Solvent-Assisted Adsorption of Cellulose on a Carbon Catalyst as a Pretreatment Method for Hydrolysis to Glucose

Cellulose hydrolysis to glucose using a heterogeneous catalyst is a necessary step in producing bio-based chemicals and polymers. The requirement for energy-intensive pretreatments, such as ball milling, to increase the reactivity of cellulose is one of the major issues in this area. Here, we show that by using solvent-assisted adsorption as a pretreatment step, cellulose can be adsorbed on the surface of a carbon catalyst. For adsorption pretreatment, phosphoric acid (H3PO4) performed better than other solvents such as sulfuric acid (H2SO4), tetrabutylammonium fluoride/dimethyl sulfoxide (TBAF/DMSO) and 1-butyl-3-methylimidazolium chloride ([BMMI]Cl). Hydrolysis after the adsorption of cellulose and the removal of H3PO4 produced a 73% yield of glucose. Partial hydrolysis of cellulose in H3PO4 before adsorption increased the final glucose yield. The glucose yield was proportional to the number of weakly acidic functional groups on the carbon catalyst, indicating the reaction was heterogeneously catalyzed. In a preliminary lab-scale life-cycle analysis (LCA), greenhouse gas (GHG) emissions per kg of glucose produced through the hydrolysis of cellulose were calculated. The H3PO4-assisted adsorption notably reduces GHG emissions compared to the previously reported ball milling pretreatment

Mechanochemical Synthesis of a Carboxylated Carbon Catalyst and Its Application in Cellulose Hydrolysis

A carbon catalyst containing a high density of carboxyl groups was prepared by solvent-free mechanochemical oxidation of activated carbon by using persulfate salts as the oxidant. The mechanochemical oxidation preferentially oxidized the carbon to introduce carboxyl groups without incorporation of sulfonated groups. The material exhibited hydrophilic behavior and was easily dispersed in water. Upon mix-milling, the oxidized carbon showed good catalytic activity for the hydrolysis of cellulose, even at a low catalyst loading. Glucose was obtained in 85% yield from mix-milled cellulose in the presence of a trace amount of HCl after a reaction time of 20min

Unraveling the hydrolysis of beta-1,4-glycosidic bonds in cello-oligosaccharides over carbon catalysts

Carbon catalysts having weakly acidic groups are uniquely active for hydrolysis of cellulose to produce cello-oligosaccharides and glucose. Although adsorption of cellulose molecules on carbon is considered as the cause for this behavior, the effect of adsorption on the reaction is not well understood. In order to understand the underlying mechanism, we investigated the hydrolysis of cello-oligosaccharides with varying chain lengths over different catalysts. Carbon catalysts favored hydrolysis of larger oligosaccharides with an 11-fold increase in the reaction rate constant from cellobiose to cellohexaose. The activation energy required to cleave the glycosidic bonds was reduced concurrently with the increase in molecule size. Based on these data, in conjugation with the stronger affinity of adsorption for larger oligosaccharides, we propose that axial adsorption within the micropores of carbon causes conformational change in the structure of cello-oligosaccharide molecules, resulting in reduction of activation energy required to cleave the beta-1,4-glycosidic bonds. Consequently, this translates to the higher rate of reaction for larger cello-oligosaccharides and explains the high reactivity of carbon catalysts towards cellulose hydrolysis

Soluble Cello-Oligosaccharides Produced by Carbon-Catalyzed Hydrolysis of Cellulose

Cello-oligosaccharides are biologically important molecules that can elicit a defensive immune response in plants and improve the health of animals. Cellulose, a polymer of glucose linked by beta-1,4-glycosidic bonds, is an ideal feedstock for synthesis of cello-oligosaccharides. However, cello-oligosaccharides rapidly degrade under the conditions used for cellulose hydrolysis. Here, cellulose was hydrolyzed over a carbon catalyst in a semi-flow reactor to achieve a high yield of cello-oligosaccharides (72 %). The excellent activity of the oxidized carbon catalyst, the adsorption of cellulose on the catalyst, and the high space velocity of products in the reactor were essential. Moreover, a method for quantification of individual cello-oligosaccharides was developed, which suggested a reduction in the rate of hydrolysis with a reduction in chain length

