selectivity engineering in on of mesitylene with isopropyl alcohol over cesium substituted hetero...

8/3/2019 Selectivity Engineering in on of Mesitylene With Isopropyl Alcohol Over Cesium Substituted Hetero Pol Ya Cid Suppo

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Selectivity engineering in isopropylation of

mesitylene with isopropyl alcohol over cesium

substituted heteropolyacid supported on K-10 clay

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Abstract

Alkylation of aromatics catalyzed by solid acids constitutes a class of reactions ofboth academic and industrial importance. Among alkylation reactions, isopropylation ofaromatic compounds has attracted considerable attention. Use of propylene, as alkylatingagent at very high temperatures leads to coke formation which results in deactivation ofthe catalyst. The use of isopropanol as an alkylating agent is attractive when propylene isnot readily available. In-situ dehydration of isopropanol leads to prolonged activity sincewater of reaction suppresses coke formation. Further, isopropanol dehydration alsogenerates diisopropyl ether (DIPE) which itself is an excellent alkylating agent.Alkylation of mesitylene with propylene or isopropanol (IPA) results in the formation of

2-isopropyl-mesitylene (2-IPMT) which is almost extensively used as a precursor in anumber of industrial chemicals. This work covers the evaluation of clay supportedheteropolyacids and sulfated zirconia. A variety of solid acid catalysts such as K-10 clay,sulfated zirconia, Filtrol-24, 20% w/w dodecatungstophosphoric acid (H3PW12O40, DTP)supported on K-10 montmorillonite clay and 20% w/w cesium substituteddodecatungstophosphoric acid (Cs2.5H0.5PW12O40, Cs-DTP) supported on K-10montmorillonite clay were investigated for the liquid phase isopropylation of mesityleneto 2-IPMT using IPA at much milder conditions vis--vis other catalysts reported so far.20% w/w Cs-DTP/K-10 clay was found to be the best catalyst which gives 98%conversion of limiting component, IPA and 98% selectivity towards the desired product,2-IPMT after 2 h of total reaction time.This catalyst could be reused without any further

chemical treatment, eliminating the effluent disposal problems. The reaction was carriedout without using any solvent and the process subscribes to the principles of green

chemistry.The catalytic activity is in the following order: 20% w/w Cs-DTP/K-10 clay(most active) > 20% w/w DTP/K-10 clay > Filtrol-24 > sulfated zirconia > K-10 clay(least active). The effect of various operating parameters and catalyst reusability werealso systematically investigated. A mathematical model was proposed to probe into theintricate reaction kinetics and mechanism consistent with the experimental results. Thereaction is free from any external mass transfer as well as intraparticle diffusionlimitations and is intrinsically kinetically controlled. An overall second order kineticequation was used to fit the experimental data, under the assumption that all the speciesare weakly adsorbed on the catalytic sites.
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Keywords: Isopropylation, Mesitylene, Isopropyl alcohol, 2-Isopropyl-mesitylene, Solidacid catalyst, Heteropolyacids, Sulfated zirconia, Green chemistry, Selectivity.

Introduction

Alkylation is an interesting industrial organic reaction having extensive

commercial utility. Products from every sector of the organic chemical industry make useof this methodology at some stage or other. Alkylation processes normally requireFriedelCrafts acid catalysts such as H2SO4, BF3, TiCl4, liquid HF, and AlCl3 withelemental iodine etc. Some of the well established processes still employ homogeneousacid catalysts in batch reactors using large excess of the substrate or solvent causing

problem of corrosion and pollution, loss of selectivity of the desired product, etc. In mostof the industrial alkylation processes different catalysts such as mineral acids, anhydrousAlCl3 etc. and solvents like nitrobenzene, carbon disulphide and halogenatedhydrocarbons are used. Relatively high concentration of catalyst is needed; often theamount being more than stoichiometric and these make most alkylation reactions highly

polluting (Olah 1963; Kirk and Othmer 1996; Ullmann 2002; Olah et al. 1991; Franck

and Stadelhofer 1988). In addition, since the reagents are mixed with acids, separation ofthe products from the catalyst is often a difficult and energy consuming process.

Since several problems are associated with FriedelCrafts acid catalysts such astoxicity, corrosiveness, low reaction selectivity, and disposal of effluents. In recent years,the demand to replace mineral acids with environment-friendly catalysts such as ionexchange resins (Harmer and Sun 2001; Jayadeokar and Sharma 1993; Chakrabarti andSharma 1993), clay-based catalysts (Yadav et al. 2003; Yadav and Asthana 2003; Yadavand Kirthivasan 1997), zeolites (Corma 1995) and metal oxides (Yadav and Nair 1999;Yadav and Murkute 2004) has increased in order to make the process cleaner and greener.

