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We develop a sequential fractionation of palm empty fruit bunches (EFB) and microwave-assisted depolymerization of lignin for producing monophenolic compounds with high yields. EFB has been known as a low-priced and abandoned residue from the palm oil milling process due to its low heating value and generation of toxic gases upon burning; therefore, valorization of EFB has been an important task for circular economy. In this study, a subsequent alkaline hot compressed water fractionation to separate hemicellulose and lignin from cellulose has been studied. The lignin separation by lignin precipitation and a filtration process followed by microwave-assisted lignin oxidative depolymerization to high value phenolic compounds was proposed. We systematically screened many catalysts as well as investigated reaction conditions (such as the concentration of hydrogen peroxide, reaction time, etc.) to achieve the highest yield of lignin-derived phenolic compounds. It was found that the optimal conditions for depolymerization of pretreated EFB lignin were (i) NaOH solution with 2.5% (w/w) hydrogen peroxide, (ii) microwave (300 W) for 15 min, and (iii) bimetallic Cu­(OH)2 and Fe2O3 catalysts. The highest percentage of the total phenolic compound concentration peak area is 91.78%, including 42.84% of syringol, 5.42% of vanillin, 8.71% of acetovanillone, 6.65% of syringaldehyde, and 28.16% of acetosyringone. The proposed sequential fractionation and microwave-assisted treatment would be promising for converting other lignocellulosic raw biomass to useful phenolic compounds.

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Rice straw (Oryza sativa) and sugarcane bagasse (Saccharum spp.) were subjected to catalytic oxidation. An oxidative cleavage of lignocellulose agro-residues was based on ferric ions and hydrogen peroxide driven by 2,5-dihydroxybenzoic acid (DHB) in weak acidic condition at room temperature. Alteration of inter-and intra-molecular bonding of cellulose and change in cellulose crystallinity which led to influence enzymatic susceptibility were investigated. By means of Fourier transform infrared spectroscopy, functional groups and chemical bonding modification in cellulosic, non-cellulosic, and lignin constituents of rice straw and sugarcane bagasse were characterized. Transformation of crystalline cellulose Iα and I β forms was observed after the oxidative reaction. The catalytic oxidative reaction by the Fe 3+ /DHB/H 2 O 2 system accelerated the modification of cellulose Iα to cellulose I β phase of sugarcane bagasse. However, the addition of DHB barely affected the oxidative degradation of rice straw. In addition, the crystallinity index of rice straw and sugarcane bagasse that decreased after oxidative reaction caused increases of hydrolytic enzyme accessibilities of treated samples.

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A series of activated carbons (ACs) derived from spent disposable wooden chopsticks was prepared via steam activation and used to separate carbon dioxide (CO2) from a CO2/hydrogen (H2) mixed gas at atmospheric pressure. A factorial design was employed to investigate the effects of the activation temperature and time as well as their interactions on the production yield of ACs and their CO2 adsorption capacity. The activation temperature exhibited a much higher impact on both the production yield and the CO2 adsorption capacity of ACs than the activation time. The interaction of both parameters did not significantly affect the yield of ACs, but did affect the CO2 adsorption capacity. The optimal preparation condition provided ACs with a desirable yield of around 23.18% and a CO2 adsorption capacity of 85.19 mg/g at 25 °C and 1 atm and consumed the total energy of 225.28 MJ/kg AC or 116.4 MJ/g-mol CO2. A H2 purity of greater than 96.8 mol% was achieved from a mixed gas with low CO2 concentration (< 20 mol%) during the first 3 min of adsorption and likewise around 90 mol% from a mixed gas with a high CO2 concentration (> 30 mol%) during the first 2 min. The CO2 adsorption on the as-prepared ACs proceeded dominantly via multilayer physical adsorption and was affected by both the surface area and micropore volume of the ACs. The adsorption capacity was diminished by around 18% after six adsorption/desorption cycles. The regeneration of the as-prepared chopstick-derived ACs can be easily performed via heating at a low temperature and ambient pressure, suggesting their potential application in the temperature swing adsorption process.