Enzymatic Synthesis of Fatty Esters

Enzymatic synthesis of fatty estersPart I. Kinetic approach<

T. Garcia, N. Sanchez, M. Martinez, J. Aracil*Department of Chemical Engineering, Faculty of Chemistry, Complutense University, 28040 Madrid, Spain

Received 26 November 1998; received in revised form 24 May 1999; accepted 1 June 1999

Abstract

A kinetic study of palmitic acid esterification reaction catalyzed by immobilized lipase Novozym 435 (fromCandida antarctica) hasbeen made in a range of 65–75°C temperature and 3–7% of initial catalyst concentration and atmospheric pressure. Influence of operatingvariables also was studied. Different values of temperature, initial lipase concentration, acid/alcohol molar ratio, and products concentrationswere tested. Experiments were carried out in a stirred batch reactor equipped with adequate control systems. Evolution of concentration ofthe species involved was found by using gas-liquid chromatography. The kinetic characteristics observed in the esterification reaction withisopropanol were found to follow an ordered bi-bi mechanism with competitive inhibition by reactants and products. According to themechanism maximum reaction rate, Michaelis–Menten constants and inhibition constants were determined. A good quality of fit wasobserved by fitting experimental rate data to the kinetic model with an average error beneath the 15%. Kinetic constants, as well as enthalpyand entropy values, have been determined for the model proposed for the esterification reaction within the experimental range studied.© 1999 Elsevier Science Inc. All rights reserved.

Keywords:Immobilized enzyme; Enzymatic esterification;Candida antarctica; Kinetic modeling; Fatty esters; Isopropyl palmitate

1. Introduction

Interest in studies of various sources lipases-catalyzedreaction has increased dramatically during the past 10 years.Many researchers have attempted to understand the func-tional properties of lipase in processes that involve modifi-cation of the properties of fats and oils [1]. Particularlychallenging tasks are those associated with developing rateexpressions to characterize several lipase-catalyzed reac-tions and deciphering the mechanisms involved [2]. Whendispersed in organic solvents, lipase can catalyze reactionspreviously unreported when the concentration of water insuch systems is maintained at levels of,1% by weight [3].Modeling of these enzyme-catalyzed organic phase reac-tions has received relatively little attention by the scientificcommunity. The purpose of this study is to contribute to theclarification of the mechanisms and to obtain the corre-sponding rate expressions of esterification reactions cata-lyzed by immobilized lipase in nonpolar media.

The most extended models are based on the applicationof Michaelis–Menten assumptions. This type of modelseems to be valid for the most simple enzymatic reactions.Dehydrogenation of several alcoholic groups by using al-cohol-dehydrogenase as catalyst was found to follow akinetic model based on the hypothesis of Michaelis–Mentenwhen reaction was carried out under optimum operatingconditions (pH 8.8 and 25°C; [4]). Similar results wereobtained for the kinetic study of hydrolysis of starch at50°C, by usingRhizopus niveusenzyme immobilized on aceramic type support [5]. Other authors proposed a modelbased on a ping-pong mechanism for the kinetic study of theinteresterification reaction of n-propyl acetate with geraniolat 40°C, by using lipases as catalysts and different solventsin the reaction media [6]. This supposition agrees with thatadopted in the study of the esterification of lauric acid withmenthol at 35°C by usingPenicillium simplicissimumlipase[7].

Most authors agree that reaction occurs via acyl-enzymeintermediate when lipases are used as catalysts. This hy-pothesis was confirmed by studies that showed that the onlypossibility for the reaction to take place is the formation of

< For Part II see pp. 591–597 of this issue.* Corresponding author. Tel.:134-91-394-4167.E-mail address: [email protected] (J. Aracil)

Enzyme and Microbial Technology 25 (1999) 584–590

0141-0229/99/$ – see front matter © 1999 Elsevier Science Inc. All rights reserved.PII: S0141-0229(99)00082-4

an active complex between an acyl group belonging to thesubstrate and one of the active centers of the lipase [8,9].

However, despite the fact that several kinetic studieshave been carried out, the information that allows the per-formance of an appropriate analysis for a later industrialscale up continues to be quite limited. On the other hand,most of the studies deal only with the synthesis of esters oflow and medium molecular weight or with collecting infor-mation on enzymatic reactions with a single substrate.

