Helium and Natural-Gas Systems Separation

Helium and Natural-Gas Systems Separation Helium is produced primarily by separation of hehum-rich natural gas. The hemim content of the natural gas from plants operated by the U.S. Bureau of Mines normally has varied from 1 to 2 percent while the nitrogen content of the natural gas has varied from 12 to 80 percent. The remainder of the natural gas is methane, ethane, and heavier hydrocarbons. 

A Bureau of Mines system for the separation of helium from natural gas is shown in Fig. 11-119. Since the major constituents of natural gas have boiling points very much different from that of helium, a distillation column is not necessary and the separation can be accomplished with condenser-evaporators. 

The first procedure for the separation of As(lll), As (V). MMA and DMA in naturai waters and urine depended on pH-selective reduction reactions with sodium borohydride and separation of the voiatiie arsines produced by selective voiatilization from a cold trap. Quantification was performed by atomic emission spectrometry (Braman and Foreback, 1973). This method was iater modified on the basis of another approach for arsenic speciation in natural waters (Andreae, 1977) 0.5 to 5 mL of unpretreated urine is diluted with 50 mL of deionized water in the reaction chamber of a mercury-hydride system. The pH is then adjusted to 1-1.5 by addition of 5 mL of oxalic acid (10% w/v). Helium is subsequently passed through the system for about 1 min to remove the oxygen. After this 6mL of sodium borohydride (4% in 0.05 M NaOH) is added. The generated arsines are trapped in a U-tube immersed in liquid nitrogen. When the U-tube is removed from the liquid nitrogen, arsines of inorganic arsenic, MMA and DMA are volatilized successively due to their different boiling points and travel via the carrier gas into the AAS detector (Norin and Vahter, 1981). 

---