0-S1385894713010796-main

3/9

n,n-dimethylformamide (>99%), purchased from SigmaAldrich,

and dimethyl sulfoxide (>99%) purchased from VWR International.Rohm & Haas Amberlyst-15 ion exchange resin was used as cat-

alyst. As water adsorbs strongly on Amberlyst-15 and it can lead toa decrease of the reaction rate, since it is a product of the reaction,anhydrous resin must be used on adsorption and reaction tests.

Hence, the resin was washed several times with deionized water,

then washed with ethanol and dried at 363 K until the mass re-mained constant, prior to its use.

2.2. Solvent selection methodology for reactiveadsorptive process

The solvent selection methodology developed comprises misci-bility, reactivity, adsorption and kinetic tests with the solvents that

were selected after a first theoretical screening.

2.2.1. Miscibility tests

Miscibility tests were performed by preparing several binarymixtures containing the solvent and one of the reactants to whichwater or GEA was added in low amounts until phase split or theformation of a single phase system was observed (depending on

if the initial binary mixture presented one or two phases, respec-tively). The tests were performed in 5 mL closed test-tubes keptat 313 K by a water bath (LAUDA, LaudaKonigshofen, Germany).The samples were initially stirred in a vortex mixer and then al-

lowed to stand to promote the phase separation.

2.2.2. Adsorption tests

Amberlyst-15 adsorption capacity towards water, GEA and the

solvents, was estimated through swelling experiments performedin 10 mL graduated cylinders where a known amount of sorbent(approximately 1.0 g) was put in contact with 5 mL of sorbate ata constant temperature of 293 K (temperature was kept this low

in order to avoid evaporation) for a period of 48 h. The final sorbentvolume was registered. The sorbent was filtered and weighted andits adsorption capacity for a given compound was considered to be

an approximation of its mass difference between the beginningand the end of the experiments. The procedure was performed atleast three times for each compound.

2.2.3. Reaction tests

Batch reactions were carried out in a 150 mL stainless steel ves-sel, equipped with a sampling valve and temperature and pressuresensors, operating at 313 K and 5 bar. A magnetic hotplate stirrerwith external temperature control was used to supply heat and

to stir the reaction mixtures composed by 25 mmol of acetalde-hyde and glycerol diluted in 50% of solvent (molar basis). Amber-lyst-15 (1.0 wt%) was used as catalyst. The experiments were

carried out for 5 h. Samples were collected at predefined timeintervals and analysed in a gas chromatograph (Shimadzu, GC

2010 Plus) using a thermal conductivity detector. Helium N50(38.5 mL min1) was used as the carrier gas for the separation of

the compounds in a CPWax57CB column (25 m0.53 mm i.d.,film thickness of 2.0 lm). The proper column temperature programwas defined for each solvent.

2.3. Detailed kinetic study: set-up and experimental procedure

The determination of the kinetics of the acetalization of glycerolwith acetaldehyde in the presence of the selected solvent was car-

ried out in a closed glass-jacketed 1 L vessel (Buchi LaboratoryEquipment, Flawil, Switzerland), mechanically stirred andequipped with a blow-off valve, pressure and temperature sensors.The reactor was operated in batch mode and its temperature was

controlled through a water bath (LAUDA, LaudaKonigshofen,Germany).

The kinetic study was performed evaluating the effect of param-

eters such as stirring speed (500 rpm and 700 rpm), temperature(303 K, 323 K and 358 K), initial acetaldehyde to glycerol molar ra-tio (0.5, 1.0 and 2.0), solvent molar fraction (0.25, 0.5 and 0.75) andcatalyst loading (0.15 and 0.3 wt% of the total reaction mediummass), according to the experiments described inTable 1.

The pressure was set to 8.0 bar with helium for all the experi-

ments. Vapourliquid equilibrium calculations indicated that atthis pressure, even at the higher operating temperature, the molaramount of the reaction medium species in the vapour phase would

not exceed 0.5% of the total molar amount introduced in the reac-tor and, therefore, the vapour phase would be mainly constitutedby helium.

Each reaction kinetic experiment was performed only once in

order to keep the tests manageable and due to high reactantsconsumption.

All the samples collected were analysed in the previously de-

scribed gas chromatograph by injecting 0.8lL of sample (split ratioof 15.0). Helium N50 was used as the carrier gas at a flow rate of38.5 mL min1. The temperatures of the injector and thermal con-ductivity detector were set to 573 K. The column was initially kept

at 373 K for 1 min and its temperature was then increased at a rateof 120 K min1 until it reached 493 K and held constant at that va-lue for the following 6 min. After this period the column tempera-ture was decreased to 463 K at a rate of 30 K min1. The total

analysis time was 60 min.

3. Results and discussion

3.1. Solvent selection for reactiveadsorptive processes

As previously stated, none of the reactants of the GEA synthesisby means of glycerol acetalization can be used as solvent in theSMBR technology. Therefore, a four stage methodology was devel-oped and applied for the selection of the most suitable solvent for

the production of this acetal by reactiveadsorptive processes. Forthat purpose, a typical set of operating conditions was defined andan extensive bibliographic review was conducted in order to iden-tify common solvents used in similar processes. The process tem-

perature was assumed to be 313 K, at a pressure of 5 bar and theinitial reaction medium composition was established as0.25:0.25:0.50, in terms of molar fractions of acetaldehyde, glyc-erol and solvent, respectively.

3.1.1. Theoretical based solvent screening

The list of approximately 100 solvents elaborated was reducedconsidering three major process variables: solvent reactivity, sol-vent physical state at the reaction conditions and hypotheticalphase split promoted by the use of the solvent. Solvents that have

Table 1

Kinetic experiments operating conditions.

Exp.

No.

Stirring

speed(rpm)

Temperature

(K)

Initial

reactantsmolar ratio

Solvent

molarfraction (n/

n)

Catalyst

loading(wt%)

1 700 323 1.00 0.50 0.15%

2 500 303 1.00 0.50 0.15%

3 500 323 1.00 0.50 0.15%

4 500 323 1.00 0.50 0.30%5 500 343 1.00 0.50 0.30%

6 500 323 0.50 0.50 0.15%

7 500 323 2.01 0.50 0.30%8 500 323 1.00 0.25 0.15%

9 500 323 1.00 0.75 0.30%

R.P.V. Faria et al. / Chemical Engineering Journal 233 (2013) 159167 161
http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-

8/12/2019 1-s2.0-S1385894713010796-main

4/9

been reported as reactive with any of the reactants or products of

the selected synthesis route, such as alcohols, aldehydes, ketonesand carboxylic acids, were eliminated from the primary list.

Due to operational requirements of the SMBR unit, the solventto be used should, preferably, be at the liquid state. Making useof published data in the open literature the melting point of each

solvent was compiled and its boiling point determined through

the Antoine equation [44], at the previously mentioned pressurevalues. Applying a safety factor of 10 K to the phase change tem-peratures considered, the solvents for which the melting point was

above 303 K and the boiling point was below 323 K were excludedfrom the screening.

