(590i) Kinetic Modeling and Optimization of a Bio-Adhesive Production Process from Lignin

Due to the gradual depletion of fossil fuel sources along with the issues of greenhouse gas emission and resulting environmental impact, interest in the development of sustainable technologies has rapidly increased over last few decades. The global wood-adhesive industry heavily depends on the petroleum-derived commercial adhesives like phenol–formaldehyde (PF), urea–formaldehyde (UF) and melamine–urea–formaldehyde (MUF)¹. These formaldehyde-based chemicals cause hazards to both human health and environment through emission of toxic volatile organic compounds^1,2. Hence, this project focuses on manufacturing of bio-based adhesives using renewable materials such as soy-protein and lignin.

Lignin, one of the main constituents of lignocellulosic biomass, is considered to be a potential raw material for bio-adhesives due to the presence of both alcohol- and phenol-type hydroxyl groups in its complex molecular structure³. In this work, kraft lignin is used as the feedstock for the BCD process. Each year, more than 50 Mt kraft lignin (KL) is produced as a waste in the paper and pulp industry, and almost 98% of it is burned as a fuel causing high emission of greenhouse gases^3–6. Production of the bio-adhesive from KL consists of two steps. In the first step, the lignin is depolymerized to smaller oligomer units. These oligomer fragments are added to the soy protein isolate in the second step to produce the bio-based adhesive. The degradation of lignin can be achieved by various thermochemical, electrochemical, or biological treatments⁴ in presence or absence of catalysts. The thermochemical method includes hydrothermal base catalyzed depolymerization (BCD) process. BCD of lignin can generate various multicomponent and multiphase products^3,7. In spite of several existing kinetic models^7,8 for depolymerization of lignin under hydrothermal conditions either in presence or absence of acid catalysts, only a handful of papers have developed a kinetic model for the hydrothermal BCD of lignin⁵. These existing kinetic models have been developed in terms of lumps like oligomers, liquid oil and SOC, gaseous products etc., and the properties of all compounds of a lump are considered to be same^3,5. In this work, reaction rate models are developed for most key components and by including the concentration of the base catalyst in the kinetic model. Kinetic parameters are optimally estimated by using the experimental data. Models of the separation section are developed for separating the oligomers from other undesired products. These oligomers are then cross-linked with soy protein isolate (SPI) to produce the bio-adhesive. A kinetic model of the reactor for producing bio-adhesive is proposed and rate parameters are estimated by using the experimental data. The lab-scale reactor models are scaled to the commercial-scale and models of additional balance of plant are developed for mass and heat integration and recycle of catalysts. A economic model of the process is developed and a mathematical optimization problem is set up to optimize the design parameters and operating conditions of the reactors for maximizing the net present value.

References:

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2. Thuraisingam, J., Mishra, P., Gupta, A., Soubam, T. & Piah, B. M. Novel natural rubber latex/lignin-based bio-adhesive: synthesis and its application on medium density fiber-board. Iran. Polym. J. (English Ed. 28, 283–290 (2019).
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