Green approach for the preparation of biodegradable lubricant base stock

Green approach for the preparation of biodegradable lubricant

base stock from epoxidized vegetable oil

Piyush https://www.360docs.net/doc/c12181803.html,thi *,Bo Mattiasson

Department of Biotechnology,Center for Chemistry and Chemical Engineering,Lund University,

P .O.Box 124,SE 22100Lund,Sweden

Received 10April 2006;received in revised form 16June 2006;accepted 20June 2006

Available online 4August 2006

Abstract

A novel process for the production of biodegradable lubricant-based stocks from epoxidized vegetable oil with a lower pour point via cationic ion-exchange resins as catalysts was developed.This involves two steps,?rst,ring-opening reactions by alcoholysis followed by esteri?cation of the resultant hydroxy group in the ?rst step.

The ring-opening reaction of epoxidized soybean oil with different alcohols such as n -butanol,iso -amyl alcohol and 2-ethylhexanol was carried out in presence of Amberlyst 15(Dry)as a catalyst;identity of products was con?rmed by IR and NMR.Pour points of the products were observed in the range of à5to à158C.The hydroxy group of ring-opening product of n -butanol was further reacted with acetic anhydride in presence of catalyst Amberlyst 15(Dry),which was previously used to carry out ring-opening reaction by alcoholysis and identity of the resulting product was con?rmed by IR.Pour point of the resulting product was observed to be à58C.#2006Elsevier B.V .All rights reserved.

Keywords:Bio-lubricants;Epoxidized soybean oil;Cationic ion-exchange resins

1.Introduction

Renewable raw materials are going to play a very noteworthy role in the development of sustainable green chemistry.They offer a large number of possibilities for applications which can be rarely met by petrochemistry [1].Oils and fats of vegetable and animal origin share the greatest proportion of the current consumption of renewable raw materials in chemical industry [2].

A steady increase in the use of eco-friendly consumer products like lubricants has occurred as a result of strict government regulation and increased public awareness for a pollution free environment [3].There are wide ranges of lubricant base oils in current use which includes mineral oils,synthetic oils,re-re?ned oils,and vegetable oils.Among these,mineral oils are the most commonly used.They consist predominantly of hydrocarbons but also contain some sulfur

and nitrogen compounds with traces of a number of metals.Due to their inherent toxicity and non-biodegradable nature they pose a constant threat to ecology and vast ground water reserves [4].Synthetic oils include others polyalphaole?ns,synthetic esters and polyalkylene glycols.Polyalphaole?ns are petrochemical derived synthetic oils that mostly resemble mineral oils.Synthetic esters form a large group of products,which can be either from petrochemical or oleochemical origin.In the preparation of re-re?ned oil,oil undergoes an extensive re-re?ning process to remove contaminants to produce fresh base oil.

These concerns have resulted in an increasing interest in vegetable oils with high content of oleic acid,which are considered to be potential substitutes to conventional mineral oil-based products [5,6].Vegetable oil lubricants are preferred not only because they are renewable raw materials but also because they are biodegradable and non-toxic [7].They also acquire most of the properties required for lubricants such as high index viscosity,low volatility and good lubricity and are also good solvents for ?uid additives.However,vegetable oils have poor oxidative and thermal stability,which is due to the presence of unsaturation [8].This unsaturation restricts their

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Applied Catalysis B:Environmental 69(2007)207–212

*Corresponding author.Tel.:+46462227363;fax:+46462224713.E-mail addresses:https://www.360docs.net/doc/c12181803.html,thi@biotek.lu.se ,lathips@https://www.360docs.net/doc/c12181803.html, ,lathips@https://www.360docs.net/doc/c12181803.html, (https://www.360docs.net/doc/c12181803.html,thi).

