Production of fermentable sugars from corn fiber using soaking in aqueous ammonia (SAA) pretreatment and fermentation to succinic acid using Escherichia coli AFP184

Exploring lignin depolymerization by a bi-enzyme system containing aryl alcohol oxidase and lignin peroxidase in aqueous biocompatible ionic liquids

Enzymatic depolymerization of lignin to produce low molecular weight products requires mild reaction conditions and exhibits higher selectivity compared to thermochemical lignin depolymerization. However, it remains challenging to depolymerize lignin enzymatically, partially due to the low solubility of lignin in aqueous phase. This study aimed to develop a novel approach to combine aqueous lignin extraction with enzymatic lignin depolymerization in biocompatible ionic liquids. A bi-enzyme system containing aryl alcohol oxidase (AAO) and lignin peroxidase (LiP) was developed to depolymerize lignin. Temperature and pH profiles for LiP and AAO were determined. Biocompatibilities of LiP and AAO in different deep eutectic solvents and ionic liquids were investigated. Aqueous cholinium glycinate was found to be an efficient and suitable solvent to solubilize lignin and serve as a biocompatible medium for enzymes to work. LiP and AAO together reduced lignin molecular weight in both solid and liquid phase after enzymatic lignin depolymerization.

Fed-batch polyhydroxybutyrate production by Paraburkholderia sacchari from a ternary mixture of glucose, xylose and arabinose

Polyhydroxybutyrate (PHB) is a biodegradable bioplastic that is comparable with many petroleum-based plastics in terms of mechanical properties and is highly biocompatible. Lignocellulosic biomass conversion into PHB can increase profit and add sustainability. Glucose, xylose and arabinose are the main monomer sugars derived from upstream lignocellulosic biomass processing. The sugar mixture ratios may vary greatly depending on the pretreatment and enzymatic hydrolysis conditions. Paraburkholderia sacchari DSM 17165 is a bacterium strain that can convert all three sugars into PHB. In this study, fed-batch mode was applied to produce PHB on three sugar mixtures (glucose:xylose:arabinose = 4:2:1, 2:2:1, 1:2:1). The highest PHB concentration produced was 67 g/L for 4:2:1 mixture at 41 h corresponding to an accumulation of 77% of cell dry weight as PHB. Corresponding sugar conversion efficiency and productivity were 0.33 g PHB/g sugar consumed and 1.6 g/L/h, respectively. The results provide references for process control to maximize PHB production from real sugar streams derived from corn fibre.

Oxidative upgrade of furfural to succinic acid using SO3H-carbocatalysts with nitrogen functionalities based on polybenzoxazine

SO₃H-carbocatalysts with nitrogen functionalities were prepared using the carbonization of polybenzoxazine derived from four different amines (aniline, ethylenediamine, triethylenetetramine, and tetraethylenepentamine) and then sulfonation. The obtained SO₃H-carbocatalysts underwent catalytic testing for furfural oxidation with H₂O₂ to produce succinic acid. The effects of nitrogen functionalities were reported for the first time. The results showed that all carbon samples exhibited a microporous characteristic with comparable textural properties and contained various nitrogen functionalities (N-6, N-5, N-Q, and N-X). After sulfonation, the SO₃H-carbocatalyst prepared from tetraethylenepentamine-based polybenzoxazine had the highest amount of sulfonic acid groups (1.45 mmol g^-1) and a high nitrogen content (4.23%), providing a maximum succinic acid yield of 93.0% within a rapid reaction time of 60 min under the optimized conditions. This was higher than from Amberlyst-type catalysts and SO₃H-carbocatalyst without nitrogen functionalities and was ascribed to the synergistic activity of the sulfonic acid groups and nitrogen functionalities. The XPS spectra and computational study confirmed that such nitrogen functionalities, especially N-5, are capable of forming hydrogen bonding with furfural, facilitating the formation of an intermediate compound and thereby enhancing the catalytic efficiency. However, after four cycles, the succinic acid yield decreased to 40% due to leaching of the sulfonic acid groups.

Hybrid dilute sulfuric acid and aqueous ammonia pretreatment for improving butanol production from corn stover with reduced wastewater generation

An efficient hybrid pretreatment method was developed for butanol production from corn stover using dilute sulfuric acid (DA) and aqueous ammonia (AA). With the optimized AA concentration, treatment temperature and time of 10% AA, 80 °C and 24 h, the hybrid pretreatment could effectively dissolve hemicellulose and lignin with solid recovery rate of 37.45% and lignin reduction rate of 86.77% compared to those of 57.75% and 45.84% from single DA pretreatment. By washing 1 time after each step treatment, sugar yield and butanol production were increased to 401.76 mg/g-CS and 10.89 g/L from 346.04 mg/g-CS and 9.33 g/L obtained without washing. Compared with conventional single DA and AA pretreatment methods, wastewater generation was reduced to 0.83 L/g-butanol from 2.11 and 3.46 L/g-butanol, indicating this hybrid pretreatment could be an effective approach for improving butanol production from lignocellulosic feedstocks.