In the following solvent screening step, Aspen Plus softwarewas used to estimate miscibility of the solvent with the initial reac-

tion medium at the defined operating conditions, considering theUNIFAC model for computing the activity of each species. If thearea of the miscibility region of the ternary phase diagram for a

specific solvent was lower than 75% that solvent was excludedfrom the solvents list. It must be noticed that due to lack of datafor 1,3-dioxolane, chloroform, dimethyl sulfoxide and n,n-dimeth-ylformamide, these solvents could not be excluded.

When designing an industrial process two main questions mustbe considered: process performance and process impact. Regardingthe studied process, the acetalization reaction catalyzed by an ionexchange resin in a SMBR unit, one can promptly conclude that

polarity will be a key performance parameter. On one hand, ahighly polar medium favours the acetalization reaction once itsrate determining step is the formation of a cation from the proton-ated hemi-acetal[23], and polar media allow the stabilization of

the intermediate cations [45]. On the other hand, as an ion ex-change resin will be used as catalyst/adsorbent, the sorption prop-erties of the solvents can be roughly approximated by theirpolarity. Water is a highly polar compound and will adsorb in large

amounts in Amberlyst-15; thus, the decrease of solvent consump-tion (that acts as desorbent), will be favoured if a highly polar sol-vent is chosen. In ideal terms, the polarity of the solvent should be

somewhere between the polarity of water and that of GEA. For thatreason, the solvents remaining in study from the previous pre-selection steps were ranked (Table 2) considering a weight of50% for process performance parameters (25% for dipole momentand 25% for dielectric constant) and 50% for process impact param-

eters (25% for lethal dose, LD50, and NFPA health hazard classifica-tion; and 25% for octanolwater partition coefficient, log Pow, andpersistence time in evaluative environment). For each variable, ascore of 100% was attributed to the solvent that presented the

higher value for that variable and a score of 0% for the lower, ifthe variable analysed is intended to be maximized. All the othersolvents were scored proportionally. The inverse scoring procedure

was applied to variables that were intended to be minimized.

In order to keep experimental tests practicable the list was

shortened, including only the solvents that had a score above50%. However, as acrylonitrile has a severe health hazard (as canbe confirmed through its NFPA health classification maximumhazard classification and through its Material Safety Data Sheet)it was also excluded. Therefore, dimethyl sulfoxide, acetonitrile,

n,n-dimethylformamide were the solvents selected for further

experimental tests.

3.1.2. Experimental based solvent selection

3.1.2.1. Miscibility tests. In an attempt to assess the miscibility ofthe solvents selected from the previous screening steps with the

compounds present in the reaction medium, ternary mixtures con-taining one of the reactants, one of the products and one solventwere prepared. Both dimethyl sulfoxide and n,n-dimethylformam-

ide have proven to be miscible with all of the reaction species. Ace-tonitrile, however, presented some miscibility problems withglycerol as can be observed in Fig. 1. This fact represents a handi-cap of acetonitrile against the remaining solvents since it is ex-

pected to originate additional mass transfer resistances.

3.1.2.2. Adsorption tests. As previously mentioned, adsorption isone of the key parameters to be analysed when dealing with SMBR

technology. It is known that the performance of these units, for in-stance in terms of desorbent consumption, is improved if the sol-vent presents an high adsorption capacity but preferablybetween the values observed for the two products that have to

be separated. For this particular system, the adsorption capacityof Amberlyst-15 towards the solvent should be higher than to-wards GEA and lower than for water. The results for the swellingtests performed are presented in Fig. 2.

As it can be concluded formFig. 2, all the three tested solventspresent adsorption capacities between water and GEA. However,dimethyl sulfoxide presents a slightly higher adsorption value thanthe rest of the solvents. Therefore it is expected that dimethyl sulf-

oxide will lead to the minimum desorbent consumption in the

SMBR unit.

3.1.2.3. Reaction tests. The first objective was to verify that none ofthe solvents would react with any of the species of the reactionmedia. Furthermore, for the assessment of the influence of the

presence of the solvents in the kinetics of the reaction betweenglycerol and acetaldehyde, experimental tests were carried out.The results are presented inFig. 3.

As Fig. 3 shows, dimethyl sulfoxide, n,n-dimethylformamide

and acetonitrile present similar kinetic performances, achievingconversions of above 50% after 100 min. Moreover, no secondaryproducts were observed during the experiments. Althoughequilibrium results are not represented in Fig. 3 (for a better

Table 2

Rank of solvents by process performance and process impact, based on their properties [44].

Solvent Dipole moment (D) Dielectric constant LD50 (mg/kg) LogPow Persistence time (h) NFPA health Score (%)

Dimethyl sulfoxide 3.96 46.45 14500 1.350 573 1 82

Acetonitrile 3.92 37.50 2460 0.340 347 2 68

N,N-dimethylformamide 3.82 38.00 2800 1.010 438 2 67

Acrylonitrile 3.87 33.00 78 0.250 258 3 60

Dimethyl carbonate 0.91 3.09 13000 0.230 185 2 41

Ethyl acetate 1.78 6.02 5620 0.730 264 2 39Methyl acetate 1.68 6.68 5000 0.180 277 2 38

1,3-Dioxolane 1.45 7.34 3000 0.370 310 2 37

Dichloromethane 1.60 9.10 1600 1.250 186 2 36Tetrahydrofuran 1.63 7.58 1650 0.460 293 2 35

1,2-Dimethoxyethane 1.71 2.00 775 0.210 354 2 32

Chloroform 1.01 4.81 695 1.970 189 2 29

1,4-Dioxane 0.00 2.21 4200 0.270 350 2 24

Tetrachloromethane 0.00 2.20 2350 2.830 177 3 18


8/12/2019 1-s2.0-S1385894713010796-main

5/9

understanding of the kinetic results), it was observed that n,n-dimethylformamide has a lower equilibrium conversion (approxi-mately 85%) than the other solvents, for which the conversion

achieved was similar (slightly above 90%), due to the effect of the

non-ideality of the mixtures.

In summary, one can say that the application of the methodol-

ogy herein developed to the production of GEA in a SMBR lead tothe identification of dimethyl sulfoxide as the most appropriatesolvent for this process, as shown by the theoretical as well asthe experimental part of the screening procedure implemented.Besides its reduced environmental impact and health hazard, this

solvent is completely miscible with the reaction mixture in oppo-

sition to acetonitrile. On the other hand, it presents the higheradsorption capacity, which will minimize its consumption in theSMBR unit, without having any negative impact on the kinetics

of the reaction or the equilibrium compositions when comparedwith the remaining solvents. However, a more detailed descriptionof the kinetics of the acetalization of glycerol in the presence of di-methyl sulfoxide will be of significant relevance for a correct eval-

uation of the SMBR process with this solvent. Therefore, the resultsof the study of the kinetics of this reaction are presented in thenext section.

