Page 90 - Biofuels for a More Sustainable Future

Indicators for sustainability assessment 81

The production of biobutanol and lignocellulose bioethanol presents
almost the same productive steps, and the main difference is the fermentation
process that utilizes the Clostridium microorganism, which transforms the
sugars of cellulose and hemicellulose into butanol, acetone, and ethanol
(ABE fermentation).

5 Thermochemical routes

Besides the biochemical routes, there are thermochemical routes that con-
vert biomass in several industrial products, through physical processes. In
thermochemical routes, there is transformation of the solid biomass into liq-
uid products, through pyrolysis, or into gaseous products, through gasifica-
tion. Pyrolysis is a process that occurs without any oxidizing agents, in which
biomass is submitted to high heat transfer rates at temperatures that reach
700–1000°C (temperatures can also be above these values). Due to the high
heat transference rates, the product is heated in a very reduced time. This
process is not fully commercially established (Basu, 2013).
Gasification is a consolidated process for raw materials based on carbon
and oil, but it is still not commercially available for biomass (Higman, 2015;
Dahlquist, 2013). In this process, partial oxidation of biomass occurs with
oxygen amounts corresponding to 20%–30% of the stoichiometric molar
amount necessary for combustion. This gas is a very versatile product that
can be a resource for the production of several chemical products, biofuels,
electricity, and so on (Rezayan and Cheremisinoff, 2005).
Syngas is a gas mixture composed mostly of hydrogen (H 2 ), carbon mon-
oxide (CO), methane (CH 4 ), carbon dioxide (CO 2 ), also having other gases
in lower concentrations. This gas can be used as raw material for the man-
ufacture of chemical inputs, in addition of serving as fuel (Dahlquist, 2013).
In theory, biomass can replace most products derived from the petrochem-
ical chain, through platforms that include sugar conversion, or through pro-
cesses that use syngas as input.
Syngas can be used for the manufacture of so-called building blocks, which
in turn can be used for the production of fumaric acid, methanol, hydrogen,
and glycerol, of great importance in transportation, textiles, food, pharmaceu-
ticals, and cosmetics (Basu, 2013; Werpy and Petersen, 2004). Fig. 4.4 depicts
the possibilities of syngas applications.
In recent years, there has been an increase in the use of syngas for the
production of chemical products from coal residues, being more intense
in China (Higman, 2015).