PROCESS CONCEPTS FOR CONVERSION OF BIOFUELS RESIDUE TO VALUEADDED PRODUCT

Abstract

The transition to biomass based processes for the production of fuels and chemicals is progressing rapidly and many first generation biorefineries are now producing products commercially. However, no robust technology for maximizing the value of wastes and residues from such biorefineries has yet been established. Furthermore, the basis for deciding between a number of potential options has not been fully explored. As a result most biofuel plants are designed on conventional chemical processing principles and usually focused around a single product (bioethanol, biodiesel etc.). There is a considerable scope in both research and development terms for the synthesis of feasible integrated processes for the complementary production of fuel compatible products in conventional sugarcane biorefineries. For example, the development of lignocellulosic ethanol production is nearing commercial reality, while progress in the production of microbial oil from suitable substrates offers the possibility of using the same lignocellulosic raw materials for direct oil production. The simpler approach of combusting the bagasse to generate energy required for ethanol distillation is also a good practical alternative, though in most cases the balance between supply and demand is not ideal. Therefore, this research aims to explore the various routes of converting sugarcane residue (i.e. sugarcane bagasse) into value added products such as fuels, electricity, and/or platform chemical, using a set of criteria to identify promising processing routes. Combustion, gasification and fermentation processing pathways (for electricity, gas, diesel and bioethanol production) were simulated using ASPEN PLUS, and were evaluated under a variety of conditions, including economic analysis; environmental sustainability; process complexity; waste stream(s) toxicity, treatment and cost; and product marketability, storage and distribution. Based on the economic analysis, combustion of Sugarcane Bagasse proves to be the most profitable process, as it has the lowest capital cost, and has the highest internal rate of return, net present value, return on investment and profits over a period of twenty years; while the fermentation processes prove to be the least marketable. The environmental sustainability evaluation (such as acidification, global warming, loss of aquatic and terrestrial ecosystems, ozone layer depletion, etc.) shows the biochemical processes as the least sustainable, due to greater use of chemicals, which results in toxic waste being produced. Regarding the product distribution and storage criterion, it shows that liquefied fuels such as bioethanol, gasoline, diesel, etc. are more valuable as they can be easily stored and transported in tanks and barrels, unlike electricity which storage facility still proves challenging, making the fermentation processes and Fischer Tropsch synthesis more valuable than bagasse combustion. Finally, the process complexity criterion indicates high maintenance requirement for the fermentation and gasification processes, due to their high complexity.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Colin Webb (Supervisor)