Combining Cost‐Efficient Cellulose and Short‐Chain Carboxylic Acid Production: The Polyoxometalate (POM)‐Ionosolv Concept

Abstract

Full cost‐effective exploitation of all wood components is key to growing a commercially successful biorefining industry. An innovative process is reported that combines fractionation of lignocellulosic biomass using a low‐cost ionic liquid (Ionosolv) and production of bio‐derived formic acid using polyoxometalates and molecular oxygen (OxFA process). We show that the hemicellulose and part of the lignin were selectively dissolved into the ionic liquid triethylammonium hydrogen sulfate and oxidised in situ to short‐chain, distillable carboxylic acids by a Keggin‐type polyoxometalate with high yields and selectivities. Characterization by several techniques, including ICP‐OES, FTIR, GC, HPLC and NMR spectroscopy confirmed stability of the catalyst over three consecutive POM‐Ionosolv recycles and stable formic acid yields.High formic acid yields of 26 % (pine chips), 23 % (beech chips), and 18 % (Miscanthus) were obtained with respect to the initial carbon content of the biomass, with unprecedented oxidation selectivities for formic acid of 54–62 % depending on vanadium substitution in the polyoxometalate, the processing temperature and the water content in the reaction mixture.. We also demonstrate that the cellulose rich pulp is a suitable source of glucose via enzymatic saccharification. We report cellulose yields of 37% for Miscanthus (from originally 48% glucan content), 33% for pine (from originally 49%) and 31% for beech (from originally 41%) were achieved, and a saccharification yield of up to 25% without optimisation. With further optimisation, this concept has the potential to generate two chemical products directly from lignocellulose in high yields and selectivities and hence a novel avenue for full utilisation of cellulose, hemicellulose and lignin.

Polyoxometalates (POMs): from electroactive clusters to energy materials

“…Moreover, POMs as weak bases could promote the formation of hydrogen-bond networks near the CO 2 coordination center to favor proton-coupled electron transfer that occurs when the proton source is close to the catalytically active center. Electrocatalytic reduction of CO 2 with POM was first reported by Kozik et al 278 273 The bonds between Zn 2+ ions on POM and carboxylates porphyrin were formed under hydrothermal conditions using M-TCPP = tetrakis[4-carboxyphenyl]-porphyrinato-M, as ligands.…”

“…The desirable photocatalyst for CO 2 RR should at least have following features: i) a suitable band gap structure for absorbing photons; ii) an efficient separation and transport of photo-generated electron-hole pairs; iii) large number of active adsorption and reaction sites for promoting photocatalytic reaction. [278][279][280] The research in photocatalytic CO 2 RR is focused on finding catalysts that can work in visible light (>380nm) and are able to sustain the multi-electron transfer process. The final products of such a process are carbon monoxide (CO), formic acid (HCOOH), formaldehyde (HCHO), methanol (CH 3 OH), and methane (CH 4 ).…”

“…Anna Bukowski et al developed a concept called the Ionosolv method in which fractionation of lignocellulosic biomass (wood) was achieved using a low-cost IL. 278 Bio-derived formic acid was produced using a POM catalyst and molecular oxygen as an oxidant. The IL alkylammonium…”

Sensitivity Analysis and Parameter Optimization for the Fractionative Catalytic Conversion of Lignocellulosic Biomass in the Polyoxometalate–Ionosolv Concept

“…The POM−ionosolv concept combines fractionation of lignocellulosic biomass and selective oxidation of the dissolved components to short-chain carboxylic acids. 10 compounds are then selectively oxidized using the HPA-5 POM catalyst to short-chain carboxylic acids like formic acid and acetic acid with yields up to 30% for each of them. Besides formic and acetic acid, a cellulose-rich pulp is produced as part of the POM−ionosolv concept which can be further converted via enzymatic saccharification and fermentation.…”

“…7−9 The recently demonstrated polyoxometalate (POM)−ionosolv concept enables fractionation of lignocellulosic biomass into a solid cellulose-rich pulp that is suitable for enzymatic saccharification and a dissolved hemicellulose and lignin fraction which are converted into formic and acetic acids. 10 It is known that a protic ionic liquid (IL) water mixture consisting of the ionosolv IL triethylammonium hydrogen sulfate, [TEA][HSO 4 ], mixed with 20−40 wt % water, 11 can be used for extracting hemicellulose and lignin from a lignocellulosic feedstock, while a soluble polyoxometalate (POM) catalyst has the ability to catalytically convert soluble components to short-chain carboxylic acids like formic and acetic acids in the presence of molecular oxygen as the oxidant. 12 Due to their structural diversity and tunable properties, POMs have attracted much attention for the valorization of biomass compounds during recent years.…”