Exergetic evaluation of biobased synthesis pathways

Abstract:
It is likely that a raw material change will soon take place in the chemical industry. While today about 75 % of the chemical products are based on crude oil, in the future bio-based materials will gain more importance. As the amount of oxygen molecules is normally higher in biomass materials, new synthesis pathways and separation processes will have to be developed. In order to compare the different pathways quantitatively and evaluate which process is the most efficient, a combination of exergy and mass balances can be adopted. Exergy balances have the advantage that a comparison of different forms of energy is possible. In the presentation, different approaches for the use of biomass as a raw material in the chemical industry will be compared and thermodynamically evaluated. One approach is the conversion to synthetic gas. From these so-called C1 building blocks all other products can be built up. Another approach is to produce more complex molecular structures, which are used as intermediates. All final chemical products are then obtained from these intermediates. In this approach, the synthesis power of the plants is efficiently used. Two examples for the approach via the synthesis of platform chemicals, based on glucose as well as lignin, will be presented. Thereby, the exergetic evaluation is focused on the subsequent separation processes. The presentation will include a holistic process evaluation from the plant to the chemical product, we wish to obtain. Thus, the different process steps, including the agricultural process and the product separation, will be discussed. The consideration focuses especially on the exergetic relevance of typical characteristics of bio-based processes, e.g. the low concentration of products in fermentative processes.

Keywords:
Exergy, Biomass, process evaluation