Sulfur open-cycle

The intervening years to 1981 have seen several world market sulfur demand cycles which have effected the rate of acceptance of these new sulfur sources but slowly the recovered sulfur product has taken its place alongside other world sulfur sources such as Frasch mined and pyrites. In very recent times there have even been moves to re-open very sour gas wells as sulfur wells as world demand for this key commodity has grown and prices have crossed 100/tonne FOB the plant gate. 

Figure 21. Schematic of open- cycle sulfur cycle...

Similar "open-cycle" scoping studies using waste SO2 from combustion flue gases and SO2 produced from sulfur show equivalent economic potential. The latter, of course, would have a higher sulfuric acid production cost because the sulfur feedstock would have an acquisition cost that must be included in the economics. Nevertheless, the cost of sulfuric acid, when tempered by the revenue obtained from the sale of hydrogen, can be extremely attractive. The reverse is also true. 

In Japan, open-cycle scrubbing of waste gases with sodium hydroxide or carbonate solutions has been popular for treating gas streams (including sulfuric acid plant tail gases) that contain relatively small total quantities of sulfur dioxide (27). Absorbent regeneration has been unnecessary because the sodium sulfite or sulfate could be sold to kraft pulp mills. 

Molecular sieves are crystalline metal aluminosilicates (1). Openings in their crystal structure permit passage of many gas constituents while preferentially adsorbing large, polar, or unsaturated compounds. Acid gas compounds may be adsorbed by certain types of molecular sieves. When used for H2S removal, the sieve is regenerated by a thermal swing cycle CL), being heated to release the H2S for downstream sulfur recovery. 

It is also possible that bacterial decomposition of sulfur containing organic compounds may account for some DMS in natural waters (31-36). Conversely, bacteria may also utilize DMS and therefore act as a sink (37-39). The contribution of bacterial processes to the DMS/DMSP cycle in open ocean environments has not been addressed and is as yet not understood. However, studies to better understand the biogeochemistry of DMS can not exclude bacterial processes (e.g. 4041). 

During the cationic polymerisation, e.g. with sulfuric acid, the process is the following at the initial stage of initiation, when organocyclosiloxanes interact with sulfuric acid, the acid proton attacks the oxygen atom of the siloxane cycle. As a result of the redistribution of the electron density, the =Si-0 bond breaks, opening the cycle and forming an active centre at the end of the chain ... 

Because of its ability for catenation, sulfur forms open and cyclic S species from n = 2 to n = 20 for cycles and higher for chains. This leads to enormous complexity in the physical and chemical behavior of the element. 

FIGURE 12.4 Open circuit potential transients for smooth polycrystalline platinum in 0.5 M sulfuric acid solution after applying 100 triangular cycles between 1.50 and 1.90 V at 0.2 V s-1. 

Kubas discovered reactions of the Cp dimers, which are part of a catalytic cycle for the hydrogenation of SO2 (equation 26). The net reactions involve the coordinated sulfur and may or may not involve the metal atoms, which may be the true spectators in this chemistry. This opens the possibility that the metal-metal bond serves to stabilize the reacting fragment without direct involvement in the chemistry. However, reaction could also occur at the metal-metal bond followed by transfer to the sulfide ligands. These types of multiple interactions give an added dimension, but also an added complexity, to metal-metal bonded chemistry with bridging functional ligands. 

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