0926-3373/$–see front matter #2006Elsevier B.V .All rights reserved.doi:10.1016/j.apcatb.2006.06.016

use as a good lubricant.Several attempts have been made to improve their oxidative stability such as transesteri?cation of trimethylopropane and rapeseed oil methyl ester[9];selective hydrogenation of polyunsaturated C C bonds of fatty acid chains[10]and conversion of C C bonds to oxirane ring via epoxidation[11,12].Among these,epoxidation received special attention because it opened up a wide range of feasible reactions that can be carried out under moderate reaction conditions due to the high reactivity of the oxirane ring[13]. For instance,the epoxide can react with different nucleophiles to produce mono-alcohols,diols,alkoxyalcohols,hydroxye-sters,N-hydroxyalkylamides,mercaptoalcohols,aminoalco-hols,hydroxynitriles,etc.[1,14].

Standard industrial production for epoxidation of vegetable oil is based on in situ epoxidation,in which peracid is generated by reacting acetic or formic acid with hydrogen peroxide in the presence of strong mineral acids such as H2SO4and H3PO4 [15].The strong mineral acid leads to many side reactions,such as oxiran-ring opening to diols,hydroxyesters,estolides and other dimers formation.Furthermore,they cause equipment corrosion and must be neutralized and also removed from the end product.

Warwel and Klaas reported an alternative process that is milder and more selective,wherein lipase is used to catalyze the peracid formation from a fatty acid and hydrogen peroxide [16].This is a new and a very promising technique for epoxidation of double bonds.It has several advantages over the chemical catalysts such as:(i)mild reaction conditions, (ii)formation of stable hydroperoxides directly from fatty acid,i.e.no need for acetic or formic acid addition,(iii)high region and stereoselectivity,(iv)signi?cant suppression of side reactions and(v)high conversion.In most of the recent publications,volatile organic solvents were used as the reaction media[17,18].However recently Orellana-Coca et al.from our department has developed the solvent free chemo enzymatic process for the epoxidation of fatty acid [19].

It was reported earlier that epoxidized unsaturated fatty acids can be used as metal working?uids and lubricating additives to eliminate corrosion from chlorine containing compounds[20,21].Adhvaryu and Erhan reported epoxidized soybean oil as a potential source for high temperature lubricants applications[12].Various procedures have been described for the preparation of alkoxyalcohols and hydro-xylated fatty acids.Gast et al.reported that the product obtained by ring-opening reaction of epoxidized fatty acid esters followed by esteri?cation of the resulting hydroxyl group shows good performance for lower temperature lubricant applications[22].

In most of these processes,sulfuric acid was used as a catalyst for alcoholysis,whereas the other homogenous catalysts such as p-toluenesulfonic acid,boron tri?uoride, and sodium methoxide were used for comparative studies.The resulting hydroxy group via alcoholysis is further reacted with acid anhydride in presences of pyridine[23–25].In some cases,the?rst step of the ring opening was performed by addition of acetic acid,perchloric acid or formic acid,and in the second step,i.e.esteri?cation of the resulting hydroxyl group with acid anhydride was done via pyridine[4,26,27]. Though these products come with the tag of green and biodegradability,the reported ways are not eco-friendly and green.Maybe therefore,these processes did not gain industrial importance.

There were few reports in which cationic ion-exchange resins such as Dowex50W-X8,Duolite C26,and Lewatit S100 were used as an acylative ring cleavage catalyst for epoxidized soybean oil[28].These organic catalysts showed poor cleavage ef?ciencies as compared to sulfuric acid.It may be due to the microporous gel type nature of Dowex50W-X8and Lewatit S 100.Since they have no discrete pores,solute ions have to diffuse through the particle to interact with the exchange site which may cause the diffusional limitation and reduce the overall ef?ciency.

