An innovative new technology that can produce hydrogen from a toxic industrial waste gas has successfully completed its pilot stage in China and will now be scaled up — with the potential to save huge amounts of money for oil refiners and other industries.

Chinese scientists have pioneered a novel electrocatalysis process that can split hydrogen sulphide (H2S) — a highly poisonous gas produced from sulphur-containing compounds in crude oil and natural gas — into hydrogen and sulphur.

As H2S cannot legally be released into the air, it must be captured. Oil refiners and other industries producing the gas (see panel below) currently process it in so-called “sulphur-recovery units” (SRUs), where it is burned to produce sulphur dioxide (SO2), which is then reacted with a catalyst to produce sulphur and water, (or further processed to produce sulphuric acid [H2SO4]).

Although the sulphur (or sulphuric acid) is then sold for profit, the income is unlikely to ever be high enough to offset the upfront costs of the SRUs, with market research firm Emergen finding that modern SRUs typically cost between $50m and $150m.

The new Chinese electrocatalysis process promises to be a cheaper method of processing H2S that also creates a second revenue stream — hydrogen.
This hydrogen can therefore be sold in addition to the sulphur — or be used directly in refineries, thus reducing the amount of H2 that otherwise needs to be produced in-house from natural gas or bought in.

Previous attempts to deal with hydrogen sulphide through electrocatalysis — electrolysis in the presence of catalysts — have failed because the sulphur has stuck to the electrodes, which stops the process from working.

However, researchers at the Dalian Institute of Chemical Physics (DICP) have found a way to solve this problem by using so-called “off-site” electrocatalysis to split H2S. This means the chemical reactions take place separately from the electrodes, thus preventing sulphur from sticking to them.

The new process works by passing H2S into a water-based solution containing iron in a highly reactive form, which absorbs the gas and chemically strips out the sulphur, causing it to precipitate as solid elemental sulphur that can then be collected.

The hydrogen ions left behind in the liquid are then converted into hydrogen gas using a second chemical system using vanadium ions and a low-cost tungsten-carbide catalyst.

After both steps, the iron and vanadium are in “used” forms, but they are not discarded: a small amount of electricity — less than required for water electrolysis — is applied in a separate electrolyser to regenerate them back to their active states, allowing the same liquid to be reused continuously.

The result is a low-energy, closed-loop process that completely removes hydrogen sulphide while simultaneously producing two valuable products — clean hydrogen and solid sulphur — without the fouling and corrosion problems that normally plague such reactions.

The pilot project, which took place at a methanol plant in Henan province owned by Henan Energy Group’s Xinxiang Zhongxin Chemical, has proved so successful that it will now be scaled up, though details of this scale-up, including its size and timeline, have not been revealed.

So far, the pilot system has converted H2S into pure hydrogen and sulphur for 1,000 hours of continuous operation, according to the DICP, and has capacity to convert 100,000 cubic meters of H2S a year.

Details of how much the new technology would cost, and how much it costs to run are not publicly available, but the generation of additional revenue from hydrogen may be beneficial for many companies.