Liquefied petroleum gas (LPG) is a flammable mixture of hydrocarbon gases, primarily propane (C₃H₈) and butane (C₄H₁₀). It is stored under pressure as a liquid in steel cylinders or tanks, which makes it highly portable. When the pressure is released, the liquid turns back into a gas for use as a fuel.

LPG is generated primarily by natural gas processing and petroleum refineries.

• Natural Gas Processing: About 60-62% of global LPG is extracted from “wet” natural gas streams. When natural gas is brought up from the ground, it contains heavier hydrocarbons (like propane and butane, which make up LPG) that are separated out.
• Petroleum Refining (Crude Oil): The remainder of LPG is produced by refining crude oil. It is collected as a byproduct during the distillation and “cracking” processes that turn crude oil into products like gasoline and jet fuel.

LPG desulfurization is the process of removing sulfur-containing compounds, such as hydrogen sulfide (H₂S) and mercaptans, from liquefied petroleum gas. This is a critical step in the refining process to ensure the final product is safe, non-corrosive, and environmentally friendly. The process is also known as "LPG sweetening," as it removes the sour, corrosive impurities to create a cleaner, "sweet" fuel.

Sulfur compounds, especially H₂S, are highly corrosive and can damage refinery equipment, storage tanks, and transportation pipelines. Removing these corrosive compounds prevents damage and extends the lifespan of the equipment. Additionally, when LPG containing sulfur compounds (like hydrogen sulfide (H₂S) or mercaptans) is burned, the sulfur is converted into sulfur dioxide (SO₂) and other sulfur oxides (SOx). SO₂ is a major air pollutant that can cause respiratory problems, aggravate conditions like asthma, and contribute to the formation of acid rain and particulate matter (haze), harming ecosystems and human health. Removing sulfur reduces these harmful emissions. Lastly, sulfur compounds, especially mercaptans, have strong and unpleasant odors. While some sulfur is intentionally added as an odorant for safety (to easily detect leaks), excessive amounts can make the fuel objectionable or fail quality standards.

• Amine and Caustic Scrubbing (Extraction) is a wet method primarily used to remove inorganic sulfur compounds, like H₂S, and light organic sulfur compounds, like mercaptans (RSH). In Amine Sweetening for H₂S, LPG is contacted with an aqueous solution of an alkanolamine (like Methyl Diethanolamine, or MDEA). The amine chemically reacts with and adsorbs the acidic H₂S, removing it from the LPG. The rich amine solution is then regenerated by heat to release the H₂S for disposal or further processing (like conversion to elemental sulfur).

Caustic/Alkali Washing for Mercaptans and H₂S involves contacting the LPG with an alkaline solution, typically sodium hydroxide (caustic soda), which reacts with mercaptans to form water-soluble sodium mercaptides. This is a highly effective conventional method for removing lighter mercaptans.

• Mercaptan Oxidation (Sweetening) is often a proprietary method (like Merox) converts the odorous and corrosive mercaptans into less objectionable sulfur compounds called disulfides (RSSR). The LPG stream is washed with a caustic soda (sodium hydroxide, NaOH) solution to extract the mercaptans. A catalyst is then used to oxidize the extracted mercaptans into disulfide oils, which are then separated from the caustic solution, allowing the caustic to be reused. The resulting disulfides are much less corrosive, less odorous, and typically remain dissolved in the LPG product, though they still contribute to the total sulfur content. This method is often sufficient for meeting “copper strip corrosion” specifications.
• Adsorption is a dry method that uses solid materials to physically or chemically trap sulfur compounds. The LPG stream is passed through a fixed bed of solid adsorbent materials and is highly effective for deep desulfurization (achieving a very low parts per million or even parts per billion levels). Adsorption can often remove multiple contaminants simultaneously. The sulfur compounds are trapped on the surface of the sorbent. For example, SulfaTrap^TM-R5P series sorbents specifically remove mercaptans for COS removal. SulfaTrap^TM-R8 series sorbents remove di-sulfides, oxygenates and BTX. The sorbent can be periodically regenerated by heating, which releases the adsorbed sulfur compounds.