Production of lactic acid from glycerol via chemical conversion using solid catalyst: A review

The production of lactic acid from glycerol has been receiving a lot of attention due to the efficient roles of glycerol as raw material in producing various useful chemicals. Selective oxidation and hydrothermal reactions using solid catalyst have been found as potential techniques in producing high selectivity of lactic acid. Typically, glycerol reaction mechanisms are proposed based on oxidative dehydrogenation, dehydration and benzylic acid rearrangement step in alkaline aqueous medium. Bifunctionals catalyst are useful to carry out multi-step reaction requiring different active sites in one pot reaction. One of the selective oxidation processes is using bifunctional catalyst with acidic site in combination with Al3+ or Cr3+' with Lewis acid sites and a redox centre i.e. polyoxometalates (POM) exhibited high activity (93.7%) and selectivity (90.5%) to lactic acid. Meanwhile, hydrothermal reaction by using 30%CuO/ZrO2 gave 100% glycerol conversion and 94.6% selectivity to lactic acid. Currently, the development of efficient catalysts through suitable combinations of non precious metals is highly proposed. This paper critically reviews the recent progress in this area of research by classifiying catalysts based on active sites and roles of catalyst characteristics. The detail discussion on the influencing parameters to enhance the selectivity of lactic acid and glycerol conversion is also provided in detail.