Environmental and political problems created by our dependence on fossil fuels combined with diminishing petroleum resources are forcing society to search for renewable sources of energy. Plant biomass is the only current sustainable source of organic carbon, and biofuels, fuels derived from plant biomass, are the only renewable source of liquid fuels. Currently solid lignocellulosic biomass resources are significantly cheaper than petroleum (at $15 per barrel of oil energy equivalent) and abundant (have the energy content of 60 % of our domestic crude oil consumption). While biofuels have a tremendous potential to alleviate problems caused by fossil fuels, the major impediment to utilization of our lignocellulosic biomass resources is the lack of economical processes for conversion of biomass resources into fuels. The goal of the Huber research group is to develop the clean technology that will allow us to economically use our biomass and other sustainable resources for the production of cheap renewable gasoline, diesel fuel, jet fuel, and chemicals.

Whereas the petroleum industry has made continuous progress over the last 100 years by studying and improving petroleum chemistry, biorefining is only in its infancy. Biomass-feedstocks are significantly different than petroleum feedstocks because of their high oxygen content leading to low thermal stability and a high degree of functionality. The major scientific challenge is how to efficiently and selectively remove oxygen from biomass-derived molecules and to functionalize this feedstock into the targeted molecules that are compatible with petroleum based liquid fuels. Heterogeneous catalysis and chemical engineering hold the key that will allow the efficient conversion of biomass-derived molecules to fuels. Understanding and controlling this chemistry allows the efficient utilization of our vast domestic biomass-resources.

The Huber research group is developing new generations of catalysts, reactors, spectroscopic and imaging tools, and computational models that are essential for understanding and controlling the chemical transformation of biomass-derived oxygenates to fuels. The main research thrusts are the development of economical processes for the production of renewable gasoline, diesel fuel, jet fuel and petrochemicals. In this respect, we are developing clean catalytic technologies for the production of the full spectrum of products that are currently derived from petroleum-derived feedstocks, from renewable lignocellulosic biomass feedstocks. A number of these technologies are moving rapidly towards commercialization. Professor Huber has authored over 155 peer-reviewed publications including three publications in Science.  He has more than 17 different patents several which are licensed to different companies.  According to Thomson Reuters he is a highly cited researcher in the field of chemistry, which is an honor given to the top 1% most cited chemists.  He has been cited over 3,975 times in 2017 and over 25,911 times in his career.

The Huber research group uses a wide range of chemical engineering tools to understand and optimize biomass conversion to fuels and chemicals, including: heterogeneous catalysis, kinetic modeling, reaction engineering, spectroscopy, analytical chemistry, nanotechnology, catalyst synthesis, conceptual process design, modeling of transport phenomena, and theoretical chemistry. These tools have been combined to develop a number of catalytic technologies for the production of clean fuels and chemicals.

Catalytic Upgrading of Ethanol into drop-in diesel fuel

As technological advancements in batteries continue, there is a projected decline in the demand for light-duty fuels over the next 20 years.1 Electrification of light-duty fleet is expected to lead to an ethanol surplus at its demand for blending in light-duty fuels diminishes. In contrast, heavy-duty transportation is expected to increase due to growth of commodities market, increasing the demand of diesel #2. Electrification of the heavy-duty fleet seems difficult for now due to technological limitations related with the weight of the batteries needed to transport merchandise for long distances.2 Current biofuel methods focus on dehydrating bioethanol for gasoline or jet fuel hydrocarbons, necessitating exploration of shifting ethanol from light-duty to heavy-duty fuel technology.

The Huber lab has been actively working on the development of a promising technology for ethanol oligomerization followed by etherification for upgrading bio-ethanol into distillate-range molecules. Our earlier approach in this technology consisted on the use of Ca-hydroxyapatite (CaHP) to upgrade ethanol into longer chain alcohols, which afterward undergo  bimolecular dehydration reactions to produce a fuel blend with diesel-like properties.3, 4  Recent advancements of this technology has led us to migrate to Copper catalyst supported on MgAl mixed oxides (MMO), which helped us to increase ethanol coupling rates. As outcome of our discoveries, the Huber group has been able to elucidate the reaction chemistry ruling the ethanol upgrading step5 and demonstrate the feasibility of upgrading ethanol into a diesel fuel, whose properties surpass those of fossil derived diesel.6

Schematic 1. Schematic representation of the process chemistry for upgrading ethanol into diesel fuel, encompassing the Guerbet coupling unit, ester hydrogenolysis unit, and dehydration unit. Source: Restrepo-Florez et al.6

