Isolation of chitin from marine biomass with deep eutectic solvents and kinetics study of n-deacetylation to chitosan : doctoral disertation

english

doktorska dela

2020

chitin   chitosan   deep eutectic solvents   fractionation of biomass   heterogeneous N deacetylation of chitin   homogeneous N deacetylation of chitin   in-line monitoring   reaction-diffusion model

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

The purpose of the dissertation is to present the development of a new methodology using green alternative solutions that represent an improvement over the traditional method of extracting components from marine biomass. The fractionation of marine biomass, in our case, the shrimp shell into components, with main chitin, which is one of the first and most commercially important biopolymers, was achieved by selectively optimizing the extraction conditions using eutectic solvents, resulting in very high chitin efficiency. The fractionation mechanism is explained by the quantitative analysis of the liquid and solid fractions obtained after dissolving the shrimp shells in DES. Eutectic solvents were recycled and reused for chitin isolation, showing slight impact on chitin recovery yield. The highest yield of chitin extraction was <90% using CCLA, with an isolated chitin purity greater than 98%. A study on the modeling of the heterogeneous N-deacetylation step of %-chitin obtained from shrimp waste using a catalytic alkaline solution at different operating temperatures and concentrations has provided new mechanistic insights. Particle size distributions for two separate experiments with smaller dusts or larger chitin morphologies were obtained in real-time. The biopolymer chain conversion mechanism was described via a mathematical reaction-diffusion lattice model solved for all fraction intervals. The reaction kinetics was second order reaction since the concentration of hydroxyl ions in the pores was not constant. The chosen mathematical model provided relatively good agreement for the cumulative experimental data on the kinetics in the initial phase as well as the subsequent diffusion for OH%. This study also developed one sustainable approach to chitin dissolution by incorporating green technology into chitin processing, to avoid negative drawbacks using conventional methods of chitin dissolution and chemical deacetylation. In this study, a variety of different eutectic chitin dissolution solvents were tested, where four proved to be very effective. CCLA (choline chloride-lactic acid) was the most promising solvent for dissolving chitin. Alkaline and neutral eutectic solvents were able to disturb the hydrogen bonds in the chitin structure, while establishing a new one and allowing faster reaction kinetics of N-deacetylation using a lower NaOH concentration. Thus, the most effective are: CCLA, GLBT (glycerol-betaine) and CCUR (choline chloride-urea), used to perform N-deacetylation with 30% NaOH solution at 80 ° C and reaction time up to 18h. The results obtained showed a DDA approximately 44-55% higher than the existing literature results where a homogeneous reaction of chitin N deacetylation took place.

07.08.2023