Holzforschung,Vol.65,pp.439–451,2011?Copyright?by Walter de Gruyter?Berlin?Boston.DOI10.1515/HF.2011.081 Review
Bio based fuels and fuel additives from lignocellulose feedstock via the production of levulinic acid and furfural 11th EWLP,Hamburg,Germany,August16–19,2010
Geertje Dautzenberg1,Mirko Gerhardt2and
Birgit Kamm2,*
1biorefinery.de GmbH,Stiftstra?e2,D-14471Potsdam, Germany
2Research Institute Bioactive Polymer Systems e.V., Kantstra?e55,D-14513Teltow,Germany
*Corresponding author.
Research Institute Bioactive Polymer Systems e.V.,Kantstra?e 55,D-14513Teltow,and Brandenburg University of Technology Cottbus,Germany
E-mail:kamm@biopos.de
Abstract
The demand for biomass-derived fuels and fuel additives, particularly in the transportation sector,has stimulated intense research efforts in the chemistry of levulinic acid and levulinic acid secondary products over the past decade.Addi-tionally,recent technological progress in lignocellulosic feed-stock(LCF)chemistry has also increased attention in this regard.As a result,several oxygenating fuel additives with potential applications in both gasoline and diesel fuels have been identified.Some of the chemicals,such as ethyl val-erate,appear to be viable alternatives to the currently used branched,short-chain ethers that are derived from side prod-ucts of petrol refining.Cost-effective applications of ligno-cellulosic biomass are a crucial aspect of its feasibility.In consideration of the LCF biorefinery concept,the feasibility must also include the chemical pulping of LCF and the com-prehensive utilisation of its main constituents cellulose,hemi-celluloses,and lignin.The present study focuses on cellulose and hemicelluloses as viable sources for the production of biofuels and biofuel additives.Multifunctional catalysis, including hydrogenation and acid catalysis are the primary instruments used for the conversion of the monomeric car-bohydrate building blocks,i.e.,mainly C5sugars,such as xylose and arabinose,and C6sugars in the form of glucose and their respective secondary products,furfural and levuli-nic acid.Lignin utilisation is not addressed in this paper.
Keywords:biofuel;furfural;LCF biorefinery;levulinic acid; levulinic acid esters;lignocellulosic feedstock(LCF);2-methyl tetrahydrofuran;pentenoic acid esters;valeric acid esters;valerolactone;g-valerolactone.
Introduction
Due to the finite nature of fossil fuels and the unbalanced CO2equilibrium that is caused by the extensive use of the former,the public increasingly asks for a substitution of fos-sil-based transportation fuels and fuel additives by bio-based substances,specifically in industrialised countries.Conse-quently,governmental directives in both the U.S.and Europe demand the gradual integration of current fossil fuels with biomass-derived fuels.The production of biomass-derived fuels,such as fatty acid methyl esters(FAME),catalytically hydrogenated fatty acids(NExBTL)from plant oils,and eth-anol from corn,is in competition with raw material use for human nutrition.Thus,a balanced and sustainable utilization of biomass is searched for.
In theory,all fuels could be produced from syngas,which can be obtained from coal,but also from lignocellulose-rich biomass(wood,straw),by Fischer-Tropsch synthesis(FTS). Currently,synthetic diesel production facilities exist in South Africa(Sasol),in Malaysia(Shell),and in other remote loca-tions(Huber et al.2006).Research on syngas and FTS focuses on the production of higher waxes,which can be cracked under hydrogenating conditions into hydrocarbons of desired chain length.Such a pilot plant that uses syngas derived from wood was operated in collaboration between Shell and the Energy Research Centre of the Netherlands (ECN),and produced a sulphur-free diesel fuel.Boerrigter (2002)reported that yields of210l per ton biomass should be reached by further improving the implied technology.The main drawback of the process is its low thermal efficiency, in which the maximum was estimated to be46.2%,in com-parison to75%with biomass gasification(Huber et al.2006). Whether syngas production from biomass,specifically from lignin-rich biomass that can be regarded as young coal (Gerhardt et al.2010),and successive FTS will be a viable route for fuel production,depends on the development of further alternatives in the conversion of lignocellulose-rich feedstock.
Short-branched alkylethers,such as methyl tert-butyl ether (MTBE),ethyl tert-butyl ether(ETBE),and tert-amyl methyl ether(TAME),are used by the fuel industry primarily because they are produced from broadly available,low molecular weight by-products of petrol refining(isobutene, isoamylene,and dipropylene).These alkylethers offer ben-efits in the combustion quality and octane number of gaso-line.Based on this experience,currently,attention is paid to the synthesis of hydrocarbon oxygen heterogens of relative low polarity from lignocellulosic feedstock(LCF).Efforts are centred specifically on levulinic acid,because of its chemical versatility.In fact,it has also been identified as one of the12potential platform chemicals in the biorefinery con-cept.The probability of its large-scale production directly from cellulosic biomass has increased significantly as a result
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Figure 1Chemical-technical major groups of lignocellulosic feed-stock according to Fengel and Wegener (1984)and product trees derived from their essential components (Kamm et al.2006).
of recently developed Biofine technology (Fitzpatrick 1990,1997,2006;Hayes et al.2006).
The principal objective of this review is to demonstrate the potential of levulinic acid chemistry for the development of alternative fuels and fuel additives,primarily for the trans-portation sector.It also aims to depict a comprehensive pro-duction scenario of levulinic acid and furfural based on the application of unfractionated lignocellulosic feedstock (LCF)as a starting material.The most recent development of alter-native fuel additives is shown,and the need for new multi-functional heterogeneous catalysts for industrial implement-ation is depicted.
Levulinic acid and furfural production from LCF
Lignocellulosic feedstock (LCF)is predominantly composed of the structural carbohydrates,cellulose (38–50%)and hemi-celluloses (23–32%),and lignins (15–25%).The amount of extractives and ashes is comparatively low (Figure 1).
