Renewable feedstocks: Beyond a one-to-one conversion*

Today, stakeholders seeking to produce platform chemicals from renewable feedstocks are evaluating competing routes — based on, for example, oxidation, reduction, selective bond breaking, selective bond formation, and the selective dehydration of sugars — for breaking down complex starting materials into simpler, more versatile building block molecules. “The focus of this approach is to zero in on a process and then identify all of the potential downstream products that the process will yield,” says Bozell of the University of Tennessee (Knoxville).

 “While a major goal of the biorenewable chemical industry of the future will be to produce many chemicals at a single site, this remains a huge challenge for the industry. “Meaningful collaboration and integration will be required among the players in this space,” will be needed if the vision of truly integrated biorefineries are ever to be realized,” says Phani Raj Kumar Chinthapalli, senior research analyst for Frost & Sullivan, who is based in Chennai, India.

“Renewable raw materials derived from agricultural and forest sources provide biorefineries with a new set of primary building blocks, including carbohydrates in the form of cellulose, starch, hemicellulose and monomeric sugars, aromatics in the form of lignin, hydrocarbons in the form of fatty acids, and polyols in the form of glycerin,” explains Bozell. While the portfolio of proven conversion technologies for renewable feedstocks still lags behind that available for fossil feedstocks, stakeholders are working hard to close the gap.

Specifically, efforts are underway worldwide to improve feedstock pretreatment (for instance, to more effectively fractionate complex lignocellulosic materials, such as biomass and sugar cane bagasse, into their useful components), to demonstrate advanced conversion technologies that are able to deliver better specific conversions and higher yields, to develop more-effective enzymes for biocatalysis, and to commercialize state-of-the-art separation technologies (such as the use of extractive fermentation, electrodialysis and inline membrane separation systems) that are optimized for biobased processes. These efforts, coupled with efforts to adapt classical petroleum-based catalysis routes for biobased feedstocks, and the economies of scale that are expected to be realized from progressive scaleup and commercialization will all help to make these processes more competitive in the years to come, says Phani Raj of Frost & Sullivan.

Growth in the number of pilot-scale demonstrations, grassroots plant announcements, and commercial facilities coming online attests to the ongoing maturation of the bio-based production chemicals and polymers production. Nonetheless, land mass issues, such as the productivity potential per unit landmass, may ultimately limit the penetration of renewable feedstocks for commodity chemicals production. While advances in biotechnology and genetic engineering are being investigated to increase yields of desired targets, “the natural inefficiency of photosynthesis may ultimately put an upper limit on the penetration of renewable feedstocks,” says Bob Maughon, hydrocarbons & energy R&D director for Dow Chemical Co. (Midland, Mich.; www.dow.com).

Similarly, barriers related to capital and process intensity requirements for the conversion of renewable feedstocks to useful chemical building blocks can also be “a significant hurdle,” says Maughon, at least in the short term. “To help process developers surmount the prevailing technical and economic challenges, government policy and regulations need to be improved to better support a sustainable bio-based chemical industry.”

“The concept of breaking a complex feedstock down into smaller chemical building blocks using thermal and catalytic processes has been the focus on the petroleum industry since its inception. After nearly two centuries, this industry has reached a level of maturity that allows it to produce a spectrum of so-called platform chemicals that serve as chemical feedstocks for the chemical industry as we know it today,” says Luc Moens, senior scientist, National Renewable Energy Laboratory’s National Bioenergy Center (NREL; Golden, Colo; www.nrel.gov).

By contrast, the biorefining industry is young by comparison, just 20-30 years old. “As a result, the primary barrier we have to surmount today is that there exists a smaller portfolio of proven technology options,” says Bozell. “With renewables, process developers are still experimenting with fundamental questions such as “What process can we use?’ and ‘What products can we make?’”

Developers of renewable routes for chemicals production have tried to take a page from the petrochemical refinery’s playbook. “The problem is that many renewable feedstocks are not well-suited for the proven thermal steps that are routinely used to crack crude oil into its various factions in a petroleum refinery. “As a result, the front end of the biorefinery tends to look very different,” says Bozell.

For instance, because crude oil tends to offer a stream of highly reduced hydrocarbons, today’s well-established petrochemical processes have been adapted and optimized to use this feedstock. “By comparison, biomass is highly oxygenated, and tends to be very reactive, leading to reactions that often go in directions you did not anticipate,” says Bozell. “Because of this, proven, existing petrochemical unit operations will not offer drop-in replacements for those designing biorefinery operations.”

“This helps to explain why biomass chemistry and processing has progressed relatively slowly to date, and why today only a few significant platform chemicals are being produced efficiently,” adds Moens of NREL.

*This story is an online-exclusive sidebar to Renewable Feedstocks: Trading Barrels for Bushels