Highlights  Biomass-based activated carbon catalysts modified with Lewis or Brønsted acid sites were prepared  Catalysts were used to convert glucose to HMF in biphasic water:THF system  51% HMF yield was obtained with catalytic mixture containing both Lewis and Brønsted acid sites  The water phase containing the catalyst was recycled successfully Abstract Selective and efficient dehydration of glucose to 5-hydroxymethylfurfural (HMF) has been widely explored research problem recently, especially from the perspective of more sustainable heterogeneous catalysts. In this study, activated carbon was first produced from a lignocellulosic waste material, birch sawdust. Novel heterogeneous catalysts were then prepared from activated carbon by adding Lewis or Brønsted acid sites on the carbon surface. Prepared catalysts were used to convert glucose to HMF in biphasic water:THF system at 160 °C. The highest HMF yield and selectivity, 51% and 78%, respectively, were obtained in 8 hours with a catalytic mixture containing both Lewis and Brønsted acid sites. Also, preliminary recycling experiments were performed. Based on this study, biomass-based activated carbon catalysts show promise for the conversion of glucose to HMF.

The depletion of fossil resources is driving forward the search for new and alternative renewable feedstocks in the production of renewable chemicals, which could replace the petroleum-based ones. One such feedstock is pine (Pinus sylvestris) sawdust, which is generated enormous amounts in Finnish sawmills yearly. However, prior to the utilization in high-value applications, it needs to be fractionated into its constituents. In this work, the objective was to produce monomeric hemicellulose sugars from pine sawdust without degrading cellulose or lignin simultaneously. The influence of the reaction temperature and time, as well as acid type and concentration, was studied. Based on the results, the temperature was the main distinguishing feature between cellulose and hemicellulose hydrolysis. Promising results were achieved with acid mixtures consisting of 0.5% sulfuric acid and 5.5 or 10% formic acid. At 120°C with the reaction time of 2 h, the mixtures produced hemicellulose sugars with the yields of 62%. These yields were comparable to the yields achieved in similar conditions with 1.5% sulfuric acid or 40% formic acid. Therefore, by using an acid mixture, the concentration of a single acid could be reduced significantly. The solid fractions remaining after the hydrolysis consisted mainly of cellulose and lignin, which verified the selectivity of the hemicellulose hydrolysis. Also, the fractionation of the remaining solids confirmed that the utilization of all the sawdust components is feasible.

Choline chloride (ChCl) / glycolic acid (GA) deep eutectic solvent (DES) media with high water content but without any additional catalyst are introduced in furfural and 5hydroxymethylfurfural (HMF) production. The effects of water content, reaction time, and reaction temperature are investigated with two feedstocks: a glucose/xylose mixture and birch sawdust. Based on the results, 10 equivalent quantities of water (32.9 wt.%) were revealed to be beneficial for conversions without rupturing the DES structure. The optimal reaction conditions were 160 °C and 10 minutes for the sugar mixture and 170 °C and 10 minutes for birch sawdust in a microwave reactor. High furfural yields were achieved, namely 62 % from the sugar mixture and 37.5 % from birch sawdust. HMF yields were low, but since the characterization of the solid residue of sawdust, after DES treatment, was revealed to contain only cellulose (49 %) and lignin (52 %), the treatment could be potentially utilized in a biorefinery concept where the main products are obtained from the cellulose fraction. Extraction of products into the organic phase (methyl isobutyl ketone, MIBK) during the reaction enabled the recycling of the DES phase, and yields remained high for three runs of recycling.

In this study, conversion of xylose to furfural was studied using lignin-based activated carbon-supported iron catalysts. First, three activated carbon supports were prepared from hydrolysis lignin with different activation methods. The supports were modified with different metal precursors and metal concentrations into five iron catalysts. The prepared catalysts were studied in furfural production from xylose using different reaction temperatures and times. The best results were achieved with a 4 wt% iron-containing catalyst, 5Fe-ACs, which produced a 57% furfural yield, 92% xylose conversion and 65% reaction selectivity at 170 °C in 3 h. The amount of Fe in 5Fe-ACs was only 3.6 µmol and using this amount of homogeneous FeCl3 as a catalyst, reduced the furfural yield, xylose conversion and selectivity. Good catalytic activity of 5Fe-ACs could be associated with iron oxide and hydroxyl groups on the catalyst surface. Based on the recycling experiments, the prepared catalyst needs some improvements to increase its stability but it is a feasible alternative to homogeneous FeCl3.

Levulinic acid is considered as one the most important platform chemicals. It is currently produced mainly from lignocellulosic biomasses. However, there are also other abundant biomass materials, which could be used as raw materials for levulinic acid production. In this work levulinic acid was produced from two novel biomasses in the presence of Brønsted (H 2 SO 4) and Lewis acid (CrCl 3. 6H 2 O or AlCl 3. 6H 2 O) catalysts. The studied materials were carbohydrate-rich potato peel waste and sporocarps of the fungus Cortinarius armillatus. Reaction conditions, i.e. time, temperature, H 2 SO 4 and Lewis acid concentrations, were studied by utilizing full 2 4-factorial experimental designs. Microwave irradiation was used as the heating method. Based on the results the reaction temperature and the H 2 SO 4 concentration had the greatest impact on the yield of levulinic acid. The highest yield obtained in this study from potato peel waste was 49% with 180ºC for reaction temperature, 15 min for reaction time and 0.5 and 0.0075 M for the concentrations of H 2 SO 4 and CrCl 3 , respectively. When Cortinarius armillatus was used as the raw material the highest yield was 62% with 180ºC for reaction temperature, 40 min for reaction time and 0.5 and 0.0075 M for the concentrations of H 2 SO 4 and CrCl 3 , respectively.