Johannes H. Reith

Ethanol-based organosolv fractionation of wheat straw for the production of lignin and enzymatically digestible cellulose

Wheat straw fractionation by ethanol organosolv was studied as pretreatment for enzymatic cellulose hydrolysis. A parametric study focusing on temperature, reaction time, acid catalyst dose, solvent concentration, and particle size was performed to determine their influence on delignification, xylan hydrolysis, and enzymatic cellulose digestibility. Major process parameters were found to be temperature, ethanol concentration, and acid dose. Optimisation of the process towards enzymatic digestibility resulted in a maximum glucose yield of 86% without the use of a catalyst (lignin yield 84%, organosolv at 210 °C, 50% w/w aqueous EtOH). Using 30 mM H2SO4 as catalyst resulted in similar glucose and lignin yields at a lower temperature (190 °C, 60% w/w aqueous EtOH). Lowering the pretreatment temperature by using an acid catalyst substantially improved the yield of the hemicellulose derivatives xylose and furfural. A systematic approach in pretreatment optimisation is vital for development of efficient lignocellulosic biorefineries.

Organosolv pretreatment of olive tree biomass for fermentable sugars.

Abstract Olive tree pruning biomass is one of the main agricultural residues available in Mediterranean countries and is currently lacking commercial applications. To take advantage of its sugar content, a pretreatment is necessary to enhance enzyme accessibility of the cellulose fraction of the residue. This paper describes for the first time the use of organosolv pretreatment in this regard. The main process variables such as pretreatment temperature, residence time, and solvent composition (aqueous ethanol) are studied. Results show that organosolv pretreatment causes delignification and hydrolysis of hemicelluloses and improves the enzymatic digestibility of olive tree pruning biomass. A higher pretreatment severity and ethanol content of the solvent were found to increase delignification (up to 64% at 66% w/w aqueous ethanol, 210°C, 60 min). By contrast, xylan hydrolysis was promoted by a lower ethanol content (maximum 92%). The highest enzymatic hydrolysis yield (90% of the structural glucan present in the raw material) has been obtained after pretreatment with 43% w/w aqueous ethanol at 210°C for 15 min. Organosolv pretreatment was found to be the most effective pretreatment for enzymatic hydrolysis of olive tree pruning biomass.

Bioenergy II : Biomass Valorisation by a Hybrid Thermochemical Fractionation Approach

The need for green renewable sources is adamant because of the adverse effects of the increasing use of fossil fuels on our society. Biomass has been considered as a very attractive candidate for green energy carriers, chemicals and materials. The development of cheap and efficient fractionation technology to separate biomass into its main constituents is highly desirable. It enables treatment of each constituent separately, using dedicated conversion technologies to get specific target chemicals. The synergistic combination of aquathermolysis (hot pressurised water treatment) and pyrolysis (thermal degradation in the absence of oxygen) is a promising thermolysis option, integrating fractionation of biomass with production of valuable chemicals. Batch aquathermolysis in an autoclave and subsequent pyrolysis using bubbling fluidised bed reactor technology with beech, poplar, spruce and straw indicate the potential of this hybrid concept to valorise lignocellulosic biomass. Hemicellulose-derived furfural was obtained in yields that ranged from 2 wt% for spruce to 8 wt% for straw. Hydroxymethylfurfural from hemicellulose was obtained in yields from 0.3 wt% for poplar to 3 wt% for spruce. Pyrolysis of the aquathermolised biomass types resulted in 8 wt% (straw) to 11 wt% (spruce) of cellulose-derived levoglucosan. Next to the furfurals and levoglucosan, appreciable amounts of acetic acid were obtained as well from the aquathermolysis step, ranging from 1 wt% for spruce to 5 wt% for straw. To elucidate relations between the chemical changes occurring in the biomass during the integrated process and type and amount of the chemical products formed, a 13C-solid state NMR study has been conducted. Main conclusions are that aquathermolysis results in hemicellulose degradation to lower molecular weight components. Lignin ether bonds are broken, but apart from that, lignin is hardly affected by the aquathermolysis. Cellulose is also retained, although it seems to become more crystalline, probably due to a higher ordering of amorphous cellulose when the samples are cooled down after aquathermolysis. These NMR results are in agreement with thermogravimetric analyses results.