3.2. Kinetic study in the presence of the selected solvent

An experimental parametric study (summarized inTable 1) was

performed in an isothermal batch reactor in order to determine thekinetic parameters for the acetalization of glycerol catalysed byAmberlyst-15, in the presence of dimethyl sulfoxide.

For kinetic modelling purposes, an assessment of the mass

transfer limitations was required. Concerning mass transferlimitations inside the catalyst, as previously reported in the openliterature[4650], a bidisperse pore size distribution, containingmicro- and macropores, was suggested for Amberlyst-15. In the

model adopted the reactants diffuse through the macropores,adsorb in its walls and then diffuse through microspheres(homogeneous gel particles) adsorbing in its active sites wherethey react. Mass transport phenomena at the microspheres can

be considered infinitely fast and, therefore, the internal masstransfer resistance can be limited to the diffusion through themacropores [46,48]. On the other hand, it was determined that

for the studied reaction system a stirring speed of 500 rpm couldsignificantly reduce external mass transfer resistances to the pointthat they became negligible.

The mathematical model implemented comprises the mass bal-ance to the bulk and intraparticle fluid given by Eqs. (1) and (2),

respectively.

dCb;idt

3

Rp

1 ebeb

Deff;i

@Cp;i@r

rRp

1

ep@Cp;i@t

1

r2@

@r Deff;ir

2@Cp;i@r

1 epmiqpR 2

Species i (i= acetaldehyde, glycerol, water, GEA, dimethyl sulf-oxide) molar concentrations in the bulk and intraparticle fluid

are represented by,Cb,iandCp,i, respectively; miandDeff,iare its stoi-chiometric and effective diffusion coefficients (computed as de-

scribed elsewhere [24]); R is the reaction rate based on thecomposition along the catalyst radius, r; eb is the bulk porosity;

Rp, ep and qp represent the catalyst particle radius (342.5lm[55]), porosity (0.36[56]) and solid density (1016 kg m3 [55]).

Eqs.(3)(6)define the initial and boundary conditions consid-ered for this model.

t 0 ! Cb;i Cb;i0 3

t 0 ! Cp;i Cp;i0 4

r0

!

@Cp;i

@r 0

5

Fig. 1. Ternary phase diagram for glycerol:acetonitrile:water and glycerol:acetoni-

trile:GEA mixtures, in molar compositions at 313 K.

Fig. 2. Adsorption tests on Amberlyst-15.

Fig. 3. Comparison of the performance of the solvents on the kinetics of the

acetalization of glycerol (T= 313 K;P= 5 bar; racet/gly= 1.0;xsolv= 0.5; cat. loading of

2.0 wt% of the total reactants mass; 500 rpm).

http://-/?-http://-/?-http://-/?-

8/12/2019 1-s2.0-S1385894713010796-main

6/9

r Rp ! Cb;i Cp;irRp

6

The reaction rate of acetaldehyde with glycerol[24], as well aswith several linear chain alcohols [5053], has been described by

several authors by a LangmuirHinshelwoodHougenWatsonmodel. This model assumes the adsorption of both reactants, fol-lowed by a surface reaction that originates a hemi-acetal. Two sub-sequent surface reactions will lead to the formation of adsorbed

water and acetal. The final step is the desorption of both products.The surface reaction leading to the formation of the adsorbedhemi-acetal is considered as the rate determining step. Previous

authors have suggested that water adsorption is significantly high-er than that of the remaining reaction species and, consequently,the adsorption of those species could be neglected. However, forthis system, as dimethyl sulfoxide is the major compound and it

is a very polar solvent (which indicates that it will adsorb stronglyon Amberlyst-15), its adsorption must also be considered. Eq. (7)presents the simplified rate expression used to describe the exper-imental data, taking into account the previous considerations.

R kcCAcCGly

CGEACWKeq

1 K

S;W

CW

KS;DMSO

CDMSO

2 7

In this equation, Keq represents the reaction thermodynamicequilibrium constant, kc, the reaction kinetic constant and KS,WandKS,DMSOthe adsorption equilibrium constants for water and di-methyl sulfoxide, respectively.

The kinetic constant depends on temperature according toArrhenius law (Eq.(8)),

kc kc0exp EaRT

8

whereEa, represents the reaction activation energy and k c0 , is thepre-exponential term.

The equilibrium constants depend on temperature according to

Vant Hoff law (Eqs.(9)(11)),

Keq exp DG0

RT

! 9

KS;W KS;W0exp DHS;W

RT

10

KS;DMSO KS;DMSO0exp DHS;DMSO

RT

11

where DG0, is the reaction free Gibbs energy, DHS,Wand DHS,DMSOare the adsorption enthalpies for water and dimethyl sulfoxideandKS;W0 and KS;DMSO0 , are the pre-exponential terms. From previouswork[24], computing the thermodynamic equilibrium constant in

terms of composition, a value of12.95 kJ mol1 was determinedfor DG0.

The studied reaction system comprises a non-ideal mixture.However, for modelling purposes, it was impossible to account tothis factor due to the absence in the open literature, as far as ourknowledge goes, of the necessary binary interaction parameters

between the species present in the reaction mixture. Althoughthe first bibliographic references to the synthesis of GEA are datedto 1865[17], the study of the non-ideality of the species involvedin the different synthesis routes has been neglected by the scien-

tific community. As a consequence, no binary interaction parame-ters involving GEA have been published so far. Without this data itis impossible to determine the activity coefficients of each specieswith the most common methods such as Wilson, NRTL or UNI-

QUAC. For the solvent free condensation of glycerol with acetalde-hyde [24], the determination of the activity coefficients was

reported using the UNIFAC group contribution method. However,

when dimethylsulfoxide is used as solvent in this reaction, theUNIFAC model cannot be applied since the binary interactionparameter between the aldehyde group and dimethyl sulfoxidedoes not exist in the open literature.

The model equations presented were solved with gPROMS

(General Process Modelling System, version 3.4.0) using one of its

integrated solvers, DASOLV, discretizing the radial dimension in28 non uniform intervals and making use of a second order cen-tered finite-difference method. The determination of the unknown

parameters,Ea,kc0 , DHS,W, KS;W0 , DHS,DMSOand KS;DMSO0 , was carriedout using the Parameter Estimation tool and fitting the experi-mental data by the maximum-likelihood method, assuming a con-stant variance model and setting the estimation tolerance to 105.

For the determination of the errors associated to the parametersestimated a Jackknife methodology[54] was applied, considering8 groups of experiments where one experiment was removed from

the original set of experiments (experiment 1 was not taken intoaccount since no external mass transfer limitations were observedand, therefore, the results are similar to those obtained in experi-ment 3, and it was considered that the same weight should be gi-

ven to every experiment, representing a unique set of operatingconditions, on the parameter estimation procedure).

