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Over 40% of known global gas reserves contain carbon dioxide (CO2) and hydrogen sulfide (H2S). That makes monetizing sour gas a key challenge for the industry: treatments have to be economical as environmental and commercial specifications keep getting more stringent. A global pioneer in sour gas, Total has turned the problem into a technological strength. We’ve developed a range of techniques to produce this type of reservoir. One of them is the HySWEET® process, which removes the sour gas and sulfur compounds at the same time during natural gas treatment. It’s a huge advantage that has already brought Total commercial success.

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Renaud Cadours

LNG

claire_weiss_exploration_production_total
Claire Weiss

LNG

The high extra cost of sulfur compounds

There are significant risks associated with sour gas, which is corrosive, toxic and even flammable. Hence the ever-stricter commercial specifications, to make sure sour gas is produced in a way as protective as possible of the environment. This applies both to carbon dioxide and hydrogen sulfide and to their sulfur compounds such as mercaptans (R-SH or thiol) and carbonyl sulfide (COS).

For COS, though, using amine solvents to remove the sour gas is insufficient. Additional treatment steps are therefore needed to remove each specific sulfur impurity, with serious repercussions for the final unit. Energy use increases, unusable byproducts are created and, of course, costs soar.

It wasn’t a feasible solution for our Lacq plant in southwestern France, for the very good reason that the declining sour gas field’s commercial production would soon come to an end.  It therefore made no economic sense to invest in additional treatment units to upgrade our production base. Although some hybrid solvents were already available in the market, they turned out to be incompatible with our facilities.

HySweet's® proven industrial efficiency

That’s why we opted in 2007 to conduct commercial-scale tests at Lacq of the HySWEET® technology developed by our researchers. Leveraging our gas treatment expertise and competencies, the process uses a hybrid solvent that combines the chemical features of an amine and the physical properties of a cosolvent to simultaneously absorb CO2, H2S and sulfur compounds such as mercaptans and COS. It has a significant advantage: compatibility with current facilities, which don’t need to be modified.

We made the switch from the water-DEA solvent formerly used to sweeten sour gas containing 17% H2S and 10% CO2 to HySWEET® DEA solvent, without having to retrofit any equipment.

The process proved reliably stable until Lacq ceased operations in late 2013. Its performance lived up to our expectations:

  • Optimized removal of mercaptans — more than 95%, versus 55% with the water-DEA solvent — during sour gas removal.
  • 8 to 15% less energy used than the amine unit.
  • Limited co-absorption of hydrocarbons, with no impact on the quality of the sulfur produced later.
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An expanded offering

We continued our R&D during the commercial-scale demonstration, focusing on the physical chemistry of the solvent and the sulfur compounds, to enhance the technology. In addition to HySWEET® DEA, our line now includes:

  • HySWEET® MDEA, which removes all the H2S and sulfur compounds and selectively separates the CO2.
  • HySWEET® EnergizedMDEA, which removes all the H2S and is selective in removing the CO2. More chemically stable, it is also more energy efficient and less corrosive than DEA.

Models for every aspect of this line of processes have been developed and integrated into an in-house simulation application that helps us scale projects.

Competitive advantages that make the difference

The process’s edge over competing technologies led in 2011, just five years after identifying the solvent, to the sale of the first commercial HySWEET® DEA unit to SOBEGI, so that thiochemicals could continue to be produced in the Lacq region. Commissioned in 2013, it was replaced in 2018 by the latest addition to our line, HySWEET® EnergizedMDEA.

HySWEET® DEA was also chosen in 2017 by the North Caspian Operating Company (NCOC) to improve removal by two gas treatment trains at Kashagan, Kazakhstan, after a study showing that the solvent could be changed without interrupting production.

We won another contract the same year, when ADNOC Gas Processing, ADNOC’s gas affiliate, decided that the HySWEET® MDEA solvent was the best option for two units at the Habshan plant in the United Arab Emirates.

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