Currently, global wood-panel industry heavily depends on petroleum-derived commercial adhesives[1], [2] like phenol–formaldehyde, urea–formaldehyde, melamine–formaldehyde etc. These formaldehyde-based chemicals cause hazards to both human health and environment through emission of toxic volatile organic compounds[3], [4]. Hence, this work focuses on manufacturing bio-adhesive using renewable materials such as lignin and soy protein isolate (SPI). Soy protein by itself can be used as an adhesive. It has the advantages of being bio-degradable, low-cost, and feasible for large volume of production[4], [5]. However, soy protein as an adhesive by itself suffers from low water–resistance, poor mechanical properties, and relatively low bonding strength[6]. On the other hand, lignin is considered to be another potential raw material for bio-adhesive due to the presence of both alcohol- and phenol-type hydroxyl groups in its complex molecular structure[7]. It has been observed that crosslinking soy protein with lignin can be an effective way to overcome the disadvantages associated with soy protein adhesive, and improve adhesive performance.
In this work, a mathematical model is developed for a bio-adhesive manufacturing process that uses kraft lignin (KL) and SPI as the feedstock. The laboratory approach that is modeled involves two steps, namely, (a) depolymerization of KL into smaller oligomer units and (b) addition of these oligomer fragments to SPI to produce the desired bio-adhesive. A kinetic model for the base-catalyzed depolymerization (BCD) of KL is developed. While lumped models for this process is available in the literature that lumps multiple components, this works develops an approach so that individual species can be identified and quantified as needed for their separation and economic evaluation. Optimal estimation of reaction and mass transfer kinetic parameters is done by using in-house experimental data. A model of the bio-adhesive production step is also developed. The lab-scale reactor is a batch reactor. For large-scale commercialization, two types of reactors are modeled and designed- commercial-scale batch reactor and commercial-scale continuous flow reactor. This study compares both type of reactors, evaluating and comparing their performances in terms of productivity and economic feasibility. It has been observed that compared to the batch reactors, continuous-flow reactors can lead to the efficiency of lignin depolymerization by reducing energy consumption, residence time, and repolymerization issues, but can add to costs and operational difficulties. A plant-wide model is developed to produce the bio-adhesive that can satisfy the desired quality specifications. A comprehensive techno-economic model of the whole process is developed. Techno-economic optimization is undertaken for maximizing the net present value by optimizing the design variables and operating conditions of the plant-wide process.
References:
[1] M. Podlena, M. Böhm, D. Saloni, G. Velarde, and C. Salas, “Tuning the adhesive properties of soy protein wood adhesives with different coadjutant polymers, nanocellulose and lignin,” Polymers (Basel)., vol. 13, no. 12, pp. 1–16, 2021, doi: 10.3390/polym13121972.
[2] A. Arias et al., “Recent developments in bio-based adhesives from renewable natural resources,” J. Clean. Prod., vol. 314, no. May, 2021, doi: 10.1016/j.jclepro.2021.127892.
[3] D. Gonçalves, J. M. Bordado, A. C. Marques, and R. G. Dos Santos, “Non-formaldehyde, bio-based adhesives for use in wood-based panel manufacturing industry—a review,” Polymers (Basel)., vol. 13, no. 23, 2021, doi: 10.3390/polym13234086.
[4] M. Bai et al., “A novel universal strategy for fabricating soybean protein adhesive with excellent adhesion and anti-mildew performances,” Chem. Eng. J., vol. 452, no. P3, p. 139359, 2023, doi: 10.1016/j.cej.2022.139359.
[5] C. Xu et al., “Soy protein adhesive with bio-based epoxidized daidzein for high strength and mildew resistance,” Chem. Eng. J., vol. 390, no. February, p. 124622, 2020, doi: 10.1016/j.cej.2020.124622.
[6] Ma, Y., Kou, Z., Hu, Y., Zhou, J., Bei, Y., Hu, L., Huang, Q., Jia, P., Zhou, Y., 2023. Research advances in bio-based adhesives. International Journal of Adhesion and Adhesives 126, 103444. https://doi.org/10.1016/j.ijadhadh.2023.103444
[7] C. Jiang, J. Hu, C. Zhang, G. Hota, J. Wang, and N. G. Akhmedov, “Lignin oligomers from mild base-catalyzed depolymerization for potential application in aqueous soy adhesive as phenolic blends,” React. Chem. Eng., vol. 8, no. 10, pp. 2455–2465, 2023, doi: 10.1039/d3re00224a.