The highly crystalline cellulose is composed of linear chains of D-glucose linked by b -1,4-glycosidic bonds with a polymerisation degree between around 9000and 15,000in native wood and plants (Goring and Timell 1962;Pettersen 1984;Y oung 2003).
Hemicelluloses are amorphous,branched heteropolymers that vary in composition depending on the type of plant material.Monomer components of hemicellulose are xylose,mannose,galactose,glucose,arabinose and methylglucoro-nic acid.Lignin is a branched and partly cross-linked poly-aromatic compound considered to be an encrusting substance
of wood and adds mechanical strength and stiffness to it (Y oung 2003).
Aside from green biomass,LCF is the most common raw material for biorefinery processes,such as wood from fast-growing lumbers,forest harvesting residues,and recovered paper and straw.In Table 1,lignocellulosic sources are sum-marised and placed into four groups.
All four LCF sources are relevant,however,significant regional differences exist.Group 2(fast-growing plantations)and group 3(lignocellulose waste from agriculture,forestry and industry)will become the fastest-growing segments.In Europe,group 1will gain more attention due to substantial changes in agricultural politics.
A LCF biorefinery system is presented in Figure 1.In an ideal case,the natural structures and structure elements are preserved completely or at least partially during biorefining.The creation of genealogical product trees is possible.Intense efforts are required in particular for the separation of cellu-lose,hemicelluloses and lignin that are three-dimensionally entangled and chemically crosslinked.
Hemicelluloses are starting materials for C-5building blocks,such as furfural.Potential C-6building blocks derived from cellulose include levulinic acid and 5-hydroxy-methyl furfural.Levulinic acid is currently produced on a small scale of approximately 450t annually (Fitzpatrick 2006).It can be produced from hexoses in acidic media or from furfuryl alcohol via ring-opening (Otsuka et al.1973;Bernd and Guy 1992;Timokhin et al.1999).Furfuryl alcohol is obtained by the catalytic reduction of furfural.Furfural is exclusively produced from hemicelluloses contained in sugar cane bagasse,corn cobs,rice,and oat hulls at an industrial scale with a worldwide production of 200,000–300,000t year -1;approximately 70%are produced in China (Corma et al.2007;Mamman et al.2008).A comprehensive pro-duction of furfural and levulinic acid from LCF appears to be feasible via the Biofine process.The current production of 5-hydroxymethyl furfural occurs by hydroxymethylation of furfural with formaldehyde (Corma et al.2007).A com-mercial process for its manufacture through the sugar route has not been developed because achieving reasonable yields requires strong acids and organic solvents that would neces-sitate costly neutralisation and separation processes.Further-more,glucose as a starting material shows relatively low reactivity,while the more reactive fructose (10007t -1)and inulin (5007t -1)would entail a market price of 5-HMF of at least 25007t -1;this price is too high for a bulk-scale chemical compound (Corma et al.2007).5-HMF secondary products include 2,5-furan dicarboxylic acid,2,5-bis-(hydroxymethyl)furan,and 2,5-furandicarboxaldehyde as monomers for polyamides,polyesters and polyurethanes.These reagents could replace petro-chemically derived com-pounds,such as terephthalic,isophthalic,and adipidic acid,and could hence be used in the production of consumer plas-tics as well as function as starting materials for the synthesis of pharmaceuticals and drugs.Therefore,5-HMF has a high potential industrial demand and is called ‘‘a sleeping giant’’(Bicker et al.2005).
Production of levulinic acid and furfural441
Table1Sources of lignocellulosic feedstock,LCF(Kamm et al.2006).
No.Source Examples for LCF
1Landscape Softwood,hardwood,residual wood and
species under-wood from forestry,reed grass,
switch grass,dry grasses,straw
2Fast-growing Poplar,willow,wood grass,eucalyptus,
plantations sudan grass
3Lignocellulose waste Straw,corn stover,press cake from crop
from agriculture,drying plant,ethanol plants and
forestry and industry oil mills,by-products from cereal mills,
whole crop refineries,paper mill and
pulp industry
4Used materials Timber,used wood,recovered paper,
and wastes cellulosic municipal solid waste
Levulinic acid and furfural
Levulinic acid Levulinic acid(4-oxopentanoic acid)is a linear C5-alkyl carbon chain containing one carboxylic acid group in position1and one carbonyl group in position4.It was first described by von Grote and Tollens(1875).The acid was obtained by heating sugar candy in equal amounts with concentrated acid in water for several days.Formations of formic acid and water,as well as large amounts of humin, were observed during the reaction.The authors gave this substance the name levulinic acid because the levorotary fructose,called levulose,was the reactant for the acid gen-eration.Previously,Malaguti(1836)and Mulder(1840) reacted sucrose with various concentrated and diluted acids without recognising the acid in question.
Later on,properties and various synthesis routes of levu-linic acid have been investigated extensively.It has never reached commercial use in significant volumes,although its potential as an industrial chemical intermediate has been recognised soon due to its exceptional reactivity by the virtue of the keto and carbonyl group and the high reactivity of its lactones(g-valerolactone and a-valerolactone).
Since1956,levulinic acid has been regarded as a platform chemical with high potential(Leonhard1956).However,the relatively cost-intensive production that proceeded through the dehydration of hexoses,formation of5-hydroxymethyl-furfural and successive cleavage of one-mole formic acid, foreclosed the possibility that levulinic acid chemistry could compete with other chemical intermediates derived from fossil raw materials.During the1970s,the attention was focussed again on levulinic acid as a chemical raw material (Kitano et al.1975;Schraufnagel et al.1975).An alternative and cost-efficient production directly from biomass was demonstrated by the Biofine process(Fitzpatrick1990,1997; Bozell et al.2000).It seemed that the problems concerning expensive raw material,low yields,excessive equipment costs,and physical properties detrimental to easy recovery and handling could be overcome.Since then,levulinic acid production is again in focus(Ghorpade and Hanna1999; Farone and Cuzens2000;Cha and Hanna2002;Fang and Hanna2002;Seri et al.2002;Chang et al.2007;Yan et al. 2008).The chemistry of levulinic acid(Timokhin et al.1999) and its derivatives(Manzer2006)were studied.
