Hydrogen sulfide-water exchange process

All of the previously mentioned plants except those employing distillation of water were parasitic to a synthetic anunonia plant. Their deuterium-production rate is limited by the amount of deuterium in ammonia synthesis gas. To produce heavy water at a sufficient rate, a growing industry of heavy-water reactors requires a deuterium-containing feed available in even greater quantity than ammonia synthesis gas. Of the possible candidates, water, natural gas, and petroleum hydrocarbons, water is the only one for which an economic process has been devised, and the dual-temperature hydrogen sulfide-water exchange process is the most economic of the processes that have been developed. 

The potential production of sulfide depends on the biofilm thickness. If the flow velocity in a pressure main is over 0.8-1 ms-1, the corresponding biofilm is rather thin, typically 100-300 pm. However, high velocities also reduce the thickness of the diffusional boundary layer and the resistance against transport of substrates and products across the biofilm/water interphase. Totally, a high flow velocity will normally reduce the potential for sulfide formation. Furthermore, the flow conditions affect the air-water exchange processes, e.g., the emission of hydrogen sulfide (cf. Chapter 4). 

ZeoHte-based materials are extremely versatile uses include detergent manufacture, ion-exchange resins (ie, water softeners), catalytic appHcations in the petroleum industry, separation processes (ie, molecular sieves), and as an adsorbent for water, carbon dioxide, mercaptans, and hydrogen sulfide. 

In the dual-temperature H2O/H2S process (61,62), exchange of deuterium between H20(l) and H2S(g) is carried out at pressures of ca 2 MPa (20 atm). At elevated temperatures deuterium tends to displace hydrogen in the hydrogen sulfide and thus concentrates in the gas. At lower temperatures the driving force is reversed and the deuterium concentrates in H2S in contact with water on the tiquid phase. 

The volatile hydrogen sulfide (b.p. —60.7°C) is then separated as an overhead gas stream. The monoethanolamine (b.p. 170°C) and diethylene glycol (b.p. 245°C) emerge as a regenerated solution, hot, from the bottom of the stripping column. To conserve heat, the hot, H2S-lean monoethanolamine stream from the stripper is heat exchanged with the cooler H2S-rich stream from the base of the absorber, sometimes with additional cooling with process water before it enters the absorber. 

This process, invented by Spevack [S7) and developed independently by Geib [C2] in Germany, makes use of the fact that the separation factor a for exchange of deuterium between liquid water and gaseous hydrogen sulfide,... 

Figure 13.24 Example of reflux by chemical conversion for water-hydrogen sulfide exchange process.

Because this reflux ratio is much lower than the reflux ratio in the distillation of water derived in Eq. (13.11), the towers of a hydrogen sulfide exchange plant could be much smaller in diameter than the towers of a water distiliation plant. Because the separation factor for the exchange process (2.32) is much greater than for water distiliation ( 1.05), the towers could contain a much smaller number of plates. 

DUAL-TEMPERATURE WATER-HYDROGEN SULFIDE EXCHANGE PROCESS... 

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