Hitzler et al. (1998) reported the Friedel-Crafts alkylation of mesitylene andanisole with propene and/or 2-propanol using a heterogeneous polysiloxane-supportedsolid acid catalyst (Degussas Deloxan) in a small fixed bed continuous reactor (10 mlvolume) using supercritical propene or CO2 as the reaction solvent. They have reportedthat, at temperature 160-180 0C with pressure 200 bar, yield of monoalkylated product (2-isopropyl-mesitylene) was only approximately 25% due to the formation of dialkylated

product as well as dimers and trimers of propene. Selectivity to the monoalkylatedproduct was significantly higher (40% yield) in case of alkylation with 2-propanol insupercritical CO2. The authors have demonstrated success in tuning the productselectivity through control of temperature, pressure and reactant concentrations.Reduction of catalyst deactivation due to coking was potential advantage for conductingthe process in a supercritical fluid. Continuous-flow reactor process operating in the

supercritical fluid regime using a heterogeneous catalyst can also affects the Friedel-Crafts alkylation or acylation reactions.We have recently reported the vapor phase alkylation of mesitylene with

isopropanol (IPA) including dehydration of various alcohols and cracking of diisopropylether over UDCaT-4 (Yadav and Murkute 2004). The novel mesoporous solid acidcatalyst UDCaT-4 was synthesized by incorporating superacidic centers of persulfatedalumina and zirconia into highly ordered and well defined hexagonal mesoporous silica.The results are novel. We found that the conversion of mesitylene was dependent on thetemperature and space time. The conversion of mesitylene increases with temperature upto 220 0C and then remains the same up to 250 0C, but above 250 0C the conversion isfound to decrease. This is due to coke formation at high temperature which leads to

decrease in conversion of mesitylene. The range of space time suggests that 40816 g hmol-1 as the optimum space time for mesitylene which gives 44% conversion of

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mesitylene with 97% selectivity towards the monoalkylation. The space time was lowenough to prohibit any significant dialkylation. We have also concluded that there is noeffect of temperature and space time on the selectivity towards monoalkyaltion ofmesitylene and remains the same. This report also suggests that dehydration of IPA wasvery fast in comparison with alkylation of mesitylene.

In present study, the alkylation of mesitylene with IPA was chosen as a reactionbecause the reaction generates water as a co-product and thus the stability of the catalystin the presence of water can be really tested. Another reason is that the reaction wascarried out without using any solvent in order to make the process cleaner and greener.The alkylated product with mesitylene is a promising precursor for a number of industrialchemicals. There is practically no literature available on liquid phase alkylation ofmesitylene with IPA over solid acids. Supercritical alkylation of mesitylene with

propylene is reported and environmentally acceptable (Hitzler et al. 1998) but it requirehigh pressure, appropriate costly instruments and become uneconomical. The currentwork covers the use of a variety of ecofriendly solid acid catalysts such as K-10 clay,sulfated zirconia, Filtrol-24, 20% w/w DTP/K-10 clay and 20% w/w Cs-DTP/K-10 clay.

The study of dehydration of IPA was also undertaken independently to throw light onmechanism and selectivity. The effects of various parameters on rates and productdistribution are used to deduce the kinetics of the reaction.

Experimental section

Chemicals and catalyst

Mesitylene and isopropyl alcohol were obtained from M/s s. d. Fine ChemicalsPvt. Ltd. Mumbai, India. Filtrol-24 which is commercially available clay was obtainedfrom Engelhard, USA and K-10 clay was obtained from Aldrich, USA. All chemicalswere of analytical reagent (A.R.) grade. These were used as received without any further

purification.

Catalysts preparation

The following catalysts were prepared by well-developed procedures andcharacterized in our laboratory: (i) 20% w/w dodecatungstophosphoric acid supported onK-10 clay (20% w/w H3PW12O40/K-10 clay i.e. 20% w/w DTP/K-10 clay) (Yadav andKirthivasan 1997), (ii) 20% w/w cesium substituted dodecatungstophosphoric acidsupported on K-10 clay (20% w/w Cs2.5H0.5PW12O40/K-10 clay i.e. 20% w/w Cs-DTP/K-10 clay (Yadav et al. 2004; Yadav and Asthana 2003), and (iii) sulfated zirconia (S-ZrO2)(Kumbhar and Yadav 1989; Kumbhar et al. 1989; Yadav and Nair 1999). All catalystswere dried in an oven at 120 0C for 1 h before use.

Experimental setup

The reactions were carried out in a 100 cm3 capacity Parr autoclave reactor withan internal diameter of 5 cm, equipped with four bladed pitched turbine impeller. Thetemperature was maintained at 1 0C of the desired value with the help of an in-built PIDcontroller. Specific quantities of desired reactants and catalyst were charged into thereactor and the temperature was raised to the desired value. Then, an initial sample waswithdrawn and agitation started. Further samples were withdrawn at periodic timeintervals up to 2 h to monitor the reaction.

Reaction procedure

In a typical reaction, 0.316 mol mesitylene was reacted with 0.079 molisopropanol (IPA) (4:1 mole ratio of mesitylene to IPA) with 2 g of catalyst; this makes

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the catalyst loading as 0.04 g/cm3 of liquid phase. The total volume of the reactionmixture was 50 cm3. The reaction was carried out at 180 0C at a speed of agitation of 1000rpm under autogenous pressure. The reaction was carried out without any solvent.Propylene formed in-situ was not allowed to escape from the reaction vessel.

