Journal of Advanced Chemical Engineering

Biocatalytic conversion of lignin residues into artificial lignin structure with predictable properties

2^nd International Conference on Advances in Chemical Engineering and Technology

November 16-17, 2017 | Paris, France

Madalina Tudorache, Cristina Opris and Nazar Almanov

University of Bucharest, Romania

Posters & Accepted Abstracts: J Adv Chem Eng

Abstract:

Lignin, the second most abundant natural polymer after cellulose of terrestrial sources plays a negative role in pulp and paper industry. Huge amount of lignin is/was produced during the paper manufacturing approach (e.g. over 70 million tons of lignin produced annually in the world). Most of this lignin is burned (95 %) and only few percents are invested in value-added products, specially phenolic polymers. In this context, we developed a biocatalytic system based on the oxy-polymerization of lignin waste-units (monolignols such as sinapyl alcohol SA and coniferyl alcohol CA) assisted by the enzyme (e.g. peroxidase enzyme) and using the oxidation reagent as enzyme cofactor (e.g. hydrogen peroxide H2O2 or tert-butyl hydroperoxide t-BHP). The process involved a radical mechanism leading to polyphenols (artificial lignin). Controlled architecture of the prepared polymers has been done using specific type/ratio of monolignols. Additionally, well-known monomers following always the same reaction route give the opportunity for diminishing the heterogeneity of ligno-polymeric products, which is an important advantage. Different peroxidase enzymes (e.g. unspecific peroxidase PADA-I, and versatile peroxidase 2-1B and R4) were tested exhibiting similar catalytic activity for the same monolignol (Figure 1). Oppositely, horseradish peroxidase (HRP) was not a suitable candidate for this system. As a general remark, SA was easier recognized and transformed by peroxidase compared to CA. Fast kinetic of the biocatalytic process allowed to achieve maximum conversion of the lignin fragments (around 90 % for couple of 4R and SA) in only 2 hours (Table 1). Also, large polymer structure was produced with 4R peroxidase enzyme (MW=3188 Da and PD=3). Detailed study of the process kinetic and optimization of the experimental parameters (e.g. reagents concentration, temperature, buffer pH, enzyme content, etc.) have been performed. Moreover, the characteristics of the synthetic biopolymer have been investigated (e.g. GPC and NMR analysis) and compared to the mother-lignin source. The efficiency of the process related to the resulted lignin can be easily modulated based on the composition of the precursor mixture (i.e. content of the mixture in terms of the monolignols ratio). Therefore, a mixture of both monolignols has been used for polymerization. For co-polymerization, maximum conversion was achieved at 50 °C with H2O2 as oxidation reagent. However, in order to produce large lignin structures, t-BHP has to be used leading to a polymer with MW around 2000 Da. Further, oligolignols from natural lignin degradation were succesefully tested in the developed system. A corelation between oligolignols structure and design/properties of the resulted artificial lignin has been found giving the opportunity to develop the requested lignin structures. This study offers new perspective on the valorization of the lignin residues (mono-/oligolignols). Thus, several applications of the developed system are predicted for the future, e.g. direct deposition of the artificial lignin on the solid surface, removing the lignin fragments from the pyrolitic polysaccharides, etc). Acknowledgments: This work was financially supported by PN III TE program, contract no. 103/2015, 27BG/2016 and 8PED/2017 from MENUEFISCDI, Romania.