(ii) Lignin breakdown products Lignin (simplified as ‘bark’) is a very heterogeneous polymeric material composed of phenolic aromatics and C 3 -units, whose
main role is to shield the cellulose from microbial attack. It can be chemically
converted via partial oxidative degradation to mono-ligninols (sinapyl, coniferyl
and hydroxycinnamoyl alcohol). Common to these compounds is their electron-rich
(phenolic) aromatic core, which renders them susceptible to auto-oxidation, which
creates serious problems upon storage. The color of lignin degradation product
streams range from dark yellow to tarry black – not an ideal starting point for
selective organic synthesis. No efficient use of these compounds for synthesis has
been found so far.
(iii) Oils and fats are predominantly composed of triglycerides. The alcohol moiety –
glycerol – resembles a sugar alcohol and thus has limited value for synthesis
4
, but
fatty acids – composed of a dominant hydrocarbon chain with a terminal carboxylic
acid group – can be synthetically utilized to some extent. However, the most efficient
production of triglycerides is palm oil, which has turned Indonesia into the third
largest CO 2 -producer worldwide – after the US and China – due to (intended and
illegal) large-scale deforestation. Not a long-term solution.
Since current technology for the synthesis of organic chemicals on industrial
scale is mainly based on the use of alkenes and aromatics, it needs a lot of research
(and optimism) for the development of highly efficient processes, which draw on
‘natural’ starting materials – carboxylic acids, alcohols and the like – to bypass
traditional industrial routes starting from hydrocarbons. In this context, it can be
expected that biotransformations will most likely play a dominant role, because
since natural carbon sources are made by enzyme catalysis, they can also be
expected to be converted by them.
If such pathways cannot be developed in an efficient manner, we have to resort to
the old-fashioned, reliable – and relatively efficient – generation of synthesis gas, in
short a mixture of CO and H 2 . The latter can be made from almost any carbonaceous material, including natural gas, coal, peat, wood and agricultural residues,
which is converted into hydrocarbons by Fischer-Tropsch synthesis.
An immediate action to be taken is the de-carbonization of energy-production, in
order to reserve our non-renewable carbon feedstocks for chemical synthesis of
long-lasting products instead of burning them for short-term energy generation.
This would extend their availability
5 for more than one order of magnitude and
would help to limit global warming as a highly desirable side effect.
There is a general need for cleaner (‘green’) and sustainable chemistry, and
although it is not the prerogative of biocatalysis, it is nevertheless an important
feature of it. Social pressure forces the chemical industry to pay more attention to
4 About 4 Mt of glycerol are annually obtained as (low-value) by-product from biodiesel production worldwide
5 Projected availability according to www.eia.doe.gov: oil 43–67 years, gas 64–150 years, coal
200–1500 years.
4 State of the Art and Outlook
413
main role is to shield the cellulose from microbial attack. It can be chemically
converted via partial oxidative degradation to mono-ligninols (sinapyl, coniferyl
and hydroxycinnamoyl alcohol). Common to these compounds is their electron-rich
(phenolic) aromatic core, which renders them susceptible to auto-oxidation, which
creates serious problems upon storage. The color of lignin degradation product
streams range from dark yellow to tarry black – not an ideal starting point for
selective organic synthesis. No efficient use of these compounds for synthesis has
been found so far.
(iii) Oils and fats are predominantly composed of triglycerides. The alcohol moiety –
glycerol – resembles a sugar alcohol and thus has limited value for synthesis
4
, but
fatty acids – composed of a dominant hydrocarbon chain with a terminal carboxylic
acid group – can be synthetically utilized to some extent. However, the most efficient
production of triglycerides is palm oil, which has turned Indonesia into the third
largest CO 2 -producer worldwide – after the US and China – due to (intended and
illegal) large-scale deforestation. Not a long-term solution.
Since current technology for the synthesis of organic chemicals on industrial
scale is mainly based on the use of alkenes and aromatics, it needs a lot of research
(and optimism) for the development of highly efficient processes, which draw on
‘natural’ starting materials – carboxylic acids, alcohols and the like – to bypass
traditional industrial routes starting from hydrocarbons. In this context, it can be
expected that biotransformations will most likely play a dominant role, because
since natural carbon sources are made by enzyme catalysis, they can also be
expected to be converted by them.
If such pathways cannot be developed in an efficient manner, we have to resort to
the old-fashioned, reliable – and relatively efficient – generation of synthesis gas, in
short a mixture of CO and H 2 . The latter can be made from almost any carbonaceous material, including natural gas, coal, peat, wood and agricultural residues,
which is converted into hydrocarbons by Fischer-Tropsch synthesis.
An immediate action to be taken is the de-carbonization of energy-production, in
order to reserve our non-renewable carbon feedstocks for chemical synthesis of
long-lasting products instead of burning them for short-term energy generation.
This would extend their availability
5 for more than one order of magnitude and
would help to limit global warming as a highly desirable side effect.
There is a general need for cleaner (‘green’) and sustainable chemistry, and
although it is not the prerogative of biocatalysis, it is nevertheless an important
feature of it. Social pressure forces the chemical industry to pay more attention to
4 About 4 Mt of glycerol are annually obtained as (low-value) by-product from biodiesel production worldwide
5 Projected availability according to www.eia.doe.gov: oil 43–67 years, gas 64–150 years, coal
200–1500 years.
4 State of the Art and Outlook
413