by Doug Rivers, Ph.D.
Biomass to Liquid Fuels: The History
Serious development to convert lignocellulosic biomass to liquid fuels and chemicals began in the U.S. following the 1973 OPEC oil embargo that left the U.S. with fuel shortages and long lines and gasoline rationing at service stations. Since that time, significant technical progress has been made across the process from feedstock supply through the production of liquid fuels and chemicals, most notably ethanol and a handful of chemicals. Many of these advances have been facilitated by the advent of genetic engineering in the early 1980’s by what we know today as synthetic biology. These advances have provided dramatically increased abilities to hydrolyze cellulose and hemicellulose to fermentable sugars that can be readily converted to products by advanced fermentation microorganisms. Advances have also been made in collecting feedstocks, most notably corn stover, and energy crops such as switchgrass, miscanthus, and energy sorghum. And while advances have been made in the materials handling and pretreatment of these feedstocks, commercial-scale attempts to produce ethanol have been met with multiple and highly visible failures measured in at least hundreds of millions of dollars, if not billions. This begs the question, can lignocellulosic feedstock conversion processes realistically become a viable commercial feedstock that can compete with other established feedstocks such as corn?
I began work at the Gulf Oil Chemicals Company in Merriam, KS in September 1976. At the time, Gulf was the seventh-largest corporation in the U.S.[1] and I began there as a lab manager working on the conversion of lignocellulosic feedstocks to ethanol for conversion to ethylene Why? Corporate management decided that they would never be held hostage again by an oil embargo that could limit their ability to produce petrochemicals. Our 35+ person group had a virtually unlimited budget. We had just filed for the patent on simultaneous saccharification fermentation (SSF). At that time,
SSF gave an average 40% increase in conversion when compared to conventional two-step hydrolysis and fermentation to ethanol process. Gulf was already constructing a cellulose conversion pilot plant at its Jayhawk Works plant located between Pittsburg, KS and Joplin, MO. Because Gulf had no engineers with this type of experience, we worked with Raphael Katzen Associates (now Katzen International, Inc. in Cincinnati, OH) who already had years of experience working with the pulp and paper industry, converting process wastes into commercial products. Since that time, significant progress has been made toward a successful commercial process, but there have also been very visible commercial-scale failures. The question remains: Can cellulosic feedstock conversion become a viable large-scale commercial process success, technically and economically?
Barriers to Commercial Success
Today, there are still barriers to commercial success. The focus of these barriers in commercial attempts have been feedstock harvesting, feedstock materials handling, and effective, consistent pretreatment process technology. What is the current state of the commercial industry? In Brazil, Raizen (JV between Royal Dutch Shell and Royal Dutch Cosan) has spent years in its first commercial plant converting sugar cane bagasse to ethanol to achieve a commercial success implementing Iogen Corporation (Ottawa, Ontario, Canada) technology. Raizen has two additional plants under construction with plans to bring a total of five total plants online by 2027[1]. Raizen is also producing biogas from sugar cane vinasse and other process wastes. GranBio is producing cellulosic ethanol at its Alagoas, Brazil commercial facility. Little public information is available on the operational success of these two commercial operations. GranBio/NextChem has also just received an award of $80 million from the U.S. DOE to demonstrate its AVAP technology acquired in a buyout of American Process at Thomaston, GA. Clariant has constructed and started up its commercial facility located in Podari, Romania in mid-2022, but is reportedly having technical difficulties maintaining process consistency. UPM Kymmene is constructing its first commercial facility in Leuna, Germany to produce renewable chemicals (Bio-Monoethylene Glycol (BioMEG), Bio-Monopropylene Glycol (BioMPG), Renewable Functional Fillers (RFF), and Industrial Sugar). Startup is now scheduled to begin in late 2024. Finally, New Energy Blue, Lancaster, PA has recently signed a deal with Dow Chemical to provide cellulosic ethanol for bioethylene production of consumer plastics. New Energy Blue has worked on the Inbicon conversion technology for over a decade with Danish energy company Ørsted A/S. New Energy Blue has bought the exclusive licensing rights to the Inbicon technology and is currently completing engineering for their first U.S. commercial biorefinery. The plant will process corn stover into cellulosic ethanol at Mason City, IA and is scheduled to be commissioned by 2026.