The U.S.Department of Energy identified levulinic acid by screening approximately300substances as one of the12 potential platform chemicals in the biorefinery concept(Wer-py and Peterson2004).The broad range of possible levulinic acid secondary products,many of high potential for indus-trial applications and as intermediates in organic chemistry, has been the fertile terrain of intense research efforts during the last decade.New synthetic routes that deliver chemical compounds of industrial relevance(Bozell et al.2000;Hayes et al.2006;Geilen et al.2010),specifically for application as solvents(Manzer2006),monomers(Isoda and Azuma 1996;Manzer2004;Brandenburg et al.2005;Manzer2006; Lange et al.2007),fuels and fuel additives(Texaco/NYSER-DA/Biofine2000;Hayes et al.2006;Huber et al.2006;Hor-vath et al.2008;Alonso et al.2010;Lange et al.2010; Serrano-Ruiz et al.2010),are developed continuously from research groups and important industrial companies all over the world.
The sale price of levulinic acid decreased from approxi-mately8.8–13$kg-1at454t year-1production in2005 (Bozell et al.2000;Fitzpatrick2006)to3.2$kg-1currently (Patel et al.2010).This trend indicates that the production volumes should have increased,although recent data on worldwide production volume could not be found.Economic projections indicate that by application of the Biofine proc-ess,the cost of levulinic acid production could fall to as low as0.08–0.22$kg-1depending on the scale of the operation (Bozell et al.2000).
Furfural Furfural(furan-2-carbaldehyde)contains a hete-roaromatic furan ring with a reactive aldehyde functional group at the C2position.It was first isolated by the German chemist Johann Wolfgang Do¨bereiner in1832.He observed that a small quantity of an ethereal oily substance,which was soluble in water and evaporated together with water,was formed as a byproduct of formic acid synthesis from sugar with manganese dioxide and sulphuric acid(Do¨bereiner 1832).In1840,the Scottish chemist John Stenhouse found that the same substance can be obtained by reacting sulphuric acid with a wide variety of plant materials like crop or saw dust of chaff;he also recognised its resin-forming tendency. Stenhouse(1840)determined the empirical formula to be
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C5H4O2,just as Fownes(1845)did.The latter scientist sug-gested the name furfurol,as Morson had done already5 years before.The ring structure of the furan group was estab-lished by the efforts of Baeyer(1877),Marckwald(1887) and Harries(1898).In1922,the Quaker Oats factory at Cedar Rapids commenced the commercial production of fur-fural.Furfural is a solvent in petrochemical refining to extract dienes from other hydrocarbons.Its derivative fur-furyl alcohol is used for resin formation either by itself or together with phenol,acetone or urea to make solid resins. Such resins are used in making fibreglass,aircraft compo-nents,and parts in the automotive sector.Furfural is further a chemical intermediate in the production of furan and tetra-hydrofuran.It was for several years the raw material for the production of Nylon6and Nylon6,6.The production of the monomer adiponitrile proceeded through decarbonylation to furan,successive hydrogenation to tetrahydrofuran,chlori-nation to1,4-dichlorobutane and replacement of chloride with cyanide.A comprehensive study on the production vol-umes and industrial use of furfural is given in a report of the Rural Industries Research and Development Corporation, Australia(Wondu Business and Technology Services2006), as well as by Mamman et al.(2008).
Furfural is considered a biomass-derived chemical inter-mediate of high potential;it is one of the13substances of the second-tier group of likewise viable chemical building blocks in the biorefinery concept individuated by the U.S. Department of Energy(Werpy and Peterson2004).The world market for furfural was estimated to be between 200,000t and300,000t annually(Wondu Business and Technology Services2006;Corma et al.2007;Mamman et al.2008)at a market price of approximately1$kg-1(Win 2005).Roughly,60–62%are used for furfuryl alcohol pro-duction(Mamman et al.2008).Approximately70%of fur-fural production is realised in China(Win2005;Wondu Business and Technology Services2006;Mamman et al. 2008)by predominantly widespread plants and relatively inefficient small-scale fixed bed processes(De Jong and Marcotullio2010);an exception is the Westpro modified Chinese Huaxia Furfural Technology,which applies fixed-bed reactors and continuous dynamic refining(Win2005). Commercially interesting furfural production processes, which are already operating or will be implemented in the near future,are described in the following.
An overview on levulinic acid and furfural production Levulinic acid synthesis from hexosanes A comprehen-sive overview on different preparation methods of levulinic acid is given by Timokhin et al.(1999).Starting from bio-mass carbohydrate raw material,the following two routes are possible:1)Acid treatment of hexoses such as glucose,fruc-tose,mannose or galactose from polymeric carbohydrates, such as cellulose,hemicelluloses,starch or mono-and disac-charides via formation of D-fructose and5-hydroxymethyl-furfural(5-HMF);2)Acidic treatment of pentoses such as xylose and arabinose from hemicelluloses to deliver furfural, followed by catalytic reduction to furfuryl alcohol and sub-sequent ring-opening in water(Otsuka et al.1973;Bernd and Guy1992).
Levulinic acid can be obtained by reacting fructose with any kind of acid at an increased temperature,following the reaction mechanism through the formation of5-HMF illus-trated in Figure2b.Fructose is present in sucrose and can be obtained by the isomerisation of glucose,and by hydrol-ysis of inulin or sucrose(Cronewitz and Munir1989).Glu-cose is the second building block of sucrose and is contained in other disaccharides such as maltose and cellobiose,which are cleaving products of amylose or starch and cellulose, respectively.Fructose can also be obtained by the isomeri-sation of mannose via glucose;however,this process is not used commercially.