The estimation of the six parameter for the model previouslydescribed led to large standard errors. For instance, the standard

errors for the pre-exponential factors from the Arrhenius and theVant Hoff laws achieved almost 100% of its absolute values. Thus,the number of parameters to be estimated had to be reduced. Sincethe range of operating temperatures can be considered narrow

(40 K), the effect of temperature on the adsorption equilibriumwas considered negligible and Eqs. (10) and (11) were removedfrom the final model. This assumption was based on the resultspublished for other acetalization reaction between acetaldehyde

and several alcohols [24,5153], described by a LHHW rate law,in which it is possible to observe a more significant temperaturedependence of the kinetic constant when compared to the adsorp-

tion constant. For instance, for the acetalization leading to the syn-thesis of 1,1-dibutoxyethane[53], considering a temperature rangefrom 303 K to 343 K, the water adsorption constant is expected todecrease to approximately one third of its value, while the increaseof the reaction kinetic constant reaches ten times its value from the

lower to the higher temperature. The parameters determined andthe corresponding errors are presented on Table 3.

The reaction rate is favoured by the increase of temperature. Asexpected,Fig. 4shows that both the experimental results, obtained

in the range of 303343 K, and the model present a higher reactionrate for higher temperatures.

Moreover, the model has also shown to be in good agreement

with the experimental observations when changes on the initialcomposition of the reaction medium were promoted. A higher

reaction rate was achieved when an excess of either of the reac-tants was used, as presented inFig. 5,where the rates for mixtures

with an initial acetaldehyde to glycerol molar ratio of 0.5, 1.0 and2.0 are compared. However, the greater difficulties in predictingthe effect of this parameter on the kinetic behaviour, when com-pared with the effect of temperature, might be related with the

major impact that changes in the reaction medium composition

Table 3

Kinetic parameters estimated for the acetalization of glycerol in presence of dimethyl

sulfoxide.

Parameter (units) Estimated Value Standard Error

Ea (kJ mol1) 77.7 0.8

kc0dm6 mol1 g1cats

1 5.97108 1.06108

KS,W(dm3 mol1) 3.45101 5.4102

KS,DMSO (dm3 mol1) 1.06101 1.9102


8/12/2019 1-s2.0-S1385894713010796-main

7/9

have on the activity coefficients of the species present in the mix-

ture that could not be accounted for due to the previously men-tioned reasons.

On the other hand, the reaction proceeded at lower rates whenthe solvent amount was enlarged due to the dilution factor appliedto the reactive species (Fig. 6). Molar fractions of 0.25, 0.50 and

0.75 of dimethyl sulfoxide were studied.

The increase of the catalyst loading from 0.15 wt% to 0.30 wt%lead to an increasing on the experimental reaction rate of approx-imately 50% (Figs. 46), estimated by the initial reaction rate meth-

od. A similar increase was observed for the model prediction.The parametric study performed showed that the model is able

to predict the effect of changes in the design variables. In order tomake a more objective assessment of the quality of the fitting of

the experiments, considering the parameters estimated for themathematical model implemented, its correlation coefficient wascomputed (Eq.(12)). The value determined was 0.980, indicating

that the model describes with high accuracy the kinetic behaviourof this reaction over the wide range of experimental conditionstested.

R2 1 PNE

i1PNP

j1 X

exp

i;j X

mod

i;j 2

PNEi1

PNPj1X

expi;j

Xexp

2 12

To conclude, the values obtained for the kinetic parameters of thereaction for the synthesis of GEA in the presence of dimethyl

sulfoxide were compared with the values obtained in a previous

work for the solvent free reaction, for which the authors have deter-mined an activation energy of 51.2 kJ mol1 [24]. The difference tothe value reported hereby (approximately 35%) may rely on several

factors. First of all, the prior model (in the absence of solvent) hasbeen described in terms of activities[24], while the model for thisnew system (in the presence of dimethyl sulfoxide) does not ac-count for the non ideality of the liquid phase, due to lack of param-eters for the computation of the activity coefficients (namely, the

binary interaction coefficient between dimethyl sulfoxide and thealdehyde group of the UNIFAC method). Additionally, the influenceof the temperature on the adsorption equilibrium was not consid-

ered for the reaction in the presence of the solvent as previously de-scribed, since the number of parameters to be estimated would notallow a reliable determination of their values. As a consequence, theenthalpies of adsorption, and their impact on the adsorption con-

stants and in the reaction rate according to the LangmuirHinshel-woodHougenWatson model, might have a slight influence on the

activation energy value. Finally, the high polarity of dimethyl sulf-oxide and its corresponding affinity towards the resin, where it is

expected to adsorb strongly, might be leading to the hindering ofsome of the available active sites of the catalyst, decreasing theoverall reaction rate. The direct comparison between the adsorptionconstant values here reported and those for the solvent free system

is not allowed. The two models have different considerations overthe non-ideality of the mixture and the values estimated for theseconstants are affected by them. However, it is important to mentionthat, as expected due to the well-known high affinity of water to-

wards ion exchange resins, as Amberlyst-15, a higher adsorptioncapacity was estimated for water than for dimethyl sulfoxide. Nev-ertheless, it is important to underline that no direct measurementof the adsorption constants was performed. Instead, the values pre-

sented were obtained through the fitting of kinetic data. In any case,it is intended that those values are coherent between them and, ifnot accurate, at least they should have some physical meaning.

The simulation of the concentration profiles along the catalystparticles radius allowed the determination of the reaction effec-tiveness factor, for which a value of 57% was obtained when eval-

uated at 343 K (the highest temperature assessed, at which higherinfluence of the mass transfer resistances is expected) and consid-ering the average particle diameter of commercial Amberlyst-15,685 lm.

4. Conclusions

Although solvent selection methodologies for different applica-tions have been the aim of several research works, the authors of

Fig. 4. Effect of the temperature on the reaction rate ( P= 8.0 bar; racet/gly= 1.0;

xsolv= 0.5 (n/n); stirring speed of 500 rpm). The full lines represent the conversion

estimated by the model.

Fig. 5. Effect of the reactants molar ratio on the reaction rate ( P= 8.0 bar;T= 323 K;

xsolv= 0.5 (n/n); stirring speed of 500 rpm). The full lines represent the conversion

estimated by the model. The full lines represent the conversion estimated by themodel.

