Nubla Mahmood

Production of polyols via direct hydrolysis of kraft lignin: Effect of process parameters

Kraft lignin (KL) was successfully depolymerized into polyols of moderately high hydroxyl number and yield with moderately low weight-average molecular weight (Mw) via direct hydrolysis using NaOH as a catalyst, without any organic solvent/capping agent. The effects of process parameters including reaction temperature, reaction time, NaOH/lignin ratio (w/w) and substrate concentration were investigated and the polyols/depolymerized lignins (DLs) obtained were characterized with GPC-UV, FTIR-ATR, (1)H NMR, Elemental & TOC analyzer. The best operating conditions appeared to be at 250°C, 1h, and NaOH/lignin ratio ≈0.28 with 20 wt.% substrate concentration, leading to <0.5% solid residues and ∼92% yield of DL (aliphatic-hydroxyl number ≈352 mg KOH/mg and Mw≈3310 g/mole), suitable for replacement of polyols in polyurethane foam synthesis. The overall % carbon recovery under the above best conditions was ∼90%. A higher temperature favored reduced Mw of the polyols while a longer reaction time promoted dehydration/condensation reactions.

Reductive de-polymerization of kraft lignin for chemicals and fuels using formic acid as an in-situ hydrogen source

In this study, formic acid (FA) was employed as an in-situ hydrogen donor for the reductive de-polymerization of kraft lignin (KL). Under the optimum operating conditions, i.e., 300 °C, 1 h, 18.6 wt.% substrate concentration, 50/50 (v/v) water-ethanol medium with FA at a FA-to-lignin mass ratio of 0.7, KL (Mw∼10,000 g/mol) was effectively de-polymerized, producing de-polymerized lignin (DL, Mw 1270 g/mol) at a yield of ∼90 wt.% and <1 wt.% yield of solid residue (SR). The MW of the DL products decreased with increasing reaction temperature, time and FA-to-lignin mass ratio. The sulfur contents of all DL products were remarkably lower than that in the original KL. It was also demonstrated that FA is a more reactive hydrogen source than external hydrogen for reductive de-polymerization of KL.

Hydrolytic depolymerization of hydrolysis lignin: Effects of catalysts and solvents.

Hydrolytic depolymerization of hydrolysis lignin (HL) in water and water-ethanol co-solvent was investigated at 250°C for 1h with 20% (w/v) HL substrate concentration with or without catalyst (H2SO4 or NaOH). The obtained depolymerized HLs (DHLs) were characterized with GPC-UV, FTIR, GC-MS, (1)H NMR and elemental analyzer. In view of the utilization of depolymerized HL (DHL) for the preparation of rigid polyurethane foams/resins un-catalyzed depolymerization of HL employing water-ethanol mixture appeared to be a viable route with high yield of DHL ∼70.5wt.% (SR yield of ∼9.8wt.%) and with Mw as low as ∼1000g/mole with suitable aliphatic (227.1mgKOH/g) and phenolic (215mgKOH/g) hydroxyl numbers. The overall % carbon recovery under the selected best route was ∼87%. Acid catalyzed depolymerization of HL in water and water-ethanol mixture lead to slightly increased Mw. Alkaline hydrolysis helped in reducing Mw in water and opposite trend was observed in water-ethanol mixture.

Hydrolytic liquefaction of hydrolysis lignin for the preparation of bio-based rigid polyurethane foam