For these reasons, in the present study, a kinetic modelfor the enzymatic synthesis of esters has been deduced from

mechanistic considerations. The validity of the model hasbeen tested experimentally for the synthesis of isopropylpalmitate by using a commercial immobilizedCandida ant-arctica lipase as catalyst. Isopropyl palmitate is widely usedin cosmetic and topical medicinal preparations for whichgood absorption through the skin is required. The synthesishas been carried out in solvent-free conditions to reducetime and cost in the product purification.

2. Materials and methods

2.1. Equipment

Experiments were carried out in a completely stirred tankreactor of 500 cm3 volume, 10 cm height, and 7 cm diam-eter. A marine-type propeller was used. The impeller speedwas set at 600 rev./min to avoid mass transfer limitations.The reactor was immersed in a water bath capable of main-taining the reaction temperature61°C. Temperature, im-peller speed, and pressure recorders and controllers wereinstalled.

2.2. Materials

Palmitic acid purity 98% w/w and isopropyl alcohol 98%w/w, used as reactants, were supplied by Henkel Iberica(Minneapolis, MN, USA). The catalyst used was a nonspe-cific triacylglycerol lipase (EC 3.1.1.3) fromCandida ant-arctica. The commercial lipase, named Novozym 435 andsupplied by Novo-Nordisk Bioindustial A/S (Copenhagen,Denmark), was immobilized on a macroporous acrylic resinwith a water content of 1–2% w/w. The ester synthesisactivity of the catalyst was 7000 Propyl Laurate Units(PLU/g). Aldrich-Sigma A/S and Fluka Chemie AG sup-plied other materials like standard products and solventsused in analytical procedures.

2.3. Analytical methods

Reaction products were monitored by gas chromatogra-phy/mass spectrometry (GC/MS) and quantitatively deter-mined by capillary column GC. GC/MS data were recordedon a HP 6890 Series Hewlett Packcard instrument and thentreated with a Hewlett Packard Vectra series 3 computer,connected on line with the GC/MS system equipped with aHP autosampler controller.

Quantitative GC analyses were performed on a HewlletPackard HP 5890 series II instrument connected to aHewlett Packard HP 3396 A integrator, by using a capillarycolumn, flame ionization detector, and split-splitless injec-tion system. The complete description of analytical methodhas been described in previous works [10].

Nomenclature

Ci [i] concentration of component i (mol/l)Ci0 initial concentration of component i (mol/l)Cieq equilibrium concentration of component i (mol/l)Ea activation energy (cal/mol) (Kcal/Kmol)

(Kcal/mol)G free Gibbs energy (cal/mol)H enthalpy (cal/mol)k rate constant (l/mol/gcat/min)K0 pre-exponential factor of Arrhenius equation (l/

mol/gcat/min)Keq equilibrium constantKij inhibition constant for component j (mol/l)Kmi Michaelis constant for component i (mol/l)P pressure (Pa) (mmHg)R gas constant (cal/mol/K)(2r i) rate of disappearance of component i

(mol/l/gcat/min)(-r i)max maximum rate of disappearance of component

i (mol/l/gcat/min)S entropy (cal/mol/K)t time (min)T temperature (°C) (K)w amount of catalyst (g)Xi conversion of component iXieq equilibrium conversion of component i

SubscriptAc fatty acidAl fatty alcoholE free enzymeE-A binary enzyme-substrate A complexE-A-B ternary substrate A-enzyme-substrate B

complexEs esterf forward reactionr reverse reactionW water

Greek lettersa, b, g, d, Ã: Parameters in Eq. (4).

585T. Garcia et al. / Enzyme and Microbial Technology 25 (1999) 584–590

2.4. Procedure

Experiments were performed according to the proceduredescribed by Garcia et al. in this journal [11], introducingsome minor modifications. Reactants were added to thereactor fitted with a reflux condenser. When the set pressurewas reached, the reaction mixture was heated up to thedesired temperature and the catalyst was introduced in thereactor. Samples were taken at regular intervals and ana-lyzed by GC. During the experiments, the following variablesremained constant: temperature, pressure, impeller speed, andacid/alcohol molar ratio. Total conversion to ester wasachieved after 1 to 2 h, depending on the reaction conditions.

3. Results and discussion

3.1. Influence of temperature

To study the influence of temperature on the esterifica-tion reaction, three temperatures were studied. The lowertemperature studied was 65°C. Lower temperatures wouldresult in poor conversion levels because of the relativelylow enzyme activity, as indicated in the specifications of thecommercial lipase. Palmitic acid melting point was also adeterminant value ('63.1°C at atmospheric pressure). Theupper temperature limit was fixed at 75°C to avoid lipasedenaturation. Both facts have been also observed in ourlaboratory in earlier works [12].