But there have been large, visible, and very expensive commercial failures. Abengoa, Beta Renewables, DuPont, and POET/DSM each invested hundreds of millions of dollars only to fail to sustain commercial operations. Abengoa (Hugoton, KS) was never able to get its technology to operate due to front end process challenges. Beta Renewables (Crescentino, Italy) like Abengoa, was never able to achieve technical success due to front end process challenges. Abengoa declared bankruptcy and the Hugoton, KS plant was eventually sold to Seaboard Energy. Seaboard produces biodiesel, renewable natural gas (RNG), and compressed natural gas (CNG) and is planning to use the site for future production – not cellulose conversion. DuPont never opened its Nevada, IA, plant, but instead sold it to Verbio, which converted it into an anaerobic digestion-based commercial corn stover-to-biogas production process. Finally, POET-DSM appeared to be on track for commercial success at its Emmetsburg, IA plant based on public releases, but stopped operations in late 2019 due to cited regulatory uncertainties.
Can Cellulosic Biomass to Ethanol be Successful?
The question remains, can large-scale commercial conversion of cellulosic biomass to ethanol as a renewable source of liquid fuels and chemicals be successful as once envisioned? The U.S. DOE has studied the availability of biomass in the U.S. in its 1 Billion Ton Study and subsequent Update. There is adequate cellulosic biomass feedstock available in the U.S. But no widespread implementation of this technology has been successful on a commercial scale today. Can it happen, and if so, what are the barriers to success that still need to be solved to make it a reality?
Little, if any public information is available that explains what advances Raizen has made that provide the basis for its plans to construct additional cellulose conversion facilities in Brazil; however, we must assume that key technical and cost challenges at commercial scale have been solved to justify the ongoing expansion efforts. Similarly, GranBio/NextChem’s continued operation of its plant in Brazil is a similar indicator that technical and cost challenges have been solved. Further, the purchase of American Process’s AVAP process and pilot plant and recent $80 million DOE award for demonstration scale work in Thomaston, GA indicate continued promise of commercial scale success. At the same time, difficulties are likely indicated by extended startup operations at Clariant’s Romanian plant. And UPM’s extended construction operations in Germany may indicate unexpected challenges, as well.
In addition to cost issues, technical operations ranging primarily from feedstock collection through pretreatment have been challenging. These areas include harvesting and collection of feedstocks in a multi-stage process, feedstock materials handling at the plant, and control of pretreatment conditions to facilitate the high conversion levels of cellulose and hemicellulose to fermentable sugars necessary for commercial success.
Feedstock Harvest and Collection
To date, commercial feedstocks have focused on agricultural crop residues – corn stover, wheat straw, and sugar cane bagasse/straw. All efforts except UPM (wood) use these feedstocks. Typically, ag feedstocks (corn stover, wheat straw) are harvested by combine. The straw is spread across the field surface, allowed to dry to about 15% moisture, and winrowed prior to baling and transport to the plant or intermediate storage site. This process typically requires multiple passes through the field and results in increased levels of inorganic ash (soil, sand, rocks) being entrained in the feedstock bales. Not only does this inert material dilute the feedstock in the process, but it also increases the abrasive qualities of an already much more abrasive feedstock than corn. Thus, this inert material not only reduces the potential quantity of product from feedstock, but also dramatically accelerates the wear of process equipment. Beyond those two key issues, multiple passes through the harvest fields wastes time and fuel when reduced or single pass harvesting is possible with today’s equipment to achieve cleaner, denser feedstock at the plant gate.
