Article

Advances in conversion of hemicellulosic biomass to furfural and upgrading to biofuels

Catalysis Science & Technology (Impact Factor: 4.76). 01/2012; DOI: 10.1039/c2cy20235b

ABSTRACT Recent approaches to furfural synthesis from hemicellulosic biomass and pentose sugars with both homogeneous and solid acidic catalysts have been summarized by addressing the associated sustainability issues. The features of deconstruction of hemicellulosic biomass by acid hydrolysis to produce pentose sugar feedstock for furfural have been discussed in brief. Several strategies including solvent extraction in a biphasic process, application of surface functionalized materials such as acidic resins, mesoporous solids and mechanistic insight in limited cases are discussed. The present status of the promising furfural platform in producing second generation biofuels (furanics and hydrocarbon) is reviewed. The performances of each catalytic system are assessed in terms of intrinsic reactivity and selectivity toward furfural production. Overall, this minireview attempts to highlight the scope of further developments for a sustainable furfural process and upgrading to fuels.

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    ABSTRACT: The production of furfural from the C5 monosaccharides xylose, arabinose and ribose, as well as from real biomass (corn fiber), was studied using H-Beta zeolite as catalyst in a monophasic system with the biomass-derived solvent, gamma-valerolactone. Due to the combination of Brønsted and Lewis acid sites on this catalyst (Brønsted:Lewis ratio = 1.66), H-Beta acts as a bifunctional catalyst, being able to isomerize (Lewis acid) and dehydrate (Brønsted acid) monosaccharides. The combination of Lewis and Brønsted acid functionality of H-Beta was shown to be effective for the isomerization of xylose and arabinose, followed by dehydration. While no advantages were found in the conversion of xylose, higher furfural yields were achieved from arabinose, using H-Beta, 73 %, compared to sulfuric acid (44 %) and Mordenite (49 %). The furfural yields from corn fiber for H-Beta, H-Mordenite and sulfuric acid were 62, 44, and 55 %, respectively, showing that H-Beta is particularly effective for conversion of this biomass feedstock composed of 45 wt% hemicellulose, of which 66 % is xylose and 33 % arabinose.
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    ABSTRACT: Furfural (FFR) was selectively hydrogenated in a single pot to tetrahydrofurfuryl alcohol (THFAL) over a Si− MFI molecular sieve supported Pd catalyst. Studies on catalyst screening revealed that both the metal function and the support were critical for directing the selectivity to the ring-hydrogenated product, THFAL. The structural feature of MFI as shown by XRD was completely retained in the used sample of the 3% Pd/MFI catalyst confirming its stability under reaction conditions. XRD, along with SEM characterization of the used samples, established retention of morphology of the structured silicate, suggesting a strong interaction between hexagonal porous silicate and Pd particles. The complete conversion of FFR with an enhanced selectivity of 95% to THFAL could be achieved by recycling the crude of the first hydrogenation experiment over the same 3% Pd/MFI catalyst. In the era of continued depletion of fossil resources, extensive research is focused on catalytic conversion of biomass as it forms a basis for sustainable production of energy and chemicals. 1−3 However, biomass-derived molecules contain high oxygen content; hence, novel catalysts for efficient protocols are being investigated for selectively tailoring their oxygen content to achieve the desired product mix. 4−6 In this context, furfural (FFR) is a highly attractive molecule derived from defunction-alization of the most abundantly available lignocellulose for the production of fuels and chemical intermediates. 7−10 FFR is mainly produced by acid hydrolysis of pentose sugars C5 (xylose, arbinose) followed by a loss of three water molecules. 11−15 It is a versatile carbohydrate-derived starting material for mainly aldol condensation and hydrogenation. 16,17 The catalytic hydro-genation of either side-chain carbonyl or ring or both gives a variety of useful products such as furfuryl alcohol (FAL), tetrahydrofurfuryl alcohol (THFAL), 2-methylfuran (2-MF), and 2-methyl tetrahydrofuran (2-MTHF). 18−23 One of these products, THFAL, is an environmentally acceptable "green" industrial solvent due to its biodegradable nature. 24,25 A variety of catalysts including both noble and non-noble metals have been reported for selective vapor as well as liquid phase hydrogenation of FFR. Noble metal catalyst systems reported for vapor phase hydrogenation of FFR under severe temperature and pressure conditions (200−300 °C and 100 bar H 2) yield not only the desired products but also a variety of byproducts including furan, tetrahydrofuran, and even ring-opening products, such as pentanol and pentanediols. 26−28 On the other hand, non-noble catalyst systems, mainly copper chromite, was most often employed in industry for the selective production of FAL from FFR in liquid as well as vapor-phase hydrogenation; however, it poses a serious drawback due to the highly toxic nature of Cr. 29,30 Although conventionally THFAL is produced by a two-step catalytic hydrogenation of furfural (FFR) via furfuryl alcohol over Cu−Cr and noble metal catalysts separately, 31 direct conversion of FFR to THFAL also has been attempted recently. Sitthisa et al. reported Cu, Pd, and Ni supported on silica, among which only 5% Ni/SiO 2 was found to give THFAL directly at 230 °C with 5% selectivity. 32 Enhanced selectivity of 26% to THFAL could be achieved using a homogeneous Ru(II) bis(diimine) catalyst, 33 while bimetallic transition metal catalysts showed only 4% selectivity to THFAL. 34 Higher THFAL selectivity of 38% was possible over a Raney nickel catalyst at a partial furfural conversion of 50%. 35 Recently, Tomoshige et al. proposed the total hydrogenation of FFR to THFAL in two steps, first step involving FFR conversion to FAL and then in the second step, FAL to THFAL, with 94% yield of THFAL. 20 In all these studies, optimum THFAL selectivity was either possible in a two-step strategy or at partial FFR conversion. There has been hardly any reports on direct conversion of FFR giving appreciable selectivity to THFAL, which could be only possible by structural modification of the catalyst and or the support. Zeolite, microporous crystalline aluminosilicate, has attracted extensive interest, owing to its uniform micropore size distribution, high thermal and hydrothermal stability, flexible
    ACS Sustainable Chemistry & Engineering. 10/2013; 2(2).

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