Hydrolysis lignin (HL) was liquefied to a low average molecular weight (Mw) intermediate by employing a 50/50 (v/v) water–ethanol mixture. The effects of process parameters including the reaction temperature, the reaction time and the HL concentration were investigated and the liquefied hydrolysis lignin (LHL) products obtained were characterized by GPC, FTIR and 1H NMR. The best operating conditions appeared to be at 250 °C, 1 h with 20% (w/v) HL concentration, leading to ∼70 wt% yield of LHL (Mw ∼ 1000 g mol−1 and OHTotal ∼ 442 mg KOH g−1). The solid form LHL was derivatized into liquid polyols via oxypropylation with 50–70 wt% bio-content, which was subsequently utilized for the preparation of bio-based rigid polyurethane (BRPU) foams. All the foams were characterized in terms of their physical, mechanical and thermal properties & morphology. BRPU foams exhibit superior compression modulus and strengths to a reference foam prepared from commercial sucrose polyols provided by Huntsman Co. At a fixed formulation, i.e., a fixed percentage of physical blowing agent, BRPU foams showed the following sequence in terms of their compression modulus: sucrose polyol reference foam (2695.0 kPa) < LHL50PO50 (9202.0 kPa) < LHL60PO40 (19 847.0 kPa) < LHL70PO30 (21 288.0 kPa). All BRPU foams were thermally stable up to approximately 200 °C and thermal conductivity was low (0.030 ± 0.001 W m−1 K−1), making them suitable candidates for insulation material.

Sustainable Bio-Based Phenol-Formaldehyde Resoles Using Hydrolytically Depolymerized Kraft Lignin

In this study bio-based bio-phenol-formaldehyde (BPF) resoles were prepared using hydrolytically depolymerized Kraft lignin (DKL) as bio-phenol to partially substitute phenol. The effects of phenol substitution ratio, weight-average molecular weight (Mw) of DKL and formaldehyde-to-phenol (F/P) ratio were also investigated to find the optimum curing temperature for BPF resoles. The results indicated that DKL with Mw ~ 1200 g/mol provides a curing temperature of less than 180 °C for any substitution level, provided that F/P ratios are controlled. Incorporation of lignin reduced the curing temperature of the resin, however, higher Mw DKL negatively affected the curing process. For any level of lignin Mw, the curing temperature was found to increase with lower F/P ratios at lower phenol substitution levels. At 25% and 50% phenol substitution, increasing the F/P ratio allows for synthesis of resoles with lower curing temperatures. Increasing the phenol substitution from 50% to 75% allows for a broader range of lignin Mw to attain low curing temperatures.

Effects of Process Parameters on Hydrolytic Treatment of Black Liquor for the Production of Low-Molecular-Weight Depolymerized Kraft Lignin

The present research work aimed at hydrolytic treatment of kraft black liquor (KBL) at 200–300 °C for the production of low-molecular-weight depolymerized kraft lignin (DKL). Various process conditions such as reaction temperature, reaction time, initial kraft lignin (KL) substrate concentration, presence of a catalyst (NaOH), capping agent (phenol) or co-solvent (methanol) were evaluated. The research demonstrated effective depolymerization of KL in KBL at 250–300 °C with NaOH as a catalyst at a NaOH/lignin ratio of about 0.3 (w/w) using diluted KBL (with 9 wt. % KL). Treatment of the diluted KBL at 250 °C for 2 h with 5% addition of methanol co-solvent produced DKL with a weight-average molecular weight (Mw) of 2340 Da, at approx. 45 wt. % yield, and a solid residue at a yield of ≤1 wt. %. A longer reaction time favored the process by reducing the Mw of the DKL products. Adding a capping agent (phenol) helped reduce repolymerization/condensation reactions thereby reducing the Mw of the DKL products, enhancing DKL yield and increasing the hydroxyl group content of the lignin. For the treatment of diluted KBL (with 9 wt. % KL) at 250 °C for 2 h, with 5% addition of methanol co-solvent in the presence of NaOH/lignin ≈ 0.3 (w/w), followed by acidification to recover the DKL, the overall mass balances for C, Na and S were measured to be approx. 74%, 90% and 77%, respectively. These results represent an important step towards developing a cost-effective approach for valorization of KBL for chemicals.

Biomass Conversion of Plant Residues

Abstract This chapter reviews a variety of biomass conversion technologies including thermo-chemical liquefaction and biological conversion technologies for producing clean and green fuels, that is, biooil, H2, and CH4. First, each biomass conversion technology is briefly described in terms of conversion process, feed stock, and conversion efficiency. Then, the characteristics of products from each biomass conversion technology are discussed. In addition, efforts that are also being made for improving the conversion efficiency for each process are introduced. Finally, utilization of biomass conversion products is described and introduced. Thus this chapter contributes to better understanding of the fundamentals and potentials of the various biomass conversion technologies.