Methane Pyrolysis: Producing Inexperienced Hydrogen With out Carbon Emissions | Dudes Tech

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Usually, after we discuss hydrogen manufacturing, the dialogue is in regards to the electrolysis of water into oxygen and hydrogen, or steam methane reforming (SMR). Though electrolysis is usually talked about as it will probably create hydrogen utilizing nothing greater than water and electrical energy, SMR is by far the commonest supply of hydrogen. A lot of this is because of SMR’s low price and excessive effectivity, however an enormous draw back to SMR is that enormous quantities of carbon dioxide are launched, which offsets among the advantages of utilizing hydrogen as a gas within the first place.

Though capturing this CO2 might be thought-about as a possible resolution right here, methane pyrolysis is a more recent technique that guarantees to supply the identical advantages as SMR whereas producing hydrogen and carbon, as an alternative of CO2. With the various makes use of of hydrogen in industrial purposes and different fields, akin to fertilizer manufacturing, a direct alternative for SMR that produces inexperienced hydrogen would appear virtually too good to be true.

What exactly is that this methane pyrolysis and what might be anticipated from it within the coming years?

carbon residue

Methane (CH4) is mostly discovered as the principle element of pure gasoline and can be prevalent on account of methanogenesis, which incorporates the well-known cow burps. With steam methane reforming and comparable processes, the objective is to take away the hydrogen atoms from the one carbon atom, releasing up the hydrogen for seize. This leaves carbon basically as a waste product, which with SMR leads to every carbon atom capturing two oxygen atoms to type carbon dioxide, our all-too-familiar greenhouse gasoline.

The fundamental SMR response is given as:

CH4 + H2OR ⇌ CO + 3H2

That is an endothermic response, which signifies that an SMR reactor is stored inside a temperature vary of about 800 to 900 °C with the intention to really produce important quantities of hydrogen. The aforementioned CO2 seems within the extra water-gas shift response (WGSR), described as:

CO+H2OR ⇌ CO2 + H2

The objective of the WGSR is to extract extra hydrogen, rising the general effectivity of the SMR course of. As well as, catalysts are used to extend the effectivity of the reactions, leading to an total SMR effectivity of as much as 75%.

Capital prices for an SMR facility are fairly minor, with ongoing prices being primarily pure gasoline feedstock and gas to warmth the reactor. If the produced carbon monoxide and carbon dioxide additionally should be captured (so-called ‘blue’ hydrogen), the capital and ongoing prices will likely be correspondingly larger and the system effectivity decrease (~60%). This makes carbon seize and storage with SMR not economically enticing, and that is the place ‘turquoise’ hydrogen is produced by pyrolysis of methane.

turning up the warmth

The primary distinction between SMR and methane pyrolysis is temperature. It makes use of the thermal decomposition of methane, with temperatures usually nicely above 900°C, with some approaches explored for many years suggesting as a lot as 1,900°C. A normal drawback with methane is that it’s a very steady molecule, on account of its CH bonds.

On account of these robust bonds, the thermal decomposition of methane with out the presence of a catalyst will usually not happen till temperatures above 1100°C. The problem over the last many years of analysis has been to discover a appropriate catalyst. Primarily metallic catalysts, together with iron and nickel, have been studied right here. A giant drawback with metallic catalysts is their fast deactivation by way of the formation of carbon deposits on the floor. Reactivating the catalyst by cleansing the carbon deposit is troublesome and can lead to the manufacturing of carbon dioxide.

Carbon catalysts have been the topic of extra analysis lately, with quite a lot of promising benefits that make them fairly enticing. Usually within the type of activated carbon and carbon black, its benefits in relation to metallic catalysts might be summarized as follows:

  • lowest price
  • Higher (thermal) stability
  • Tolerance to impurities (for instance, sulfur in pure gasoline)
  • It isn’t essential to regenerate the catalyst.
  • The ultimate product is pure carbon, with out metals.
  • The catalyzed carbon deposit can nonetheless act as a catalyst.
Applicability temperature range of different catalysts for methane pyrolysis.  (Credit: Fang et al., 2015)
Applicability temperature vary of various catalysts for methane pyrolysis. (Credit score: Fang et al., 2015)

A last, and really completely different, strategy includes molten metals and salts, each in liquid bubble column reactors. In these columns of molten supplies, methane is launched on the backside, the place the methane is thermally decomposed inside pure gasoline bubbles. As soon as these bubbles attain the floor of the column, the hydrogen and carbon are launched, and the lighter hydrogen is separated from the carbon that continues to be suspended above the salt or molten metallic.

These bubble column reactors would offer a reasonably superb steady course of during which carbon might be faraway from the floor with out contaminating the soften or hydrogen produced. At present, nevertheless, analysis remains to be ongoing to search out the appropriate sort of salt or metallic that can work for such a response column that can even settle for the excessive working temperatures.

Because of this, for the second, carbon catalysts look like one of the simplest ways to supply hydrogen from methane with pyrolysis, aside from the upper temperature vary required.

Preparation for prime time

Configuration of a fluidized bed reactor using a carbon catalyst.  (Sánchez-Bastardo et al., 2020)
Configuration of a fluidized mattress reactor utilizing a carbon catalyst. (Sánchez-Bastardo et al., 2020)

Though one benefit of methane pyrolysis is that it will probably right now obtain SMR-like efficiencies with CCS, creating industrial-scale reactors that may run repeatedly with out fixed downtime for upkeep stays an ongoing problem. . A promising sort of reactor right here is the fluidized mattress reactor, together with packed mattress reactors.

Regardless of the challenges with methane pyrolysis, plainly its time has come. At the moment, greater than 95% of hydrogen is produced with SMR. If the free launch of carbon dioxide into the environment is not acceptable, alternate options akin to methane pyrolysis have a preventing probability within the hydrogen manufacturing market. In fact, there are numerous extra methods to supply hydrogen, all with their very own benefits and downsides.

An actual concern is that many of those applied sciences require plenty of electrical energy or excessive temperatures. As Sánchez-Bastardo et al. identified, renewable vitality is unlikely to supply the quantity of electrical energy wanted for water electrolysis, even only for industrial demand. Concurrently, thermal decomposition as with methane pyrolysis requires a supply of thermal vitality, which in the end influences the ultimate price and carbon footprint of the hydrogen produced.

That is the place Technology IV nuclear reactors can play a important position, with the VHTR (excessive temperature, helium cooled) sort offering an exit temperature of 900 to 1000°C, which might be ample for methane pyrolysis. One in every of these VHTRs, China’s HTR-PM, is meant for use for hydrogen manufacturing, along with electrical energy manufacturing.

One factor that does appear pretty sure, nevertheless, is that hydrogen manufacturing will likely be a lot greener, with increasingly carbon from the methane being extracted from pyrolytic reactors slightly than launched into the environment certain to oxygen atoms.

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Methane Pyrolysis: Producing Green Hydrogen Without Carbon Emissions

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