Fig. 1 is a plot of conversion versus time for threedifferent temperatures. As expected, conversion was foundto increase with increasing temperature. After 120 min, an8.3% conversion increase was observed when temperaturewas increased from 65°C to 70°C. A temperature increasefrom 70°C to 75°C led to a conversion increase of 14%.

3.2. Influence of catalyst concentration

As shown in Fig. 2, conversion increased with increasingcatalyst concentration. An average increase in conversion of

10% was obtained when the catalyst concentration wasincreased by 2%. To study the effect of the catalyst con-centration and further kinetic modeling, conversion to iso-propyl palmitate was plotted versus catalyst concentrationfor different reaction times. Fig. 3 is the plot correspondingto 70°C and a Ac/Al molar ratio of 1. A linear relationshipwas observed for all reaction times. Similar results wereobtained for all temperatures and molar ratios tested. Nosaturation effects were observed within the experimentalrange studied. This fact has been observed for analog sys-tems of reaction [13].

3.3. Influence of acid/alcohol molar ratio

To perform a subsequent kinetic analysis, two series ofexperiments were carried out at different acid/alcohol molarratios. The first series was carried out in excess of isopropylalcohol to study the change in reaction rate with palmiticacid concentration. In the second group of experiments,palmitic acid was added in excess to study the dependenceof the reaction rate on isopropyl alcohol concentration. Inboth cases, the operating temperature range used was 65°C–70°C–75°C, and the catalyst concentration was 5 wt%. Fig.4 represents the rate of ester formation versus alcohol con-centration for different acid/alcohol molar ratios, in exper-

Fig. 1. Influence of reaction temperature on isopropyl palmitate synthesis(5% catalyst, acid/alcohol molar ratio: 1/1).

Fig. 2. Influence of initial concentration of immobilized lipase on theesterification process (T: 70°C, acid/alcohol molar ratio: 1/1).

Fig. 3. Change in conversion with catalyst concentration at different reac-tion times (T: 70°C, acid/alcohol molar ratio: 1/1).

586 T. Garcia et al. / Enzyme and Microbial Technology 25 (1999) 584–590

iments with an excess in acid. As observed in this plot, foralcohol concentrations larger than 0.4 mol/l, the reactionrate increases with increasing isopropyl alcohol concentra-tion for any value of acid concentration. However, below0.4 mol/l, when the alcohol concentration decreases, there isa strong decrease in reaction rate for large molar ratios (1/7and 1/10). This behavior indicates the presence of inhibitioneffects at long reaction times. Therefore, it will be necessaryto include an inhibition factor in the reaction rate expressiondue to the concentration of palmitic acid in the reactionmixture.

A similar situation was observed when operating in anexcess of isopropyl alcohol. For acid concentrations below0.4 mol/l, the decrease in the reaction rate was larger thanexpected for some acid/alcohol molar ratios. This effectindicates the existence of inhibition due to the presence ofisopropyl alcohol.

3.4. Study of the concentration of products in the reactionmedia

To determine the influence of the products on the ester-ification reaction, two additional groups of experimentswere carried out, a series operating in excess of isopropylpalmitate and a series operating in excess of water. Tocompare the effect produced by the presence of each of thetwo products in the reaction medium, these experimentswere compared with experiments in the same operatingconditions but without initial addition of products. Asshown in Fig. 5, a strong negative effect was observed bythe presence of an excess of ester because conversion de-creased drastically when the product was added. A similareffect was observed for experiments in which water wasadded at the beginning of the reaction. Although this be-havior would be expected for the chemical equilibrium ofthe species, the drastic decrease observed indicates the pos-sibility of inhibition effects due to the concentration of bothspecies.

3.5. Initial rate analysis

The maximum initial rate of substrates consumption(2rAc)max and Michaelis–Menten constants (Km) were de-termined by linear regression using the Lineweaver–Burkapproach. Fig. 6a and b shows these plots at different Ac/Almolar ratios. Both slopes and intercepts then were plottedversus the inverse of the specie in excess concentration.This way, we can obtain the above constants. These valueswere given as initial values in the subsequent kinetic mod-eling.

Fig. 4. Plot of reaction rate versus oleyl alcohol concentration: influence ofacid/alcohol molar ratio (5% catalyst, T: 65°C).