The use of homogenous catalysts is very common in the chemical and re?nery industries,and those technologies employ highly corrosive,hazardous and polluting liquid acids. The present work deals with the preparation of lubricant-based stock by using cationic ion-exchange resins,particularly,the macroporous variety.It is very well documented that resins are very versatile catalysts and are known for carrying out number of reactions such as esteri?cation,etheri?cation,transalkyla-tions,hydration and alkylation[29].They also offer distinct advantages over homogenous catalysts with respect to corrosion,product recovery,selectivity,etc.,both from the standpoint of catalysis as well as engineering of reactions for commercial purposes[30].Hence,it is worthwhile to develop a green and environmental friendly process based on macro-porous resins with an emphasis on biodegradability of the lubricant.As previously mentioned,the preparation of lubricant-based stock from epoxidized vegetable oil involves two steps,ring-opening reaction via alcoholysis followed by esteri?cation of the resulting hydroxy group through alcoho-lysis.Novelty of the current work is that the same catalysts without any treatment can be used for both the reactions,i.e. ring-opening reaction via alcoholysis and also for esteri?cation of the resulting hydroxyl group.

2.Materials and methods

2.1.Materials

The epoxidized soybean oil was a gift sample from Akzo Nobel Industrial Coatings Sweden,and was used as received. Unless otherwise speci?ed,all other chemicals including alcohols,Amberlyst15(Dry)(%water content 1.5m3/m3of resin,ionic form H+)and acetic anhydride were purchased from Sigma and used without further puri?cation.

2.2.Analytical methods

The oxirane value was determined titrimetrically with perchloric acid[31].The infrared(IR)spectra were recorded on a Fourier transform IR8300from Shimadzu.All the spectra’s were recorded by spreading the samples between

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NaCl plates.The spectra were recorded in transmittance mode. The1H and13C NMR spectra were recorded qualitatively using a Bruker ARX-400spectrometer(Bruker,Rheinstetten, Germany)at a frequency of400and100MHz,respectively, using a5mm dual probe.For1H and13C experiments,sample solutions were prepared in deuterated chloroform(CDCl3 99.8%D,Aldrich Chemical Company).Proton NMR spectra were obtained from16co-added FIDs with a delay time of1s and13C experiment was carried out with NS=5000,AQ 0.62s,DW019m s,D1=0.1s.Pour point measurement was done using a Freezer Hetofrig CB8(ISO3106).Kinematic viscosity measurement was done at408C by using a Schott-Gera¨te CT42(ISO3104)and dynamic viscosity measurement was done at28and408C by using a Bohlin Visco88 Viscometer.

3.Experimental set-up

3.1.Ring-opening reaction

The experimental set-up consisted of a3cm i.d.fully baf?ed mechanically agitated reactor of150cm3capacity,with a four-bladed pitched-turbine impeller.The entire reactor assembly was immersed in a thermostatic oil bath maintained at a desired temperature with an accuracy of?18C.

In a typical experiment,the reaction mixture consisted of epoxidized soybean oil1(60g,0.285mol of epoxy group)and an alcohol.The reaction mixture was agitated at708C for 15min at a speed of1000rpm and1.5%of(w/w of epoxidized soybean oil)catalyst Amberlyst15(Dry)was added to initiate the reaction to obtain the products2a,2b and2c.Table1 summarizes the reaction conditions.Clear samples were withdrawn periodically and titrated to measure the concentra-tion of epoxide.

3.2.Esteri?cation of resulting hydroxyl group in the ring opened product

The same experimental set-up mentioned in Section3.1was used.The reaction mixture consisted of50g of product obtained by ring-opening reaction of epoxidized soybean oil with n-butanol(2a)and50mL of acetic anhydride.The reaction mixture was agitated at908C for15min at a speed of 1000rpm and the catalyst which was used in the previous reaction was added without any further treatment to initiate the reaction to obtain product3

.

