How do coatings contribute to advances in the hydrogen economy? Read on to discover how coatings are used in the manufacture and use of hydrogen power.
Silicon Coatings Help Fuel the Hydrogen Economy
Climate change and a focus on cleaner energy are driving innovation in hydrogen powered vehicles, as well as in hydrogen production and transport. In this blog we'll discuss how SilcoTek® coatings contribute to making hydrogen a viable energy source for transportation.
In this blog post you will learn:
How hydrogen is produced.
The primary sources of hydrogen contamination and why it's important to minimize contamination.
How SilcoTek® coatings contribute to improving the reliability of hydrogen power, production, and transport.
Background: How Hydrogen is Produced
Hydrogen (H2) can be found in many compounds and materials on Earth. It's quite common and literally falls from the sky in water (H2O). Unfortunately pure hydrogen is virtually non existent on Earth. H2 combines relatively easily with other elements but pure H2 can be found in only small amounts in our atmosphere. In order to produce large quantities of hydrogen, hydrogen producers are forced to extract H2 from compounds that are hydrogen rich and relatively easy to process.
Hydrogen production can be broken down into 4 basic processes.
Thermal chemical processes, including natural gas reforming, coal gasification, biomass gasification, biomass based liquid reforming and solar thermochemical hydrogen. (produces greenhouse gases during production, production systems are well established)
Electrolytic processes like electrolysis (produce no greenhouse gases but is expensive and requires electricity in most cases sourced from the grid, requires further development to scale the process efficiently)
Solar water splitting processes like photoelectrochemical (PEC) and photobiological processes. (in development)
Biological process include microbial based biomass conversion and photo biological production. (in development)
Natural gas reforming is the predominant source of hydrogen production. Other sources of hydrogen production come from oil, coal, and water, but the primary hydrogen source currently comes from natural gas reforming. To help understand how coatings can contribute to hydrogen use and production, let's briefly review the hydrogen reforming process.
Figure 1: Diagram of a basic hydrogen production system. ("Hydrogen Fuel Quality Specifications for Polymer Electrolyte Fuel Cells in Road Vehicles", US Department of Energy, 2016)
Natural Gas Hydrogen Reforming
In the reforming process, hydrogen is produced from methane (CH4) found in natural gas. Hydrogen is extracted from natural gas through a process called steam methane reforming (SMR). In the SMR process, high temperature steam (up to 1000c) is injected into the methane stream under pressure. With the help of a catalyst, the methane and steam react to produce hydrogen and carbon monoxide (see figure 1 above). The reaction looks like this:
CH4 + H20 (+heat) CO + 3H2
To increase the hydrogen yield, the carbon monoxide by-product is further processed to form additional hydrogen. That reaction looks like this:
CO + H2O (+heat) CO2 + H2
As you can see, greenhouse gases are emitted during processing but the reforming process produces about half the greenhouse gases (production to tailpipe) when compared to fossil fuels like gasoline production.
Unfortunately natural gas contains contaminants that can either poison the catalyst used in production or potentially harm distribution facilities. Additionally, hydrogen contamination can affect the performance of fuel cells or internal combustion engines that utilize hydrogen as a fuel. That's where our coatings come into the picture. Refiners and natural gas processors use our coatings to enhance the reliability and detection limits of analyzers used to detect contamination in the natural gas feedstock and in hydrogen fuels.
Figure 2: A typical gas purification system, (source: Argonne National Laboratory and "Hydrogen Fuel Quality Specifications for Polymer Electrolyte Fuel Cells in Road Vehicles", US Department of Energy, 2016)
To prevent damage to downstream systems, gas streams are purified. A typical purification system may look something like the diagram (figure 2) above. Why spend the time and money to remove contaminants from hydrogen?
The Primary Sources of Hydrogen Contamination and Why it's Important to Keep Them Under Control
Table 1 below highlights contaminants that can affect the performance of hydrogen powered systems, either in the production of hydrogen, the delivery of hydrogen, or in the efficient operation of the power system (internal combustion engines or fuel cell systems).
Some contaminants can reduce the efficiency of hydrogen production or damage catalysts which can result in catalyst poisoning and premature system failure. Contaminants can also damage hydrogen transport systems. For example water can freeze valves, regulators or filters while particulates can damage or interfere with gaskets and seal areas or clog filters.
Still other contaminants, like N2, NOx or CO2, may not directly damage the fuel delivery system or damage the fuel cell, but can reduce the overall energy density of the fuel. This can result in poor performance in fuel cells or internal combustion engines. An increase in air emissions (NOx, SOx, etc.) may also result from contamination in the fuel stream.
Table 1: Directory of limiting characteristics (maximum allowable limits of contaminants) from ISO FDIS 14687-2. ( "Hydrogen Fuel Quality Specifications for Polymer Electrolyte Fuel Cells in Road Vehicles", US Department of Energy, 2016 )
According to a study by the US Department of Energy, the contaminants that pose the greatest danger to the performance of hydrogen production, delivery, and power systems like fuel cells or internal combustion (IC) engines include:
Carbon monoxide (CO) - CO can absorb onto the fuel cell surface and prevents hydrogen production.
