Desulfurization chemistry

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

The desulfurization chemistry appears to depend on the presence of free sulfur in the contacting gas and works in conjunction with organic sulfur pyrolytically released from the coke. Gases that decompose to form free sulfur or react to form free sulfur are suitable desulfurization agents and include, for example, refinery sour gas, pure and dilute S, mercaptans, mixtures of CO and SO2 or COS and H2O. 

Scheme 18 Construction of homogeneous antifreeze glycoproteins (AFGPs) using ligation-desulfurization chemistry...

Scheme 22 Ligation-desulfurization chemistry at p- (n = 0) or y-thiol ( = 1) amino acids...

Scheme 30 One-pot total synthesis of madanin-1123 using kinetically-controlled ligation-desulfurization chemistry with trifluoroethanethiol (TFET) 124...

Using a similar synthetic approach to the one employed for the synthesis of p-thiol Asp building block 97, Cergol et al. reported the preparation of y-thiol Glu derivatives 99 and 100 (Scheme 23) and their application in ligation-desulfurization chemistry [128]. Initial attempts to incorporate building block 99 into model... 

Malins LR, Cergol KM, Payne RJ (2013) Peptide ligation-desulfurization chemistry at arginine. ChemBioChem 14 559-563... 

Thompson RE, Liu X, Alonso-Garcia N, Pereira PJB, Jolliffe KA, Payne RJ (2014) Trilluor-oethanethiol an additive for efficient one-pot peptide ligation — desulfurization chemistry. J Am Chem Soc 136 8161-8164... 

In Figure 15 we compare the empirically observed severity required to achieve 0.05 % S as a function of total sulftir content of feeds for a variety of distillate boiling range materials which contribute to the diesel pool (Shih et al, 1990). Figure 15 clearly shows that reactor temperature required to achieve 0.05 wt% S in product is not correlated with the total sulfur in feed. Additional insight in the desulfurization chemistry is gained by exploring the detailed sulfur distribution in the feed and product. 

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