The results from our development show that it is possible to produce a diesel #2 surrogate, derived from ethanol. The final product of the process has been demonstrated to have environmental benefits while meeting ASTM standards. For instance, life cycle analysis of our process indicates a reduction of greenhouse gas emissions of 50% compared to fossil diesel, cetane number of ~70 and outstanding cold flow properties. Moreover, assessment of our technology through technoeconomic analysis is promising for cost competitiveness against existing biodiesel production methods, by obtaining a fuel with a minimum selling price of $5.89 USD when using lignocellulosic ethanol.6

References

  1. The road to 2040: What’s fueling transportation growth, https://energyfactor.exxonmobil.com/insights/focus/road-to-2040/, (accessed 12/24/2022).
  2. M. KAH, W. S. LANG, J. CHIU and H. X. WONG, Forecasts of electric vehicle penetration and its impact on global oil demand, Columbia University Center on Global Energy Policy, 2022.
  3. N. M. Eagan, B. M. Moore, D. J. McClelland, A. M. Wittrig, E. Canales, M. P. Lanci and G. W. Huber, Green Chemistry, 2019, 21, 3300-3318.
  4. N. M. Eagan, M. D. Kumbhalkar, J. S. Buchanan, J. A. Dumesic and G. W. Huber, 2019, 3, 223-249.
  5. P. A. Cuello-Penaloza, J. Chavarrio-Cañas, Y. Du, M. P. Lanci, D. A. Maedke, J. A. Dumesic and G. W. Huber, 2022, 318, 121821.
  6. J.-M. Restrepo-Flórez, P. Cuello-Penaloza, E. Canales, D. Witkowski, D. A. Rothamer, G. W. Huber and C. T. Maravelias, Sustainable Energy & Fuels, 2023.

Chemical manufacturing constitutes 17 vol% of global oil usage and is responsible for the emission of over 2 billion metric tons of carbon dioxide equivalents (MtCO2e) annually. Decarbonization of the chemical industry will not be feasible without the switch to renewable feedstocks like lignocellulosic biomass. With over 50 publications and a dozen patents, members of the Huber group are continuing to discover new catalytic technologies to produce chemicals from biomass. Currently, we are working on three main research areas listed below.

Research Area I: Development of a network of reactions for the production of five-carbon (C5) chemicals from furfural.

Unlike their C4 or C6 analogs, C5 chemicals are extremely expensive to produce due to the lack of C5 feedstock in petroleum. But biomass is rich in C5 sugars like xylose – the second most abundant sugar in the world. Xylose is hydrogenated to produce furfural, a major platform chemical. As shown in the figure below, have developed and patented a 3-step route from tetrahydrofurfuryl alcohol to 1,5-pentanediol (PDO) via dehydration to 3,4-dihydropyran (DHP) and hydration to 2-hydroxytetrahydropyran (HTHP).[1-3] Technoeconomic analysis showed that this technology produces PDO at much lower cost than previous routes, resulting in the formation of a startup company, Pyran. In 2023, we also discovered a new route to delta-valerolactone (DVL) from dehydrogenation of HTHP.[4] PDO and DVL are polymer precursors to biobased polyesters, polyols, and polyurethanes. We can also synthesize tetrahydropyran (THP) from hydrogenation of DHP as a green solvent to replace petroleum-derived tetrahydrofuran (THF).[5]

Research Area II: Synthesis of biodegradable polymers from 5-hydroxymethylfurfural (HMF) derivatives.

As part of the BOTTLE consortium, we have shown that 5-hydroxymethylfurfural (HMF) can be converted to HMF-acetone-HMF dimer (HAH) by Aldol condensation with acetone in high yield (>90%).[6] HAH has potential to be used in pharma, polymer, fuel and organic dye industries. HAH is further converted into more flexible compounds, partially hydrogenated HAH (PHAH) and fully hydrogenated HAH (FHAH) using Cu and Ru catalysts in about 90% yield.[7] Currently, we are working on applying HAH and HAH derivatives (PHAH and FHAH) for the synthesis of biodegradable polymers and pharmaceutical ingredients.

Research Area III: Production of potassium sorbate for use in food preservatives.

As part of the CABBI consortium, we have shown that Triacetic Acid Lactone (TAL) can be converted to Potassium sorbate through hydrogenation, dehydration, and ring-opening & hydrolysis in 77.3% yield. Potassium sorbate is used in the pharma and food industries as a preservative. Currently, we are working on synthesizing greener potassium sorbate from biomass. Manuscripts for this work are in prep.

References

[1]. Li, L.;  Barnett, K. J.;  McClelland, D. J.;  Zhao, D.;  Liu, G.; Huber, G. W. “Gas-phase dehydration of tetrahydrofurfuryl alcohol to dihydropyran over γ-Al2O3,” App Catalysis B: Environmental, 2019, 245, 62-70.

