Various methods already exist for harnessing solar energy to split water and generate hydrogen. However, the production of “green” hydrogen from these methods has typically been more expensive than conventional “gray” hydrogen derived from natural gas. A new study, conducted by the Helmholtz-Zentrum Berlin (HZB) and the Technical University of Berlin, offers a promising solution to make green hydrogen cost-effective: divert a portion of the hydrogen produced to upgrade raw biomass-derived chemicals into high-value industrial products. This co-production concept offers flexibility, enabling a single plant to produce diverse by-products as needed.
To combat climate change, it’s imperative to transition away from fossil fuels as swiftly as possible. In the envisioned energy landscape of the future, green hydrogen is poised to play a pivotal role in energy storage and serve as a renewable feedstock for manufacturing chemicals and materials across numerous applications.
Presently, the majority of hydrogen production relies on fossil natural gas (known as gray hydrogen). In contrast, green hydrogen is manufactured through the electrolysis of water using renewable energy sources. Among the promising approaches is the use of photoelectrochemical (PEC) devices that utilize solar energy for hydrogen production. However, hydrogen generated from PEC plants has remained considerably more costly compared to hydrogen produced from fossil methane sources.
Gaining Control Over Reactions
The study, led by Fatwa Abdi (formerly at HZB, now at City University in Hong Kong) and Reinhard Schomäcker (UniSysCat, TU Berlin), explores how the cost dynamics change when a portion of the hydrogen produced within a PEC device is redirected to react with itaconic acid (IA), leading to the formation of methylsuccinic acid (MSA) — all within the same device.
Itaconic acid, a biomass-derived starting material, is introduced into the process, and MSA serves as a high-value compound highly sought after by the chemical and pharmaceutical industries.
The research details the control of chemical reactions within the PEC device by manipulating process parameters and adjusting the concentration of the water-soluble rhodium-based catalyst, which remains active at room temperature. This approach enables the selective allocation of hydrogen to the hydrogenation of itaconic acid, thereby increasing or decreasing MSA production as needed.
Profitability Achieved at 11 Percent Hydrogen for MSA
Considering an overall PEC plant efficiency of 10 percent, along with primary costs and ongoing expenses for operation, maintenance, and decommissioning, the standalone production of pure hydrogen remains cost-prohibitive compared to hydrogen produced from fossil gas. This holds true even when assuming a PEC plant lifespan of 40 years.
However, the equation changes when the PEC reaction is linked to the hydrogenation process. Even if just 11 percent of the hydrogen generated is converted into MSA, the cost of hydrogen drops to 1.5 € per kilogram, equivalent to the cost of hydrogen derived from methane steam reforming. Remarkably, this cost parity is maintained even with a shorter PEC plant lifespan of just 5 years.
Given the substantially higher market price of MSA compared to hydrogen, enhancing MSA production increases overall profitability. The experimental results indicated that hydrogen utilization for MSA production could range from 11 to as much as 60 percent.
Additionally, a prior study has shown that co-production of MSA concurrently reduces the energy payback time, representing the duration required for the plant to recover the energy consumed during its production process.
The PEC plant’s versatility extends to the production of other co-products by simply altering the feedstock and deploying a soluble catalyst. For example, acetone can be hydrogenated into isopropanol, showcasing the substantial advantages of the co-production concept.
In summary, this innovative approach to co-producing green hydrogen alongside high-value chemicals not only demonstrates economic viability but also offers a promising avenue for driving the cost-effective production of solar hydrogen, thereby contributing to a greener and sustainable energy landscape.
By Impact Lab