TECHNOLOGY
Sulfur recovery process sweetens sour gas Hydrogen sulfide, sulfur dioxide react completely, rapidly in molten sulfur; high-volume technique may aid pollution control
A new sulfur recovery process may be the closest thing yet to an antipollutionist's dream. The inventor, Dr. Tadeusz K. Wiewiorowski of Freeport Sulphur Co., Belle Chasse, La., says that his process is inexpensive, simple, and efficient. It will even produce income, he adds, if the sulfur can be sold. Whether the process is ever actually used in antipollution control remains to be seen. While investigating liquid sulfur as a reaction medium, Dr. Wiewiorowski determined that the reaction between hydrogen sulfide and sulfur dioxide (2H._,S + SO. -> 3S + 2HL>0) goes nearly to completion very rapidly in molten sulfur and in the presence of a
Sulfur recovery process adapts to different feeds Desulfurized gas -f steam
Recovered sulfur
Turboreactor
Molten sulfur reaction medium
Amine catalyst Adjusted sour gas (H 2 S/S0 2 z2) H 2 S a orS0 2 a Sour feed gas containing H2S and/or S0 2 68 C&EN APRIL 27, 1970
a
Added if and as needed to obtain stoichiometric H2S/SO2 ratio in feed gas
catalyst. Any of a long list of nitrogen compounds can catalyze the reaction. Dr. Wiewiorowski says, but he has found ethylenediamine to be the most suitable catalyst for his process. The mechanism for the reaction of hydrogen sulfide and sulfur dioxide is not definitely known, Dr. Wiewiorowski says, but he believes that it probably involves nucleophilic scission of the S-S bond by the amine catalyst. Turboreactor. The reaction is preferably run in a turboreactor but may also be carried out in other contacting devices such as packed columns or bubble-cap columns. The patent spécifies that the feed may contain r 1 to 67 /i hydrogen sulfide by volume, and 0.5 to 34r/r sulfur dioxide. Process temperatures must be kept between 120° and 160 e C. At lower temperatures the molten sulfur solidifies and at higher temperatures quickly increases in viscosity. The catalyst may be present in concentrations of 1 to 5000 p.p.m., but the preferred concentration is about 50 p.p.m. A major advantage of the process is that the reaction medium is identical with one of the reaction products, thereby eliminating the need for the expensive separate reaction medium required in many other processes. Probably the most common sulfur recovery processes are the Clans and Townsend processes. The inventor, while recognizing certain reaction similarities to those processes, maintains that his new process is substantially different. Slurry. In the Townsend process the catalytic reaction is carried out at low temperature in a hygroscopic organic liquid, such as diethylene glycol. All of the sulfur produced by the Townsend process is obtained as a slurry of sulfur in the reaction medium; additional processing is necessary to recover the sulfur from the medium. In the Claus process the feed gas is passed over a solid catalyst at temperatures higher than the dew point of the sulfur. All sulfur produced must, therefore, be condensed from the vapor. Further, the susceptibility of the catalysts to poisoning usually requires pretreatment of the feed to remove hydrocarbons and concentrate
GC/MS system operates without splitter; chemical ionization allows direct link
Inventor Wiewiorowski An adaptable reaction medium the sulfur gases. Even so, the cat alysts are said to have limited life. Though the Wiewiorowski proc ess was developed primarily for sul fur recovery from sour gases, it ap pears to offer promise in a number of areas of pollution control, principally as a high-volume gas treatment. Be cause there is no solid catalyst, there is no need for huge reactor volumes. With ethylenediamine as catalyst, the reaction is very specific; in most cases where the process has been used on a pilot basis, side reactions have been virtually nonexistent. Consequently, there appears to be no need for any significant pretreatment for feed gases, nor for postreaction purification of the product sulfur. Connections. By judicious arrange ment of the processing connections, it is possible to remove hydrogen sulfide alone, sulfur dioxide alone, or both together. However, the gas stream fed to the reactor must contain hydro gen sulfide and sulfur dioxide in ap proximately stoichiometric ratio ( 2 : 1 ) . If the feed gas lacks sulfur dioxide, part of the stream is diverted to a burner, where hydrogen sulfide is ox idized to sulfur dioxide and water, then returned to the main stream. Alter natively, the burner can be fueled with molten sulfur from the reactor. If, instead, hydrogen sulfide must be added to achieve the 2:1 ratio, it can be generated by heating natural gas with molten sulfur from the reactor. As a proponent of liquid sulfur as a reaction medium, Dr. Wiewiorow ski notes that the medium is particularly adaptable to study by in frared measurements. Sulfur has no absorption bands over the range 1400 to 4000 c m 1 . The medium is also inert with respect to sodium chloride windows and is obviously suitable for moderate to high temperatures.