Method of analysisClear liquid samples were withdrawn at regular time intervals by reducing the

speed of agitation momentarily to zero and allowing the catalyst to settle at the bottom ofthe reactor. Analysis of the samples or compounds were performed by GasChromatograph (Chemito Model 8610 GC) equipped with a 10% SE-30 (liquid stationary

phase) stainless steel column (3.175 mm diameter 4 m length) with FID detector.Products were isolated and confirmed through GC-MS and their physical properties andretention times were recorded and compared with authentic samples. Calibrations weredone with authentic samples for quantification of data. The conversions were based on thedisappearance of isopropanol (IPA), the limiting reactant in the reaction mixture.

Results and discussionsCatalyst characterization

The catalyst was fully characterized, and the details are reported recently by us(Yadav et al. 2003, 2004; Yadav and Asthana 2003). Only a few salient features arereported here. Crystallinity and textural patterns of the catalysts predicted from X-raydiffraction data of 20% w/w Cs-DTP/K-10 clay (Yadav et al. 2003) show that DTP iscrystalline while K-10 is amorphous. The diffractogram obtained suggested that, althoughthe Cs-DTP salt loses some of its crystallinity in the process of supporting it on K-10, theKeggin structure of DTP remains intact. The Fourier transform infrared analysis fortifiedthe preservation of the keggin structure of DTP in the catalyst. A characteristic split in theW = O band of Cs-DTP suggested the existence of direct interaction between the Keggin

polyanion and Cs+. The scanning electron micrographs reveal that both K-10 and 20%w/w Cs-DTP samples possess rough and rugged surfaces, whereas 20% w/w Cs-DTP/K-10 clay shows a smoother surface because of a layer of Cs salt of DTP over the externalsurface of K-10. The Brunauer-Emmett-Teller surface area of 20% w/w Cs-DTP/K-10clay (Yadav et al. 2004) was measured to be 207 m2 g-1, and the pore volume and porediameter were 0.29 cm3 g-1 and 58 , respectively. The adsorption-desorption isothermfor 20% w/w Cs-DTP/K-10 clay showed that they have the form of a type IV isothermwith the hysteresis loop of type H3, which is a characteristic of a mesoporous solid.

Effect of different catalysts

Different solid acid catalysts were used to assess their efficacy in this reaction. A0.04 g/cm3 loading of catalyst based on the organic volume of the reaction mixture wasemployed at 180 0C. The catalysts were 20% w/w DTP/K-10 clay, 20% w/w Cs-DTP/K-10 clay, sulfated zirconia (S-ZrO2), Filtrol-24 and K-10 clay. It was found that 20% w/wCs-DTP/K-10 clay showed higher conversion compared to other catalysts and the order ofactivity was: 20% w/w Cs-DTP/K-10 clay (most active) > 20% w/w DTP/K-10 clay >Filtrol-24 > sulfated zirconia > K-10 clay (least active) (Fig. 1). The acid strength ofinorganic catalysts such as 20% w/w DTP/K-10 clay (Yadav and Kirthivasan 1997), 20%w/w Cs-DTP/K-10 clay (Yadav and Asthana 2003) and sulfated zirconia (Kumbhar andYadav 1989; Kumbhar et al. 1989) was determined by temperature-programmeddesorption of ammonia. This has been already reported by us earlier and hence the details

are avoided. The purpose of using several different solid acid catalysts was to study theeffect of nature, strength and distribution of acidity, pore size distribution and stability of

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the catalyst on conversion of isopropanol and selectivity to monoalkylated product, 2-isopropyl-mesitylene (2-IPMT). The catalyst properties and final conversion are given inTable 1.

Conversion of isopropanol was more (98%) with 20% w/w Cs-DTP/K-10 clay ascompared to conventional sulfated zirconia (61%) and also the catalyst gave maximum

selectivity (98%) towards the desired product, 2-isopropyl-mesitylene. The comparison ofinitial activity of catalysts suggested that 20% w/w Cs-DTP/K-10 clay was far superior toothers, mainly because of its nano-size, higher surface area and ease of accessibility of theactive sites to reacting molecules. Hence further experiments were conducted with 20%w/w Cs-DTP/K-10 clay. The observed concentration profile of different products for thisreaction at 180 0C is depicted in Fig. 2, whichclearly shows that the selectivity of 98%for 2-isopropyl-mesitylene was achieved. The pores of the catalyst get narrowed when K-10 clay is impregnated with Cs-DTP nanoparticles as reported in our earlier work (Yadavand Asthana 2003). Thus, only monoalkylated product, 2-IPMT is formed as the major

product with trace amount of dialkylated product, 2,6-diisopropyl-mesitylene (2,6-DIPMT) while the trialkylated product, 2,4,6-triisopropyl-mesitylene (2,4,6-TIPMT) does

not form during the reaction course.

