Page 98 - Biodegradable Polyesters

76 4 Synthesis, Properties, and Mathematical Modeling of Biodegradable Aliphatic Polyesters

resulted in a drastic rise in the demand for 1,3-PD and the market position of 1,3-
PD has changed in recent years. The development of new technologies to produce
1,3-PD and the increased quantity produced (about 50 000 tons per year) resulted
in a reduction of market prices to $1.5–1.70 per kg.
Most of the commercial synthesis of 1,3-PD is from acrolein by Degussa (now
owned by DuPont) and from ethylene oxide by Shell [13]. The Degussa Com-
pany starts from acrolein and the process consists of the following three steps
(Scheme 4.1). The first step is the oxidation of propylene to acrolein, the second
is the addition of water to produce 3-hydroxypropionaldehyde, and the third is
the catalytic hydrogenation of 3-hydroxypropionaldehyde to 1,3-PD. The selec-
tivity of water addition to acrolein is only around 70–80% when zeolites or ion
exchange resins are used. Recently, Tsunoda and Nomura [14] reported that a
silicoaluminophosphate-based molecular sieve afforded a selectivity of 96% when
∘
the reaction was conducted in aqueous solution at 60 C.
1. CH 2 CH CH + O 2 CH 2 CH CHO
3
2. CH 2 CH CHO + H 2 O O CHCH 2 CH 2 OH

3. O CHCH 2 CH 2 OH + H 2 HOCH 2 CH 2 CH 2 OH

Scheme 4.1 Chemical synthesis of 1,3-propanediol by Degussa method starting from
acrolein.
Shell produces 1,3-PD by the hydroformylation of ethylene oxide followed by
catalytic hydrogenation in a two-step process (Scheme 4.2). In the first-stage, ethy-
lene oxide reacts with carbon monoxide in the presence of an organometallic
catalyst such as cobalt to produce a hydroxyaldehyde, which, in the second stage, is
reduced to 1,3-PD by hydrogenation. For the second stage, a copper chromite cat-
alyst can be used [15]. During the procedure used, there are some problems as the
high pressure applied in the hydroformylation and hydrogenation steps along with
high temperature, use of expensive catalyst, and release of toxic intermediates.
O
O CHCH 2 CH 2 OH
1. H 2 C CH 2 + CO + H 2
3. O CHCH CH OH + H 2 HOCH CH CH OH
2
2
2
2
2
Scheme 4.2 Chemical synthesis of 1,3-propanediol by Shell method starting from ethylene
oxide.
1,3-PD can also be produced chemically from glycerol. This route has gained
increased attention due to the large production of biodiesel, which generates glyc-
erol as a by-product in 10% by weight. Furthermore, it is estimated that by 2016
the world biodiesel market will achieve the quantity of 37 billion gallons, which
means that significantly more than 4 billion gal of crude glycerol will be produced
every year [16]. The production of such high quantities of glycerol also pushes the