Sulfur and sulfur species like hydrogen sulfide (H2S) - Sulfurs will contaminate the fuel cell catalyst and hydrogen production catalysts. Even trace sulfur contamination can quickly and irreversibly damage catalysts, causing poor performance and eventual premature catalyst replacement.
Ammonia (NH3) - Ammonia can can also poison catalysts and impede hydrogen production. Levels of ammonia as low as 2 ppm have been shown to result in degradation of hydrogen production.
Inert gases like nitrogen (N2) or oxides of nitrogen (NOx), or carbon dioxide (CO2) - inert gases do not damage catalysts or other system flow path components but they will reduce the overall energy density of the gas stream, reducing the performance of the downstream equipment like fuel cells or internal combustion engines using hydrogen as a fuel.
Methane CH4 - Methane can also dilute the hydrogen gas stream. Methane contamination in production processes can reduce the overall hydrogen production efficiency.
Water - Water can freeze in process and transport flow paths, inhibiting operation or damaging valves, regulators, orifices, or filters.
Aromatic hydrocarbons - Aromatic hydrocarbons, like benzene BTEX (the name for benzene, toluene, ethylbenzene, and xylene contaminants) can absorb onto the catalyst surface and block or inhibit hydrocarbon production.
Fine Particulates (below 10 microns) - particulates can damage flow path seals and blind filters.
The combined effects of contaminants in hydrogen production and use can result in an increase in production cost, impact reliability and performance of catalysts, can increase air emissions, and can potentially lead to safety and reliability issues in transportation systems. All of these negative effects can inhibit the expansion of hydrogen use in the greater economy and limit hydrogen's potential as a contributor to achieving carbon neutrality in energy use and production.
How SilcoTek® Coatings Contribute to the Hydrogen Economy
SilcoTek inert, corrosion resistant, hydrophobic and icephobic CVD coatings benefit hydrogen use and production by improving trace detection of sulfurs, ammonia, and other reactive compounds; allowing hydrogen process facilities, transport systems, and down stream users to reliably detect potentially catastrophic damaging contaminants. SilcoTek coatings also enable users to detect emissions of target contaminants at trace levels, improving emission compliance. Need help finding the right coating for your application? Contact our Technical Service Team or try our easy to use Coating Selector Guide.
SilcoTek coatings can also boost the water repelling and ice removal properties of flow path surfaces, improving moisture management and minimizing water retention and ice formation/removal problems. Let's review some of the performance benefits of various coatings.
Trace Sulfur and Sulfur Compound Detection
Stainless steel is a material commonly used in hydrogen production and transport systems. Unfortunately sulfur (one of those natural gas contaminants) is readily adsorbed onto stainless steel flow path surfaces. This makes detecting and managing sulfur poisoning more challenging. Sulfur detection is generally a manageable problem when testing at higher concentrations, usually at higher percent levels but at trace levels, detection is much more difficult.
Unfortunately, hydrogen catalysts are vulnerable to trace level sulfur poisoning. The damage from sulfur can add up quickly, resulting in reduced efficiency and shorter catalyst life. Both very expensive results. This makes testing for even trace level sulfur essential to cost efficient hydrogen production and use.
When testing for sulfur using materials like stainless steel, metal alloys, or even glass, the sulfur is adsorbed in the flow path and never reaches the sulfur detector. This results in reduced sulfur response at the detector and a false negative test; when in fact the feedstock stream may be poisoning the catalyst.
The flow test plot below demonstrates how various surfaces perform in trace sulfur analysis. The coated surfaces provide fast response and result in a higher detection signal when compared to uncoated stainless steel.
SilcoNert® radically improves sulfur response over uncoated stainless steel in analytical systems. This helps to maintain consistent and reliable detection, keeping hydrogen processing and fuel cell catalysts safe from poisoning.
Ammonia Detection
Like sulfur contamination detection, improved ammonia detection can also contribute to preventing damage to catalysts. SilcoNert improves test reliability and lowers the detection limit of ammonia, helping to detect ammonia contamination before catalysts are damaged.
A University of Helsinki study found that SilcoNert improves the trace detection of ammonia by 95% when compared to uncoated 316L stainless steel. Improved detection will enable refiners and users to better manage hydrogen fuel quality and maintain high efficiency in production and use.
Inert Gas Detection
As noted earlier, some gases may not physically harm production, transport, or use but can reduce the energy density of hydrogen fuels. Reliable detection of nitrogen, N2, or other contaminants assures hydrogen powered systems run at peak efficiency.
Emissions Detection
Advances in instrumentation and test procedures help, but inert surfaces like SilcoNert® andDursan®enable testing agencies to repeatably detect part-per-million and part-per-billion levels of NOxand sulfurs and other emissions.
