Under the WP4 (Catalytic convertion of pure ethanol into butanol with an heterogeneous structured catalystic), activities related to the catalytic valorisation of ethanol to 1-butanol have been implemented by IRC-CNR. Bio-ethanol can be catalytically converted into butanol through alcohol dimerization called Guerbet reaction. Basic sites are essential to get Guerbet coupling of alcohol and addition of a metal function gives better dehydrogenation/hydrogenation properties. Powder γ-Al2O3, hydroxyapatite and MgO have been synthesized according to different techniques to obtain high surface area materials. Ruthenium or Nickel have been dispersed on the supports. Textural, acid and basic properties of the three supports and redox properties of the metals have been characterized in order to optimize the catalyst formulation. Ru/MgO and Ni/MgO provided good butanol yields and are the candidates for the preparation of structured catalysts for operation in the pilot-scale rig.
Simultaneously, BGU has been working on two alternative catalytic routes:
i) Catalytic conversion of ethanol-water mixtures produced by waste biomass fermentation to butanol included conversion of ethanol-water mixtures to butylene that further reacts with water yielding butanol.
ii) Catalytic conversion of ethanol-water and aceton-butanol-ethanol (ABE) – water mixtures produced by waste biomass fermentation into biogasoline and hydrocarbon biofuels components boiling out in the temperature range of 30 – 300oC.
In both cases, catalytic materials have been developed and process conditions have been validated.
Under the WP3 (ABE fermentation solvent recovery), TU WIEN conducted activities aimed at recovery and concentration of the butanol mixture produced by fermentation. To this end, TU WIEN investigated pervaporation for product recovery in ABE fermentation. Focus was given to the comparison of different membrane materials near real process conditions. Obtained design parameters are used for modeling and comparing upgrading techniques, to select a suitable process to be coupled to the ABE fermenter.
Activities concerning the WP2 (metabolic engineering for biomass conversion to butanol) have been carried out by WEIZMANN. A library of ligno-cellulolytic enzymes has been developed and a panel of mixtures tested on the four different types of untreated agrowastes. High levels of enzymatic degradation was observed on brewer’s spent grain by a mixture of 3 cellulases, 1 xylanase and 1 bifunctional xylanase-laccase. These five enzymes were attached to scaffoldins to form a designer cellulosomal complex, which was found to be even more efficient than the free enzyme mixture.
After one year of activities, several results have been achieved:
Under the WP1 (selection of renewable feedstock for ABE fermentation), a preliminary analysis has been conducted by ITACYL together with ENCO on agrofood waste, in order to select the most suitable AFWs wastes to be investigated for biobutanol production. The selected agrofood waste (potato peel, apple pomace, brewers’ spent grain and coffee silverskin) have been chemically characterised and a conservation protocol established.
Recently, the selection of the most suitable biomass degradation pre-treatment for the agro-food waste has been carried out with the aim to improve the ABE fermentation. The task has been completed by ITACYL, which has been working in cooperation with IRIS, TOMSA, IRC-CNR, BIOPOX. Different pre-treatment techniques (autohydrolysis, dilute chemical pretreatment, ultrasound pretreatments, microwave pretreatments, deep eutectic solvents and enzymatic pretreatments), in order to determine the optimal methods for hydrolyzation of the cellulose and hemicellulose fractions and to remove and recovery the ligning fraction. The selection of pre-treatment techniques was based on cost- and energy-efficiency criteria; high fermentable sugar yield; low concentration of inhibitory compounds for the subsequent enzymatic hydrolysis and fermentation steps. The pre-treatments have been compared in terms of simple sugars released (glucose, xylose, etc.) and inhibitors generated for the subsequent hydrolysis and fermentation steps.