a b s t r a c tBiotechnology also holds tremendous opportunities for realizing functional polymeric materials. Biocatalytic pathways to polymeric materials are an emerging research area with not only enormous scientific and technological promise, but also a tremendous impact on environmental issues. Many of the enzymatic polymerizations reported proceed in organic solvents. However, enzymes mostly show none of their profound characteristics in organic solvents and can easily denature under industrial conditions. Therefore, natural enzymes seldom have the features adequate to be used as industrial catalysts in organic synthesis. The productivity of enzymatic processes is often low due to substrate and/or product inhibition. An important route to improving enzyme performance in non-natural environments is to immobilize them.In this review we will first summarize some of the most prominent examples of enzymatic polymerizations and will subsequently review the most important immobilization routes that are used for the immobilization of biocatalysts relevant to the field of enzymatic polymerizations.

The one-pot hydrogenation of levulinic acid to 2-methyltetrahydrofuran (MTHF) was performed using a series of Ni-Cu/Al2 O3 catalysts in green solvents, such as water and biomass-derived alcohols. Ni/Al2 O3 provided the highest activity, whereas Cu/Al2 O3 was the most selective, reaching a 75 % MTHF yield at 250 °C after 24 h reaction time. Synergetic effects were observed when bimetallic Ni-Cu/Al2 O3 catalysts were used, reaching a 56 % MTHF yield in 5 h at 250 °C for the optimum Ni/Cu ratio. Remarkably, these high yields were obtained using non-noble metal-based catalysts and 2-propanol as the solvent. The catalytic activity and selectivity results are correlated to temperature programmed reduction (TPR), XRD, and STEM characterization data, identifying the role associated with mixed Ni-Cu particles in addition to monometallic Cu and Ni.

Among all biomass sources, the lignocellulosic biomass derived from agricultural and forestry wastes is considered as the most adequate substitute for fossil sources due to its abundance, versatility and lack of competition with food resources. Yet, the efficient and economically feasible conversion of lignin into fuels and chemicals remains one of the major technology gaps for the development of lignocellulosic biorefineries. Here, the chemical nature of the lignin biopolymers will be described based on their botanical origin and the isolation process. After summarizing the most relevant advances in the catalytic conversion of lignin, the recently developed Ligninto-Liquids (LtL) process will be described and its major challenges addressed. 1.1 Energy transition: from crude oil to a biomass based energy system According to the results of the 2015 Revision 1 published by the Department of Economic and Social Affairs of United Nations (UN-DESA), the world population reached 7.3 billion as of mid-2015. The global population is expected to rise in the short-to-medium term, reaching between 8.4 and 8.6 billion in 2030 and between 9.5 and 13.3 billion by the end of the century 1. Hence, the demand of natural resources for the production of food, energy and chemicals is expected to increase significantly in the course of the century. It is important, therefore, to develop an integrated production model that addresses the sustainable and environmentally friendly production and distribution of these three basic commodities: food, energy and raw materials (chemicals). The challenge is of immense magnitude. In terms of food supply, the Food and Agriculture Organization (FAO) expects an steady growth of the total agricultural product consumption of 1.1 % per year until 2050 2. The global energy demand is estimated to grow even faster, by 48 % between 2012 and 2040 (Figure 1.1, above); fossil fuels being the major contributor providing over 78 % of the demand 3. The same trend is observed for the bulk chemicals, of which organic chemicals account for 4 CHAPTER 1

No abstract

No abstract