COS in liquefied gas -- the issue of carbonyl sulfide
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Who has a systematic understanding of carbonyl sulfide (COS) in liquefied gas? Is it generated during catalytic cracking or during coking processes? How can it be reduced and removed?
They will all be generated, and can be removed using a specialized COS hydrolysis method, which is quite mature. It can only be partially removed during alkali washing.
They will all be produced; generally, current desulfurization agents such as methyl diethanolamine (MDEA) can remove most of them
It is present in both catalytic and coked liquefied gas; MDEA and alkaline extraction can only remove a portion of it. Due to its lower boiling point, it generally ends up in the C3 fraction during the subsequent liquefied gas separation process. Current removal methods include a one-step method (adsorption removal) and a two-step method (hydrolysis + desulfurization). All can be reduced to below 0.1 ppm. Our company has relevant products and technical solutions; feel free to contact me for more details. qq3797236
COS can be removed through hydrolysis, or it can be eliminated using alkaline solutions via fiber membrane contactor technology.
COS is present in large amounts in the gases generated during hydrogenation processes; it is mainly removed using DIPA. Another method involves using a hydrolysis reaction to produce hydrogen sulfide, which is then removed with amine solutions – this is also a process for alkali-free purification of liquefied gas.
Desulfurizing agents (methyl diethanolamine MDEA) can generally only remove sulfur dioxide from liquefied gas; thiols require the use of catalysts for removal through reaction
The common method for removing H2S is the alcohol amine absorption process, in which a weak organic base (amine solution) is used as the absorbent. In the liquefied gas desulfurization tower (extractor tower), there is counter-current contact between the liquefied gas and the amine solution; as a result, H2S and some CO2 in the liquefied gas are absorbed by the amine solution, thereby purifying the liquefied gas. The absorption of H2S and CO2 by the amine solution is a reversible process. The amine solution that has absorbed H2S and CO2 can be decomposed by heating under low pressure, releasing H2S and CO2 back. This reversible reaction allows the amine solution to be regenerated in a solvent regeneration tower, turning it into a lean solution. Meanwhile, the acidic gas containing H2S and CO2 is discharged from the system, while the lean solution is reused as an absorbent. The LPG desulfurization process employs an alkali-free desulfurization method; the LPG from which H2S has been removed enters a fixed-bed reactor, where, thanks to the dissolved oxygen in the LPG itself and under the action of a catalyst, the thiol compounds undergo oxidation reactions, resulting in their conversion into disulfides that remain dissolved in the LPG and are thus carried out of the plant. (PS: We rarely use alkali washing for liquefied gas these days; we don’t do alkali washing at all – I think the first step is sufficient.)
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