Research Articles

To obtain a higher furfural yield from Pisum sativum (pea pod) waste, the effects of the process variables phosphoric acid concentration (wt.%), reaction temperature, and liquid solid ratio (LSR) were investigated. A new reaction scheme was proposed consisting of series and parallel reactions for the formation of furfural. Kinetic models were developed to describe changes in the concentration of furfural with time. A modified Arrhenius equation was used to find out correlations between kinetic coefficients and reaction parameters. A maximum furfural concentration of 5.27 g/L (40.6% yield based on total conversion of pentosans) was obtained using 6% (wt.%) H3PO4 and liquid-to-solid ratio of 1:10 at 160 °C. Reaction parameters such as acid concentration, reaction temperature, and liquid solid ratio had a strong effect on the yield of furfural.

Cork is one of the most important forest products in Portugal. The cork processing industry is highly resource-efficient, and the only residue is cork powder, which is too small for agglomerate production. This work studied the usage of cork powder for the production of added-value products via polyol liquefaction. Liquefactions were performed in a reactor using a mixture of polyethylene glycol (PEG 400) and glycerol as solvents, which were catalyzed by the addition of sulphuric acid. Several cork-to-solvent ratios, reaction temperatures, and reaction times were tested. Polyurethane foams were prepared by combining polyol mixtures with a catalyst, surfactant, blowing agent, and polymeric isocyanate. Mechanical tests of the produced foams were conducted, and compressive modulus of elasticity and compressive stress at 10% deformation were determined. The results show that the best conditions for obtaining high liquefaction yields are as follows: 160 °C for 1 h; glycerol-to-PEG 400 ratio of 1:9; cork-to-solvent ratio of 1:6; and 3% H2SO4 catalyst addition. The Fourier Transform Infrared (FTIR) spectra indicated that the lignocellulosic fractions of the cork were more selectively dissolved during acidified polyol liquefaction than the suberin. With liquefied cork powder using these optimized conditions, it is possible to produce polyurethane foams with desired properties.

A graphene/hemin (H-GN) catalyst for lignin degradation was prepared by a wet-chemistry method with graphene oxide and hemin. Hemin was absorbed onto the graphene surface through π-π interaction. Graphene served as a supporting material for hemin, providing a large contact area between the active molecules of catalyst and substrate, as well as protecting hemin from self-oxidation and maintaining its active molecules. The H-GN catalyst showed high catalytic efficiency in the degradation of alkaline lignin under gentle conditions. At pH 13.0, the degradation rate was 49.7% with H-GN and H2O2 (mass ratio of H2O2 to lignin of 10:1) under 60 °C, which was higher than 34.9% for non-catalyst degradation. At pH 13.2, it was as high as 92.9 wt.% at 100 °C. The lignin was decomposed into small molecules with styrene as the main final product below pH 13 and with the major products of 4-hydroxy-4-methyl-2-pentanone and bis(2-ethylhexyl) phthalate at pH 13.2.

This work examined differences encountered when machining juvenile wood vs. mature wood. Difference in the blunting of the cutting tool when processing types of juvenile and mature wood from pine (Pinus sylvestris L.) and poplar (Populus tremula L.) were studied. The experimental model process included milling at various feed (2.5 and 15 m∙min-1) and cutting speeds (pine 20 m∙s-1, poplar 30 and 60 m.s-1), at various angle geometries (rake angle, cutting edge, and clearance angle). The blunting of cutting edge was measured after milling at 100, 300, and 500 meters on milling machine with the lower spindle. The results showed that milling of juvenile wood gives a longer technical lifetime for cutting instruments than milling of mature wood.

The feasibility of incorporating purified kraft lignin, at different concentrations ranging from 5 to 29%, into fiberboards made from corn residues was studied. The lignin was obtained from black liquor, which is a residue of the paper industry. Corn stalk raw material and its thermomechanically produced fiber were characterized in terms of their chemical composition. The physical and mechanical properties of the resulting fiberboards were evaluated. The fiberboards produced following a wet process had good mechanical and water resistance properties that satisfied the requirements of the relevant standards. In addition, a Life Cycle Thinking (LCT) approach suggested that lignin-based fiberboards are environmentally preferable than those based on thermosetting resins.

During the steam explosion pretreatment of plant biomass, degradation products are generated, and some of these have inhibitory activity against biogas production. The aim of this study was to investigate and quantify the effect of selected model inhibitory compounds on methane production. The results showed no significant inhibition of methane production by furfural at concentrations below 1 g/L. In addition, the microbial community was able to restore biogas production inhibited by this compound after a certain time. 5 hydroxymethylfurfural was evaluated as a more potent inhibitor, with a significant effect above 0.2 g/L. Both compounds were more effective inhibitors with cellulose as the carbon substrate, probably reflecting higher sensitivity of the cellulolytic step in biogas production. No significant inhibition was observed for the phenolic compounds tested, gallic and tannic acids, at concentrations of up to 2 g/L. Thus, the compounds investigated should not represent a problem for the biogas production involving steam explosion preprocessed plant biomass.

The anionic groups (AGs) present in mulberry stem sulfonated chemi-mechanical pulp (SCMP) were studied relative to the adsorption of methylene blue (MB) dye. Adsorption isotherm experiments were carried out for the unbleached pulp, and for pulp that had been subjected to hydrogen peroxide (H2O2) bleaching. AGs present in the pulps appeared to govern the adsorption of MB. MB adsorption kinetics were evaluated for the bleached pulp. The methylene blue adsorption by SCMP, made from mulberry stems, conformed to the Langmuir adsorption model, which is consistent with a monolayer adsorption process. The adsorption thermodynamics showed that the adsorption process was spontaneous and exothermic. A pseudo-second order kinetic model described the adsorption mechanism of MB by the SCMP made from mulberry stems.