Fig. 5. Acid conversion versus time: influence of an excess of isopropylpalmitate (5% catalyst, T: 70°C, acid/alcohol molar ratio: 1/1).

Fig. 6. Lineweaver–Burk plots. (A) Excess of isopropyl alcohol. (B)Excess of palmitic acid (5% catalyst, T: 70°C).


3.6. Kinetic modeling

The esterification of palmitic acid with isopropyl alcoholcan be considered in this research as an enzymatic reactionsystem, which involves two reactants and two products. Thereaction mechanism was studied on this basis. Three possi-bilities were taken into account: (1) a random-order mech-anism, (2) a ping-pong mechanism, and (3) an ordered bi-bimechanism. Fig. 7 shows the general reaction schemes forthe three possibilities. According to the studies of someresearchers [14], the active conformation of this type oflipase comes via an acyl-enzyme intermediate. That is thereason because the reaction sequence must be started withthe bond formation between the carboxyl group of fattyacid. Then, random mechanism can be considered as ne-glected.

On the other hand, several authors [15,16] considered theping-pong mechanism as the most appropriate to explainlipase catalysis becoming very common to describe by thismean the interesterification and transesterification reactions.However, in the case of a simple esterification reaction, itseems much more adequate to consider an ordered bi-bimechanism, in which two reactants and two products areinvolved. The fatty acid would be the first reactant involvedin the reaction mechanism producing the active enzyme-acid complex; in a next step, the alcohol would be incor-porated to form the ternary complex alcohol-enzyme-acid,followed by the chemical reaction step, i.e. the transforma-tion of the ternary complex into an ester-enzyme-watercomplex. In the next step, an ester molecule would bereleased, and finally water would be released.

The above constitute the simple reaction mechanism.However, it is necessary to add inhibition steps correspond-ing to formation of binary and ternary complexes. The mostfrequent inhibition phenomena in this type of reactionsinvolve the formation of either (1) binary complexes be-tween the free enzyme and the alcohol or the ester or (2)inactive ternary complexes between the fatty acid or theester and the active enzyme-acid complex. Therefore, bothreactants and products are involved in inhibition phenom-

ena. Being the most frequent inhibition type to be consid-ered, the so-called competitive inhibition, where competi-tion for the formation of a free lipase complex, or theformation of ternary complexes with the most active com-plex, enzyme-acid appear. Thus, the general mechanism forthis kind of reactions would consist of two groups of steps.

Main steps

E 1 Ac7 EAc [ KmAc KiAc

EAc 1 Al 7 EAcAl [ KmAl KiAl

EAcAl7 EEsW [ Keq~2rAc!maxf ~2rAc!max

r

EEsW7 EW 1 Es [ KmEsKiEs

EW7 E 1 W [ KmW KiW

Inhibition steps:

E 1 Al 7 EAl [ K9iAl

EAc 1 Ac7 EAcAcT [ KiAc

By taking into account the steps involved in the abovereaction scheme, a general kinetic equation for the esterifi-cation reaction can be proposed:

~ 2 rAc! 5

~ 2 rAc!maxf ~ 2 rAc!max

r SCAcCAl 2CEsCW

KeqD

~2rAc!maxr KiAc

KmAlS11CAl

K9iAlD1~2rAc!max

r KmAlCAcS11

CAc

K9iAcD

1 ~2rAc!maxr KmAc

CAlS1 1CAl

K9iAlD

1~2rAc!max

f KmWCEs

Keq1

~2rAc!maxf KmEs

CW

Keq

1 ~2rAc!maxf CAcCAl 1

~2rAc!maxf KmW

CAcCEs

KeqKiAc

1~2rAc!max

r CEsCW

Keq1

~2rAc!max)r KmAc

CAlCW

KiW

1(2rAc)max

r CAcCAlCEs

KiEs

12rAc)max

f CAlCEsCW

KiAlKeq

(1)

For a 1/1 molar ratio acid/alcohol,

CAc0 5 CAl0 XAc0 5 XAl0

CAc0 z XAc0 5 CAc0 z XAl0

CAc 5 CAl 5 CAc0 z ~1 2 XAc

(2)

CEs5 Cw 5 CAc0 z XAc

And boundary conditions,

Fig. 7. General mechanisms for the enzymatic esterification.


t 5 0 [ CAc 5 CAc0 [ XAc 5 0(3)

t 5 t [ CAc 5 CAc [ XAc 5 ~CAc0 2 CAc!/CAc0

By integrating the general equation, the following expres-sion is obtained:

t 5 a.Ln~ÎKeq2 1!~XAc z ~ÎKeq1 1! 2 ÎKeq!

