Page 99 - Biodegradable Polyesters

4.1 Introduction 77

market for alternative applications such as the production of 1,3-PD. It causes the
necessary development of a new technology to convert glycerol into other prod-
ucts of high value, among others 1,3-PD [17]. The process involves selective deoxy-
genation of the secondary alcohol using organometallic catalysts (Scheme 4.3). In
such a procedure, Kurosaka et al. [18] reported the production of 1,3-PD from
glycerol using platinum as heterogeneous organometallic catalyst and tungsten
∘
trioxide on a zirconium dioxide support. The reaction took place at 170 Cand
elevated pressures of hydrogen to provide a 24% yield of 1,3-PD, a 12% yield of
1,2-propanediol, and a 28% yield of 1-propanol.

Pt, WO 3
OH on ZrO 2 OH
HO CH CH CH 2 OH HO CH CH CH 2 OH + CH 3 CHCH 2 OH + CH CH CH 2 OH
2
2
2
2
3
H 2
Scheme 4.3 Chemical synthesis of 1,3-propanediol starting from glycerin.
Chemical synthesis of 1,3-PD, as described previously, requires expensive pro-
duction processes and generally contains impurities from the chemical processes.
Many of these intermediates are known to be harmful irritants and even toxic in
some cases. Recently, microbial production of 1,3-PD from renewable sources has
been widely investigated by researchers as an alternative to traditional petrochem-
ical routes [19]. It has a number of advantages as low-cost renewable resources can
be used as fermentation substrates, which provides solutions to environmental
pollution and petroleum depletion. Furthermore, biologically synthesized 1,3-PD
has higher purity than chemically synthesized 1,3-PD. Production of 1,3-PD by
several groups of bacteria such as Clostridium butyricum, Clostridium pasteuri-
anum, Citrobacter freundii, Klebsiella pneumoniae, Lactobacillus brevis, Lacto-
bacillus buchneri,and Bacillus welchii has been known for a long time and the
progress made in recent years is described in some reviews [20–22].
1,3-PD can be biologically produced from glycerol by several microorganisms,
but no natural microorganism is able to synthesize it directly from glucose. The
conversions of glucose to 1,3-PD occurs in nature in two stages; first by yeast
to an intermediate product, glycerol then by bacteria to 1,3-PD. In this area, the
groundbreaking work of DuPont and Genencor International Inc. in the success-
fuldevelopmentofarecombinant E. coli strain to produce 1,3-PD from glucose
still represents the state of the art [20]. The recombinant strain in commercial use
contains genes from Saccharomyces cerevisiae for producing glycerol from glu-
cose and genes from Klebsiella pneumoniae for producing 1,3-PD from glycerol,
respectively.
Yeast Bacterium
Glucose Glycerol 1,3-PD
For the microbial production of 1,3-PD from glucose or technical glycerol, the
substrate cost can make up to about half of the whole production cost. To reduce
the cost of substrate, two strategies can be followed: use of cheaper substrate or
increase in the product yield. As regards the yield, the theoretically maximal yield