Renewable Fuels & Chemicals

Replacement of petroleum as a carbon source to produce fuels and chemicals with new sustainable resources is crucial due to depletion of petroleum reserves, increasing global energy demand, and arising environmental concerns. To that end, a promising option is to use non-edible lignocellulosic biomass, which can be transformed into various useful products in biorefineries that integrate multiple technologies and conversion processes. Conversion of lignocellulosic biomass to valuable intermediates is a critical step to develop effective biomass-to-biofuel strategies. Levulinic acid (LA) is one of these platform chemicals that can be produced from lignocellulosic biomass and transformed into liquid fuels, fuel additives and even other specialty chemicals. In this respect, in collaboration with the group of Prof. Dumesic, we study LA-based catalytic processes to convert lignocellulosic biomass into liquid hydrocarbon fuels for use in the transportation sector.

Using experimental results for all associated reactions, we synthesize novel biomass-to-fuels strategies that have a number of advantages over existing strategies. Our strategies are based on selective catalytic routes, which produce a mixture of hydrocarbons that are compatible with gasoline and jet fuels used today. We carry out detailed process simulation and optimization studies as well as explore heat integration approaches. Also, we perform capital/operational cost calculations to determine the economic potential of these strategies – we calculate the minimum selling price of liquid fuels at the break-even point. Finally, we evaluate feedstock options, perform sensitivity analyses on various technical and economic parameters, and explore how the proposed strategies can be integrated with existing facilities.

Integrated biomass-to-fuels strategy

In order to reduce carbon dioxide emissions from fossil-fuel-based power plants, CO₂ can be captured and further processed to obtain fuels that readily integrate into the current transportation infrastructure. This upgrading of CO₂ can be accomplished in a solar refinery, which uses sunlight as a renewable energy source to drive catalytic reactions as shown in Figure 1 (Herron et al., 2015).

The two main methods for CO₂ conversion include: (1) catalytic conversion using solar-derived hydrogen, and (2) direct reduction of CO₂ using H₂O and solar energy. Solar utilities can be utilized in the form of heat (e.g., in thermolysis and thermochemistry), electricity (e.g., in electrocatalysis), and as a photon source (e.g., in photo-chemical reactions).

We perform systems-level, techno-economic and conceptual design and operational analyses of different process configurations for the solar refinery. In particular, we assess the energetic and economic feasibility of the process by quantifying the impact of key areas, such as solar energy capture and conversion, CO₂ capture, catalytic conversion processes, and chemical storage (Kim et al., 2011; Kim et al., 2012; Herron & Maravelias, 2016).

bruno — Figure 1. Schematic for solar fuels production. The approximate temperature requirements for the solar-driven conversion processes are color-coded (red = high temperature, yellow = ambient temperature).

References

Kim, J., Henao, C. A., Johnson, T. A., Dedrick, D. E., Miller, J. E., Stechel, E. B., & Maravelias, C. T. (2011). Methanol Production from CO₂ Using Solar-Thermal Energy: Process Development and Techno-Economic Analysis. Energy & Environmental Science, 4(9), 3122–3132.
Kim, J., Johnson, T. A., Miller, J. E., Stechel, E. B., & Maravelias, C. T. (2012). Fuel Production from CO₂ Using Solar-Thermal Energy: System Level Analysis. Energy & Environmental Science, 5(9), 8417–8429.
Herron, J. A., Kim, J., Upadhye, A. A., Huber, G. W., & Maravelias, C. T. (2015). A General Framework for the Assessment of Solar Fuel Technologies. Energy & Environmental Science, 8(1), 126–157.
Herron, J. A., & Maravelias, C. T. (2016). A General Framework for the Assessment of Solar Fuel Technologies. Energy Technology, 4(11), 1369–1391.

Solar energy has the potential to reduce power generation dependence on fossil fuels. However, the periodic nature and uncertainty of the solar insolation call for the deployment of energy storage. Thermal chemical storage (TCES), which stores and releases energy by breaking and reforming chemical bonds, has high energy density and the potential for long storage period. To this end, we perform system level studies for TCES systems in concentrating solar power (CSP) plants. Specifically, we develop general optimization-based methods for the synthesis and evaluation of various reaction candidates and technology alternatives (see Figure 1).

Lignocellulosic biomass is an abundant and sustainable feedstock that can be used to produce biofuels and bioproducts. However, the low price of crude oil and the challenges in applying biorefinery technologies at scale hamper the commercial production of biofuels from biomass. Another option for biorefineries to become more profitable is to produce high value commodity chemicals that are expensive to synthesize from petroleum-derived feedstocks. ?,?-diols, like 1,4-butanediol (1,4-BDO) and 1,6-hexanediol (1,6-HDO), are such chemicals with projected market prices of $1,600—2,800 ton^-1 and $2,500—4,500 ton^-1, respectively. These ?,?-diols are widely used for industrial polyester, elastic fiber, and polyurethane production. 1,5-pentanediol (1,5-PDO) can be an alternative to these conventional ?,?-diols because of analogous molecular structure and physical properties.