Feedstock Materials Handling at The Plant
The challenges of cellulosic biomass feedstock are not only related to harvest and collection, but also to materials handling in the conversion process at the plant. Handling fibrous materials that don’t flow like water – corn does – presents significant challenges. While the pulp and paper industry has done this successfully, only UMP Kymmene in the biochemicals space is attempting to use timber as a feedstock. All others are using agricultural crop residues – corn stover, wheat straw – or dedicated energy crops such as switchgrass, miscanthus, and energy sorghum. From handling 1500 lb. bales and milling to a practical processing particle size, to slurrying and pumping the slurries until liquefied, materials handling can be more than challenging. Fibrous solids also don’t slurry at the percent solids of corn, not even close. Thus, the high solids loading of corn – about 32% on average – is not feasible with cellulosic biomass. And many traditional types of equipment just don’t work. Adapting methods and equipment from unrelated industries may help provide the answers. Further, materials of construction are crucial; because, fibrous feedstocks, along with the soil and other inert debris added by windrowing ag feedstocks prior to baling, is much more abrasive than corn and results in greatly accelerated wear rates on traditional processing equipment such as piping and pumps. The status quo does not work as proven in very public failures.
Feedstock Pretreatment
Pretreatment has probably been the most common area for process challenges, including processing methodology and conditions. Nevertheless, autohydrolysis and dilute acid hydrolysis in conjunction with steam explosion technology is the most practiced pretreatment approach. This type of pretreatment does work; however, the ability to control the process is not easy. Plugging lines, fowling surfaces, consistency/solids loading with accurate temperature, pressure, and pH control is crucial to success. With consistent, accurate controls of these parameters cellulosic biomass can be a highly convertible feedstock by well-known enzymatic methods to 5- and 6- carbon sugars for fermentation to ethanol or other end products can be a commercial reality. However, control of pretreatment unit operations remains a difficult challenge. Andritz and Valmet are known providers of commercial scale pretreatment equipment, but success at commercial scale is still a major challenge.
Possible Solutions
Having grown up in Kansas, I am very familiar with the “custom combine” crews that harvest wheat every year. Is something like that a possibility at a much more complex operations level? In the case of corn stover, for example, there is no question that today’s harvesting equipment can harvest corn and simultaneously put down chopped stover in a row that balers can process without the need for a separate windrowing operation. That saves both time and fuel. To compress the harvest operation further, it should not be a big logistical stretch for equipment manufacturers to feed that chopped material either directly into a baler without hitting the ground or alternatively blowing the chopped stover directly into a truck for transport to a centralized pretreatment/densification center, most likely as part of a Gen 2 processing plant. That saves even more time and fuel. Where feedstock is outside a maximum 50- radius from a Gen 2 plant a separate dedicated pretreatment/densification processing plant may be practical, but we are not there yet. We need commercial successes.
For those that remember the late Stephen Covey, he promoted doing “First Things First.” He even wrote a book by the same title. We need to look down the road to the future for new and improved strategies, but we must have commercial scale successes. We cannot afford more commercial scale failures. With that in mind, there are operational efficiencies that we can implement today using existing technologies/equipment or modifications thereof that simplify the overall process, save time, save fuel, reduce wear on process equipment, and thus reduce costs.
About the Author: Doug Rivers, PhD, has over 45 years of experience in thermo-chemical conversion technologies and serves as a Project Director at Lee Enterprises Consulting, overseeing matters involving Bioprocess Development & Scale Up, Fermentation Processes, Ethanol, Enzyme Technology, Cellulose Conversion, Renewable Chemicals.
About Lee Enterprises Consulting: Lee Enterprises Consulting was founded in 1995 and has grown to become the world’s premier consulting group specializing in the bioeconomy with over 170 experts around the globe. The group’s experts are renowned, hand-selected leaders, with over 97% holding advanced degrees and averaging over 30 years in their respective fields.
[1] https://www.biofuelsdigest.com/bdigest/2022/05/15/raizen-raising-the-roof-on-2-new-cellulosic-ethanol-plants-with-395m-investment/
[1] https://money.cnn.com/magazines/fortune/fortune500_archive/full/1975/