The isomerisation of glucose into fructose proceeds through the endiol form by the use of immobilised glucose isomerase(Figure2a).Currently,the conversion of glucose for the production of high-fructose corn-syrups(HFCS)has become the largest immobilised biocatalytic process world-wide,with an annual production exceeding8=106t year-1 (Moliner et al.2010).
Heterogeneous isomerisation catalysts for glucose-fructose isomerisation that could integrate the acid catalysis of fruc-tose into the valuable chemical intermediates5-HMF and levulinic acid were also subject of a study(Moliner2010) and could provide a new breakthrough in carbohydrate chemistry for chemical raw material production from biomass.
Levulinic acid production from fructose proceeds through the formation of5-HMF(Figure2b),where the yield and reaction velocity depend on the nature of the acid,acid con-centration,temperature,pressure,and the type of solid-state acid catalyst implied.Several kinetic studies starting from glucose were published.Even if the reaction mechanism was not fully clear and several reaction intermediates were found, the authors(Wiggins1949;McKibbins et al.1962;Moye 1964;Feather and Harris1973;Schraufnagel and Rase1975) are in accordance that:1)the carbohydrate is first hydrolysed by acid catalysis to form glucose;2)5-HMF is the inter-mediate formed from D-Fructose by an overall1st order reac-tion via successive dehydration steps;and3)5-HMF is finally hydrated and cleaved into levulinic and formic acid in equal molar ratios(Timokhin et al.1999).Grethlein (1978)posted a complicated reaction scheme for the con-version of lignocellulosic feedstock to levulinic acid on a molecular level.Timokhin et al.(1999),and also other authors(Kochetkov et al.1967;Horvat et al.1985,1986; van Dam et al.1986),reported detailed reaction schemes for the formation and degradation of the5-HMF intermediate. Most important findings of recent kinetic studies were as follows:
?Humin formation(Girisuta et al.2006)and a higher glu-cose decomposition rate(Chang et al.2006)were favour-ed at higher temperatures;increasing HMF formation occurred with increasing temperature and acid concentra-tion(Chang et al.2006);and increasing selectivity of levulinic acid formation occurred by raising the acidity at lower temperatures around1008C,whereby large differ-
Production of levulinic acid and furfural443
Figure2(a)Isomerisation of glucose into fructose via the endiol form.(b)Formation of levulinic acid from fructose.(c)Formation of furfural from xylose.(d)Formation of g-valerolactone by catalytic hydrogenation of levulinic acid.(e)Catalytic hydrogenation of g-valerolactone and successive cyclisation of1,4-pentanediol to2-methyl tetrahydrofuran.(f)Possible reaction pathways for the conversion of levulinic acid to levulinic acid esters.(g)Catalytic reduction of furfural and successive esterification of furfuryl alcohol to levulinic acid esters.(h)Reaction of GVL to valeric acid by acid-catalysed ring-opening to pentenoic acid and successive hydrogenation.(i)Transester-ification of GVL with methanol via the formation of the hydroxy pentenoate intermediate(Lange et al.2007).
444G.Dautzenberg et al.
ences were found in the activity of the implied acids.HCl was found to be12times more active than H2SO4at nearly equal selectivity,while H3PO4was too weak for application as a catalyst(Tarabanko et al.2002).?Two different reaction regimes for the conversion of car-bohydrates containing biomass into levulinic acid that dif-fer in the reaction conditions,but not essentially in the reaction pathway,can be distinguished:1)the dilute acid treatment at high temperature and pressurised atmosphere;
and2)the treatment with highly concentrated acid at low-er temperatures and normal pressure.The low temperature treatment of hexosanes delivers the maximum levulinic acid yield of65%of theoretical based on hexose content.
The high temperature treatment of cellulose and starch delivers maximum yields of approximately70–80%of the theoretical quantity based on polymeric hexose content.
Dehydration process at low temperature and high acid concentration Hydrolysis of cellulose to hexoses at atmospheric pressure is typically performed with strong acids (HCl,H2SO4)at approximately1008C.In a second step,the resulting hydrolysate is heated to1108C with20%HCl and remains at this temperature for24–48h.Free halogens,tran-sition metals,and anion-exchange resins can accelerate the reaction(Timokhin et al.1999).The reaction mixture is fil-tered to separate humin compounds and concentrated.Levu-linic acid is isolated by distillation at reduced pressure or by extraction with ether,ethyl acetate or ethyl methyl ketone. The yield of levulinic acid is approximately40%with respect to the hexose content.
Dahlmann(1968)reacted the polymeric hexoses in1:10 ratio with20%HCl at1088C for6–8h.Humin compounds were filtered and the reaction mixture was concentrated to one-fifth of the initial volume by distilling of the HCl.An appropriate solvent was added to the reaction mixture for levulinic acid extraction.After extraction,the solvent was distilled off and the levulinic acid was distilled at reduced pressure.Dahlmann reported a yield of65%of the theoret-ical based on hexose content.
Ion-exchange resins were also tested as acid catalysts (Redmon1956;Schraufnagel and Rase1975),but the reac-tion rates were low.
