Leveraging Biomass
A comprehensive review in Clean Technologies and Environmental Policy summarizes current advances in liquid biofuel production and solid catalysts prepared from waste biomass, as well as their advantages, drawbacks and statistical data.
The authors, from chemical engineering and chemistry departments at universities in Mexico and Colombia, offer an extensive perspective, covering conventional methods and cutting-edge techniques, such as biochemical and thermochemical biomass conversion technologies — hydrolysis, fermentation, pyrolysis and gasification — to produce bioalcohols, biodiesel, renewable diesel, bio-jet and bio-oil (Figure 1).
They also analyze the preparation of heterogeneous catalysts using residual biomass and different synthesis routes and their role in biofuel production.
The article notes sustainable biofuels production depends on feedstock, reagents, processes and technologies, all of which have different social, economic, environmental and political impacts.
The article emphasizes that a successful circular economy hinges on ramping up biofuel production using an effective waste-to-wealth strategy. This requires input from various fields of expertise. However, the authors note that society is still a long way from making this a reality.
These issues were the focus of the annual European Biomass Conference and Exhibition (EBCE) that took place in Marseille, France, in late June.
While acknowledging that strong bonds forged between the research and academic community and industry are helping to close knowledge gaps, the EBCE heard that serious hurdles stand in the way of large-scale advanced biofuel plants — as highlighted by a spate of recent closures.
In February, Enerkem Alberta Biofuels announced the closure of its biofuels plant in Edmonton, Alberta. The plan was to transform garbage that couldn’t be recycled or composted into biofuels.
The facility would have generated enough biofuels to supply over 400,000 cars per year running on a 5% ethanol blend.
"We felt we had reached our main objectives, which was to demonstrate this technology at commercial scale," Chornet said in an interview with CBC News. "Now we are retiring this facility."
Similarly, Clariant has closed its bioethanol plant in Podari, Romania, and downsized related activities in Germany. German newspaper Frankfurter Allgemeine Zeitung reported that technical problems with processing raw materials at an industrial scale were to blame.
The company planned a 50,000 t/yr plant using its proprietary Sunliquid technology to produce cellulosic ethanol from wheat and other cereal straw from local farmers. Sunliquid uses enzymes to break down lignocellulose from plant fibers.
Nevertheless, there are opportunities.
Both Evonik and BASF are upping their production capacities for sodium methylate in South America. Sodium methylate is a catalyst designed to promote higher yields and lower costs during biodiesel production.
In Evonik’s case, the plan is to increase production capacity at its Rosario plant in Sante Fe, Argentina, by 50% to 90,000 t/yr and to significantly increase biodiesel productivity and reduce production costs across South America.
The announcement is of particular importance to the region due to the Brazilian government’s recent increase of mandatory quotas for blending fossil diesel with 15% biodiesel in 2025. It also aligns with the objectives of New Industry Brazil, which aims to boost the national industry and expand the share of biofuels in the transportation energy mix.
BASF, too, is upping capacity for sodium methylate production at its site in Guaratinguetá, Brazil, to 90,000 t/yr (Figure 2).
Polymer Posers
Despite the industry’s progress with catalysts to recycle and reuse polymers, significant hurdles remain to creating a genuine circular economy.
These include the need for milder reaction conditions, more robust catalyst design, selective product yields, and experimental and feedstock standardization.
Researchers from the Artie McFerrin Department of Chemical Engineering, Texas A&M, College Station, Texas, take aim at these in a Chem Catalysis review. They note that experimental standardization is required so results obtained by different experimental and analytical methods can be compared and contradictory results avoided. This, they say, also is a problem inherent to both biomass and plastic conversion.
Uniformity in catalyst characterization and reporting is lacking, as is catalyst-to-feed ratio.
Selectivity and yield are significant challenges, too. While high selectivity is desirable, catalysts also need to be versatile for mixed feedstocks. Catalysts are currently being designed for substrate specificity. As such, highly specific catalysts cannot effectively convert mixed post-consumer plastic streams, the Texas A&M research team writes.
Then there is the issue of process design for upcycling plastics. For example, hydroconversion is efficient for upcycling polyolefins, while solvolysis and solvent extraction are efficient for upcycling condensation polymers, such as polyesters and composite plastic materials, respectively.
Plastic feed streams typically come with a variety of polymer components, all with different impurities and additives, and the level of contamination of the feed can vary drastically. An amalgam of processes and methods will be necessary to effectively handle this plastics problem, they suggest.
As with chemical processes in general, upstream and downstream processing can prove critically expensive. For reactions with either gaseous or solvent reagents, both require separation processes to extract the hydrocarbon products from the catalyst and/or solvent. Thus, process design and selection must include a holistic perspective of the processes accompanying the core depolymerization reaction.
One solution proposed is versatile catalytic processes to handle mixed streams. Series reactors with discrete catalyst beds may be applied to sequentially process the mixed substrate. In addition, solvent-assisted separation of a mixed plastic feed can be done before the catalytic reaction.
As such, say the authors, a careful balance must be struck between reaction conditions and downstream/upstream separation techniques.
