Reimagining Roads with Hydrogen and Modern Solid Carbon

Among the many industries worldwide that have committed to achieving net-zero emissions (by various deadlines from 2030 to 2100) is the asphalt industry. It is considered one of the “hard-to-abate" sectors due to its raw material needs and high-temperature requirements.

Methane pyrolysis offers the asphalt industry an opportunity to economically reduce emissions while improving performance of end products and actively sequestering carbon, a win-win-win scenario.

Our study explored the integration of methane pyrolysis within asphalt plants, highlighting the benefits of utilizing Modern Solid Carbon to improve asphalt durability and performance while taking advantage of hydrogen as a cleaner energy source. The paper outlines the technical and infrastructural modifications required for this integration and presents case studies demonstrating the efficacy of Modern Solid Carbon in asphalt mixtures and hydrogen in fuel applications.

The asphalt industry can reduce its environmental footprint, enhance material properties, and lower production costs by leveraging these products.

Environmental and economic analyses underscore the benefits of adopting methane pyrolysis in asphalt production. The reduction of greenhouse gas emissions and waste, coupled with cost savings from the use of carbon and hydrogen, position this method as a viable alternative to traditional practices.

The paper addresses the technical and regulatory challenges associated with this transition and proposes solutions and areas for future research. By integrating methane pyrolysis, the asphalt industry stands to make significant strides towards sustainability and economic efficiency, setting a precedent for other industrial applications of this technology

Introduction

The United States has over 2.8 million miles of roads, with approximately 94% paved using asphalt. Moreover, the global asphalt market is expected to grow at a compound annual growth rate (CAGR) of about 5% over the next decade. This growth is largely driven by urbanization and population increases, necessitating the expansion of robust transportation networks.

Asphalt is the material of choice for these projects due to its durability, cost-effectiveness, and flexibility.

Recent developments in binder additives have enhanced asphalt's resistance to traffic loads, temperature fluctuations, and other external factors. However, this expansion carries significant environmental liabilities, particularly due to the unsustainable carbon dioxide (CO?) emission levels from both cradle-to-gate and cradle-to-grave processes.

The production of asphalt up to "the gate" involves three main stages: raw materials extraction, transportation, and hot mix production. The production of the binder and the high temperatures required for mixing asphalt at plants are primary sources of emissions. Specifically, asphalt binder—which is derived from crude oil—accounts for 94% of the emissions from raw materials and 53% of total cradle-to-gate emissions.

Although reducing emissions from oil extraction remains challenging, the industry can lower its carbon footprint through binder extenders that sequester carbon. In 2019, emissions from hot mix production in the U.S. were approximately 21.7 million tons of CO?, equivalent to 4.8 million passenger cars’ annual CO? emissions. These emissions largely stem from the fuel consumed to heat aggregates and to produce asphalt binder.

While the industry has made strides by adopting clean-burning natural gas—which now represents 70% of burner fuel sources— simply switching to natural gas is not enough to meet net-zero targets by 2050. More comprehensive strategies will be required to significantly reduce the asphalt industry's carbon emissions. Realizing the limitations of the current strategies, the asphalt industry has been looking for innovative solutions.

Among these is switching from natural gas to clean fuels and using advanced clean materials, both of which require significant sums of investment.

Methane pyrolysis, however, offers an alternative and affordable solution to this problem. It is a process by which a molecule of methane (CH?) is split into its elemental components (carbon and hydrogen). The main advantage of this process is that it produces hydrogen without significant carbon emissions as carbon is removed in solid form before it is ever combusted, preventing the formation of CO?. The carbon produced can then be used to reduce the embodied emissions of the materials in asphalt pavement. As a result, this process can greatly contribute to drastic cuts in carbon emissions.

Below are continued excerpts from the paper. Click here to download the full paper from Asphalt Pro Magazine.

Utilization of Hydrogen in Asphalt Plants

When used as a fuel, hydrogen offers several environmental and operational advantages. Primarily, hydrogen combustion produces only water vapor as a byproduct, significantly reducing CO? emissions and other pollutants like sulfur oxides (SOx) and nitrogen oxides (NOx) associated with traditional fossil fuels.

This shift could significantly decrease the carbon footprint of asphalt production, aligning with global efforts to combat climate change.

The single largest energy load in any asphalt plant is the central burner. This burner is critical to dry and heat the aggregates and ensure the hot mix is at suitable temperatures for transport. These burners are typically well over 100 MMBTU/hr in size, with the most common fuel being natural gas, and contribute approximately 77% of the emissions associated with HMA plant operations.

The next largest energy user in the plant is the binder tank heating system, which is also typically natural gas powered and accounts for 11% of emissions. By blending in hydrogen or switching to pure hydrogen as the main burner fuel, the emissions from HMA plant production can be greatly reduced.

Moreover, hydrogen has a high energy content per unit mass, which means it can provide a more efficient and powerful energy source compared to conventional fuels. This efficiency can lead to improved plant performance and potentially lower operating costs over time, despite the current higher costs of hydrogen production and infrastructure modifications.

Environmental and Economic Analysis

Approximately 70% of the asphalt plants in the US use natural gas. Natural gas produces ~53 kg CO? per MMBTU burned for fuel. The impact is, on average, 15 kg CO? per ton of asphalt.

Today, the asphalt industry may be running behind its emission reduction targets. However, eliminating the CO? emissions from natural gas combustion by adopting alternative fuels used in hot mix production could rapidly yield impactful results.

Clean hydrogen is an important alternative source to investigate and on-site methane pyrolysis utilizes the same natural gas infrastructure in place to produce clean hydrogen. If clean hydrogen is used, the net reduction could be as high as 15 kg CO? per ton of hot mix (AsphaltPavement.com ).

Over the entire US asphalt market, that would translate to emissions reductions of over 5 million tons of CO? per year.

While clean hydrogen offers an attractive reduction in CO? emissions, the bulk of emissions (53% of cradle-to-gate emissions) comes from the liquid binder component of asphalt.

Crude oil extraction for the liquid binder has been seen as an irreplaceable component of production that causes the high level of emissions. However, it is possible to reduce the percentage of liquid binder used in asphalt by using binder extenders with lower emissions.

These binder extenders can also increase the performance and lifetime of asphalt, reducing lifetime emissions.

Asphalt binder is also one of the most expensive line items in hot mix production, accounting for up to ~80% of direct materials costs. Using Modern Solid Carbon from methane pyrolysis to replace a portion of asphalt binder can reduce material costs.

The solid carbon can be utilized as a partial substitute for asphalt binder, which is traditionally derived from petroleum. Since the production cost of methane pyrolysis is generally lower than the extraction and refinement of oil, the solid carbon obtained from this process provides a cheaper alternative to the more expensive asphalt binder.

Utilizing the Modern Solid Carbon product in road construction can reduce the need for virgin asphalt binder and contribute to a circular economy. This approach helps decrease reliance on petroleum resources and stabilizes costs, as natural gas prices are less volatile than asphalt products.

Overall, the use of Modern Solid Carbon from Modern Hydrogen Methane Pyrolysis in asphalt mixtures presents a cost-effective and sustainable solution for infrastructure projects.

Click here to download the full paper from Asphalt Pro Magazine.