We study catalytic processes for converting biomass into oxygenated commodity chemicals (1,5-PDO and 1,6-HDO), which are difficult to produce from petroleum derived feedstocks (see Figure 1). We use process systems engineering methods to assess the economic feasibility of the proposed strategies as well as identify areas where further technology improvements are needed [1-4]. The objective is to synthesis detailed reaction, separation and utility subsystems; develop process simulation models based on experimental data; perform techno-economic and life cycle analyses; and, ultimately, suggest future research directions.

Figure 1. Sankey diagram on cost contribution and carbon flow for each process section

References

Huang, K.; Brentzel, Z. J.; Barnett, K. J.; Dumesic, J. A.; Huber, G.W.; Maravelias, C. T. Conversion of furfural to 1,5-pentanediol: process synthesis and analysis. Submitted.
Han, J.; Luterbacher, J. S.; Alonso, D. M.; Dumesic, J. A.; Maravelias, C. T. A lignocellulosic ethanol strategy via nonenzymatic sugar production: Process synthesis and analysis. Bioresour. Technol. 2015, 182, 258–266.
Han, J.; Sen, S. M.; Alonso, D. M.; Dumesic, J. A.; Maravelias, C. T. A strategy for the simultaneous catalytic conversion of hemicellulose and cellulose from lignocellulosic biomass to liquid transportation fuels. Green Chem. 2014, 16 (2), 653–661.
Sen, S. M.; Henao, C. A.; Braden, D. J.; Dumesic, J. A.; Maravelias, C. T. Catalytic conversion of lignocellulosic biomass to fuels: Process development and technoeconomic evaluation. Chem. Eng. Sci. 2012, 67 (1), 57–67.

To be economically viable, any biomass-to-fuels strategy must also involve the effective conversion of biomass-derived oxygenated compounds to high-value chemicals. Although many of the pathways for these conversions are known, it is unclear which high-value chemicals should be produced to make the overall process economically attractive or which chemistries should be integrated and how. To address these questions, we develop a strategy for the evaluation of existing and emerging technologies, as well as the synthesis of novel chemical processes that include these technologies.

In particular, we develop a network design approach where existing fossil-fuel-based and emerging biobased-based technologies are considered. In addition, we consider known as well as potentially new intermediates that can be used to satisfy demand. Using the above network-based representation (see figure below), we formulate optimization models that allow us to evaluate in a systematic manner a large number of alternatives, and thereby address a series of challenging questions: Which chemicals can be produced more effectively from biomass? Which emerging technologies could have the greatest impact? Can biomass-based technologies be used today to replace fossil-fuels technologies? What biomass-to-chemicals conversion levels are necessary to support biomass-to-fuel production at different oil prices?

Here is an interface to implement the framework: https://bus.glbrc.org/

Thermochemical processing of biomass to obtain fuel and chemicals has received significant attention for a wide range of feedstocks. Early studies of thermochemical conversion of biomass focused mainly on fast pyrolysis, which involves rapid heating of biomass in the absence of air at approximately 500 °C. While fast pyrolysis is the simplest method of obtaining liquid from solid biomass, the resulting bio-oil contains a large number of oxygenated compounds (e.g., organic acids, aldehydes, ketones, etc.), which are chemically unstable and difficult to upgrade catalytically. Multi-stage thermal decomposition of biomass provides a promising alternative for overcoming these issues because biomass is fractionated into simpler streams (with a smaller number of species), thereby enabling their effective upgrading via tailored catalytic bed reactors. There are multiple options for the design of the catalytic upgrading system, including the number, types, and sequence of chemistries to perform (Figure 1). Therefore, identifying the optimal strategy, after accounting for performance metrics such as fuel-range carbon yield and hydrogen consumption, is a classic process-synthesis problem.

In this work, we use a multi-pronged approach to address the above problem. First, we use a superstructure-based optimization framework to identify the promising routes to convert biomass to liquid fuel. Second, based on reasoning, and insight obtained from experimental data (procured in part through our collaborations), we synthesize alternative catalytic upgrading strategies and rigorously evaluate them using Aspen Plus. For a realistic evaluation, our models in both the approaches are based on experimental data. Using a wide range of technoeconomic parameters, we identify (1) the relationship between process complexity and the resulting fuel-range carbon yields and economic feasibility, (2) the economic advantage of integrating different thermal decomposition fractions, and (3) the key cost drivers of the integrated processes.

Figure 1. General structure of thermal decomposition followed by catalytic upgrading biorefinery processes.