Fig. 6. Effect of the solvents molar fraction on the reaction rate (P= 8.0 bar;

T= 323 K; racet/gly = 1.0; stirring speed of 500 rpm). The full lines represent the

conversion estimated by the model.

http://-/?-http://-/?-http://-/?-http://-/?-

8/12/2019 1-s2.0-S1385894713010796-main

8/9

this study have perceived that for integrated reactiveadsorptive

processes as SMBR, the information on this topic was scarce andtherefore there was a need to develop a concise and prompt meth-odology for this purpose. The methodology suggested in this papercomprises a two stage screening. First, an extensive list of the mostcommonly used solvents in chemical processes is reduced based on

their properties, reported in the literature. Then, experimental

tests are performed with the solvents selected from the previousscreening step. When the methodology developed was applied tothe synthesis of GEA, through the acetalization of glycerol, cata-

lyzed by Amberlyst-15, dimethyl sulfoxide has demonstrated tobe the most suitable solvent for this reaction, presenting top per-formances on almost every topic. It proved to be unreactive andmiscible with the reaction medium and most importantly, it pre-

sented an adsorption capacity for the catalyst/adsorbent of the pro-cess that can predictably reduce the solvent consumption on afuture SMBR unit. Moreover, its use has low health and environ-

mental impact.Finally, a detailed study of the kinetic of the acetalization of

glycerol was conducted. The mathematical model developed wasable to predict with high accuracy the effect on the reaction rate

promoted by changes in the design variables, with a correlationcoefficient of 0.980. The kinetic law was described by the Lang-muirHinshelwoodHougenWatson method. A value of77.7 kJ mol1 was estimated for its activation energy. When com-

pared with the solvent free reaction, the presence of dimethyl sulf-oxide appears to have some impact on the reaction performance,consequence of the dilution factor and the reduction of availablecatalyst active sites due to its adsorption.

Acknowledgments

The research leading to these results received funding from theEuropean Union Seventh Framework Programme (FP7/2007-2013)under Grant Agreement 241718 EuroBioRef. This work was also

financially supported by Fundao para a Cincia e a Tecnologia,Project Grant PTDC/EQU-EQU/100564/2008. C.P. gratefullyacknowledges financial support from Fundao para a Cincia e aTecnologia, Postdoctoral Research Fellowship SFRH/BPD/71358/

2010.

References

[1] G. Sorda, M. Banse, C. Kemfert, An overview of biofuel policies across theworld, Energy Policy 38 (2010) 69776988.

[2] A. Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Improved utilisation ofrenewable resources: new important derivatives of glycerol, Green Chem. 10(2008) 1330.

[3] C.J.A. Mota, C.X.A.d. Silva, V.L.C. Gonalves, Gliceroqumica: novos produtos eprocessos a partir da glicerina de produo de biodiesel, Quim. Nova 32 (2009)

639648.[4] C.H. Zhou, J.N. Beltramini, Y.X. Fan, G.Q. Lu, Chemoselective catalyticconversion of glycerol as a biorenewable source to valuable commoditychemicals, Chem. Soc. Rev. 37 (2008) 527549.

[5] H. Serafim, I.M. Fonseca, A.M. Ramos, J. Vital, J.E. Castanheiro, Valorization ofglycerol into fuel additives over zeolites as catalysts, Chem. Eng. J. 178 (2011)291296.

[6] I. Agirre, I. Garca, J. Requies, V.L. Barrio, M.B. Gemez, J.F. Cambra, P.L. Arias,Glycerol acetals, kinetic study of the reaction between glycerol andformaldehyde, Biomass Bioenergy 35 (2011) 36363642.

[7] A. Jaecker-Voirol, I. Durand, G. Hillion, B. Delfort, X. Montagne, Glycerin fornew biodiesel formulation, Oil Gas Sci. Technol. 63 (2008) 395404 .

[8] B. Delfort, I. Durand, A. Jaecker-Voirol, T. Lacome, X. Montagne, F. Paille, DieselFuel Compounds Containing Glycerol Acetals; US 2003/0163949, in, 2003.

[9] G.W. Mushrush, S.C. Basak, J.E. Slone, E.J. Beal, S. Basu, W.M. Stalick, D.R. Hardy,Computational study of the environmental fate of selected aircraft fuel systemdeicing compounds, J. Environ. Sci. Health Part A Toxic/Hazard. SubstancesEnviron. Eng. 32 (1997) 22012211.

[10] G.W. Mushrush, E.J. Beal, D.R. Hardy, J.M. Hughes, J.C. Cummings, Jet fuel

system icing inhibitors: synthesis and characterization, Ind. Eng. Chem. Res. 38(1999) 24972502.

[11] G.W. Mushrush, E.J. Beal, D.R. Hardy, W.M. Stalick, S. Basu, D. Grosjean, J.Cummings, Jet fuel system icing inhibitors: synthesis and stability, ACS Div.Fuel Chem., Preprints 43 (1998) 6062.

[12] G.W. Mushrush, W.M. Stalick, E.J. Beal, S.C. Basu, J. Eric Slone, J. Cummings, Thesynthesis of acetals and ketals of the reduced sugar mannose as fuel systemicing inhibitors, Pet. Sci. Technol. 15 (1997) 237244.

[13] E. Garca, M. Laca, E. Prez, A. Garrido, J. Peinado, New class of acetal derivedfrom glycerin as a biodiesel fuel component, Energy Fuels 22 (2008) 42744280.

[14] S.D. Varfolomeev, G.A. Nikiforov, V.B. Volieva, G.G. Makarov, L.I. Trusov, Agent

for Increasing the Octane Number of a Gasoline Automotible Fuel; WO/2009/145674, 2009.

[15] J.M. Delgado Puche, Procedure to obtain biodiesel fuel with improvedproperties at low temperature; US 7 637 969, Industrial Management S.A.,Madrid, 2009.

[16] G.H. Hillion, B.P. Delfort, I.R.M. Durand, Method For Producing Biofuels,Transforming Triglycerides Into At Least Two Biofuel Families: Fatty AcidMonoesters And Ethers and/or Soluble Glycerol Acetals; US 2007/0283619 A1,2007.

[17] T. Harnitzky, N. Menschutkine, Ueber die Verbindungen des Glycerins mit denAldehyden, Justus Liebigs Annalen der Chemie 136 (1865) 4.

[18] J.U. Nef, Dissociationsvorgnge in der Glycol-Glycerinreihe, Justus LiebigsAnnalen der Chemie 335 (1904) 191245.

[19] H.S. Hill, H. Hibbert, Studies on reactions relating to carbohydrates andpolysaccharides V. The use of acetylene for the synthesis of cyclic acetals, J.Am. Chem. Soc. 45 (1923) 31083116.

[20] H.S. Hill, A.C. Hill, H. Hibbert, Studies on the reactinos relating tocarbohydrates and polysaccharides. XVI. Separation and Identification of the

isomeric ethylidene glycerols, J. Am. Chem. Soc. 50 (1928) 22422249.[21] M. Martin Maglio, C.A. Burger, Condensation reactions: a laboratorypreparation of ethylidene glycerol, J. Chem. Educ. 23 (1946) 174175 .

[22] A.S. Shevchuk, V.A. Podgornova, E.G. Piskaikina, Features of synthesis of 4-hydroxymethyl-1,3-dioxolanes from glycerol and aldehydes, Russ. J. Appl.Chem. 72 (1999) 853856.

