Catalytic routes towards bio-renewable glucaric acid
Biomass-derived glucaric acid has the potential to become an important bio-derived chemical due to its wide range of potential industrial applications, but most notably due to its application as detergent builder as a substitute for phosphates or citric acid and, as a precursor to renewable adipic acid. Typically, glucaric acid is synthesised from the oxidation of glucose, which involves using nitric acid as a stoichiometric oxidant, which brings about problems in pollution, separation and increased greenhouse gas emissions. Other routes are being explored and chemo-catalysis has received considerable interest, with several companies taking steps to begin large-scale commercialisation of these routes to glucaric acid and derivatives using heterogeneous catalysts. In this perspective review, we summarise the recent scientific and patent literature and critically evaluate the merits of each of the emerging routes towards glucaric acid.
One of the most widely available and well-studied biomass feedstocks is glucose, the monomeric unit contained in widely abundant cellulose and starch. In general, industrial-scale glucose production involves firstly isolating starch from the plant source, followed by acidic or enzymatic hydrolysis to give glucose (1). The high abundance of starch-containing compounds and thus the relatively low price of glucose, makes it a prime candidate for biomass conversions. As a result, glucose is one of the most important bio-based feedstock for various biomass conversions, ranging from fermentations to bioethanol for fuels, to dehydrations to polymer precursors, as seen in Figure 1 (2).
The US department of energy classified glucaric acid (also saccharic or glucosaccharic acid) as one of the top 12 value added chemicals from biomass in 2004 (3). Today, it is mostly synthesised by the non-selective nitric acid oxidation of glucose (Figure 2), forming 85 lbs of waste nitric acid per 100 lbs of glucaric acid produced (4). The use of nitric acid as the oxidising agent was cited as one of the reasons for removing glucaric acid from this list in a ...