Transformation of Biomass and Shale Gas Carbon to Fuels and Chemicals
thesisposted on 03.01.2019 by Taufik Ridha
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Currently, fossil resources dominate fuel and chemical production landscape. Besides concerns related to the ever-increasing greenhouse gas emission, fossil resources are also limited. In a petroleum-deprived future, sustainably available biomass can serve as a renewable carbon source. Due to its limited availability, however, this biomass resource must be utilized and converted effciently to minimize carbon losses to undesirable by-products. A modeling and optimization approach that can identify optimal process congurations for chemical and fuel production from biomass using stoichiometric and thermodynamic knowledge of the underlying biomass reaction system is proposed in this dissertation. Several case studies were performed with this approach, and the outcomes found agreement with reported experimental results. In particular, a case study on fast-hydropyrolysis vapor of cellulose led to the discovery of new reaction route and provided insights in comprehending the formation of experimentally observed molecules. The modeling and optimization approach consists of two main steps. The rst step is the generation of the search space and the second step is the identication of all optimal reaction routes.
For the rst step, literature review and automated reaction network generator are employed to identify all possible processes for biomass conversion. Through literature review, yield data on processes that generate biomass-derived molecules are collected. As these biomass-derived molecules often possess multiple functional groups, utilization of automated reaction network generator, which considers a set of biomass-derived molecules and reaction rules, enables generation of all possible reactions. In this work, an automated reaction network generator tool called Rule Input Network Generator is utilized. Using this generated search space, a mathematical optimization problem, which identies the optimal reaction network, is constructed. For the second step, the optimization problem identies all reaction routes with the minimum number of reactions for a given set of biomass and target products. This formulation constructs a process superstructure that contains processes that generate biomass-derived molecules and all possible reactions from biomass-derived molecules. In this optimization problem, the main constraint for the reaction is its thermodynamic favorability within a certain temperature range. Using optimization solver, optimal solutions for this problem are obtained.
Using this developed approach, a case study on upgrading fast-hydropyrolysis vapor of cellulose to higher molecular weight products was investigated. Levoglucosan and glycolaldehyde are major components from fast-hydropyrolysis of cellulose. This approach identied a reaction route that can upgrade these molecules to hydrocarbons with carbon number ranging from eight to 12 and this route has not been reported in the literature. The coupling of levoglucosan and glycolaldehyde requires a key intermediate, levoglucosenone, which is identied by this approach. Preliminary experimental results suggest that the proposed reactions are feasible and this serves as another validation for this approach. Other potential pathways to not only branched alkanes, but also substituted cycloalkanes and aromatics, were also identied. Molecules with those structures have been observed experimentally, and potential pathways to those molecules can provide insights for experimentalists as to how these products can form and which intermediates may lead to their formations. This approach has not only revealed unknown reaction routes, but also provided insights for experimentalists for analyzing complex systems.
Toward reduction of carbon losses toward char during fast pyrolysis, potential pathways toward char formation during fast pyrolysis were proposed. Investigating proposed char precursors identied using mass spectroscopy, several potential pathways toward the formation of these char precursors were obtained, which include initial insights to the potential driving force for the formation of these char precursors and, ultimately, char itself.
Going beyond fast pyrolysis, primary processes that have been developed in C3Bio along with several existing primary processes were considered in order to identify optimal biorenery congurations. This approach identied biorenery congurations with carbon effciencies from 60-64%. These congurations generate not only fuel type molecules, but also commodity chemicals that are being produced in a traditional renfiery. In addition, it is capable of providing these products at their current relative production rates in the United States. Other studies on biorefinery reported only 25-59% carbon effciency and generated mostly fuel-type molecules. Therefore, this approach not only indicates the appropriate reaction sequences, but also optimal utilization of carbon in biomass-derived molecules. This dissertation provides an initial roadmap toward sustainable production of fuels and chemicals from lignocellulosic biomass.
Considering that the transition to renewable energy is gradual and shale resource is an abundant fossil resource in the United States, opportunities to valorize shale gas condensate are explored. Recent shale gas boom has transformed the United States energy landscape. Most of the major shale basins are located in remote locations and historically non-gas producing regions. Therefore, many major shale basins regions are lacking the infrastructure to distribute the extracted gas into the rest of the US and particularly the Gulf Coast region. In this dissertation, shale gas catalytic upgrading processes were synthesized, designed, and simulated using Aspen Plus Simulation. Using Aspen Economic Analyzer, preliminary techno-economic analysis and evaluation of its economic potential were assessed at varying scales to assess its impact on the
United States chemical industry landscape.