A Promising Platform for Bio-refining

Biomass is the only widely available carbon source apart from oil and coal. Unlike these fossil feedstocks, biomass is CO2 neutral, since the CO2 release during use equals the amount taken up by the plants during their growth. Thus biomass is a highly attractive alternative feedstock for production of chemicals and energy. Unlike fossil feedstocks, biomass contains a relatively large quantity of oxygen. The project focusses on removal of oxygen from biomass, in the form of carbon monoxide, which is used in further “bio-refinery” processes.

It is generally accepted that the most effective use of biomass is in so called bio-refineries, which – just like refineries based on crude oil as feedstock – are able to produce a range of both fuels and chemicals. Further, it seems clear that bio-refineries will need a technology platform based on intermediate substances suited for further processing into the desired end products. One such promising platform is the furanic platform based on HMF (5-hydroxymethyl furfural).

In the first part of the project a Pd-catalyzed methoxycarbonylation reaction with HMF was investigated. The reaction yielded methyl heptanoate (MH), methyl levulinate (ML), and γ–valerolactone (GVL). The latter is a promising green fuel, while MH and ML are well-known intermediate products in chemical industry. The reactions were optimized, both in terms of utilized catalysts, reaction time, the nature and the amount of the palladium precursor and ligand, reaction temperature, and different alkene and alcohol substrates.

The optimized catalytic system gave good yields in a one-pot reaction from HMF. The use of a catalytic Pd complex with the ligand 1,2-bis(di-tert-butylphosphinomethane)- benzene (DTBPMB) in the transfer hydrogenation for the production of GVL was reported successfully for the first time. The presence of a dissolved Brønsted acid proved of crucial importance. An inverse proportionality between ML and GVL was discovered and explained in a mutual conversion of ML to GVL, via hydrogenation.

Further, a small screening of various cheap alkenes and alcohols was carried out, proving the viability of the reaction on different reagents. Products such as ethyl heptanoate and dimethylsuccinate were yielded.

In a second part of the project, the same methodology was tested with sugars as substrates. Fructose and glucose proved to be susceptible to the reaction conditions and gave considerably high yields of both MH and GVL. Glucose, in particular, yielded notable amounts of MH, despite its lower reactivity towards the catalytic complex.

A screening of different carbohydrates – aldoses, ketoses, pentoses, disaccharides, and polysaccharides – proved the catalytic system to be active on all these compounds. Structural differences were shown to be crucial for the variation in the yields of the final products. In conclusion, further experiments on polymers can be recommended to expand this catalytic system to a broader range of compounds in order to improve the utilization of biomass and minimizing waste.