Effect of speed of agitation

To assess the role of external mass transfer on reaction rate, the effect of speed ofagitation (Fig. 3) was studied. The speed of agitation was varied from 800 to 1200 rpm. Itwas observed that the conversion of isopropanol was practically the same in all the cases.The external mass transfer effects did not influence the reaction. Hence, all furtherreactions were carried out at 1000 rpm. The influence of external solidliquid masstransfer resistance must be ascertained before a true kinetic model could be developed.Depending on the relative magnitudes of external resistance to mass transfer and reactionrates, different controlling mechanisms have been put forward (Yadav et al. 2003, 2004;Yadav and Asthana 2003). This reaction is a typical solidliquid slurry reaction involvingthe transfer of limiting reactant IPA (A), and mesitylene (B) from the bulk liquid phase tothe catalyst wherein external mass transfer of reactants to the surface of the catalyst

particle, followed by intraparticle diffusion, adsorption, surface reactions, and desorption,take place. Thus experimental and theoretical analyses were also done to establish thatthere was no effect of external mass transfer limitations.

Effect of catalyst loading

In the absence of external mass transfer resistance, the rate of reaction is directlyproportional to catalyst loading based on the entire liquid phase volume. The catalyst

loading was varied over a range of 0.01-0.05 g/cm3

on the basis of total volume of thereaction mixture. Fig. 4 shows the effect of catalyst loading on the conversion of IPA.The conversion increased with an increase in catalyst loading, which was due to the

proportional increase in the number of active sites. The final conversion obtained with0.05 g/cm3 loading was not much different than that of 0.04 g/cm3, which suggested thatthe number of active sites available were little more than those required. Hence all furtherexperiments were carried out at 0.04 g/cm3 loading. At this loading, the intra-particlediffusion resistance sets in.

Proof of absence of intra-particle resistance

Because the average particle size of 20% w/w Cs-DTP/K-10 clay was found to be

in the range of 2-10 m and the catalyst is amorphous in nature, it was not possible tostudy the effect of catalyst particle size on the rate of reaction. The average particle

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diameter of 20% w/w Cs-DTP/K-10 clay used in the reactions was 0.001 cm, and thus atheoretical calculation was done based on the Weisz-Prater criterion (Fogler 1995; Reid etal. 1977) to asses the influence of intraparticle diffusion resistance. According to theWeisz-Prater criterion, the value of {-robs pRp2/De[As]} has to be far less than unity forthe reaction to be intrinsically kinetically controlled and which can be evaluated from the

observed rate of reaction (-robs), density of catalyst particle ( p), the particle radius (RP),the effective diffusivity of the limiting reactant (De), and the concentration of the reactantat the external surface of the particle ([AS]). The calculated value 4.1810-3 further revealsthat the absence of mass transfer limitation at the reaction conditions and therefore, thereaction is intrinsically kinetically controlled. A further proof of the absence ofintraparticle diffusion resistance was obtained through the study of the effect oftemperature and it will be discussed later.

Effect of mole ratio

The mole ratio of mesitylene to IPA was varied from 1:1 to 5:1 under otherwisesimilar operating conditions to assess its effect on the rate and selectivity. The overallreaction rate of IPA increased with an increase in the mole ratio of mesitylene to IPAfrom 1:1 to 4:1. Further increase in mole ratio did not have any significant effect onconversion of IPA. Thus, all the subsequent reactions were carried out with a mole ratioof 4:1 (Fig. 5). A mole ratio of 4:1 was maintained: (i) to avoid the formation of largeamounts of secondary products, such as the oligomers of propylene and dialkylated

products, and (ii) to diminish the influence of water formed by the dehydration of IPA insitu. The reaction was also carried out with mesitylene to IPA mole ratio 1:4. Eventhough the conversion of isopropanol was significant, the rate of alkylation of mesitylenewith propylene formed was very slow under the same reaction conditions. Also the

products formed mainly were diisopropyl ether (DIPE) and monoalkylated product.

Effect of temperature

Intrinsically kinetically controlled reactions show significant increase in theconversion profile with temperature. Since almost all mass transfer limitations wereeliminated, the effect of temperature was studied on two reaction steps.

Case 1: Dehydration of IPA

CH3 CH3

OH

2- H

2O

IPA

O

CH3

CH3 CH3

CH3

- H2O

2

CH3

CH2

DIPE Propylene

Cs-DTP/K- 10 Cs-DTP/K- 10

IPA dehydration reaction was studied in the temperature range of 160190 0C.Propylene and diisopropyl ether (DIPE) were the products formed. The rate ofdehydration increased with increase in temperature (Fig. 6). The product distribution isshown in Fig. 7. It was found that the formation of DIPE increased sharply withtemperature from 9% at 160 0C to 41% at 190 0C after 2 h. Since propylene is difficult tosample and quantify, the concentrations of isopropanol and diisopropyl ether were firstquantified by GC and then a mass balance was established to calculate the concentrationof propylene.

