LPG desulfurization alcohol issue

It is a disulfide that often clogs pipelines; it is formed after the regeneration of alkali-based desulfurization products: RSH + NaOH → RSNa + H2O; RSNa + O2 + H2O → RSSR + NaOH. This substance affects the efficiency of regeneration and reduces the effectiveness of the alkali solution in dealing with thiols. It finds itself in the layer between liquefied gas and the alkali solution in the regeneration tank, where it emulsifies with the alkali solution. Sometimes it’s hard to distinguish the interfaces. The challenge is how to effectively separate it from the alkaline solution after regeneration, and currently, no better methods exist in various factories.

The content of thiol in liquid hydrocarbons is very low; currently, there are no facilities in China designed specifically for removing thiol from liquid hydrocarbons. The main purpose is still to remove sulfur so as to ensure that corrosion is within acceptable levels. There is no need to pay excessive attention to this issue; it can be easily resolved from an engineering perspective.

It is estimated that the solvent extraction effect is poor; the regenerated alkali solution contains disulfides, and continuous recycling leads to an increasing concentration of these disulfides, thereby causing blockages in the pipelines. Consider extending the residence time of the regenerated alkali solution in the extraction tank.

On the third floor, the level of thiol sulfur in liquefied gas is also around 100–200 ppm, I guess. I’m not sure what kind of oil you process; when we receive gas condensate oil, after MDEA is used to remove hydrogen sulfide, the thiol sulfur level still remains above 500 ppm.

Hehe, after removing hydrogen sulfide from the liquefied gas produced in coking, the total sulfur content is still above 2000 PPm. There is only about 200 units of distilled liquefied gas.

Refinery liquefied gas mainly comes from catalytic cracking units and serves as a key raw material for the production of propylene and MTBE. Polymer-grade propylene requires a sulfur content of no more than 0.5 ppm. As the requirements for sulfur content in gasoline decrease (in major cities such as Beijing and Shanghai, it should be below 50 ppm by 2008, and across the country it should be below 150 ppm by the end of 2009), the sulfur content in MTBE has also become a matter of great concern. At present, the vast majority of refineries have propylene and MTBE units. Since liquefied gas was primarily used as a domestic fuel in earlier years, it is still controlled according to the old quality standards to this day; that is, the sulfur content must be ≤343 mg/Nm3, and copper sheet corrosion testing must yield satisfactory results. Regarding refinery liquefied gas alone, over 90% of it consists of thiolic sulfur that is easy to remove; overly lenient refining specifications result in high total sulfur levels in MTBE, and subsequent propylene feedstock requires complex and costly purification measures. After amine treatment and alkaline washing, the levels of H2S and COS in liquefied gas are very low. The boiling points of all other sulfides are equal to or greater than that of butane; as a result, most of them remain in the heavy fractions after gas separation, causing the sulfur content in butane to increase by 1.5 times compared to that in the feed before gas separation. Furthermore, under MTBE production conditions, thiol can also undergo etherification reactions with isobutylene; self-etherification reactions may occur as well. Coupled with the higher solubility of the product in sulfides, the sulfur content in MTBE is certainly higher than that in C4 hydrocarbons. For example: A certain factory controls the total sulfur content in liquefied gas after purification to be no more than 343 mg/Nm3; the total sulfur content in MTBE products ranges from 100 to 200 ppm, with values reaching up to 600 ppm at times. Due to MTBE’s solubility characteristics for sulfides, as well as the transformation of sulfur forms that occurs during the production process, it is quite difficult to desulfurize MTBE products again. Therefore, deep desulfurization at the source of liquefied gas is highly necessary. For details on advanced desulfurization technologies: Let’s resolve the issue through a phone call; our company possesses mature processes as well as proven track records of successful implementation. 15031768711 This post was last edited by chengkang on 2009-4-15 13:49 ]

Desulfurization of liquefied gas catalysts using alcohol is the most basic method, but even the most advanced approaches cannot eliminate lower hydrothiols; the cobalt phthalocyanine sulfonation method is probably the best option available. Theoretically, it is impossible to completely remove hydrothiols – they merely transform into another form

The thiol content in liquefied gas is related to its source. The mercaptan level in coker liquefied gas is very high, generally around 900 ppm, with levels as high as 3000 ppm in some cases ； The catalytic liquefied gas typically contains 100–300 ppm of such compounds. The alkali washing process can remove the majority of thiol compounds, but it is essentially ineffective against neutral sulfur compounds such as sulfides, carbonyl sulfides, and disulfides. Through alkaline oxidation regeneration, the thiolols removed by alkali washing can be converted into disulfides. A portion can be removed through the exhaust gas from the oxidation tower or by reverse extraction of gasoline, but much of it still has to be discharged along with the alkaline sludge.

Reply to Floor 1: As far as I know, in the MERICHEM technology used in the United States, bituminous coal layers are employed for the adsorption and separation of disulfides from alkaline solutions, but the effectiveness of this method is not clear. Could it be that disulfides have aggregated on the anthracite, and the pulverization of some of the anthracite has produced a black tar-like substance?

LPG desulfurization is a highly mature technology; why seek solutions from abroad when we can use domestic ones that also deliver excellent results?