Dehydration process at high temperature,increased pressure and low acid concentration When the reaction is performed at higher temperatures and under increased pressure,the reaction time is shorter and allows for lower concentrations of the acid.There are different statements on the effectiveness of the various acids.The effectiveness of the various acids differs with the kind of raw material used (Efremov et al.1997).However,at dilute conditions,strong acids(HBr)HCl)H2SO4)acetic acid)appear to perform better(Ghorpade and Hanna1997).Zeolites were found to manifest high catalytic activity in the preparation of levulinic acid from glucose and fructose during the high temperature conversion(Lourvanij and Rorrer1993;Lourvanij and Ror-rer1997;Zeng et al.2010).Recently developed processes attained levulinic acid yields of approximately60–80%of the theoretical yield based on polymeric hexose content of the starting LCF material(Fitzpatrick2006;Hayes et al. 2006;Yan et al.2008).The only pilot plant for the produc-tion of levulinic acid from biomass raw material at a com-mercial scale is the Biofine process,which is reported below. Furfural production from pentosanes No synthetic route exists for the production of furfural;it is produced exclusively from biomass feedstock.Furfural is obtained industrially by a variety of processes from pentosane-rich sugar cane bagasse,corn cobs,and rice and oak hulls.Fur-thermore,it could be obtained as a side product of the hemi-cellulosic fraction,namely the polymeric pentoses of xylose and arabinose,in the production of levulinic acid from ligno-cellulosic feedstock.The reaction pathway involves acid hydrolysis of hemicelluloses,such as pentosanes or xylans into monomeric pentoses(xylose and arabinose)or xylose, and successive cyclodehydration of the latter to form furfu-ral,according to Figure2c.
Currently,yields of the earlier established commercial processes(Quaker-Oats,Agrifurane,Rosenlew,Escher Wyss, Batch process operated in China)that run at temperatures below2008C amount to approximately40–50%of the the-oretical yield of72.7%w/w,based on pentosanes content of the starting material(Zeitsch2000a).The processes differ primarily by the operational mode,batch or continuous pro-cess,and reaction temperature.Zeitsch(2000a)observed that there was a large difference in furfural yield between the industrial processes(approx.50%)and the analytical deter-mination of the pentose content through furfural formation, known as the sealed ampule process(100%).The author attributed the difference to the reactions that furfural under-goes in the liquid reaction medium.In the case of conven-tional industrial processes,the reaction medium does not boil,and furfural remains in the liquid phase.In the presence of the acid catalyst,it can react with itself or intermediates from the pentosane-furfural conversion.Alternatively,in the analytical process,the reaction medium boils and furfural cannot dissolve.It is stripped off from the liquid into the vapour phase where no acid catalyst is present.
All recently developed processes aim at the diminution of side-reactions in the liquid phase,although in a different manner.They operate at temperatures at approximately 2008C,or favourably,at230–2408C.At increasing temper-atures,the‘‘entropy effect’’in the reaction medium works against the formation of larger molecules,such as the furfural condensation products.Examples of such processes are the Supratherm process,developed by Krupp,and the Stakes process,developed by the Canadian company Stake Tech-nologies(Zeitsch2000a).
A decisive step forward in the furfural production was performed by Zeitsch(1999,2000a),who invented the Suprayield process patented by International Furan Technol-ogy Ltd.,South Africa(Zeitsch2000b).The process tech-nology was recently owned by Proserpine Corporative Sugar Milling Association Ltd.,Australia.In this process,the liquid phase is heated with steam for a short time to2408C.During
Production of levulinic acid and furfural445
heating,the steam condenses and increases the moisture con-tent of the reactor charge.By gradually reducing the pressure in the reactor below the vapour pressure of the liquid,the liquid is forced to boil and furfural is stripped off from the reaction solution.As the vapour is flashed from the liquid phase,the solution cools and its vapour pressure decreases, making it necessary to continue lowering the reactor pressure in a carefully controlled fashion.Yields of the Suprayield process are reported to be approximately70%of the theo-retical yield.Proserpine Mills in Australia had planned to start production of furfural by the Suprayield process with a production of5000t year-1in2009.Additionally,the India Arcoy Biorefinery Private Ltd.is planning a furfural plant at 11,000t year-1(De Jong and Marcotullio2010).
The Multi-Turbin-Column(MTC)process developed by De Jong and Marcotullio(2010)at the Technical University of Delft,analogously to the Suprayield process,attempts to improve the furfural yield through the reduction of loss reac-tions by continuous removal of furfural from the liquid phase.This goal is realised by a reactor configuration in which the acidified raw material slurry(LCF such as straw) enters the reactor in counterflow to the steam that is intro-duced from the bottom of the reactor.To prevent reactions of furfural with organic acids that were stripped off with the steam from the reaction fluid,extractions with toluene and distillation at reduced pressure are used for separation and purification of furfural.Assuming a plug flow behaviour for the reactor,possible yields higher than86%were calculated for a residence time of24.6min.In this process,5-HMF can also be separated from furfural as a bottom product.After acid recycling,cellulose and lignin are obtained as residues and should be further valorised to added value products to improve the economics of the process.