Case 2: Alkylation of mesitylene with IPA

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CH3

CH3CH3

+CH3 CH3

OH

CH3

CH3CH3

CH3 CH3

Cs-DTP/K-10

180C

IPA 2-IPMTMesitylene

CH3

CH3CH3

CH3

CH3CH3

CH3

180C

2,6-DIPMT

Cs-DTP/K-10

The alkylation of mesitylene with IPA is highly temperature dependent. Thetemperature effect was studied from 160190 0C to investigate the influence oftemperature on the rate of reaction and the selectivity of product. Fig. 8 shows the effectof temperature on the conversion of limiting reactant, IPA. With an increase intemperature from 160 0C to 190 0C, both the rate of reaction as well as the selectivitytowards 2-IPMT was increased. The overall reaction rate of IPA increased with anincrease in temperature from 160 0C to 180 0C. Further increase in temperature did nothave any wide effect on conversion of IPA. At the typical operating condition, theconversion of IPA was 98% with 98% selectivity towards 2-IPMT. No oligomerisation of

propylene was occurred in this temperature range. The formation of dialkylated producti.e. 2,6-diisopropyl-mesitylene (2,6-DIPMT) increases with an increase in temperaturewhile the trialkylated product, 2,4,6-triisopropyl-mesitylene (2,4,6-TIPMT) does not formduring the reaction course.

Reaction kinetics

Case 1: Dehydration of IPA

The dehydration of IPA over solid acids leads to propylene and also diisopropylether which we have earlier studied independently over a number of catalysts includingsulfated zirconia and heteropolyacids supported on clay. Independent study of IPAdehydration have been studied over 20% w/w Cs-DTP/K-10 clay and reported in ourrecent paper (Yadav and Kamble 2009). Solid superacids have both Lewis and Bronstedsites and thus the mechanism involves bifunctional sites S1 and S2. These two species

participate in the reaction. Furthermore when mesitylene was reacted with IPA over 20%w/w Cs-DTP/K-10 clay, the reaction was found to follow second order. Thus, it is seenthat the alkylation with alcohols does not follow a simple reaction. Thus, a model basedon two catalytic sites was proposed according to which IPA (A) gets adsorbed on to twodifferent sites S1 and S2. These two adsorbed species participate in the reaction. Assumingthat the rate determining step is the reaction of AS1 and AS2 to form diisopropyl ether andwater as the surface complexes (ES1) and (WS2) respectively and ES1 subsequentlydecomposes instantly into propylene (P) in the gas phase.

11

1 ASSA AK

+

(1)22

2 ASSA AK

+ (2)

1

1 2 1 2

SRk

AS AS ES WS + + (3)

2

1 12SRk

ES P WS + (4)

The site balance in this case is

11111 SWSESASVSTCCCCC

+++= (5)

2222SWSASVST

CCCC

++= (6)

The following adsorption equilibria for different species hold

11

1 WSSW WK

+ (7)

222

WSSWW

K

+

(8)11

1 ESSE EK

+ (9)

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Thus the rate of formation of propylene, -rP'(mol gcat-1 s-1) is:

( ) ( )1 1 21 2

1 1 1 2 2

'1 1

SR A A A A T S T S

P

A A W W E E A A W W

k K C K C C C r

K C K C K C K C K C

=

+ + + + +(10)

When the adsorption of all species are very weak, equation (10) is reduced to2

' AP kwCr = (11)Where,

211 21 STSTAASRCCKKkk

= (12)

Writing in terms of conversion, and further integration results into the following equation:

tkwCX

XA

A

A

01=

(13)

Thus a plot ofA

A

X

X

1against t (Fig. 9) was made to get an excellent fit thereby

supporting the model. This is an overall second order reaction for weak adsorption of IPA(A).

Case 2: Alkylation of mesitylene with IPA

Various models were tried, including typical first order kinetics (weak adsorptionof IPA and strong adsorption of mesitylene) and overall second order kinetics (weakadsorption of IPA and mesitylene). The overall second order dehydration model wastaken as a basis. As is validated above, IPA dehydration follows second order kinetics byadsorption of IPA on two adjacent sites S1 and S2 and the product diisopropyl ether (E) isformed, which is decomposed instantaneously to propylene (P). We have also reportedearlier (Yadav and Murkute 2004), the dehydration of IPA over a broad range oftemperatures (110150 0C and 180220 0C), which showed that DIPE, although formed atlower temperature, cracks faster than IPA and also the rate of alkylation is not controlled

by the dehydration rate. Thus in the temperature range studied, the rate of alkylation isnot controlled by the dehydration rate, but the alkylation of mesitylene adsorbed on site S 2with IPA adsorbed on adjacent site S1, to give the monoalkylated product i.e. 2-isopropyl-mesitylene (D), which is formed due to the surface reaction as shown below.

11

1 ASSA AK

+ (14)

22

2 BSSB BK

+ (15)

12122 WSDSASBS

SRk

++ (16)Analogously, the site balance can be written to obtain:

( )( )DDBBEEWWAA

STSTBBAASR

A

CKCKCKCKCK

CCCKCKkr

+++++

=

22111

21

11' 212 (17)

With weak adsorption of all species, equation (17) is reduced toBASRA

CwCkr = ' (18)

Where,212 21 STSTBASRSR

CCKKkk

= (19)

Writing in terms of conversion, and further integration results into the following equation:

( )( )tMwCk

XM

XMASR

A

A 11

ln0

=

(20)

Thus, a plot of( )

A

A

XM

XM

1ln against tis shown in Fig. 10 in the isopropylation

reaction of mesitylene with IPA as the alkylating agent. It is seen that the data fit very

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well, thereby supporting the model. This is an overall second order reaction for weakadsorption of IPA (A) and mesitylene (B).

