84 Introduction to Renewable Biomaterials
Synthesis of methanol and dimethyl ether (DME)– Both methanol and dimethyl ether
(DME) are promising chemicals with application in fuels and beyond. Hydrogenation
of gasification products results in the synthesis of methanol. Both CO and CO 2 can be
hydrogenated in the presence of various catalysts yielding methanol as an end prod-
uct [23]. Condensation reaction between the two molecules of methanol results in the
production of DME.
CO+2H 2 ↔CH 3 OH
CO 2 +3H 2 ↔CH 3 OH+H 2 O
2CH 3 OH↔CH 3 OCH 3 +H 2 O
The synthesis of methanol from syngas requires however some major adjustments
of gas composition. The reaction requires even higher content of hydrogen to proceed
than FTS, and the ratio of H 2 to CO should exceed 2:1 for the successful synthesis [24].
This raises concerns about the supply of hydrogen required to perform this reaction on
largescale.Moreover,methanolsynthesisislimitedbythepresenceofothergaseous
compounds such as CH 4 or N 2 [24].
3.4.6 Pyrolysis
Pyrolysis is process of endothermic conversion that produces a number of high-energy
intermediates that may become valuable feedstocks for the production of biomaterial
and bio-fuels. The process of pyrolysis starts with biomass drying analogous to com-
bustion and gasification processes. Once the moisture is removed, the biomass decom-
poses into volatile products: gasses and tars and solid char. The reaction, however, is
not allowed to proceed to the oxidation stage due to the lack of an oxidant. Instead,
the gaseous streams are separated into condensable gasses that are cooled down and
condensed to form bio-oil, and non-condensable high-energy gasses that are separated.
These gasses undergo a series of chemical reactions among themselves largely analogous
to those in gasification process. After the separation is complete, these products can be
combusted to provide the energy necessary to power further endothermic reactions in
the pyrolysis reactor. The final product of the transformation is char, which is analogous
to the char produced in the other two conversion processes. The ratio of these prod-
ucts is dependent on the conditions of pyrolysis such as temperature, particle size and
effects of catalysts, but the most important criterion of pyrolysis is time of reaction and
heating rate. Pyrolysis technology has many modifications that yield different products.
Differences between pyrolytic processes and the products they yield are influenced by
the control parameters of the process and the form and chemical composition of the
feedstock being processed. The summary of different variants of pyrolysis technologies
and their products is presented in Table 3.2 [25].
Historically, one of the variants of slow pyrolysis (carbonisation) was a milestone
technology in the development of metallurgy. Carbonisation is a process that maximises
the production of char (charcoal) from biomass, usually wood. Because of its high
porosity and combustion temperatures, charcoal is an excellent fuel for metallurgy.
Production of charcoal still remains a major application of carbonisation technology.
Thisconversionprocesscantakeseveraldaysatrelativelylowtemperaturesofabout
400 ∘C and results in the conversion of biomass into solid products. An important
variant of pyrolysis technology is fast pyrolysis. This variant is designed to maximise the