[23] A.C. Da Silva Ferreira, J.C. Barbe, A. Bertrand, Heterocyclic acetals from glyceroland acetaldehyde in port wines: evolution with aging, J. Agric. Food. Chem. 50(2002) 25602564.

[24] R.P.V. Faria, C.S.M. Pereira, V.M.T.M. Silva, J.M. Loureiro, A.E. Rodrigues,Glycerol valorization as biofuel: thermodynamic and kinetic study of theacetalization of glycerol with acetaldehyde, Ind. Eng. Chem. Res. 52 (2013)15381547.

[25] D.J. Miller, L. Peereboom, A.K. Kolah, N.S. Asthana, C.T. Lira, Process forproduction of a composition useful as a fuel; US2006/0199970 A1, UnitedStates, 2008.

[26] X. Hong, O. McGiveron, C.T. Lira, A. Orjuela, L. Peereboom, D.J. Miller, A reactivedistillation process to produce 5-hydroxy-2-methyl-1,3-dioxane from mixedglycerol acetal isomers, Org. Process Res. Dev (2011).

[27] X. Hong, O. McGiveron, A.K. Kolah, A. Orjuela, L. Peereboom, C.T. Lira, D.J.Miller, Reaction kinetics of glycerol acetal formation via transacetalizationwith 1,1-diethoxyethane, Chem. Eng. J. 222 (2013) 374381.

[28] X. Hong, A.K. Kolah, C.T. Lira, D.J. Miller, An improved approach for cyclicacetals from glycerol, Nashville, TN, 2009.

[29] A.E. Rodrigues, C.S.M. Pereira, J.C. Santos, Chromatographic reactors, Chem.Eng. Technol. 35 (2012) 11711183.

[30] C.S.M. Pereira, P.S. Gomes, G.K. Gandi, V.M.T.M. Silva, A.E. Rodrigues,Multifunctional reactor for the synthesis of dimethylacetal, Ind. Eng. Chem.Res. 47 (2008) 35153524.

[31] A.E. Rodrigues, V.M.M.D. Silva, Industrial Process for Acetals Production in aSimulated Moving Bed Reactor; WO/2005/11347, 2005.

[32] V.M.T.M. Silva, A.E. Rodrigues, Novel process for diethylacetal synthesis, AlChEJ. 51 (2005) 27522768.

[33] N.S. Graa, L.S. Pais, V.M.T.M. Silva, A.E. Rodrigues, Analysis of the synthesis of1,1-dibutoxyethane in a simulated moving-bed adsorptive reactor, Chem. Eng.Process.: Process Intensification 50 (2011) 12141225.

[34] S. Luo, J.L. Falconer, Acetone and acetaldehyde oligomerization on TiO2surfaces, J. Catal. 185 (1999) 393407.

[35] R. Gani, C. Jimnez-Gonzlez, D.J.C. Constable, Method for selection of solventsfor promotion of organic reactions, Comput. Chem. Eng. 29 (2005) 16611676.

[36] M. Folic, R. Gani, C. Jimnez-Gonzlez, D.J.C. Constable, Systematic selection ofgreen solvents for organic reacting systems, Chin. J. Chem. Eng. 16 (2008) 376383.

[37] S. Perez-Vega, E. Ortega-Rivas, I. Salmeron-Ochoa, P.N. Sharratt, A system viewof solvent selection in the pharmaceutical industry: towards a sustainablechoice, Environ. Dev. Sustain. 15 (2013) 121.

[38] A.I. Papadopoulos, P. Linke, Integrated solvent and process selection forseparation and reactive separation systems, Chem. Eng. Process.: ProcessIntensification 48 (2009) 10471060.

[39] J.P. Taygerly, L.M. Miller, A. Yee, E.A. Peterson, A convenient guide to helpselect replacement solvents for dichloromethane in chromatography, GreenChem. 14 (2012) 30203025.

[40] R. Hu, Y. Pan, Recent trends in counter-current chromatography, TrAC TrendsAnal. Chem. 40 (2012) 1527.

[41] C. Jimnez-Gonzalez, A.D. Curzons, D.J.C. Constable, V.L. Cunningham,Expanding GSKs Solvent selection guide application of life cycle

assessment to enhance solvent selections, Clean Technol. Environ. Policy 7(2004) 4250.