From Fig. 10, the slopes obtained at 160, 170, 180 and 190 0C were found to be2.83 10-4, 3.65 10-4, 4.97 10-4 and 9.22 10-4 s-1 respectively. Hence the value of rateconstants (korkSR) at different temperature for alkylation reaction can be calculated as

kSR (160 0C) = 0.82 cm6 gcat-1 mol-1 s-1kSR (170 0C) = 1.06 cm6 gcat-1 mol-1 s-1

kSR (180 0C) = 1.44 cm6 gcat-1 mol-1 s-1

kSR (190 0C) = 2.67 cm6 gcat-1 mol-1 s-1

Similarly, in case of IPA dehydration (Fig. 9), the slopes obtained at 160, 170, 180and 190 0C were found to be 3.02 10 -4, 4.88 10-4, 9.10 10-4 and 3.77 10-3 s-1

respectively. Hence the rate constants (korkSR) at different temperature can be calculatedaskSR (160 0C) = 0.38 cm6 gcat-1 mol-1 s-1

kSR (170 0C) = 0.62 cm6 gcat-1 mol-1 s-1

kSR (180 0C) = 1.16 cm6 gcat-1 mol-1 s-1

kSR (190 0C) = 4.79 cm6 gcat-1 mol-1 s-1Arrhenius plot (Fig. 11) was used to estimate the frequency factor (k0) and

activation energy (E). The value of frequency factor and activation energy for alkylationreaction was calculated as 3.78 107 cm6 gcat-1 mol-1 s-1 and 15.3 kcal/mol respectively.In case of IPA dehydration, the value of frequency factor and activation energy was 76.92 1014 cm6 gcat-1 mol-1 s-1 and 32.5 kcal/mol respectively. The value of activation energyalso supported the fact that the overall rate of reaction is not influenced by either externalmass transfer or intraparticle diffusion resistance and it is an intrinsically kineticallycontrolled reaction on active sites.

Reusability of catalyst

The change in the texture of the catalyst from white to gray suggested itsdeactivation due to coking. After each reaction, reactivation of the catalyst was done bymaintaining the catalyst in a solution of IPA at reflux temperature for 4 h in order toremove any adsorbed material from catalyst surface and pores and dried at 120 0C for 2 hand weighed before using in the next batch. There were small losses during filtration. Theactual amount of catalyst used in the next batch was almost 5% less than the previous

batch. The catalyst was reused with a make-up quantity and the experiments onreusability were repeated.

Although the catalyst was washed after filtration to remove all adsorbed reactantsand products, there was still a possibility of retention of small amount adsorbed reactants

and products species which might cause the blockage of active sites of the catalyst. Theseare apparent factors for the loss in activity. It was observed that there was only a marginaldecrease in conversion, but there was no change in the selectivity of the product tosuggest that the catalyst is stable. Fig. 12 depicts the observed conversion profiles.

Conclusion

The liquid phase isopropylation of mesitylene with IPA was studied with differentsolid acid catalysts such as K-10 clay, sulfated zirconia, Filtrol-24, 20% w/w DTP/K-10clay and 20% w/w Cs-DTP/K-10 clay. 20% w/w Cs-DTP/K-10 clay catalyst was the mostactive and selective catalyst, which lead to 98% conversion of the limiting reactant, IPAwith 98% selectivity towards 2-isopropyl-mesitylene. The kinetics of the reaction is also

reported. The reactions were found to be intrinsically kinetically controlled. The overallsecond order kinetic equation fits the data very well and the activation energy was found

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to be 15.3 kcal/mol, which suggested that the reaction was an intrinsically kineticallycontrolled on active sites of the catalyst. The reaction is solvent free which could beadvantageous as a green and clean process.

Acknowledgement

GDY acknowledges receipt of a research grant and chair from Darbari SethProfessorship Endowment. SBK acknowledges receipt of Senior Research Fellowship(SRF) from University Grants Commission (UGC), Government of India, New Delhi.

Nomenclature

A Limiting reactant species A, IPAB Excess reactant species B, MesityleneD Monoalkylated desired product i.e. 2-isopropyl-mesityleneP PropyleneE Diisopropyl ether (DIPE)W WaterM Mole ratio of mesitylene to isopropyl alcoholCi Concentration of species i, mol/cm3

CA Concentration of A, mol/cm3

CB Concentration of B, mol/cm3

CV Concentration of vacant sites of catalyst, mol/cm3

CT Concentration of total sites of catalyst, mol/cm3

CA0 Initial concentration of A at solid catalyst surface, mol/cm3

K1 Surface reaction equilibrium constant, k1/k1'k1 Surface reaction rate constant for forward reactionk1' Surface reaction rate constant for reverse reactionKA Adsorption equilibrium constant for A, cm3/molKB Adsorption equilibrium constant for B, cm3/molkSR Second order rate constant, cm6 gcat-1 mol-1 s-1

k Second order rate constant, cm6 gcat-1 mol-1 s-1

k0 Frequency factor, cm6 gcat-1 mol-1 s-1

-ri' Rate of reaction of species i, mol gcat-1 s-1

E Apparent activation energy, kcal/molSi Site of type iSR Surface reactioni-j Species j adsorbed on site iT-Si Total sites S of type i

V-Si Vacant sites S of type iw Catalyst loading, g/cm3 of liquid phaset Reaction time interval, min.XA Fractional conversion of A

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References

Chakrabarti A, Sharma MM (1993) Cationic ion exchange resins as catalyst. React Polym20(1-2): 1-45.

