Acid hydrolysis of cellulose as the entry point into biorefinery schemes

Hydrolysis of cellulose over functionalized glucose-derived carbon catalyst in ionic liquid

A sulfonated carbon material was prepared by incomplete hydrothermal carbonization of glucose followed by sulfonation. The carbon material contained -SO(3)H, -COOH, and phenolic -OH groups, and exhibited high catalytic performance for the hydrolysis of cellulose. A total reducing sugar (TRS) yield of 72.7% was obtained in ionic liquid 1-butyl-3-methyl imidazolium chloride at 110 °C in 240 min reaction time. The effect of water on the hydrolysis of cellulose in the catalytic system was studied. A water content of less than 2% in the ionic liquid promoted the formation of TRS, whereas a water content of greater than 2% lead to a decrease in TRS. The sulfonated carbon material catalyst was demonstrated to be stable for five cycles with minimal loss in catalytic activity. The use of an ionic liquid with functionalized carbon catalyst derived from glucose provides a green and efficient process for cellulose conversion.

Nickel-promoted tungsten carbide catalysts for cellulose conversion: effect of preparation methods

A series of Ni-promoted W(2) C catalysts was prepared by means of a post-impregnation method and evaluated for the catalytic conversion of cellulose into ethylene glycol (EG). Quite different from our previously reported Ni-W(2) C/AC catalysts, which were prepared by using the co-impregnation method, the introduction of Ni by the post-impregnation method did not cause catalyst sintering, but resulted in redispersion of the W component, which was identified and characterized by means of XRD, TEM, and CO chemisorption. The highly dispersed Ni-promoted W(2) C catalyst was very active and selective in cellulose conversion into EG, with a 100% conversion of cellulose and a 73.0% yield in EG. The underlying reason for the enhanced catalytic performance was most probably the significantly higher dispersion of active sites on the catalyst.

Kinetic study of acid-catalyzed cellulose hydrolysis in 1-butyl-3-methylimidazolium chloride

In this paper, the kinetics of acid-catalyzed cellulose hydrolysis in ionic liquids (ILs) was investigated by using 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as the model IL. General kinetic equations for the formation of glucose as well as cellooligomers were constructed at a molecular level, assuming that cellulose is fully dissolved to form a homogenous solution and that the scission of the glycosidic bond occurs randomly within the cellulose chain. Experimental data were well fitted according to these equations. Variations of kinetic parameters in the presence of different water content indicated that water behaved also as a base to decrease the acidity of the reaction medium. More importantly, it offered a profile of the evolution of cellooligomers. These results provided insights into the detailed mechanisms of cellulose hydrolysis in a non-aqueous, homogenous environment and should be valuable for developing strategies to depolymerize lignocellulosic biomass.

Solid acid-catalyzed cellulose hydrolysis monitored by in situ ATR-IR spectroscopy

The solid acid-catalyzed hydrolysis of cellulose was studied under elevated temperatures and autogenous pressures using in situ ATR-IR spectroscopy. Standards of cellulose and pure reaction products, which include glucose, fructose, hydroxymethylfurfural (HMF), levulinic acid (LA), formic acid, and other compounds, were measured in water under ambient and elevated temperatures. A combination of spectroscopic and HPLC analysis revealed that the cellulose hydrolysis proceeds first through the disruption of the glycosidic linkages of cellulose to form smaller cellulose molecules, which are readily observed by their distinctive C-O vibrational stretches. The continued disruption of the linkages in these oligomers eventually results in the formation and accumulation of monomeric glucose. The solid-acid catalyst accelerated the isomerization of glucose to fructose, which then rapidly reacted under hydrothermal conditions to form degradation products, which included HMF, LA, formic acid, and acetic acid. The formation of these species could be suppressed by decreasing the residence time of glucose in the reactor, reaction temperature, and contact with the metal reactor. The hydrolysis of regenerated cellulose proceeded faster and under milder conditions than microcrystalline cellulose, which resulted in increased glucose yield and selectivity.

Peculiarities of β-pinene autoxidation

The thermal oxidation of the renewable olefin β-pinene with molecular oxygen was experimentally and computationally investigated. Peroxyl radicals abstract weakly bonded allylic hydrogen atoms from the substrate, yielding allylic hydroperoxides (i.e., myrtenyl and pinocarvyl hydroperoxide). In addition, peroxyl radicals add to the C=C bond of the substrate to form an epoxide. It was found that a relatively high peroxyl radical concentration, together with the high rate of peroxyl cross-reactions, make radical-radical reactions surprisingly important for this particular substrate. Approximately 60 % of these peroxyl cross-reactions lead to termination (radical destruction), keeping a radical chain length of approximately 4 at 10 % conversion. Numerical simulation of the reaction-based on the proposed reaction mechanism and known or predicted rate constants-demonstrate the importance of peroxyl cross-reactions for the formation of alkoxyl radicals, which are the precursor of alcohol and ketone products.