Selective Oxidation of Furfural to Succinic Acid over Lewis Acidic Sn-Beta

Selective production of succinic acid from furfural with H2O2 over Sn-Beta, a pure Lewis acid catalyst, is reported. Under optimized reaction conditions, 53% yield of succinic acid was obtained, and the catalyst was recyclable. 2(3H)-Furanone was detected as an intermediate using H-1 nuclear magnetic resonance (NMR), HH correlation NMR spectroscopy, liquid chromatography-mass spectrometry (MS) and gas chromatography-MS. Kinetic modeling revealed that Baeyer-Villiger oxidation of furfural to 2(3H)-furanone was accelerated in comparison to other competing reactions in the presence of the pure Lewis acidic Sn-Beta catalyst. The Lewis acid density of the Sn-Beta catalyst was directly correlated to the formation rate of products, confirming a Lewis acid-catalyzed mechanism. Detailed characterization showed that Sn-Beta activates furfural by coordinating to the carbonyl group and does not activate H2O2. On the other hand, the parent HBeta-38 zeolite produced activated H2O2 in solution, which caused side reactions to produce maleic acid. Selectivity of Sn-Beta was also compared with that of TS-1, another Lewis acid zeolite, which produced maleic acid because of the ability of TS-1 to activate H2O2 as a hydroperoxy species. Therefore, Sn-Beta is a selective and reusable catalyst for succinic acid synthesis from biomass-derived furfural

Structure and activity of activated carbon functionalized with maleic anhydride by diels-alder reaction

Diels-Alder reaction is a useful method for modifying the surface of carbon materials. In this work, we functionalized activated carbon with a large number of carboxyl groups using the Diels-Alder reaction. Polyaromatic structure of activated carbon acted as a diene for addition of maleic anhydride (MA) that acted as a dienophile. Upon hydrolysis of the anhydride group in the adduct, vicinal carboxyl groups were formed. The formation of carboxyl groups by Diels-Alder reaction was proved by FTIR, solid-state C-13 NMR, CO and CO2 evolution from TPD and Boehm titration. Titration results showed that the number of carboxyl groups increased from 0.09 mmol g(-1) to 3.06 mmol g(-1). DFT calculation showed that the concave site of the armchair edge on carbon surface was the most favorable for the Diels-Alder addition. The formation of exo-adduct was preferred with a reaction energy (Delta E) of -24 kJ mol(-1). The synthesized catalyst was tested for acid-catalyzed hydrolysis of cellobiose. The catalyst showed higher activity than a catalyst prepared by oxidation in the presence of air

Hydrolysis of woody biomass by a biomass-derived reusable heterogeneous catalyst

Biomass is the sole carbon-based renewable resource for sustaining the chemical and fuel demands of our future. Lignocellulose, the primary constituent of terrestrial plants, is the most abundant non-food biomass, and its utilisation is a grand challenge in biorefineries. Here we report the first reusable and cost-effective heterogeneous catalyst for the depolymerisation of lignocellulose. Air oxidation of woody biomass (Eucalyptus) provides a carbonaceous material bearing an aromatic skeleton with carboxylic groups (2.1 mmol g(-1)) and aliphatic moieties. This catalyst hydrolyses woody biomass (Eucalyptus) to sugars in high yields within 1 h in trace HCl aq. Furthermore, after the reaction, the solid residue composed of the catalyst and insoluble ingredients of woody biomass is easily transformed back to fresh catalyst by the same air oxidation method. This is a self-contained system using woody biomass as both the catalyst source and substrate for realising facile catalyst preparation and recycling

Mechanochemical Synthesis of a Carboxylated Carbon Catalyst and Its Application in Cellulose Hydrolysis

A carbon catalyst containing a high density of carboxyl groups was prepared by solvent-free mechanochemical oxidation of activated carbon by using persulfate salts as the oxidant. The mechanochemical oxidation preferentially oxidized the carbon to introduce carboxyl groups without incorporation of sulfonated groups. The material exhibited hydrophilic behavior and was easily dispersed in water. Upon mix-milling, the oxidized carbon showed good catalytic activity for the hydrolysis of cellulose, even at a low catalyst loading. Glucose was obtained in 85% yield from mix-milled cellulose in the presence of a trace amount of HCl after a reaction time of 20min