Limitations of a Glucose-Fueled Bioeconomy for a Sustainable Chemical Industry
Using biocatalysis and bio-based manufacturing as a cornerstone for a sustainable chemical industry has gained traction, with benefits ranging from a finite to renewable catalyst switch, mild operating conditions and usually exquisite chemical selectivity.
However, for some chemical processes, biocatalysts require chemical energy, often provided in the form of glucose. Since glucose is derived from renewable biomass, this might still seem a good alternative to high-energy chemical strategies, but are there unintended consequences, and what can we do about them?
Despite its potential, there are significant challenges and limitations to consider before bio-based manufacturing it can be classed as a truly sustainable alternative.
Hydrogenation reactions
Hydrogenation reactions account for 14% of all chemical steps, and put simply, require precise insertion of 2 Hydrogen atoms into a chemical to make the desired product. Traditional chemistry has an elegant solution, where the 2 Hydrogen atoms are derived from Hydrogen gas (H2), a 100% atom efficient ‘fuel’ or reductant. However, for these reactions to proceed on a relevant time scale, and with an acceptable degree of precision, a metal catalyst is required, typically a heavy metal such as Palladium, Platinum or Nickle.
However, alongside challenges in heavy metal supply chains, these reactions require high temperatures and pressures, contributing to strong commercial need for next-generation manufacturing solutions.
Redox biocatalysis: next generation bio-manufacturing?
Answering the call for next-generation manufacturing strategies, biocatalysts (enzymes) can carry out these reactions with excellent chemical precision and under mild reaction conditions. This brings about improvements in energy demands, down steam processing and decreasing reliance on metal supply chains.
However, bio-based manufacturing strategies use biological-fuels, typically in the form of glucose.
An introduction to Glucose
A 6-carbon structure with the chemical formula C6H12O6. Glucose is a simple sugar produced by plants through photosynthesis which turns carbon dioxide and water into oxygen and sugar. It is a ubiquitous energy source for every organism worldwide; essential to fuel aerobic and anaerobic cellular respiration. Within the chemical industry there is potential for it to be used as both an energy source and carbon feedstock.
However, in terms of using glucose in place of Hydrogen gas to power hydrogenation reactions, there are significant limitations. Most significantly in terms of waste accumulation.
Whereas Hydrogen gas is a 100% atom efficient fuel for hydrogenation reactions, glucose is 1% efficient, with the product (C6H10O6) typically burnt at the end of a process.
This provides a significant limitation to the sustainability benefits of bio-based manufacturing, and if we continue to ‘shift’ the chemicals sector from traditional feedstocks to bio-based manufacturing, there are other limitations.
Resource Availability and Land Use
Producing glucose on a large scale requires vast amounts of arable land, water, and fertilisers. This is particularly true when derived from crops like corn, sugarcane, and lignocellulosic biomass. Such demand could lead to competition with food production, driving up prices and affecting food availability, especially in regions already facing food insecurity.
With the global population projected to exceed ten billion by the end of the century, competition for habitable land, freshwater, and food will only intensify. The ethical implications of diverting crops from food production to chemical industry feedstocks must be carefully considered.
If fossil fuels are used during cultivation or processing, the environmental benefits of switching to glucose could be negated. Additionally, large-scale agricultural practices pose risks of soil degradation, deforestation and biodiversity loss, further complicating the sustainability narrative.
Ultimately, the environmental impact of expanding agriculture for glucose production might offset the potential sustainability benefits of using it as a widespread chemical feedstock.
Energy and Carbon Footprint
The production of glucose-based chemicals involves several processing steps. Converting lignocellulosic biomass (like wood or agricultural residues) to glucose requires pretreatment and enzymatic hydrolysis, both of which can be energy intensive. This reduces the overall carbon savings compared to fossil fuels, especially if the energy used in these processes comes from non-renewable sources.
The cost of glucose
The economic viability of glucose-derived chemicals depends on many factors, including the price of glucose, the efficiency of conversion processes, and the market prices of the resulting chemicals. Currently, many of these processes are more expensive than traditional petroleum-based routes and require considerable investments in new technology and infrastructure. Without significant subsidies or regulatory support, it’s unlikely that glucose-derived chemicals will compete in the market.
Sustainability Beyond Carbon Emissions
True sustainability goes beyond just reducing carbon emissions. It involves considering the entire lifecycle of a product, including resource use, waste generation, and overall environmental impact. While glucose is renewable, its production and conversion processes can still generate waste and involve hazardous chemicals. The use of catalysts and solvents can lead to environmental and safety concerns and the production of glucose from crops involves the use of fertilizers and pesticides, which can cause water pollution and harm ecosystems.
Bio-based catalysts help reduce many of these issues, but only in part.
A Complex Picture
While bio-base manufacturing has the potential to play a role in making the chemical industry more sustainable, it's not a silver bullet. The challenges of resource availability, energy use, technical limitations, economic factors, and broader sustainability concerns mean that glucose-driven chemical processes won't revolutionise the industry.
A more holistic approach is needed, one that includes a mix of renewable feedstocks, improved process efficiencies, sustainable energy sources, and innovations in green chemistry. It's crucial to weigh the benefits and limitations of glucose against other alternatives, such as waste-derived feedstocks, algae, CO₂ utilization, and advances in bio-based technologies that bridge chemistry and biology. Only by addressing these complexities can we move toward a truly sustainable chemical industry.
At HydRegen
We bring together the benefits and expertise of bio-manufacturing advances with the efficiency and infrastructure of using H2 gas as a reductant, resulting in H2-driven biomanufacturing.
Check out the video featuring our NED Joe de Sousa and our CEO Holly Reeve discussing the potential of the HydRegen technologies for sustainable chemical manufacturing.