~XAc z ~ÎKeq2 1! 2 z ÎKeq z ~ÎKeq1 1!!

1 b.Ln~XAc2 z ~Keq2 1! 2 2Keq z XAc 1 Keq!

1 v# .Ln~ÎKeq2 1!

~ÎKeq1 1!1 g.LnKeq1 d.XAc

2 1 «.XAc

(4)

where greek symbols are the coefficients defined by math-ematical relations which involve the kinetic constants. Theentire development of kinetic model can be seen in a recentwork [17]. The general flowchart used to obtain the kinetic

parameters and to optimize the model is shown in Fig. 8.Multiple linear regression and nonlinear regression methodsbased on Marquardt’s algorithm were applied for the esti-mation of parameters and are given in Table 1 for the threetemperatures tested. These parameters define the completekinetic model for the esterification reaction.

As observed in Table 1, the values of all the parametersdecrease with increasing temperature, except for the equi-librium constant. This fact indicates that high temperatureslead to a decrease in the formation of inhibition complexesand to larger ester conversions.

To know the influence of temperature on the parameters,the standard free energy of reaction as a function of theequilibrium constant and the enthalpy and entropy changewere considered. This makes possible the estimatation ofthermodynamic parameters from experimental data of tem-perature and equilibrium constant. The effect produced bythe variation of temperature on the equilibrium constant isgiven by Van’t Hoff’s equation, which allows the estima-tion of enthalpy changes. The activation energy can beestimated from Arrhenius equation.

In Table 2, the values obtained for activation energy,pre-exponential factor, and enthalpy and entropy changesare given. The thermodynamic parameters obtained fromMichaelis constants and inhibition constants are summa-rized in Table 3. To obtain the preexponential factor andactivation energy, the Arrhenius equation has been em-ployed from the kinetic constant values for different tem-peratures. Enthalpy variations have been obtained from theMichaelis–Menten and inhibition constants applying theVan’t Hoff equation and the entropy variations from thesecond law of the thermodinamics.

Fig. 8. Flowchart of kinetic study.

Table 1Kinetic parameters obtained for the enzymatic esterification of palmiticacid and isopropyl alcohol

Parameter 65°C 70°C 75°C

(2rAc)max (l/mol min) 0.1251 0.1750 0.2042K

mAc(mol/l) 0.3411 0.2048 0.1344

KmAl (mol/l) 0.8282 0.6481 0.5244K iAc (mol/l) 0.0653 0.0526 0.0432KiAl (mol/l) 0.0022 3.963 1024 2.653 1024

K9iAc (mol/l) 0.0053 0.0041 0.0028K9iAl (mol/l) 0.6479 0.5242 0.3708Keq 2.1584 3.3011 6.3561KmEs (mol/l) 3.7443 1024 2.4363 1024 3.6443 1025

KmW (mol/l) 0.0288 0.0168 0.0047K iEs (mol/l) 2.5243 1024 1.3883 1024 7.6823 1025

K iW (mol/l) 0.1268 0.0768 0.0404

Table 2Thermodynamic parameters, pre-exponential factor and activation energy

DH0 (Kcal/mol) 25.226 0.51DS0 (cal/mol z K) 76.066 1.5k0 (l/mol/gcat/min) 1.4693 105 6 2.93 103

Ea (Kcal/mol) 11.666 0.23


4. Conclusions

The enzymatic synthesis of isopropyl palmitate can bewell described by a bi-bi ordered kinetic model. The esti-mated rate constants show an Arrhenius dependence ontemperature. The activation energy calculated for the over-all reaction is 11.66 Kcal/mol.

The model developed in the present work was used tosimulate the esterification process and to evaluate the tem-perature, enzyme concentration, and molar ratio effect onthe reaction. Fig. 9 shows one of the simulation curves fromthe kinetic model and the corresponding experimental re-sults. The quality of fit was estimated by residual analysis.In most cases, the residuals were lower than 15%, and arandom error distribution was obtained, which indicated agood fit between the models and the experimental results.The average error for all the experiments was 8.55%. Theseresults indicate that the models developed are adequate to

describe the kinetics of the esterification of palmitic acidand isopropyl alcohol over an immobilized lipase.

References

[1] Gandhi NN. Applications of lipase. J Am Oil Chem Soc 1997;74:621–34.