http://refhub.elsevier.com/S1385-8947(13)01079-6/h0005http://refhub.elsevier.com/S1385-8947(13)01079-6/h0005http://refhub.elsevier.com/S1385-8947(13)01079-6/h0010http://refhub.elsevier.com/S1385-8947(13)01079-6/h0010http://refhub.elsevier.com/S1385-8947(13)01079-6/h0010http://refhub.elsevier.com/S1385-8947(13)01079-6/h0015http://refhub.elsevier.com/S1385-8947(13)01079-6/h0015http://refhub.elsevier.com/S1385-8947(13)01079-6/h0015http://refhub.elsevier.com/S1385-8947(13)01079-6/h0020http://refhub.elsevier.com/S1385-8947(13)01079-6/h0020http://refhub.elsevier.com/S1385-8947(13)01079-6/h0020http://refhub.elsevier.com/S1385-8947(13)01079-6/h0025http://refhub.elsevier.com/S1385-8947(13)01079-6/h0025http://refhub.elsevier.com/S1385-8947(13)01079-6/h0025http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0035http://refhub.elsevier.com/S1385-8947(13)01079-6/h0035http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0045http://refhub.elsevier.com/S1385-8947(13)01079-6/h0045http://refhub.elsevier.com/S1385-8947(13)01079-6/h0045http://refhub.elsevier.com/S1385-8947(13)01079-6/h0050http://refhub.elsevier.com/S1385-8947(13)01079-6/h0050http://refhub.elsevier.com/S1385-8947(13)01079-6/h0050http://refhub.elsevier.com/S1385-8947(13)01079-6/h0055http://refhub.elsevier.com/S1385-8947(13)01079-6/h0055http://refhub.elsevier.com/S1385-8947(13)01079-6/h0055http://refhub.elsevier.com/S1385-8947(13)01079-6/h0060http://refhub.elsevier.com/S1385-8947(13)01079-6/h0060http://refhub.elsevier.com/S1385-8947(13)01079-6/h0060http://refhub.elsevier.com/S1385-8947(13)01079-6/h0065http://refhub.elsevier.com/S1385-8947(13)01079-6/h0065http://refhub.elsevier.com/S1385-8947(13)01079-6/h0070http://refhub.elsevier.com/S1385-8947(13)01079-6/h0070http://refhub.elsevier.com/S1385-8947(13)01079-6/h0075http://refhub.elsevier.com/S1385-8947(13)01079-6/h0075http://refhub.elsevier.com/S1385-8947(13)01079-6/h0075http://refhub.elsevier.com/S1385-8947(13)01079-6/h0080http://refhub.elsevier.com/S1385-8947(13)01079-6/h0080http://refhub.elsevier.com/S1385-8947(13)01079-6/h0080http://refhub.elsevier.com/S1385-8947(13)01079-6/h0085http://refhub.elsevier.com/S1385-8947(13)01079-6/h0085http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0095http://refhub.elsevier.com/S1385-8947(13)01079-6/h0095http://refhub.elsevier.com/S1385-8947(13)01079-6/h0095http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0105http://refhub.elsevier.com/S1385-8947(13)01079-6/h0105http://refhub.elsevier.com/S1385-8947(13)01079-6/h0105http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0115http://refhub.elsevier.com/S1385-8947(13)01079-6/h0115http://refhub.elsevier.com/S1385-8947(13)01079-6/h0120http://refhub.elsevier.com/S1385-8947(13)01079-6/h0120http://refhub.elsevier.com/S1385-8947(13)01079-6/h0120http://refhub.elsevier.com/S1385-8947(13)01079-6/h0125http://refhub.elsevier.com/S1385-8947(13)01079-6/h0125http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0135http://refhub.elsevier.com/S1385-8947(13)01079-6/h0135http://refhub.elsevier.com/S1385-8947(13)01079-6/h0135http://refhub.elsevier.com/S1385-8947(13)01079-6/h0140http://refhub.elsevier.com/S1385-8947(13)01079-6/h0140http://refhub.elsevier.com/S1385-8947(13)01079-6/h0140http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0150http://refhub.elsevier.com/S1385-8947(13)01079-6/h0150http://refhub.elsevier.com/S1385-8947(13)01079-6/h0150http://refhub.elsevier.com/S1385-8947(13)01079-6/h0155http://refhub.elsevier.com/S1385-8947(13)01079-6/h0155http://refhub.elsevier.com/S1385-8947(13)01079-6/h0155http://refhub.elsevier.com/S1385-8947(13)01079-6/h0160http://refhub.elsevier.com/S1385-8947(13)01079-6/h0160http://refhub.elsevier.com/S1385-8947(13)01079-6/h0160http://refhub.elsevier.com/S1385-8947(13)01079-6/h0165http://refhub.elsevier.com/S1385-8947(13)01079-6/h0165http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0170http://refhub.elsevier.com/S1385-8947(13)01079-6/h0165http://refhub.elsevier.com/S1385-8947(13)01079-6/h0165http://refhub.elsevier.com/S1385-8947(13)01079-6/h0160http://refhub.elsevier.com/S1385-8947(13)01079-6/h0160http://refhub.elsevier.com/S1385-8947(13)01079-6/h0160http://refhub.elsevier.com/S1385-8947(13)01079-6/h0155http://refhub.elsevier.com/S1385-8947(13)01079-6/h0155http://refhub.elsevier.com/S1385-8947(13)01079-6/h0155http://refhub.elsevier.com/S1385-8947(13)01079-6/h0150http://refhub.elsevier.com/S1385-8947(13)01079-6/h0150http://refhub.elsevier.com/S1385-8947(13)01079-6/h0150http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0145http://refhub.elsevier.com/S1385-8947(13)01079-6/h0140http://refhub.elsevier.com/S1385-8947(13)01079-6/h0140http://refhub.elsevier.com/S1385-8947(13)01079-6/h0135http://refhub.elsevier.com/S1385-8947(13)01079-6/h0135http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0130http://refhub.elsevier.com/S1385-8947(13)01079-6/h0125http://refhub.elsevier.com/S1385-8947(13)01079-6/h0125http://refhub.elsevier.com/S1385-8947(13)01079-6/h0120http://refhub.elsevier.com/S1385-8947(13)01079-6/h0120http://refhub.elsevier.com/S1385-8947(13)01079-6/h0120http://refhub.elsevier.com/S1385-8947(13)01079-6/h0115http://refhub.elsevier.com/S1385-8947(13)01079-6/h0115http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0110http://refhub.elsevier.com/S1385-8947(13)01079-6/h0105http://refhub.elsevier.com/S1385-8947(13)01079-6/h0105http://refhub.elsevier.com/S1385-8947(13)01079-6/h0105http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0100http://refhub.elsevier.com/S1385-8947(13)01079-6/h0095http://refhub.elsevier.com/S1385-8947(13)01079-6/h0095http://refhub.elsevier.com/S1385-8947(13)01079-6/h0095http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0090http://refhub.elsevier.com/S1385-8947(13)01079-6/h0085http://refhub.elsevier.com/S1385-8947(13)01079-6/h0085http://refhub.elsevier.com/S1385-8947(13)01079-6/h0080http://refhub.elsevier.com/S1385-8947(13)01079-6/h0080http://refhub.elsevier.com/S1385-8947(13)01079-6/h0080http://refhub.elsevier.com/S1385-8947(13)01079-6/h0075http://refhub.elsevier.com/S1385-8947(13)01079-6/h0075http://refhub.elsevier.com/S1385-8947(13)01079-6/h0075http://refhub.elsevier.com/S1385-8947(13)01079-6/h0070http://refhub.elsevier.com/S1385-8947(13)01079-6/h0070http://refhub.elsevier.com/S1385-8947(13)01079-6/h0065http://refhub.elsevier.com/S1385-8947(13)01079-6/h0065http://refhub.elsevier.com/S1385-8947(13)01079-6/h0060http://refhub.elsevier.com/S1385-8947(13)01079-6/h0060http://refhub.elsevier.com/S1385-8947(13)01079-6/h0060http://refhub.elsevier.com/S1385-8947(13)01079-6/h0055http://refhub.elsevier.com/S1385-8947(13)01079-6/h0055http://refhub.elsevier.com/S1385-8947(13)01079-6/h0055http://refhub.elsevier.com/S1385-8947(13)01079-6/h0050http://refhub.elsevier.com/S1385-8947(13)01079-6/h0050http://refhub.elsevier.com/S1385-8947(13)01079-6/h0050http://refhub.elsevier.com/S1385-8947(13)01079-6/h0045http://refhub.elsevier.com/S1385-8947(13)01079-6/h0045http://refhub.elsevier.com/S1385-8947(13)01079-6/h0045http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0040http://refhub.elsevier.com/S1385-8947(13)01079-6/h0035http://refhub.elsevier.com/S1385-8947(13)01079-6/h0035http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0030http://refhub.elsevier.com/S1385-8947(13)01079-6/h0025http://refhub.elsevier.com/S1385-8947(13)01079-6/h0025http://refhub.elsevier.com/S1385-8947(13)01079-6/h0025http://refhub.elsevier.com/S1385-8947(13)01079-6/h0020http://refhub.elsevier.com/S1385-8947(13)01079-6/h0020http://refhub.elsevier.com/S1385-8947(13)01079-6/h0020http://refhub.elsevier.com/S1385-8947(13)01079-6/h0015http://refhub.elsevier.com/S1385-8947(13)01079-6/h0015http://refhub.elsevier.com/S1385-8947(13)01079-6/h0015http://refhub.elsevier.com/S1385-8947(13)01079-6/h0010http://refhub.elsevier.com/S1385-8947(13)01079-6/h0010http://refhub.elsevier.com/S1385-8947(13)01079-6/h0010http://refhub.elsevier.com/S1385-8947(13)01079-6/h0005http://refhub.elsevier.com/S1385-8947(13)01079-6/h0005

8/12/2019 1-s2.0-S1385894713010796-main

9/9

[42] K. Alfonsi, J. Colberg, P.J. Dunn, T. Fevig, S. Jennings, T.A. Johnson, H.P. Kleine, C.Knight, M.A. Nagy, D.A. Perry, M. Stefaniak, Green chemistry tools to influencea medicinal chemistry and research chemistry based organisation, GreenChem. 10 (2008) 3136.