The California Energy Commission conducted a study comparing SilcoNert®(noted as Silcosteel®in the study) to other materials commonly used in sampling systems. The results show the SilcoNert coated surface reduces surface reactivity with NOx, sulfurs and other common emissions, enabling more reliable testing of trace emissions.
Water and Ice Management
Hydrophobic coatings, like Notak®, repel water and ice to help to maintain a water free surface. This helps to control moisture contamination in hydrogen production, fuel delivery, and use. Notak prevents moisture carryover by preventing trace water from attaching to hydrogen flow path surfaces and hydrogen sampling flow paths. This allows the user to detect moisture before it becomes a problem in hydrogen manufacturing and transport flow paths.
Goniometer water contact evaluation (below) compares hydrophobicity data of various SilcoTek coatings. The water repelling properties of Notak, evident in the water droplet and 143 degree contact angle, prevent wetting and water retention of the stainless steel substrate. For reference, an uncoated stainless steel water droplet surface contact angle ranges from 30 to 40 degrees, making stainless steel a wettable surface that can retain water in tubing, valves, filters and other flow path surfaces.
Ice formation and removal is also a problem in hydrogen storage and transport. Surfaces with ice repelling or icephobic properties help operators to manage the accumulation and removal of ice. The ice repelling and removal properties of Notak® coated stainless steel are compared in the photo and table below. The frozen Notak droplet has the highest contact angle when compared to other coated and uncoated surfaces, indicating an icephobic surface.
Notak also made ice removal easier. After freezing coated and uncoated metal coupon samples, a metal pick was inserted at the point of ice attachment to the coupon. Gradual increasing force was applied laterally to the ice sample until the ice dislodged from the surface. The effort required (1 = easy, 10 = difficult) to remove the ice and associated observations are listed in the table below.
316 SS Coupon Surface
Effort (1-10)
Observations
Notak®
2
complete removal with little effort
Dursan®
6
partial removal from surface with effort
Silcolloy® 1000
7
partial removal from surface with greater effort
Dursox®
8
difficult, bulk chipped with minimal surface separation
Uncoated
8
difficult, bulk chipped with minimal surface separation
The ice and water repelling property tests demonstrate how SilcoTek coatings can improve the moisture detection, reduce the accumulation of water in flow paths and help to make ice removal from surfaces easier.
Corrosion Resistance
SilcoTek corrosion resistant barrier coatings prevent flow path surface interaction with corrosives; extending component life while preventing hydrogen contamination. Our corrosion resistant coatings, Silcolloy®, Dursox® and Dursan®, are particularly useful for fighting corrosion in high purity or otherwise sensitive processes found in hydrogen production, transport and use. (see graph below)
In addition to extending the usable life of precision stainless steel parts, SilcoTek coatings prevent nano-scale corrosive reactions that can cause metal ion leaching and contamination, ultimately increasing process yield and reducing failure rates.
Because hydrogen reacts with most elements, hydride formation may be a concern in hydrogen production, transport and in downstream power systems. SilcoTek coatings act as a barrier to reduce or prevent ion leaching and interaction of flow path substances with the metal substrate.
In the example graph below, methanol (CH3OH) extracted metal ions from uncoated alloy surfaces. Metal ion extraction can contaminate flow path fluids and may result in system system corrosion.
Conclusion
SilcoTek® coatings contribute to the hydrogen economy by enhancing contaminant detection, improving system reliability, and system operation. Overall coating contributions to the hydrogen economy include:
Detection
Detecting impurities in hydrogen fuel samples.
Hydrogen quality monitoring.
Accurately detecting emissions from current hydrogen production methods in refineries.
Permeation barrier / purity
Stability of hydrogen in storage; reducing contamination from storage materials.
Maintaining purity of hydrogen by preventing corrosion of storage and processing components – electrolysis, marine/salty environments, etc.
Slowing/preventing hydrogen embrittlement of metals
Improved dielectric properties.
Potential benefit to tritium permeation.
Production
Contribute to the control desired/undesired catalysis and improved detection of catalyst poisoning.
Environmentally-friendly hydrogen
Our coatings complement the “green” hydrogen effort; our coatings are inert and do not introduce additional contaminants or potentially harmful substances into the hydrogen process while enhancing the performance of components and flow paths used to produce, transport, and use hydrogen energy.
Physical improvements
In some applications, SilcoTek coatings improve friction and durability properties. Sliding Rings, pistons, sliding valves and other components used in compressors or other process components could benefit from using SilcoTek coatings.
Improve water detection and icephobicity in hydrogen flow paths.
The overall value of using coatings in the hydrogen economy result in reduced cost and improved efficiency of hydrogen use and production.
Interested in using SilcoTek® coatings in your process? Our Research and Development Team are here to help you select, evaluate, and use our coatings in your application. Contact our Technical Service Team to learn more. To keep in touch with the latest in coating development, subscribe to our blog, or follow us on LinkedIn.
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