Corma A (1995) Inorganic Solid Acids and Their Use in Acid-Catalyzed HydrocarbonReactions. Chem Rev 95: 559-614.

Fogler HS (1995) Elements of Chemical Reaction Engineering. 2nd edn. Prentice-Hall,New Delhi, India.

Franck HG, Stadelhofer JW (1988) Industrial Aromatic Chemistry. Springer, Berlin.Harmer MA, Sun Q (2001) Solid acid catalysis using ion-exchange resins. Appl Catal A:

Gen 221(1-2): 45-62.Hitzler MG, Smail FR, Ross SK, Poliakoff M (1998) Friedel-Crafts alkylation in

supercritical fluids: continuous, selective and clean. Chem Commun 3: 359-360.Jayadeokar SS, Sharma MM (1993) Ion exchange resin catalysed etherification of

ethylene and propylene glycols with isobutylene. React Polym 20(1-2): 57-67.Kirk and Othmer (1996) Encyclopedia of Chemical Technology. 4th edn. Wiley-

Interscience, New York.

Kumbhar PS, Yadav GD (1989) Catalysis by sulfur-promoted superacidic zirconia:Condensation reactions of hydroquinone with aniline and substituted anilines. ChemEng Sci 44(11): 2535-2544.

Kumbhar PS, Yadav VM, Yadav GD in: D. E. Layden (Ed.) (1989) Chemically ModifiedOxide Surfaces. Gordon and Breach, New York.

Olah GA (1963) Friedel-Crafts and Related Reactions. Wiley-Interscience, New York,vol. 1-4.

Olah GA, Krishnamuri R, Suryaprakash GK (1991) Comprehensive Organic Synthesis.Pergamon, Oxford, vol. 3, chapter 1.8.

Reid RC, Prausnitz MJ, Sherwood TK (1977) The Properties of Gases and Liquids. 3rdedn. McGraw-Hill, New York.

Ullmann F (2002) Encyclopedia of Industrial Chemistry. 6th edn. Wiley-VCH VerlagGmbH, Weinheim, Germany.

Yadav GD, Asthana NS (2003) Selective decomposition of cumene hydroperoxide intophenol and acetone by a novel cesium substituted heteropolyacid on clay. ApplCatal A: Gen 244(2): 341-357.

Yadav GD, Asthana NS, Kamble VS (2003) Cesium-substituteddodecatungstophosphoric acid on K-10 clay for benzoylation of anisole with

benzoyl chloride. J Catal 217(1): 88-99.Yadav GD, Asthana NS, Salgaonkar SS (2004) Regio-selective benzoylation of xylenes

over caesium modified heteropolyacid supported on K-10 clay. Clean Tech Environ

Policy 6: 105-113.Yadav GD, Kamble SB (2009) Alkylation of xylenes with isopropyl alcohol over acidicclay supported catalysts: Efficacy of 20% w/w Cs2.5H0.5PW12O40/K-10 clay. Ind EngChem Res (In Press).

Yadav GD, Kirthivasan N (1997) Synthesis of bisphenol-A: Comparison of efficacy ofion exchange resin catalysts vis--vis heteropolyacid supported on clay and kineticmodeling. Appl Catal A: Gen 154(1-2): 29-53.

Yadav GD, Murkute AD (2004) Novel Efficient Mesoporous Solid Acid CatalystUDCaT-4: Dehydration of 2-Propanol and Alkylation of Mesitylene. Langmuir20(26): 11607-11619.

Yadav GD, Nair JJ (1999) Sulfated zirconia and its modified versions as promising

catalysts for industrial processes. Micro Meso Mater 33(1-3): 1-48.

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Table 1. Properties of catalysts and conversion of IPAa

Catalyst SourceParticle

size (m)

Surface

area

(m2/g)

Pore

volume

(cm3/g)

Average

pore

diameter

(nm)

Conversion

of IPA after

2 h

(%)

Filtrol-24 Engelhard 30-400 350 0.42 7.5 76Sulfated zirconia This work 50-300 100 0.115 2.8 61K-10 Aldrich 50-200 230 0.36 6.4 5220% w/w DTP/K-10 This work 50-200b 107 0.32 7.1 8120% w/w Cs-DTP/K-10 This work 200-300c 207 0.29 5.8 98

a Reaction conditions: speed of agitation1000 rpm; catalyst loading0.04 g/cm3; moleratio of mesitylene:IPA4:1; temperature180 0C; total reaction volume50 cm3;autogenous pressure. b The particle size of the HPA on the K-10 support was 150 nm andc The particle size of the HPA on the K-10 support was 5 nm.

