Mizuho Yabushita

Quantitative evaluation of ball-milling effects on the hydrolysis of cellulose catalysed by activated carbon

The synthesis of glucose from cellulose is a critical roadblock for establishing a new sustainable cycle of biorefinery to produce bio-based and environmentally-benign chemicals. We have previously demonstrated that the pre-treatment ball-milling of solid cellulose and a solid catalyst (mix-milling) drastically improves the yield of glucose and oligosaccharides; however, the effect of this type of ball-milling has not been quantitatively evaluated. In this study, we performed several model reactions and found that the mix-milling method drastically enhanced the solid–solid reactions, such as the hydrolysis of insoluble cellulose to soluble oligomers on the solid catalyst, but not liquid–solid reactions. The kinetic study indicated that the rate constant of hydrolysis of cellulose to oligomers using mix-milling was 13-fold higher than that using individual milling. Owing to the fast depolymerisation of cellulose, we achieved a 72% yield of glucose with 97% conversion of cellulose and 74% selectivity at 418 K.

Entropically Favored Adsorption of Cellulosic Molecules onto Carbon Materials through Hydrophobic Functionalities

Carbon-based materials have attracted interest as high-performance catalysts for the aqueous-phase conversion of cellulose. The adsorption of β-glucans plays a crucial role in the catalytic performance of carbons, although the primary driving force and details of the adsorption process remain unclear. This study demonstrates that adsorption occurs at hydrophobic sites on the carbon surface and that hydrophilic groups are not involved. Analysis of adsorption temperature dependence also reveals that the entropy change associated with adsorption is positive. Our results indicate that adsorption occurs by entropically driven hydrophobic interactions in addition to CH-π hydrogen bonding. These same CH-π hydrogen bonds are also confirmed by DFT calculations. The adsorption of β-glucans on carbons is significantly stronger than the affinity between β-glucans. The adsorption equilibrium constants of β-glucans on carbons increase exponentially with increasing degrees of polymerization, which supports the theory of strong interactions between the carbon and the long β-glucans found in cellulose.

Catalytic Depolymerization of Chitin with Retention of N‐Acetyl Group

Chitin, a polymer of N-acetylglucosamine units with β-1,4-glycosidic linkages, is the most abundant marine biomass. Chitin monomers containing N-acetyl groups are useful precursors to various fine chemicals and medicines. However, the selective conversion of robust chitin to N-acetylated monomers currently requires a large excess of acid or a long reaction time, which limits its application. We demonstrate a fast catalytic transformation of chitin to monomers with retention of N-acetyl groups by combining mechanochemistry and homogeneous catalysis. Mechanical-force-assisted depolymerization of chitin with a catalytic amount of H2SO4 gave soluble short-chain oligomers. Subsequent hydrolysis of the ball-milled sample provided N-acetylglucosamine in 53% yield, and methanolysis afforded 1-O-methyl-N-acetylglucosamine in yields of up to 70%. Our process can greatly reduce the use of acid compared to the conventional process.

Unprecedented selectivity in molecular recognition of carbohydrates by a metal–organic framework

Metal-organic framework (MOF) material NU-1000 adsorbs dimers cellobiose and lactose from aqueous solution, in amounts exceeding 1250 mg gNU-1000(-1) while completely excluding the adsorption of the monomer glucose, even in a competitive mode with cellobiose. The MOF also discriminates between dimers consisting of α and β linkages, showing no adsorption of maltose. Electronic structure calculations demonstrate that key to this selective molecular recognition is the number of favorable CH-π interactions made by the sugar with pyrene units of the MOF.

Insights into Supramolecular Sites Responsible for Complete Separation of Biomass-Derived Phenolics and Glucose in Metal–Organic Framework NU-1000

The molecular origins of adsorption of lignin-derived phenolics to metal-organic framework NU-1000 are investigated from aqueous solution as well as in competitive mode with glucose present in the same aqueous mixture. A comparison of adsorption equilibrium constants (Kads) for phenolics functionalized with either carboxylic acid or aldehyde substituents demonstrated only a slight increase (less than a factor of 6) for the former according to both experiments and calculations. This small difference in Kads between aldehyde and carboxylic-acid substituted adsorbates is consistent with the pyrene unit of NU-1000 as the adsorption site, rather than the zirconia nodes, while at saturation coverage, the adsorption capacity suggests multiple guests per pyrene. Experimental standard free energies of adsorption directly correlated with the molecular size and electronic structure calculations confirmed this direct relationship, with the pyrene units as adsorption site. The underlying origins of this relationship are grounded in noncovalent π-π interactions as being responsible for adsorption, the same interactions present in the condensed phase of the phenolics, which to a large extent govern their heat of vaporization. Thus, NU-1000 acts as a preformed aromatic cavity for driving aromatic guest adsorption from aqueous solution and does so specifically without causing detectable glucose adsorption from aqueous solution, thereby achieving complete glucose-phenolics separations. The reusability of NU-1000 during an adsorption/desorption cycle was good, even with some of the phenolic compounds with greatest affinity not easiliy removed with water and ethanol washes at room temperature. A competitive adsorption experiment gave an upper bound for Kads for glucose of at most 0.18 M-1, which can be compared with Kads for the phenolics investigated here, which fell in the range of 443-42 639 M-1. The actual value of Kads for glucose may be much closer to zero given the lack of observed glucose uptake with NU-1000 as adsorbent.

