Ludicrous future vision or innovation stimulator? What is the current status of bio-based platform chemicals? Whatever potential people might see in renewable resources — the new “green gold” — , the overriding consideration must be the competitiveness of “green” production.
The established routes in the oil-based chemical industry have been enhanced and fine-tuned for efficiency over the course of many years. An elaborate plant and process infrastructure supports cost-efficient production of an entire chemical genealogy. However a lot of work still needs to be done before biomass can replace naphtha at the head of a chemical value-add chain which produces useful chemicals at competitive prices. As long as oil is readily available at affordable prices, the transition to alternative raw materials is quite simply a cost issue for the chemical industry.
“The basic volatility of agricultural commodity prices, e.g. sugar and vegetable oil, is problematic,” warns Dr. Thomas Haas, who is in charge of the Biotechnology Science-to-Business-Center at Evonik. Commodity prices fluctuate, and the price per tonne of carbon from renewables repeatedly rises above the equivalent price of carbon from oil-based raw materials. In March of this year, a tonne of carbon from bioethanol cost € 1508 compared to € 1384 from propylene. According to Haas, increasing the flexibility of bio-based processing in this regard would boost competitiveness significantly.
More Innovation Needed
However, commodity prices are not the only obstacle to competitive production. White biotechnology provides the engineering toolkit for many renewable-based scenarios, but process development alone is a costly and time-consuming process.
Engineering development is needed to provide microorganisms which have the right metabolism for the target reactions, and researchers have to find biocatalysts which can handle stubborn substances. Neither of these challenges can be resolved overnight. Haas says that process development — from concept to commercialization — can take up to ten years when the goal is to produce bulk chemicals from renewables.
There are also inherent process limitations, e.g. in downstream processing. “Purification of the end products to meet chemical industry standards is one hurdle. Metabolism is a basic characteristic of microorganisms, and we find all of the metabolic products in the fermentation broth,” explained Dr. Joachim Schulze, head of Uhde Biotechnologie in Leipzig.
Product inhibition during fermentation is another problem as soon as the organisms you are using are inhibited by high product concentrations. “Innovative strategies such as in-situ product recovery or processing at low pH could possibly provide solutions, but more work needs to be done in this area,” said Haas. Downstream processing can be expensive. Product extraction from a fermentation broth can be the main cost factor (up to 80 percent).
Process upscaling also tends to cause difficulties, and more development work will be needed to exploit combined bio-based/ conventional methodologies. The hybrid approach to chemical production is evident in some recent development activity, said Haas: “Intensive work is currently underway on polybutylene succinate in the US and China. Biological fermentation is being used in combination with chemical hydrogenation.”
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