4.Results and discussion

4.1.Effect of alcohols on pour point and viscosity

For investigation of alkyl group effect on the low-temperature

properties,three different alcohols,namely n-butanol,iso-amyl

alcohol and2-ethylhexanol were chosen[32,33].The main

purpose for choosing the above three alcohols is that n-butanol is

a short straight chain alcohol,iso-amyl alcohol is a short branch

chain alcohol and2-ethylhexanol is a medium branch chain

alcohol.Pour point values for the ring-opening product of the https://www.360docs.net/doc/c12181803.html,thi,B.Mattiasson/Applied Catalysis B:Environmental69(2007)207–212209

Table1

Reaction conditions

Product entry Alcohol Temperature(8C)Mole ratio Catalysts loading(%)Reaction time(h) 2ai n-Butyl alcohol1001:2215

2aii n-Butyl alcohol1001:3215

2b iso-Amyl alcohol1101:2217

2c2-Ethyl hexanol1201:2224

3Esteri?cation of resulting hydroxyl

group in the ring opened product2ai

901:2215

respective alcohols were in the range 0to à5,à5to à10and à10to à158C.Thus,it was observed that as the chain length of branched alcohol increased,it gives lower pour point.2-ethylhexanol,a branched medium chain alcohol,gives low pour point values as compared to other alcohols.

The ring-opening reaction was monitored by epoxy titration and stopped when the ring-opening reaction was 100%.The structure of the product was con?rmed from infrared spectra by the disappearance of epoxy group at 822cm à1and appearance of the hydroxy peak at 3450cm à1.The reaction completion was further con?rmed by 1H NMR spectra.As summarized in Table 1,different alcohols required different conditions to complete the reaction.Longer or bulkier alcohols required longer reaction time and higher temperature.

The retention of the triacylglycerol backbone is important for maintaining the biodegradability of the vegetable oil and this was con?rmed by 1H NMR spectra given in Fig.1.1H NMR measurement on epoxidized vegetable 1indicates that the epoxy group is present in the d 3.0–3.2ppm region.The methine proton of –CH 2–C H –CH 2backbone at d 5.1–5.3ppm,methylene proton of –C H 2–CH–C H 2–glycerol’s backbone at d 4.0–4.4ppm,C H 2proton adjacent to two epoxy group at d 2.8–3.0ppm,–C H –proton of the epoxy ring at d 3.0–3.2ppm,a -C H 2to C O at d 2.2–2.4ppm,a -C H 2to epoxy group at 1.7–1.9ppm,b -C H 2to C O at d 1.55–1.7ppm,b -C H 2to epoxy group at d 1.4–1.55ppm,saturated methylene group at d 1.1–1.4ppm and terminal –C H 3groups at d 0.8–1.0ppm region.

Compounds 2a and 3retain most of the characteristic peaks of compound 1except the one at d 2.8–3.2and 1.4–1.55ppm region,corresponding to hydrogen’s attached to the epoxy groups and methylene groups adjacent to epoxy,respectively.13

C NMR measurement on epoxidized vegetable 1indicates that the epoxy group is present in the d 56.9–58.5ppm region.

P https://www.360docs.net/doc/c12181803.html,thi,B.Mattiasson /Applied Catalysis B:Environmental 69(2007)207–212

https://www.360docs.net/doc/c12181803.html,parison of the 1H NMR spectra of the epoxidized vegetable oil (1),product of the ring-opening reaction of epoxidized vegetable oil with n -butanol (2ai )and product of the esteri?cation reaction of resulting hydroxyl group in the product 2ai with acetic anhydride (3

).

https://www.360docs.net/doc/c12181803.html,parison of the 13C NMR spectra of the epoxidized vegetable oil (1),product of the ring-opening reaction of epoxidized vegetable oil with n -butanol (2ai )and product of the esteri?cation reaction of resulting hydroxyl group in the product 2ai with acetic anhydride (3).

Compounds 2a and 3retain most of the characteristic peaks of compound 1except the one at d 56.9–58.5ppm region,corresponding to carbon’s attached to the epoxy groups (Fig.2).This gives the con?rmation that no epoxide group remains in the products.

The resulting hydroxyl group in 2a was further reacted with acetic anhydride to obtain the corresponding product 3.The product was con?rmed by IR spectra by the disappearance of the hydroxyl peak at 3450cm à1.IR spectra of 1,2a and 3are given in Fig.3.The reaction completion was further con?rmed by 1H NMR spectra by the presence of an additional peak at d 2.0ppm for product 3.