[2] Malcata FX, Reyes HR, Garcia HS, Hill CG, Amundson CH. Kineticsand mechanisms of reaction catalysed by immobilised lipases. En-zyme Microb Technol 1992;14:426–46.

[3] Halling PJ. Thermodynamic predictions for biocatalysis in noncon-ventional media: theory, test and recommendations for experimentaldesign and analysis. Enzyme Microb Technol 1994;16:178–206.

[4] Khmelnitsky YL, Neverova IN, Polyakov VI, Grinberg VY, Le-vashov AV, Martinek K. Kinetic theory of enzymatic reactions inreversed micellar systems. Application of the pseudophase approachfor partitioning substrates. Eur J Biochem 1990;190:155–59.

[5] Shiraishi F. Experimental evaluation of the usefulness of equationsdescribing the apparent maximum reaction rate and apparent Michae-lis constant of an immobilized enzyme reaction. Enzyme MicrobTechnol 1993;15:150–4.

[6] Chulalaksananukul W, Condoret JS, Combes D. Geranyl acetatesynthesis by lipase-catalyzed transesterification in supercritical car-bon dioxide. Enzyme Microb Technol 1993;15:691–8.

[7] Stamatis H, Xenakis A, Menge U, Kolisis FN. Esterificacion reac-tions catalyzed by lipases in microemulsions: The role of enzymelocalization in relation to its selectivity. Biotechnol Bioeng 1993;42:103–10.

[8] Guit RPM, Kloosterman M, Meindersma GW, Mayer M, Meijer EM.Lipase kinetics: hydrolysis of triacetin by lipase from Candida cylin-dracea in a hollow-fiber membrane reactor. Biotechnol Bioeng 1991;38:727–32.

[9] Lortie R, Trani M, Ergan F. Kinetic study of the lipase-catalyzedsynthesis of triolein. Biotechnol Bioeng 1993;41:1021–6.

[10] Garcia T, Coteron A, Martinez M, Aracil J. Optimization of theenzymatic synthesis of isobutyl palmitate using a central compositedesign. Trans Chem 1995;73:140–4.

[11] Garcı́a T, Martı́nez M, Aracil J. Enzymatic synthesis of an analogueof jojoba oil: optimisation by statistical analysis. Enzyme MicrobTechnol 1993;15:607–10.

[12] Garcia D, Garcia T, Martinez M, Aracil J. Enzymatic synthesis ofesters of high molecular weigh: optimisation of the synthesis of asperm whale analogue. Ind Crops Prod 1995;4:105–11.

[13] Garcı́a T, Martı́nez M, Aracil J. Kinetics of the enzymatic synthesisof an analogue of jojoba oil. Trans Chem 1993;71:47–51.

[14] Brzozowski AM, Derewenda U, Derewenda ZS, Godson GG, Law-son DM, Turkenburg JP, Bjorkling F, Huge–Jensen B, Patkar SA,Thim L. A model for interfacial activation in lipases from the struc-ture of a fungal lipase-inhibitor complex. Nature (London) 1991;351:491–4.

[15] Tsai SW, Chiang CL. Kinetics, mechanism and time course analysisof lipase-catalysed hydrolysis of high concentration olive oil in aot-isooctane reversed micelles. Biotech Bioeng 1991;38:206–11.

[16] Chulalaksananukul W, Condoret JS, Combes D. Kinetics of geranylacetate synthesis by lipase-catalyzed transesterification in n-hexane.Enzyme Microb Technol 1992;14:293–8.

[17] Garcia T, Coteron A, Martinez M, Aracil J. Kinetic of esterificationreactions catalysed by immobilized lipases. Chem Eng Sci 1996;51:2841–6.

Table 3Thermodynamic parameters for Michaelis—Menten and inhibitionconstants

Parameter -DH0

(Kcal/mol)2DS0

(cal/mol z K)

KmAc 21.66 57.30KmAl 9.89 25.21KmEs 54.62 138.97KmW 52.28 111.92K

iAc10.80 22.83

K iAl 42.89 107.42K iEs 24.69 82.88KiW 26.75 28.04K9iAc 14.35 28.04K9iAl 13.03 35.23

Fig. 9. Simulation of the esterification reaction for isopropyl palmitate (P:101325 Pa, 5% catalyst, T: 70°C, acid/alcohol molar ratio: 1/1).


Enzymatic Synthesis of Fatty Esters

Documents

Transcript of Enzymatic Synthesis of Fatty Esters