Verdernikov(1996,1998a,b)has patented a single-step furfural process including a two-step selective acid catalysis of pentosane-rich materials,such as wood,for which he claims yields of70–80%.According to his mechanistic stud-ies,pentosanes are first hydrolysed by acetic acid,which is formed during the treatment of wood with steam.The pen-toses diffuse from the inside to the surface of the wood par-ticles and are dehydrated to furfural at an increased rate under the influence of concentrated strong acids,such as sulphuric acid,when compared to diluted acids(Gravitis et al.2000,2001).The authors reported that,by applying this technology,the degree of cellulose degradation is reduced by a factor of5.In this process,the cellulosic residues are con-templated for further chemical processing into valuable prod-ucts,such as levoglucosan and bioethanol.The authors report that a plant in Russia based on their technology produces 4300t furfural and8800t ethanol annually. Lichtenthaler(2002)observed that furfural appears to be the only unsaturated large-volume organic chemical that is able to compete with low-cost,fossil fuel-based materials. Vedernikov considers that furfural production alone is a doubtful process(Wondu Business and Technology Services 2006).A good overview on existing biomass-based furfural co-production processes is provided by De Jong and Mar-cotullio(2010).Production of levulinic acid and furfural by the Biofine process A breakthrough in levulinic acid production from LCF was achieved by the inventor Fitzpatrick(1990,1997) of the Biofine process.The process technology was de-scribed in detail by Fitzpatrick(2006);and Hayes et al. (2006).In the process,a novel reactor configuration is used that promotes levulinic acid production at high temperature through acid-catalysed hydrolytic breakdown of cellulose to form levulinic acid while reducing char formation.Yields of levulinic acid from cellulose with H2SO4as an acid catalyst exceeded70%of the theoretical yield based on hexose poly-mer content.The reactor system consists of a plug flow reac-tor followed by a completely mixed reactor.The conditions of210–2208C,25bar gauge pressure,12s residence time, acid concentration between1.5and3%,in the first state favour the dominant first order reaction of acid hydrolysis of cellulose and hemicellulose to soluble hexoses and pen-toses intermediates.The completely mixed conditions in the second-stage reactor favour the first-order reaction sequence leading to levulinic acid at the expense of the higher-order condensation reactions leading to tar(Fitzpatrick1990, 1997).Typical conditions include a continuously-stirred tank reactor(CSTR)mixing configuration,190–2008C,1.5–3% acid concentration,14bar gauge pressure,and20min resi-dence time.Additionally,the reaction conditions in the first stage,followed by vapour separation in the second lower-pressure stage,favour high yields of furfural from the hemi-cellulosic fraction of the feed.Advantages of the Biofine process over other technologies are:1)a short residence time and a small reactor volume at high throughput,2)high feed-stock flexibility within a wide range of low-grade variable composition cellulosic feedstock,3)continuous process con-trol,and4)ease of scale-up.The process uses low-cost acid catalyst that is recycled within the process.By using only dilute mineral acid-catalysed hydrolysis,the process is unaf-fected by contaminants often found in waste feedstock and is very robust.Finally,the process is reported to be energy self-sufficient(Fitzpatrick2006).
The process technology is reported to be mature enough for industrial implementation.Several development phases have been passed:a first reactor system was installed at Dart-mouth College in New Hampshire under a grant from Bio-fine and NYSERDA and operated in the period from1988 to1996.In1997,the reactor system was scaled up to process 1dry t day-1of biomass in a pilot plant built at Epic Ven-tures,Inc,South Glens Falls,New Y ork.This project dem-onstrated that high yields of levulinic acid of approximately 70–80%based on the theoretical maximum yield of71.6% w/w of levulinic acid on hexose polymer content(the remainder accounts to formic acid)were obtainable in a mul-ti-day operation on a larger scale.Approximately50%of the mass of hexosanes is converted to levulinic acid,20%to formic acid and30%is converted to tars(Hayes et al.2006). Yields of furfural in the Biofine process are reported to be approximately70%of the theoretical value of72.7%w/w based on pentose polymer content of the biomass feedstock implied;it is equivalent to50%of the mass of pentosanes (Hayes et al.2006).In2006,the1t day-1plant was moved
446G.Dautzenberg et al.
Table 2Reaction conditions,yields,selectivity,and conversion for the catalytic hydrogenation of levulinic acid into GVL.
c LA p H2T WHSV t Yiel
d Conver.Select.Catalyst (m%)(bar)(8C)(h -1)(h)(%)(%)(%)Reference
Ru (5%)/C
5035150 4.8n.r.n.r.n.r.96(Serrano-Ruiz et al.2010)5035150n.r.4n.r.10097(Manzer 2004)512130n.r. 2.6n.r.9299(Yan et al.2009)
Ru (5%)/Al 2O 3n.r.145150n.r.2n.r.99.599.7(Manzer and Hutchenson 2004)Ru (5%)/SiO 275100200n.r.n.r.99n.r.n.r.(Bourne et al.2007)Ru (acac)3
270140n.r.1295n.r.n.r.(Mehdi et al.2008)Ru (acac)3/P(nOct)3n.r.100160n.r.1899n.r.n.r.(Geilen et al.2010)Ru (CO)4I 2n.r.100150n.r.8n.r.85n.r.(Braca et al.1991)RuCl (PPh 3)315.8
12180n.r.248699n.r.(Osakada et al.1982)Pt (1%)/TiO 25=10-3mol/mol H 2
402000.5–15n.r.n.r.n.r.)95(Lange et al.2010)Re (black)
100150106n.r.1871n.r.n.r.(Broadbent et al.1963)ReO 2=2,5H 2O 100200152n.r.12)99100n.r.(Broadbent et al.1963)PtO 2
28324n.r.4487n.r.n.r.(Schu ¨tte and Thomas 1930)Raney-Ni n.r.60220n.r.394n.r.n.r.(Christian et al.1947)Ni-Kat
n.r.
62
185
n.r.
4.5
93
n.r.
n.r.
(Kyrides et al.1945)
n.r.s not reported.
to its current location in Gorham,Maine,where the plant is capable of sustained multi-day operations at a 2t day -1capacity.The plant was designed for development,process testing and feedstock evaluation but not for production.A 50t day -1facility is currently being planned for Old Town,Maine,and will use forest biomass from the same sources that supply large biomass-fired power plants throughout the region.That facility will be focused on large-scale produc-tion of ethyl levulinate for use as home heating oil (Oil and Energy Magazine 2009).
The first commercial plant that was based on the Biofine technology was built in Caserta,Italy,by Le Calorie S.p.A.in 2006,and had planned LCF (waste sludge from tobacco and paper industry)processing volumes of initially 50t day -1,bringing the total capacity to 300t day -1(Hayes et al.2006).
Fuels and fuel additives from levulinic acid and furfural The over-functionalisation of lignocellulosic feed-
stock and primary derived chemicals,such as the presence of hydroxyl,keto and carboxyl groups,i.e.,the high content of oxygen and thus the lower energy content is not favou-rable for fuels or fuel additives.However,because LCF is the only true sustainable raw material source without con-curring human nutrition,intense efforts are undertaken,in addition to the improvement of the energetic aspects of the syngas and FTS-process for synthesis of synthetic biomass-based fuels.Levulinic acid is one of the focus,because it appears that the implementation of the Biofine process,in which formic acid and furfural are obtained as side-products in large quantities,could make it to a largely accessible chemical raw material.Furfural can be converted through catalytic reduction to furfuryl alcohol,which opens two acid-catalysed reaction scenarios.Ring-opening in water delivers levulinic acid (Otsuka et al.1973;Bernd and Guy 1992)and esterification with selected biomass-derived alcohols would yield levulinic acid esters that can be used directly as fuel
(Hsu and Chasar 1980;Khusnutdinov et al.2007;Van De Graaf and Lange 2007).