Hydrolysis of cellulose in SO₃H-functionalized ionic liquids

Influence of acidity and structure of ionic liquids on microcrystalline cellulose (MCC) hydrolysis was investigated. MnCl₂-containing ionic liquids (ILs) were efficient catalysts and achieved MCC conversion rates of 91.2% and selectivities for 5-hydroxymethyl furfural (HMF), furfural and levulinic acid (LA) of 45.7%, 26.2% and 10.5%, respectively. X-ray diffractometry indicated that catalytic hydrolysis of MCC in ionic liquids resulted in the changes to MCC crystallinity and transformation of cellulose I into cellulose II. SO₃H-functionalized ionic liquids showed higher activities than non-functionalized ILs. The simplicity of the chemical transformation of cellulose provides a new approach for the use this polymer as raw material for renewable energy and chemical industries.

On the Diels-Alder approach to solely biomass-derived polyethylene terephthalate (PET): conversion of 2,5-dimethylfuran and acrolein into p-xylene

Polyethylene terephthalate (PET) is a polymeric material with high global demand. Conventionally, PET is produced from fossil-fuel-based materials. Herein, we explored the feasibility of a sustainable method for PET production by using solely bio-renewable resources. Specifically, 2,5-dimethylfuran (derived from lignocellulosic biomass through 5-(hydroxymethyl)furfural) and acrolein (produced from glycerol, a side product of biodiesel production) were converted into the key intermediate p-xylene (a precursor of terephthalic acid). This synthesis consists of a sequential Diels-Alder reaction, oxidation, dehydration, and decarboxylation. In particular, the pivotal first step, the Diels-Alder reaction, was studied in detail to provide useful kinetic and thermodynamic data. Although it was found that this reaction requires low temperature to proceed efficiently, which presents a limitation on economic feasibility on an industrial scale, the concept was realized and bio-derived p-xylene was obtained in 34% overall yield over four steps.

Renewable chemicals: dehydroxylation of glycerol and polyols

The production of renewable chemicals is gaining attention over the past few years. The natural resources from which they can be derived in a sustainable way are most abundant in sugars, cellulose and hemicellulose. These highly functionalized molecules need to be de-functionalized in order to be feedstocks for the chemical industry. A fundamentally different approach to chemistry thus becomes necessary, since the traditionally employed oil-based chemicals normally lack functionality. This new chemical toolbox needs to be designed to guarantee the demands of future generations at a reasonable price. The surplus of functionality in sugars and glycerol consists of alcohol groups. To yield suitable renewable chemicals these natural products need to be defunctionalized by means of dehydroxylation. Here we review the possible approaches and evaluate them from a fundamental chemical aspect.

Saccharification of natural lignocellulose biomass and polysaccharides by highly negatively charged heteropolyacids in concentrated aqueous solution

Highly negatively charged heteropolyacids (HPAs), in particular H(5) BW(12) O(40) , efficiently promoted saccharification of crystalline cellulose into water-soluble saccharides in concentrated aqueous solutions (e.g., 82 % total yield and 77 % glucose yield, based on cellulose with a 0.7 M H(5) BW(12) O(40) solution); the performance was much better than those of previously reported systems with commonly utilized mineral acids (e.g., H(2) SO(4) and HCl) and HPAs (e.g., H(3) PW(12) O(40) and H(4) SiW(12) O(40)). Besides crystalline cellulose, the present system was applicable to the selective transformation of cellobiose, starch, and xylan to the corresponding monosaccharides such as glucose and xylose. In addition, one-pot synthesis of levulinic acid and sorbitol directly from cellulose was realized by using concentrated HPA solutions. The present system, concentrated aqueous solutions of highly negatively charged HPAs, was further applicable to saccharification of natural (non-purified) lignocellulose biomass, such as "rice plant straw", "oil palm empty fruit bunch (palm EFB) fiber", and "Japanese cedar sawdust", giving a mixture of the corresponding water-soluble saccharides, such as glucose (main product), galactose, mannose, xylose, arabinose, and cellobiose, in high yields (≥77 % total yields of saccharides based on holocellulose). Separation of the saccharides and H(5) BW(12) O(40) was easy, and the retrieved H(5) BW(12) O(40) could repeatedly be used without appreciable loss of the high performance.

Efficient hydrolytic hydrogenation of cellulose in the presence of Ru-loaded zeolites and trace amounts of mineral acid

The hydrolytic hydrogenation of cellulose in the presence of a bifunctional Ru-loaded zeolite and trace amounts of mineral acid shows excellent hexitol yields.