Bioethanol from lignocellulosic biomass by a chemical-free route
16/3/2015
The invention that brings about successful results for the environment and green economy
The main novelty of such invention lies in the environmentally-friendly, chemical-free system that makes use of vapour and air alone: the substances inhibiting the fermentation of the sugars obtained from biomass are removed without loss of soluble carbohydrates, which are fundamental to obtain a high-performance in bioethanol production. Such inhibitors, obtained as a byproduct of biomass pretreatment, can be then recovered by condensation and exploited as “green” building blocks in the chemical industry. Lignocellulosic biomass is mainly composed of cellulose, hemicellulose, lignin, and other organic (oils, waxes, etc.) and inorganic (mineral salts) components, combined in considerably varying quantities depending on the biomass type.
Cellulose crystallinity and the complex structure of lignin make the lignocellulosic biomass so compact that it cannot be directly converted into the desired product. Hence, to change its morphology lignocellulosic biomass must necessarily undergo a pretreatment phase causing the chemical bonds among the various biomass components to break down, so that the biological and chemical agents are more efficient and hemicellulose, cellulose and lignin are easily separated. Such hydrothermal pretreatment is particularly interesting as it requires low energy consumption, relatively low-cost facilities and no particular chemical reactants.
A typical steam explosion plant is run at the ENEA Trisaia Research Centre. The treatment consists in using high-pressure saturated vapour to quickly heat biomass, which is kept at a temperature between 180 and 220 °C for a maximum of ten minutes and then pressure is lowered down to the atmospheric values. This causes an explosive decompression which breaks biomass further down, making it immediately available to produce bioethanol trough cellulose hydrolysis and alcoholic fermentation. Yet, pretreatment can produce some substances which inhibit the fermentation process and are harmful to the yeast specifically used (e.g. Saccharomyces cerevisiae). Such substances –e.g., formic acid, acetic acid, furfural, hydroxymethylfurfural, and benzaldehyde – are generally low-weight compared to the exploded product, and usually volatile.
The detoxification methods so far used for the exploded material are: water washing –that removes soluble oligomers ensuring higher quantities of fermentation-produced ethanol– or oven drying at 60 °C for a number of hours, which makes the fiber stiffer and saccharification less efficient, consequently decreasing the amount of substances produced– or other highly-contaminating methods which make wide use of conventional chemicals, posing the consequent additional problem of waste disposal.
The invention has been tested at bench scale and, besides biofuels, can be very important for similar industrial plants aiming to produce green chemicals from low cost sugars.
Source:
Giacobbe Braccio, Trisaia Research Centre, giacobbe.braccio@enea.it
Francesco Zimbardi, Trisaia Research Centre, francesco.zimbardi@enea.it
For more information:
Sustainable alcohol from wood
Energia Ambiente e Innovazione no. 4/2014
Hydrolysis of concentrated suspensions of steam pretreated Arundo donax