To date,it has been shown that,in addition to alcohols (ethanol,butanol)and ethers (methyl tetrahydrofuran,terti-ary and secondary ethers),esters,depending of their molec-ular weight,are also suitable as fuel additives for both gasoline and diesel.A comprehensive overview on current progress follows.
g -Valeolactone (GVL)g -valerolactone (GVL)is obtained
from levulinic acid by catalytic hydrogenation (Figure 2d).Manzer et al.(2004)investigated a wide range of metal catalysts.Ruthenium was determined to be the catalyst that showed the best selectivity and led to the highest yields at comparable reaction conditions and substrates (carbon).Sev-eral catalysts,predominantly ruthenium-based,and different substrates were investigated.Depending on the catalyst sys-tem and the reaction conditions (H 2pressure,temperature,levulinic acid concentration,residence time),yields of up to 99%with a selectivity of almost greater than 95%were obtained (Table 2).
Considering the relatively uncomplicated process and high yields of GVL-production,Horvath et al.(2008)investigated the applicability of GVL as a biofuel additive.The authors suggested an admixing of 10%to gasoline.A benefit is the lower vapour pressure of GVL in comparison to other oxy-genates,such as methanol,ethanol,MTBE,and ETBE.GVL has a higher energy density compared to ethanol and it shows chemical stability under normal conditions (hydrolysation to g -hydroxypentanoic acid was excluded),no peroxide for-mation,and the absence of corrosion problems.In addition,GVL can be converted to 2-methyltetrahydrofuran (MTHF),which has already been considered as a renewable compo-nent of an alternative fuel mixture (Paul 1996;Alternative Fuel Transportation Program 1998).It is the chemical inter-mediate for other interesting biofuel additives reported later in this review.
Production of levulinic acid and furfural447
2-Methyl tetrahydrofuran(MTHF)2-Methyl tetrahydro-furan can be obtained from GVL by catalytic hydrogenation and successive thermally-or acid-induced ring closure of the formed intermediate,1,4-pentanediol(Figure2e).It can also be obtained by a single process that passes through the dif-ferent reaction steps described by the use of a bimetallic catalyst and hydrogen directly from levulinic acid.
Yields of nearly90%were achieved by the direct conver-sion of levulinic acid in the presence of a bimetallic catalyst on a carbon substrate of the composition Re(5%)/Pd(5%)/ carbon with100%conversion and selectivity of89.5%(Elli-ott et al.1999).
Several attempts were made to obtain2-MTHF by liquid-phase hydrogenation from furfural.All of them delivered the product in low yields.However,catalytic hydrogenation by a continuous vapour-phase process was claimed to be com-mercially viable in a patent by Ahmed(2005).
According to Lucas et al.(1993),2-MTHF can be admixed to conventional gasoline up to60%without requiring engine https://www.doczj.com/doc/854003477.html,pared to conventional fuels,2-MTHF shows a reduced ozone building potential and reduced emis-sions(approx.1/3less).Primary drawbacks of MTHF include the high polarity that leads to swelling of elastomers in the tank and pumping equipment,the formation of per-oxides and high vapour pressure(Hayes et al.2006). Levulinic acid esters Esters of levulinic acid,particularly ethyl levulinate,were suggested by the inventors and ope-rators of the Biofine processes as oxygenating additives for transportation fuels and for heating purposes.The esters can be obtained by esterification of levulinic acid via heteroge-neous acid catalysis(Drehpfahl and Gross1955)or by an acid-catalysed reaction of a-angelicalactone(Manzer2006) with the respective alcohols.The synthesis from a-angeli-calactone and olefins was also reported(Fagan and Manzer 2006).The three synthetic routes are reported in Figure2f. Levulinic acid esters can also be obtained from furfural through catalytic reduction to furfuryl alcohol and acid-cata-lysed esterification with the respective alcohols(Hsu and Chasar1980;Khusnutdinov et al.2007;Van De Graaf and Lange2007),as shown in Figure2g.Texaco,in collaboration with the Biofine operators,developed an oxygenated diesel blend that contains79%petrodiesel,20%ethyllevulinate and 1%of an unspecified coadditive(Texaco/NYSERDA/Biofine 2000;Hayes et al.2006).This blend can be used by con-ventional diesel engines and shows,likewise oxygenated gasoline,cleaner combustion.When compared to diesel,a decrease in soot particle emission is observed.The good lubrication properties of the blend positively influence the engine’s life span.
Valeric acid esters Recently,Lange et al.(2010)and Ser-rano-Ruiz et al.(2010)have synthesised valeric,or penta-noic,acid from levulinic acid via the formation of GVL.The reaction proceeds through an acid-catalysed ring-opening to pentenoic acid and a successive catalysed hydrogenation and is illustrated in Figure2h.Both reaction steps can be per-formed in a single process(Lange et al.2010).
Valeric acid was successively esterified with various alco-hols(methanol,ethanol,propanol,pentanol,ethylene glycol, propylene glycol,glycerol)by Lange et al.(2010).All esters showed promising properties for applications as oxygenating fuel additives for gasoline and/or diesel.Lower valeric alkyl-esters are reported to be suitable for blending with gasoline, while higher valeric alkylesters,like pentylvalerate and the di-and tri-valerates from ethylene and propylene glycol and glycerol,appear to comply with the requirements for diesel fuel.The lower cetane number of di-and tri-valerates limits however their use in reasonable quantities.