[2] Barnett, K. J.;  McClelland, D. J.; Huber, G. W. “Autocatalytic hydration of Dihydropyran to 1, 5-Pentanediol precursors via in situ formation of liquid-and solid-phase acids,” ACS Sustainable Chem & Eng, 2017, 5 (11), 10223-10230.

[3] Brentzel, Z. J.;  Barnett, K. J.;  Huang, K.;  Maravelias, C. T.;  Dumesic, J. A.; Huber, G. W. “Chemicals from biomass: Combining ring‐opening tautomerization and hydrogenation reactions to produce 1, 5‐pentanediol from furfural.” ChemSusChem 2017, 10 (7), 1351-1355.

[4] Dastidar, R. G.,  & Huber, G. W. “Catalytic synthesis of δ-valerolactone (DVL) from furfural-derived 2-hydroxytetrahydropyran (HTHP)”, Provisional US Patent P230055US01, 2023.

[5] Dastidar, R. G.,  Kim, M. S., … & Huber, G. W. (2022). Catalytic production of tetrahydropyran (THP): a biomass-derived, economically competitive solvent with demonstrated use in plastic dissolution. Green Chemistry, 24 (23), 9101-9113.

[6] Chang, Hochan, et al. “Synthesis of biomass-derived feedstocks for the polymers and fuels industries from 5-(hydroxymethyl) furfural (HMF) and acetone.” Green Chemistry 21.20 (2019): 5532-5540.

[7] Chang, Hochan, et al. “Synthesis of performance-advantaged polyurethanes and polyesters from biomass-derived monomers by aldol-condensation of 5-hydroxymethyl furfural and hydrogenation.” Green Chemistry 23.12 (2021): 4355-4364.

Over the last 15 years, the production of Greek yogurt has gone from almost nothing to over 700,000 tons per year. This rapid rise of Greek yogurt has caused the dairy industry to be flooded with the main byproduct of Greek yogurt, a yellowish liquid called Greek yogurt acid whey. Each year, 2 million tons of Greek yogurt acid whey are produced, but the existing disposal methods available to dairy manufacturers are economically and environmentally unsustainable. We are developing catalytic solutions to convert this dairy waste into profitable products, such as a sweetener which can be used in the dairy and confectionary industries.

Our technology focuses breaking down lactose, a disaccharide poorly digested by 70% of the world, into two sweeter monosaccharides, glucose and galactose. This has been done by either enzymes or acid catalysts, but the high cost of enzymes has made the whey-to-sweetener process economically uncompetitive. Acid catalysis relies on cheaper catalysts, but the prevalence of side reactions causes the Greek yogurt acid whey to turn an unsightly brown color. We have employed various filtration steps to purify the Greek yogurt acid whey, leading to improvements in the yield of glucose and galactose and decreases in the brown color developed during the reaction [1,2]. We are currently developing a flow system capable of continuously reacting the lactose in the Greek yogurt acid whey. In the future, we seek to develop a catalytic process that could react the lactose in dairy streams without the need for any filtration.

References

[1] Lindsay, Mark J., et al. “Production of monosaccharides and whey protein from acid whey waste streams in the dairy industry.” Green Chemistry 20.8 (2018): 1824-1834.

[2] George W. Huber, Scott A. Rankin, Mark J. Lindsay. “METHOD OF CONVERTING WHEY WASTE INTO MONOSACCHARIDES” Patent Application. Submitted 2018.

In the past decades, the production of plastic increased exponentially. 380 million metric tons of plastic were produced in 2015, but less than 9% of the plastic was recycled.[1] Unrecycled plastics are landfilled, incinerated or dumped, which can potentially cause energy and environmental challenges. Pyrolysis is being commercialized to recycle waste plastics. It is a technique to thermally decompose plastics to shorter chain hydrocarbons. The Chemical Upcycling of Waste Plastics (CUWP) center and the Huber group are investigating the fundamental chemistry and kinetics for plastic pyrolysis which can potentially better tune the product distribution. The obtained plastic pyrolysis oil can then be catalytically upgraded to other valuable chemicals like aldehydes and alcohols.

A fluidized bed reactor is used for polyolefin pyrolysis. We have studied the pyrolysis of polyethylene (PE) which produces a wide range of C1-C60 hydrocarbons including mono-olefins, di-olefins, paraffins, and aromatics.[2] The structure of the polyolefins also affects the product distributions and structures. Further studies will be conducted on understanding the fundamental chemistry of polyolefin pyrolysis, the trace elements balances during pyrolysis (impurities for PCR plastics), and how to catalytically upgrade the pyrolysis products.

Our group has demonstrated that pyrolysis oil can be used to produce aldehydes through hydroformylation, taking advantage of the olefin functionality.[3] These aldehydes can then be reduced to mono- and dialcohols, oxidized to mono- and dicarboxylic acids, or aminated to mono- and diamines by using homogeneous and heterogeneous catalysis. This route produces high-value oxygenated chemicals from low-value postconsumer recycled polyethylene. We project that the chemicals produced by this route could lower greenhouse gas emissions ~60% compared with their production through petroleum feedstocks.