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0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() 20% w/w Cs-DTP/K-10 clay, () 20% w/w DTP/K-10 clay, () Filtrol-24, ()Sulfated zirconia (S-ZrO2), () K-10 clay

Fig. 1. Effect of different catalysts on conversion of IPA: speed of agitation1000 rpm;catalyst loading0.04 g/cm3; mole ratio of mesitylene:IPA4:1; temperature180 0C; total

reaction volume50 cm3; autogenous pressure.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 20 40 60 80 100 120 140

Time (min)

Concentration(mol/cm

3)10

3

() IPA, () 2-Isopropyl-mesitylene, () Propylene, () Diisopropyl ether, () 2,6-Diisopropyl-mesitylene

Fig. 2. Concentration profile of various products in isopropylation of mesitylene withIPA: catalyst20% w/w Cs-DTP/K-10 clay; speed of agitation1000 rpm; catalyst

loading0.04 g/cm3; mole ratio of mesitylene:IPA4:1; temperature180 0C; total reactionvolume50 cm3; autogenous pressure.

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0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() 800 rpm, () 1000 rpm, () 1200 rpmFig. 3. Effect of speed of agitation on conversion of IPA: catalyst20% w/w Cs-DTP/K-10 clay; catalyst loading0.04 g/cm3; mole ratio of mesitylene:IPA4:1; temperature180

0C; total reaction volume50 cm3; autogenous pressure.

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() 0.01 g/cm3, () 0.02 g/cm3, () 0.04 g/cm3, () 0.05 g/cm3

Fig. 4. Effect of catalyst loading on conversion of IPA: catalyst20% w/w Cs-DTP/K-10

clay; speed of agitation1000 rpm; mole ratio of mesitylene:IPA4:1; temperature1800C; total reaction volume50 cm3; autogenous pressure.

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0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() 1:1, () 3:1, () 4:1, () 5:1Fig. 5. Effect of mole ratio of mesitylene:IPA on conversion of IPA: catalyst20% w/w

Cs-DTP/K-10 clay; speed of agitation1000 rpm; catalyst loading0.04 g/cm3;temperature180 0C; total reaction volume50 cm3; autogenous pressure.

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() 160 0C, () 170 0C, () 180 0C, () 190 0CFig. 6. Effect of temperature on the cracking of IPA: catalyst20% w/w Cs-DTP/K-10

clay; speed of agitation1000 rpm; catalyst loading0.04 g/cm3; temperature180 0C; totalreaction volume50 cm3; autogenous pressure.

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0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Selectivity(%)

() 160 0C, () 170 0C, () 180 0C, () 190 0C(______) Propylene, (______) Diisopropyl ether

Fig. 7. Effect of temperature on selectivity of products in dehydration of IPA: catalyst20% w/w Cs-DTP/K-10 clay; speed of agitation1000 rpm; catalyst loading0.04 g/cm3;

temperature180 0C; total reaction volume50 cm3; autogenous pressure.

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() 160 0C, () 170 0C, () 180 0C, () 190 0CFig. 8. Effect of temperature on isopropylation of mesitylene with IPA: catalyst20%

w/w Cs-DTP/K-10 clay; speed of agitation1000 rpm; catalyst loading0.04 g/cm3; moleratio of mesitylene:IPA4:1; total reaction volume50 cm3; autogenous pressure.

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y = 0.0181x

R2

= 0.9733

y = 0.0293x

R2 = 0.9933

y = 0.0546x

R2

= 0.9939

y = 0.2261x

R2

= 0.9866

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120 140

Time (min)

XA/1-XA

() 160 0C, () 170 0C, () 180 0C, () 190 0CFig. 9. Validation of mathematical model for dehydration of IPA

y = 0.0553x

R2

= 0.9992

y = 0.0298x

R2

= 0.9856

y = 0.0219x

R2

= 0.9841

y = 0.0170x

R2

= 0.9862

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20 25

Time (min)

ln[(M

-XA)/M(1-XA)]

(

) 1600

C, () 1700

C, () 1800

C, (

) 1900

CFig. 10. Validation of mathematical model for isopropylation of mesitylene with IPA

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y = -16346x + 36.579

R2

= 0.9229

y = -7677x + 17.447

R2

= 0.9445

-3.50

-2.50

-1.50

-0.50

0.50

1.50

2.50

2.12E-03 2.16E-03 2.20E-03 2.24E-03 2.28E-03 2.32E-03

1/T (K-1

)

lnk

() Dehydration of IPA, () Alkylation of mesitylene with IPAFig. 11. Arrhenius Plot

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time (min)

Conversion(%)

() Fresh catalyst, () First reuse, () Second reuseFig. 12. Reusability of catalyst: catalyst20% w/w Cs-DTP/K-10 clay; speed of

agitation1000 rpm; catalyst loading0.04 g/cm3; mole ratio of mesitylene:IPA4:1;temperature180 0C; total reaction volume50 cm3; autogenous pressure.

18

selectivity engineering in on of mesitylene with isopropyl alcohol over cesium substituted hetero...

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