A method using solid catalysts to simultaneously produce racemic
lactic acid and propylene glycol was developed. The synergistic
functions of a base catalyst and a dehydrogenation catalyst enable the
production of lactic acid and propylene glycol without external hydrogen
supply. The reaction pathway was elucidated and attested by our
systematically experimental study. Compared to previous studies on
lactic acid production from glycerol via chemocatalysis, this solventfree
method achieved higher productivity while eased corrosion problem
associated with the use of a homogeneous base catalyst such as
NaOH or KOH. Different combinations of catalysts and reaction conditions
provided a tunable range for the yield of lactic acid and propylene
glycol. The catalysts are partially reusable after regeneration. Although
at the current stage of development, a portion of the base catalyst
(CaO) cannot be recovered, the dehydrogenation ingredient (CuO) is
fully recoverable.
Future development along this way should consider the full recycle
of catalysts together with the downstream separation of products.
Furthermore, the advantage of using inexpensive CaO as solid base
should be emphasized. Because CaO (or other solid bases) has been
used in the production of biodiesel via transesterification, future development
should consider the further use of CaO or other suitable solid
bases for the production of LA/PG from crude glycerol to ease product
separation and ultimately lead to an integrated production of biodiesel
and value-added chemicals.