Sequential Fractionation of Palm Empty Fruit Bunch and Microwave-Assisted Depolymerization of Lignin for Producing Monophenolic Compounds

Abstract

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.

Lignin-Derived Syringol and Acetosyringone from Palm Bunch Using Heterogeneous Oxidative Depolymerization over Mixed Metal Oxide Catalysts under Microwave Heating

“…Just newly reported, microwave-assisted catalytic depolymerization of birch sawdust lignin over Pt/C, Pd/C, or Ru/C in water/alcohol mixture facilitated in situ hydrogen generated and simultaneously promoted the hydrogenolysis of β-O-4 ether linkage which markedly yield S-type lignin relatively to Guaiacyl or G-type lignin as main products [42]. The result was in good agreement with our previous study on microwave-assisted depolymerization of alkaline lignin from palm bunch over dual Cu(OH) 2 and Fe 2 O 3 catalysts which gave highly selective syringyl-type products within only 15 min [26].…”

“…Further, supercritical fluids although provides high selectivity than acid and base-catalyzed reactions, nevertheless supercritical solvents facility limited their applications on biomass treatment in commercial scale [21,22]. Conversion of lignin to vanillin or phenolic aldehydes e.g., p-hydroxybenzaldehyde, vanillaldehyde, syringaldehyde [23], which are used in pharmaceutical application, has been widely studied via mild oxidative reaction that required either air, molecular oxygen [24] or oxidant such as H 2 O 2 [25][26][27].…”

“…Most of early research on lignin oxidation was proceeded with oxidant or with Zr 4+ , Mn 3+ , Co 2+ and Cu 2+ which were simple transition metal ions [32,33]. After that, Mn, Co, Cu and Fe based metal oxides (e.g., CuO, MnO 2 ), metal chlorides (e.g., MnCl 2 , CoCl 2 , FeCl 3 ) [26,34] and composite metal oxides were subsequently investigated to augment oxygen catalytic efficiency for lignin depolymerization [35][36][37][38].…”

Tandem Triphosgene-Assisted Metal-Free One-pot Preparation of Nitriles and Amides from Aldehydes and Ketones

“…[20][21][22][23][24][25] Among the alternatives from biomass valorization, the production of 5-hydroxymethylfurfural (HMF) from hexoses is a versatile platform for the synthesis of furan-based chemicals such as furyl diamide, diamidine, diimidate, and diformylfuran. [26][27] Therefore, oxidative depolymerization of lignin and lignin model compounds can obtain aromatic aldehydes and ketones [28][29][30][31][32][33][34][35][36][37][38] such as vanillin veratraldehyde, acetovanillone, acetosyringone, and syringaldehyde. To further demonstrate the utility of our protocol, we used our one-pot strategy for the efficacious synthesis of 2,5-dicyanofuran from biomass-derived 2,5-diformylfuran.…”

Microporous 3D aluminum MOF doped into chitosan‐based mixed matrix membranes for ethanol/water separation

“…Moreover, ethanol is used as a fuel in many vehicles including cars and buses . Bioethanol is a biofuel that is extracted from plant products such as starch, sugars, and cellulose . Generally, ethanol is extracted using different techniques such as, pervaporation, extractive or azeotropic distillation, mixed matrix membrane (MMM) separation, and molecular sieve adsorption‐separation etc.…”