A Study on Catalytic Conversion of Non-Food Biomass into Chemicals

Title A Study on Catalytic Conversion of Non-Food Biomass into Chemicals [an abstract of dissertation and a summary of dissertation review] Author(s) 藪下, 瑞帆 Issue Date 2015-03-25 Doc URL http://hdl.handle.net/2115/58997 Rights(URL) http://creativecommons.org/licenses/by-nc-sa/2.1/jp/ Type theses (doctoral abstract and summary of review) Additional Information There are other files related to this item in HUSCAP. Check the above URL. File Information Mizuho_Yabushita_review.pdf (審査の要旨)

Depolymerization of Cellulosic Biomass Catalyzed by Activated Carbons

Efficient hydrolysis of cellulosic biomass to glucose is a grand challenge for the realization of a nonfood biorefinery. In recent years, solid catalysts have attracted significant attention for biomass conversion, as they can be separated from product solutions and their functions can be designed. In this chapter, we describe activated carbons that can hydrolyze cellulose and real biomass to glucose in yields up to 88 % in the presence of a trace amount of hydrochloric acid. Creating contacts between the solid catalyst and the solid substrate by ball-milling is the key to realizing the potential of this catalytic system. Activated carbon adsorbs cellulosic molecules by van der Waals forces, CH−π hydrogen bonds, and hydrophobic interactions between the polyaromatic surface of the carbon and the axial planes of glucans, namely, hydrophobic groups. Subsequently, the weakly acidic groups of the carbon surface such as carboxylic acids cleave the glycosidic bonds of cellulose via oxocarbenium intermediates, for which the salicylic acid structure is especially effective.

Mechanistic Study of Cellulose Hydrolysis by Carbon Catalysts

The structure-activity correlation by carbon catalysts for hydrolysis of glycosidic bonds in cellulosic molecules has been investigated. The characterization of carbon materials by titration and infrared spectroscopy indicates that weakly acidic hydrophilic functionalities contribute to catalytic activity; especially, vicinal oxygenated functional groups as in salicylic acid and phthalic acid specifically show high catalytic performance due to increase of frequency factor but not to decrease of activation energy. One of the functional groups forms a hydrogen bond with hydroxyl groups of the substrate and another group gains an opportunity to activate and hydrolyze a glycosidic bond. Besides, hydrophobic surface of carbon plays important roles for adsorption process of cellulosic molecules, and this function also enhances the possibility to hydrolyze the substrate. Finally, the author proposes reaction mechanism for cellulose hydrolysis by carbon catalyst.

Hydrolysis of Cellulose to Glucose Using Carbon Catalysts

High-yielding one-pot production of glucose from cellulose has been achieved using an alkali-activated carbon K26 as a catalyst bearing weak acid sites. The hydrolysis of solid cellulose by solid catalyst is limited due to low physical contact between the substrate and catalyst, but a new ball-milling pretreatment, ball-milling cellulose and carbon together (named mix-milling), has drastically improved the hydrolysis rate. As a result, 90 % yield and 97 % selectivity of water-soluble glucans have been obtained by K26 at 453 K for 20 min. Model reactions and kinetic studies have shown that the mix-milling pretreatment selectively accelerates solid-solid reaction (cellulose to water-soluble oligosaccharides), but does not liquid-solid reaction (soluble oligosaccharides to glucose). Hence, a trace amount of HCl (0.012 wt%) is used to depolymerize oligosaccharides to glucose and as high as 88 % yield of glucose with 90 % selectivity has been achieved. This reaction system is also effective for the hydrolysis of cellulose/hemicellulose in bagasse kraft pulp to hexoses/pentoses.

Catalytic Depolymerization of Chitin to N -Acetylated Monomers

Chitin, the most abundant nitrogen-containing biopolymer, includes both glycosidic bonds and N-acetyl groups in its structure and is an attractive source of useful monomers such as N-acetylglucosamine (GlcNAc) and 1-O-methyl-N-acetylglucosamine (MeGlcNAc). In order to synthesize the N-acetylated monomers in high yields, selective hydrolysis of glycosidic bonds in chitin without deacetylation is absolutely necessary. In this chapter, new two-step catalytic depolymerization of chitin to the N-acetylated monomers has been developed: (i) mechanical force-assisted hydrolysis of chitin to water-soluble oligomers and (ii) thermocatalytic solvolysis, hydrolysis, and methanolysis in this study, of the oligomers to the N-acetylated monomers. In both steps, deacetylation does not happen, resulting in good yields of GlcNAc (53 %) and MeGlcNAc (70 %).