Food Waste and Catering Waste; Focus on Valorisation of Used Cooking Oil and Recovered Triglycerides - The Economic Utilisation of Food Co-Products - page 124

OH

OH

Catalyst-H 2 -MeOH

HO OH

OH

200 °C, 20-40 bar

GLYCEROL 1,2-PROPANEDIOL

d n 9 r 3 n g | 0

Scheme 6.17 General conditions for the hydrogenolysis of glycerol.

1,2-PDO has been obtained from crude glycerol using copper chromite and
copper/carbon as catalysts, with good results (Scheme 6.17). The use of
CuCrO 3 as the preferred catalyst is justified by the high selectivities and
conversions reported by Suppes and others. The process involved a two-step
reaction, wherein glycerol is converted first to pure acetol, at 0.65 bar and
consequently into glycol by changing the pressure (up to 13.8 bar) in the
presence of the same catalyst. The reaction has proved to be a truly reactive
distillation process. The use of a single-step process proves to be dicult in
achieving selectivities higher than 80% with the surface of

d y y f n n 3 .

the catalyst

becoming coated by carbon deposits/oligomers.
CuCrO 3 has proven to be a suitable catalyst for the hydrogenation of
biodiesel glycerin into 1,2-PDO, however, the removal of salts (chlorides,
sulfates and/or phosphates) is likely to be required in order to avoid CuCrO 3
catalyst poisoning as much as possible. 185
The isomer 1,3-propanediol is also of interest, with potential in the fibre and
polymer industries; it is produced primarily by biochemical transformation
from crude glycerol. 186 The market for these glycols is expected to grow over
the next few years, with an estimated annual global demand of 535 000-717 000
tonnes and growth of 4%/pa. 187
Davy Ltd. and Eastman Chemicals Co. have filed at least two patents on the
chemical hydrogenation of crude glycerol for the production of
1,2-propanediol. 188 In these patents, the terminology ''glycerol from any
source'' implies the use of biodiesel glycerine for this invention. There is no
mention of a pretreatment for the feedstock in these examples. By contrast,
biodiesel glycerine is clearly acknowledged in a patent where it is claimed that
water/methanol solutions of minimum 40 wt% content of glycerol 189 are
reacted in the presence of mixed oxide (CuO-CeO 2 -SiO 2 ) at high temperatures
and pressure.

6.6.10 Acetalisation and Hydrogenolysis
Hemicetals and acetals of glycerol have a number of interesting properties,
from fuel additives to solvents, synthons for pharmaceutical production and
other uses. Different approaches to these products have been taken in the past,
with the use of homogeneous catalysts such as p-toluenesulfonic acid as a
traditional

route to deriving cyclic acetals from glycerol and other

carbohydrates. 190
The possibility of in situ formation of carbonyl compounds from glycerine
and their sequential acetalisation with glycerol is an interesting approach. This