Pour point becomes very important in cold weather applications and in cylinder and packing lubricant with very cold suction temperature.The pour points of 2a –2c and 3were measured by using a standard method mentioned in materials and method and the results are shown in Table 2.

Viscosity is of paramount importance to a lubricant.The kinematic viscosity of 2a –2c and 3were measured and the results are shown in Table 2.The product 2a was synthesized with two different mole ratios of epoxidized oil to n -butanol and it was found that the viscosity of 2aii is higher than that of 2ai .Product 2aii was prepared by using higher molar concentration of n -butanol.

Dynamic viscosity of 2ai was measured at 28and 408C at different shear rates.Figs.4b and 5b show that viscosity does not change with an increasing shear rate,whereas the plots of shear stress versus shear rate (Figs.4a and 5a )show a straight

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211

https://www.360docs.net/doc/c12181803.html,parison of the infrared spectra of the epoxidized vegetable oil (1),product of ring-opening reaction epoxidized vegetable oil with n -butanol (2a )and product of esteri?cation reaction of resulting hydroxyl group in the product 2a with acetic anhydride (3).

Table 2

Kinematic viscosity and pour point values Serial no.Product entry Kinematic

viscosity (mm 2/s)Pour point (8C)12ai 232.7>à5,<022aii 312.9>à5,<032b 172.4>à5,<042c 73.2>à15,<à105

3

350.8

>à5,<

Fig.5.Dynamic viscosity study performed at 408C at different shear rates to observe its effect on the viscosity:(a)shear rate vs.viscosity and (b)shear rate vs.shear

stress.

Fig.4.Dynamic viscosity study performed at 288C at different shear rates to observe its effect on the viscosity:(a)shear rate vs.viscosity and (b)shear rate vs.shear stress.

line passing through the origin,thereby indicating Newtonian type?uid.

4.2.Biodegradability study

A biodegradability and toxicity study for the lubricants was performed.It was observed that lubricants are non-toxic and biodegradable.In toxicity studies following tests such as toxicity screening,phytotoxicity[34]and algal toxicity[35] were executed.In each case no-observed-effect-concentration (NOEC);the highest concentration without adverse effects was 2000,1000and1000mg/L,respectively.In biodegradability study,values for biochemical oxygen demand(BOD)and chemical oxygen demand(COD)were measured.It has been documented that if the ratio of BOD5/COD is around0.5and higher it means compounds are easily biodegradable[36,37]. This value for the present prepared lubricant products is in the range of0.43–0.63,which shows that compounds are biodegradable.

4.3.Reusability of catalyst

Reusability of Amberlyst15(Dry)was tested by conducting four runs.After the reaction,the catalyst was ?ltered and then re?uxed with50mL of alcohol for30min to remove any adsorbed material from the catalyst surface and pores and dried at1108C after every use.It was observed that there is only a marginal decrease in conversion.Some catalyst was lost during?ltration.There was no makeup catalyst added during each reuse study.Thus,the catalyst was reusable up to four times.

5.Conclusion

The current work has focused on the synthesis of bio-lubricant from epoxidized vegetable oil and alcohol using solid acid catalyst Amberlyst15.This investigation showed that the introducing branching on epoxidized soybean oils leads to dramatic improvement of low pour point value.The ring-opening reaction of epoxidized soybean oils with2-ethylhex-anol gives the low pour point value.It was observed that the catalyst has excellent reusability and stability.Lubricants are non-toxic and biodegradable.

Acknowledgements

The work is a part of the GREENCHEM program sponsored by MISTRA(The Swedish Strategic Fund for Environmental Research)and the authors thank the same for the?nancial support.The authors are very grateful to Mrs.Birgit Vainio (Binol BioSafe Oy Laboratory,Finland)for the measurement of the viscosity and the pour point tests.References

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