Towards the development of a novel “bamboo-refinery” concept : Selective bamboo fractionation by means of a microwave-assisted, acid-catalysed, organosolv process

This work addresses a novel microwave-assisted, acid-catalysed, organosolv (EtOH/H2O) system for the selective fractionation of bamboo, examining the effects of the temperature (110–190 °C), solvent system (EtOH/H2O) and catalyst amount (0–5 vol.% formic acid) on the process. The statistical analysis of the results revealed that the operating variables have a significant influence on bamboo fractionation, allowing the selective production of (i) a cellulose-rich solid fraction, (ii) a hemicellulose rich water-soluble fraction and (iii) a lignin rich solid fraction. The yields of each of these fractions varied between 51 and 94%, 2 and 23% and 2 and 32%, respectively. Increasing temperature exerted a positive effect on bamboo decomposition, increasing the overall bamboo conversion and influencing the effect that the solvent system (EtOH/H2O) has on the process. At low tem- perature (110 °C) the solvent system does not have much influence, while a synergetic interaction between EtOH and H2O took place at higher temperatures, which allowed better results to be obtained with EtOH/H2O mix- tures than with the pure solvents alone. The effect of the catalyst was relatively weak, being greatest when using a high temperature (190 °C) and high proportions of water (> 85 vol.%) in the solvent system. With respect to the properties of each fraction, the cellulose rich solid fraction was made up of un-reacted cellulose (44–83 wt. %), hemicellulose (0–21 wt.%) and lignin (12–34 wt.%); the water-soluble hemicellulose rich fraction consisted of a mixture of oligomers, sugars, carboxylic acids, ketones and furans; and the solid rich lignin fraction com- prised high purity (> 95 wt.%) organosolv lignin. The optimisation of the process revealed that by using a temperature of 190 °C, a solvent system consisting of 45 vol.% EtOH and 55 vol.% H2O with a concentration of formic acid of 5 vol.% it is possible to fractionate bamboo into a high purity (84 wt.%) cellulose solid fraction, very pure (> 95%) organosolv lignin and a rich water-soluble hemicellulose fraction consisting of a mixture of oligomers (27 wt.%), sugars (56 wt.%) and carboxylic acids (14 wt.%); thus converting this process into a very promising method for the selective fractionation of bamboo

Wood structure during pretreatment in ionic liquids

Cellulose makes up for most of the material in the lignocellulosic’s cell wall, and it could provide an abundant source for fuels, materials and chemicals. Mild and selective conversion processes would be desirable for decentralized value-generation from the synthesis power of nature. However, the utilization is still difficult due to the composition and the structure of the biomass’ cell wall. Cellulose shows a dense, crystalline structure and the access to these macromolecules is further restricted by lignin and hemicellulose. An efficient conversion hence requires the application of a pretreatment to gain access to cellulosic macromolecules for subsequent conversion processes.Mechanistic understanding of the pretreatment can likely be gained at the molecular level. However, the cellulose in the cell wall exists in fibrils made of several cellulose chains, which are hold together via intermolecular hydrogen bonds. This regular arrangement forms crystalline structures that are a major obstacle in enzymatic hydrolysis [1]. Hence, molecular analysis needs to be extended by structural analysis to monitor the mechanistic steps of pretreatment.Ionic liquids proved to be good solvents for the cellulose and the hydrophobic lignin [2], and the high concentrations of acetate at elevated temperatures around 100°C give rise to chemical reactions that constitute the desired pretreatment and improve the enzymatic hydrolysis [3]. Due to the abundance of water in such processes, we systematically studied the effect of water on this pretreatment. Using small angle neutron scattering (SANS), the tissue after the pretreatment was compared to the native wood and a first time-resolved setup was established for this pretreatment.The crystallinity of the cellulose has decayed at low water concentrations, and the cell structure of the wood is rather destroyed. At higher water contents, the crystallinity is enhanced, and the cell structure is rather preserved but cellulose fibrils show coalescence. Apart from that, various methods have been applied to support the results and will be presented selectively. Latest kinetic SANS measurements reveal the pretreatment process in more detail. [1] S.P. Chundawat, G.T. Beckham, M.E. Himmel, B.E. Dale, Annual Review of Chemical and Biomolecular Engineering, 2, 121–145 (2011).[2] J. Viell, W. Marquardt, Holzforschung, 65(4), 519 (2011).[3] J. Viell, H. Wulfhorst, T. Schmidt, U. Commandeur, R. Fischer, A. Spiess, W. Marquardt, Bioresource Technology 146, 144–151 (2013)

Fractionation of lignocellulosic biomass using the OrganoCat process

The fractionation of lignocellulose in its three main components, hemicellulose, lignin and cellulose pulp can be achieved in a biphasic system comprising water and bio-based 2-methyltetrahydrofuran (2-MeTHF) as solvents and oxalic acid as catalyst at mild temperatures (up to 140 °C). This so-called OrganoCat concept relies on selective hemicellulose depolymerization to form an aqueous stream of the corresponding carbohydrates, whereas solid cellulose pulp remains suspended and the disentangled lignin is to a large extent extracted in situ with the organic phase. In the present paper, it is demonstrated that biomass loadings of 100 g L−1 can be efficiently fractionated within 3 h whereby the mild conditions assure that no significant amounts of by-products (e.g. furans) are formed. Removing the solid pulp by filtration allows to re-use the water and organic phase without product separation in repetitive batch mode. In this way, (at least) 400 g L−1 biomass can be processed in 4 cycles, leading to greatly improved biomass-to-catalyst and biomass-to-solvent ratios. Economic analysis of the process reveals that the improved biomass loading significantly reduces capital and energy costs in the solvent recycle, indicating the importance of process integration for potential implementation. The procedure was successfully scaled-up from the screening on bench scale to 3 L reactor. The feedstock flexibility was assessed for biomasses containing moderate-to-high hemicellulose content