Compared with levulinic acid esters,the valeric acid esters have a higher energy density due to the higher C/O ratio. These esters are lower in polarity and are thus less miscible with water;they are more miscible with hydrocarbons of higher chain length,like those present in diesel fuel.Lower polarity has positive effects on the durability of elastomers, which are used in the tank and line system.Polarity,volatil-ity,ignition properties and flow characteristics can be adjust-ed for the needs of the fuel type,gasoline or diesel,by the chain length of the alcohol that is used for esterification. Thus,butyl and pentyl esters of valeric acid show ignition properties and flow characteristics that are even more com-patible with diesel fuel than are the fatty acid methyl esters that are derived from plant oil and currently used as diesel additive up to7%.Drawbacks of valeric acid esters,com-pared to FAME,include a lower energy density.
Ethyl valerate was studied in depth as a gasoline additive at concentrations between10and20%.In particular,the authors investigated a gasoline blend that contained ethyl valerate at15%.It is reported that no measurable drawbacks on engine performance and driving behaviour,pollutant emission,corrosion and gum formation were observed.Pos-itive effects observed included an increase in octane number (RON and MON)and a reduction of the volatility of blends (Lange et al.2010).
The target of current research efforts is the integration of the different reaction steps for the production of valeric acid esters into a single process by the use of combined hydro-genation and acid catalysis.The applied and suggested mul-tifunctional catalysts are composed of metal(Pt,Pd,Rh, Ru)-supported catalysts,whereby the substrate is also the acidic catalyst(SiO2-bound zeolite like H-ZSM-5,amor-phous silica alumina ASA or solid acid oxides,like TiO2, Nb2O5,or ZrO2).
Pentenoic acid esters Alkyl pentenoates are obtained by catalytic transesterification of g-valerolactone(Hoelderich et al.1991;Lange et al.2007),as shown in Figure2i.They can be successively hydrogenated to alkyl valerates.Based on thermodynamic calculations,Lange et al.(2007)sug-gested a reaction mechanism through the formation of a hydroxy pentenoate intermediate,and they consider the route through ring-opening of GVL to pentenoic acid and succes-sive esterification as less likely.
Esterification with methanol delivers methyl pentenoate in form of a mixture of different isomers at yields up to98% (Lange et al.2007).During the reaction,methyl pentenoate
448G.Dautzenberg et al.
is continuously distilled off to shift the reaction equilibrium in favour of the ester.Ethyl pentenoate was obtained in sig-nificantly lower yields.However,the authors found that it shows properties that make it suitable for application as a gasoline additive.The octane number of ethyl pentenoate is reported to be higher than the one of ethyl valerate(Lange et al.2010).In general,it appears that esterification with higher alcohols proceeds only at low yields and a high num-ber of side products(ether,higher alkyl pentenoates).Dif-ferent homogenous and heterogeneous acid catalysts were tested in which the initial catalyst activity was correlated with the acidity of the catalyst.The acidity ranked from H2SO4)p-toluene sulphonate,in the case of homogenous catalysis,and Nafion NR50)zeolithes)amorphous silica-aluminate(ASA),in the case of heterogeneous catalysis. Conclusion
The lignocellulosic feedstock biorefinery concept and related technologies focus on the efficient co-production of consum-er products,platform or base chemicals,specialty chemicals, and fuels from the LCF components such as cellulose,hemi-celluloses,and lignin.
Two main approaches can be distinguished.1)Hemicel-luloses,cellulose,and lignin are fractionated previous to chemical conversion of its monomers.Examples include the organosolve pre-treatment,in the case of the Lignol Biore-finery Technology(Arato et al.2005),or organic acid hydrol-ysis,such as the CIMV process(Avignon and Delmas2008; Delmas and Benjelloun-Mlayah2008).2)One or more of the LCF constituents can be processed directly by a multi-step technology into one or more products,whereas the other constituents can be considered as side products or residues that should be converted into valuable products,depending on the level of degradation.Examples for the second approach include the acid hydrolysis of hemicelluloses and/ or cellulose,followed directly by the dehydration of the car-bohydrate monomers,such as the Vernikov and Biofine processes.
High potential to be platform chemicals have levulinic acid and furfural,which can be produced from hexosanes and pentosanes,respectively.These sugars are contained in large quantities in lignocellulosic raw material,in particular hard wood,straw,residues from sugar cane,corn,oak and rice processing.Currently levulinic acid is produced only on a small scale.Recently,the fuel industry envisaged levulinic acid as a starting material for the synthesis of potential fuels and fuel additives for the transportation sector.Today,the only process for levulinic acid production from biomass, which has been proven for several years in pilot plants of different size and appears to be feasible for use on a com-mercial scale,is the Biofine process.Furfural has been pro-duced from pentosane-rich raw material in50%yields of the theoretical yield at an industrial scale since1922.Several processes with improved yields,20–30%higher than the cur-rent yields,have been developed over the last20years and should be implemented commercially in the near future.Additionally,a variety of approaches to co-produce furfural from the hemicellulosic fraction of LCF(sugar cane bagasse, corn cobs,oak and rice hulls,straw and hard wood)with other secondary products of the cellulosic fraction exist and have been summarised by De Jong and Marcotullio(2010). Acid catalysis plays a prominent role both in biomass frac-tionation by chemical hydrolysis and in levulinic acid and furfural secondary chemistry,where it is often combined with hydrogenation catalysis for the synthesis of fuels or fuel additives.The input of strong acids,such as sulphuric acid or hydrochloric acid,implicates environmental and mainte-nance problems due to their corrosive and highly toxic nature.Accordingly,improvements are necessary and should be researched for including solid acid catalysis.In particular, heterogeneous bifunctional catalysts for combining hydro-genation and acid catalysis need to be developed. Acknowledgement
Dedicated to Michael Kamm,Founder of biorefinery.de GmbH. References
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