Abstract
Objective of this study was the investigation on the up-scaling of base-catalyzed depolymerization (BCD) of lignin to pilot plant dimension. The cleavage process was carried out in dilute alkaline solution at temperatures up to 340°C and a pressure of 25 MPa in a continuously operated tubular flow reactor with throughputs up to 20 kg/h. Investigations included the proof of the feasibility of the scale-up as well as a parameter study on the cleavage of hardwood Organosolv lignin and softwood Kraft lignin within the established pilot plant. Yields and molecular compositions of the isolated product fractions BCD-oil (liquid phenolic fraction) and BCD-oligomers (solid phenolic fraction) are similar to those described in technical lab scale, showing a good scalability. Here, BCD-oils rich in phenolic monomers such as guaiacol, catechol and/or syringol were obtained with a content of up to 13.3 wt% and 14.5 wt% from Organosolv lignin and Kraft lignin, respectively. Formation of BCD-oligomers strongly depends on temperature and residence times within the reactor.
Highlights
The valorization of lignin is one of the most important challenges for the development of cost-effective biorefinery processes based on lignocellulosic biomass
The feasibility of base-catalyzed depolymerization (BCD) using a pilot scale flow reactor was demonstrated for cleaving Organosolv lignin and Kraft lignin
Parametric studies were performed on the catalytic depolymerization in order to evaluate the influence of the process parameters on the isolated yields and the molecular composition of the obtained product fractions (BCD-oil, BCD-oligomers)
Summary
The valorization of lignin is one of the most important challenges for the development of cost-effective biorefinery processes based on lignocellulosic biomass. The alkylphenolic structure of the lignin molecule can be catalytically transferred into low molecular weight compounds such as phenols, alkylphenols and phenol resins and replacing those obtained from fossil resources [1] [2]. The natural complexity and high stability of lignin bonds make lignin depolymerization still a challenging task. The process of base-catalyzed depolymerization (BCD) of lignin results in hydrolysis of the aryl-aryl-ether bonds and the arylalkyl-ether bonds in the lignin macromolecule and thereby in the production of monomers as well as dimeric and oligomeric alkyl-functionalized phenolic compounds [7] [8] [9]. The BCD process is carried out in aqueous or alcoholic systems at temperatures of up to 350 ̊C, pressures up to 25 MPa and mainly at short residence times (
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