[43] P.G. Jessop, Searching for green solvents, Green Chem. 13 (2011) 13911398 .[44] C.L. Yaws, Yaws Handbook of Physical Properties for Hydrocarbons and

Chemicals, 2008.[45] G. Wypych, Handbook of Solvents, ChemTec Publishing, 2001.[46] R.M. Quinta Ferreira, C.A. Almeida-Costa, A.E. Rodrigues, Heterogeneous

models of tubular reactors packed with ion-exchange resins: simulation of

the MTBE synthesis, Ind. Eng. Chem. Res. 35 (1996) 38273841 .[47] S.-K. Ihm, J.-H. Ahn, Y.-D. Jo, Interaction of Reaction and Mass Transfer in Ion-

Exchange Resin Catalysts, Ind. Eng. Chem. Res. 35 (1996) 29462954.[48] T. Dogu, E. Aydin, N. Boz, K. Murtezaoglu, G. Dogu, Diffusion resistances and

contribution of surface diffusion in TAME and TAEE production usingAmberlyst-15, Int. J. Chem. React. Eng. 1 (2003).

[49] K. Sundmacher, R.-S. Zhang, U. Hoffmann, Mass transfer effects on kinetics ofnonideal liquid phase ethyl tert-butyl ether formation, Chem. Eng. Technol. 18(1995) 269277.

[50] V.M.T.M. Silva, A.E. Rodrigues, Kinetic studies in a batch reactor using ionexchange resin catalysts for oxygenates production: role of mass transfermechanisms, Chem. Eng. Sci. 61 (2006) 316331.

[51] G.K. Gandi, V.M.T.M. Silva, A.E. Rodrigues, Process development fordimethylacetal synthesis: thermodynamics and reaction kinetics, Ind. Eng.Chem. Res. 44 (2005) 72877297.

[52] V.M.T.M. Silva, A.r.E. Rodrigues, Synthesis of diethylacetal: thermodynamicand kinetic studies, Chem. Eng. Sci. 56 (2001) 12551263 .

[53] N.S. Graa, L.S. Pais, V.M.T.M. Silva, A.E. Rodrigues, Oxygenated biofuels frombutanol for diesel blends: synthesis of the acetal 1,1-dibutoxyethane catalyzed

by amberlyst-15 ion-exchange resin, Ind. Eng. Chem. Res. 49 (2010) 67636771.

[54] R.G. Miller, The jackknife: a review, Biometrika 61 (1974) 115.[55] C.S.M. Pereira, M. Zabka, V.M.T.M. Silva, A.E. Rodrigues, A novel process for the

ethyl lactate synthesis in a simulated moving bed reactor, Chem. Eng. Sci. 64(2009).

[56] F. Lode, M. Houmard, C. Migliorini, M. Mazzotti, M. Morbidelli, Continuousreactive chromatography, Chem. Eng. Sci. 56 (2001) 269291.

http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0180http://refhub.elsevier.com/S1385-8947(13)01079-6/h0185http://refhub.elsevier.com/S1385-8947(13)01079-6/h0190http://refhub.elsevier.com/S1385-8947(13)01079-6/h0190http://refhub.elsevier.com/S1385-8947(13)01079-6/h0190http://refhub.elsevier.com/S1385-8947(13)01079-6/h0195http://refhub.elsevier.com/S1385-8947(13)01079-6/h0195http://refhub.elsevier.com/S1385-8947(13)01079-6/h0195http://refhub.elsevier.com/S1385-8947(13)01079-6/h0195http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://refhub.elsevier.com/S1385-8947(13)01079-6/h0210http://refhub.elsevier.com/S1385-8947(13)01079-6/h0210http://refhub.elsevier.com/S1385-8947(13)01079-6/h0210http://refhub.elsevier.com/S1385-8947(13)01079-6/h0215http://refhub.elsevier.com/S1385-8947(13)01079-6/h0215http://refhub.elsevier.com/S1385-8947(13)01079-6/h0215http://refhub.elsevier.com/S1385-8947(13)01079-6/h0220http://refhub.elsevier.com/S1385-8947(13)01079-6/h0220http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0230http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h0235http://refhub.elsevier.com/S1385-8947(13)01079-6/h0235http://refhub.elsevier.com/S1385-8947(13)01079-6/h0235http://refhub.elsevier.com/S1385-8947(13)01079-6/h0235http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h5235http://refhub.elsevier.com/S1385-8947(13)01079-6/h0230http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0225http://refhub.elsevier.com/S1385-8947(13)01079-6/h0220http://refhub.elsevier.com/S1385-8947(13)01079-6/h0220http://refhub.elsevier.com/S1385-8947(13)01079-6/h0215http://refhub.elsevier.com/S1385-8947(13)01079-6/h0215http://refhub.elsevier.com/S1385-8947(13)01079-6/h0215http://refhub.elsevier.com/S1385-8947(13)01079-6/h0210http://refhub.elsevier.com/S1385-8947(13)01079-6/h0210http://refhub.elsevier.com/S1385-8947(13)01079-6/h0210http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://refhub.elsevier.com/S1385-8947(13)01079-6/h0205http://-/?-http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://refhub.elsevier.com/S1385-8947(13)01079-6/h0200http://-/?-http://refhub.elsevier.com/S1385-8947(13)01079-6/h0195http://refhub.elsevier.com/S1385-8947(13)01079-6/h0195http://-/?-http://refhub.elsevier.com/S1385-8947(13)01079-6/h0190http://refhub.elsevier.com/S1385-8947(13)01079-6/h0190http://refhub.elsevier.com/S1385-8947(13)01079-6/h0190http://-/?-http://refhub.elsevier.com/S1385-8947(13)01079-6/h0185http://refhub.elsevier.com/S1385-8947(13)01079-6/h0185http://-/?-http://-/?-http://refhub.elsevier.com/S1385-8947(13)01079-6/h0180http://-/?-http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://refhub.elsevier.com/S1385-8947(13)01079-6/h0175http://-/?-

Documents

1-s2.0-S1385894713010796-main