[1]      Li, H., Aguirre-Villegas, H. A., Allen, R. D., Bai, X., Benson, C. H., Beckham, G. T., … & Huber, G. W. (2022). Expanding plastics recycling technologies: chemical aspects, technology status and challenges. Green Chemistry.

[2]      D. Zhao, X. Wang, J.B. Miller, G. Huber, ChemSusChem 13 (2020) 1764 – 1774

[3]      Li, H., Wu, J., Jiang, Z., Ma, J., Zavala, V. M., Landis, C. R., … & Huber, G. W. (2023). Hydroformylation of pyrolysis oils to aldehydes and alcohols from polyolefin waste. Science, 381(6658), 660-666.

Solvent-targeted recovery and precipitation (STRAP)

Many plastic packaging materials are manufactured in the form of multilayer films. Combining different layers of plastics results in stronger and impermeable materials with unique properties that help preserve food quality and lifetime (Figure 1) [1]. In most cases, these multilayer materials are intended for single use and current mechanical recycling methods cannot process them. The recently reported strategy called Solvent-Targeted Recovery and Precipitation (STRAP) is used to deconstruct multilayer films into their constituent resins using a series of solvent washes that are guided by thermodynamic calculations of polymer solubility (Figure 2) [2]. Three computational methods are used for solvent selection and process conditions: Hansen Solubility Parameters (HSPs), molecular dynamics (MD) simulations, and COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS). In this process, a single polymer layer is selectively dissolved in a solvent system, is later separated from the insoluble layers and then precipitated by the addition of an antisolvent and/or decreasing the solvent temperature. STRAP can enable a recycling pathway for rigid and flexible multilayer films, recovering polymers like polyethylene (PE), ethylene vinyl alcohol (EVOH), and polyethylene terephthalate (PET) with > 95 wt% material efficiency [3]. In addition to this, STRAP has been demonstrated with printed flexible multilayer films and disposable facemasks [4-5]. This approach can produce polymers with similar properties to pure resins, can be economically feasible, and can introduce environmental benefits when compared to film production from pure polymers [4,6].

Figure 1. Multilayer plastic film composed of polyethylene terephthalate (PET), polyethylene (PE), and ethylene vinyl alcohol (EVOH) [1].

Figure 2. Solvent-targeted recovery and precipitation (STRAP) [2].

References

[1] Xu, Z., Sanchez-Rivera, KL., Munguia-Lopez, A., Ochs, M., Nelson, K., Van Lehn, R., Bar-Ziv, E., Aguirre-Villegas, H., Huber, GW. Recycling of Plastic Films through Solvent Targeted Recovery and Precipitation. (2023)

[2] Walker, T., Frelka, N., Shen, Z., Chew, AK., Banick, J., Grey, S., Kim, MS., Dumesic, JA., Van Lehn, RC., Huber, GW. Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation. Science Advances. (2020), eaba7599

[3] Sánchez-Rivera, KL., Zhou, P., Kim, MS., González Chávez, LD., Grey S., Nelson, K., Wang, SC., Hermans, I., Zavala, VM., Van Lehn, RC., Huber, GW. Reducing Antisolvent Use in the STRAP Process by Enabling a Temperature‐Controlled Polymer Dissolution and Precipitation for the Recycling of Multilayer Plastic Films. ChemSusChem, 14 (2021), 4317-4329.

[4] Sánchez-Rivera, KL, Munguia-Lopez, A, Zhou, P., Cecon, V., Yu, J., Xu, Z., Nelson, K., Miller, D., Grey, S., Zavala, VM., Bar Ziv, E., Van Lehn, RC., and Huber, GW. Recycling of a printed multilayer plastic films containing polyurethane inks by solvent-targeted recovery and precipitation. Resources, Conservation & Recycling, 197 (2023), 107086

[5] Yu, J., Munguia-Lopez, A., Cecon, VS., Sánchez-Rivera, KL, Nelson, K., Kolapkar, S., M. Zavala, VM., Curtzwiler, GW., L. Vorst, KL., Bar Ziv, E., and Huber, GW. High-purity Polypropylene from Disposable Face Masks via Solvent-Targeted Recovery and Precipitation. Green Chem., 2023, 25, 4723-4734.

[6] Munguia-Lopez, A., Goreke, D., Sánchez-Rivera, KL, Aguirre-Villegas, HA., Avraamidou, S., Huber, GW., and Zavala, VM. Quantifying the environmental benefits of a solvent-based separation process for multilayer plastic films. Green Chemistry. 25 (2023), 1611-1625.