Using renewable natural gas (RNG) from biogas to produce hydrogen via methane pyrolysis and achieve negative emissions involves several steps. Here’s a step-by-step breakdown:
- Organic waste (e.g., agricultural waste, food waste, sewage sludge) undergoes anaerobic digestion in a biodigester. This process breaks down the organic matter in the absence of oxygen, producing biogas. Dairy digesters, for example, are “currently considered one of the most effective climate investments states can make,” according to a study from the California Air Resources Board.
- Biogas primarily consists of methane (CH4) and carbon dioxide (CO2), along with trace amounts of other gases.
Purification of Biogas to RNG:
- Biogas is processed and purified to remove impurities, especially CO2, to produce RNG which has a much higher methane content.
- The CO2 removed during this process can be captured and sequestered, reducing its release into the atmosphere.
- Carbon is removed from RNG using a safe, clean, high temperature process.
- The reaction is CH4→H2.
- This method of removing carbon from RNG also produces hydrogen.
- Unlike the commonly used steam methane reforming (SMR), pyrolysis does not release CO2.
- The solid carbon produced by methane pyrolysis can be permanently sequestered, preventing it from re-entering the carbon cycle.
- This can be done by burying the carbon underground, or using it in industrial applications such as the production of asphalt and other materials.
Net Negative Emissions:
- The carbon in the biogas originally comes from atmospheric CO2 that was absorbed by plants during photosynthesis. When these plants decay or are consumed and excreted by animals, they would naturally release methane to the atmosphere.
- By capturing the methane from decomposing organic matter and converting it to hydrogen and solid carbon, and then sequestering the solid carbon, we are effectively removing CO2 from the cycle and preventing pollution.
- Additionally, the hydrogen produced in this process can be used as a clean fuel, potentially displacing other carbon-intensive fuels, further reducing CO2 emissions.
Utilization of Hydrogen:
- The hydrogen produced can be utilized in process heat and steam, in transportation as a fuel, in industry for reducing iron ore to produce steel, or in many other application where hydrogen is utilized, without any CO2 emissions.
For this process to result in negative emissions, the carbon capture and sequestration steps need to be effective and long-term, such as in Modern Hydrogen’s asphalt binder and sealer solutions. Furthermore, any emissions associated with the energy required for the pyrolysis process and other ancillary processes need to be accounted for and minimized, ideally using recycled hydrogen or renewable energy sources.
The Imperative of Achieving Negative Emissions
As climate change increases in importance at the forefront of global concerns, the necessity of achieving negative emissions gains prominence in discussions on environmental stability. The Intergovernmental Panel on Climate Change (IPCC) has been vocal about the urgent need to cap the global temperature increase this century to under 2 degrees Celsius from pre-industrial levels. An ambitious but necessary target is a limit of 1.5 degrees. To meet these goals, especially with an existing rise of over 1-degree, negative emissions may play a pivotal role.
The possibility looms of global emissions overshooting acceptable thresholds before comprehensive mitigation measures get fully implemented. In such “overshoot” situations, negative emissions become indispensable, serving as a mechanism to extract and sequester the surplus CO2, bringing atmospheric concentrations back within desired limits.
Complicating the picture, certain economic sectors, including aviation and specific industrial operations, may be resistant to complete decarbonization. The persistent emissions from these hard-to-abate sectors can be offset by implementing negative emissions strategies.
Counterbalancing Indirect Consequences
Beyond the evident climatic ramifications, there are indirect consequences to excessive atmospheric CO2. Oceans absorb a significant portion of this both heat from global warming and excess CO2. Absorbed CO2 leads to change in ocean chemistry, posing threats to marine ecosystems and especially to shell-forming marine organisms. Drawing down atmospheric CO2 could be a solution to this escalating problem.
Another impending concern is the potential diminished efficacy of natural carbon sinks, like forests, as global temperatures rise. In a warmer world, these sinks might not only become less effective but could also start releasing stored carbon back into the atmosphere. Negative emissions technologies can counterbalance this potential carbon release.
Moreover, the risk of activating feedback loops, such as methane emissions from thawing permafrost, intensifies with elevated CO2 levels. Negative emissions strategies can help counter these feedback mechanisms.
At the intersection of climate science and ethics, the moral responsibility to address the carbon crisis cannot be ignored. The onus falls on present generations, the primary contributors to the surge in atmospheric CO2, to ensure future generations inherit a sustainable planet.
A Dual Strategy Approach is Needed
While the development and deployment of negative emissions technologies are crucial, they should complement, not replace, earnest endeavors to reduce current and future emissions. The path forward necessitates a dual-pronged strategy: reducing emissions while developing effective solutions to achieve negative emissions.