A chemical ionization quadrupole mass spectrometer has successfully operated as a monitor for gas chromatograph effluents through a direct link, without the usual splitter or helium separator. Using methane—subse quently needed in the chemical ioniza tion system—as a carrier gas, Finnigan Corp. operated the setup in its booth at the annual meeting of the Federa tion of American Societies for Experi mental Biology in Atlantic City, N.J. A key feature of the GC-MS setup is the mass spectrometer's chemical ionization source, designed and built by Scientific Research Instruments Corp., Baltimore, Md. Another im portant part of the GC-MS system is the quadrupole mass filter used in the mass spectrometer instead of electro magnetic ion separation. Finnigan introduced Scientific Re search Instruments' chemical ioniza tion system for use with its Model 1015 quadrupole mass spectrometer at the Pittsburgh Conference in Cleve land last month (C&EN, March 16, page 4 4 ) . In the chemical ionization technique, methane carrier gas is ion ized by electron impact to form posi tively charged particles such as CH 4 + , CH 8 + , and CH.> + . These ions react with methane to produce a set of stable particles, chiefly CH 5 + and C 2 H 5 + . However, these ions don't react further with methane but do re act on virtually every collision with other molecules present. These ionmolecule reactions generally result in a proton transfer to the compound of interest. Comparison. Compared to electron impact ionization spectra, chemical ionization spectra are quite simple; they contain relatively small numbers of ion types. There is much less breakdown of compound, so mass spectra are easier to interpret; they have 100 to 1000 times greater inten sity at the peak of the molecular ion. Much pioneering work on chemical ionization mass spectrometry has been done by Dr. F. H. Field, Dr. M. S. B. Munson, and their coworkers at Esso Research and Engineering Co. Recently, Dr. H. M. Fales, Dr. G. W. A. Milne, and their associates at the National Institutes of Health, using a Scientific Research Instruments chem ical ionization source, have shown that the technique is useful for determining the structure of complex molecules such as alkaloids and photodimers of cyclic α,β-unsaturated ketones. In February 1968, Esso granted ex clusive rights for its chemical ioniza
tion patents to Scientific Research In struments. Scientific Research Instru ments and Finnigan Corp. have teamed up to make and market the chemical ionization quadrupole mass spectrometers. Chemical ionization can simplify process control, Marvin L. Vestal of Scientific Research Instruments be lieves. "You get less fragmentation and more sensitivity with chemical ion ization than with electron impact," he stresses. "The technique could pro vide a way of screening urine speci mens for drugs quickly enough to save people's lives." Because of the absence of a separa tor in the chemical ionization quad rupole MS-GC system, it's possible to detect as little as 1 0 _ 1 - gram of com ponent. The system could thus find use in pollution studies. For example, it's sensitive to a few parts per billion benzaldehyde. It could also be used in trace analysis for biochemical stud ies. Using the GC-MS system in its FASEB meeting booth, Finnigan sep arated and obtained mass spectra for methyl decanoate and methyl laurate. Pressure. In a mass spectrometer with an electromagnetic ion separator, very low gas pressures are used— about 10~ :> torr. Therefore, when this type of spectrometer is linked to a gas chromatograph, a splitter or sep arator is needed to reduce the amount of carrier gas entering the ion source. As a result the sample size is also re duced by a large amount. Chemical ionization and quadrupole ion separation, however, permit much higher gas pressures in the instru ment's ion source. Typical pressures in the ion source during a run are about 1 torr. This means that the gas leaving the chromatograph has to flow only through a constriction in the out let to get the proper pressure in the spectrometer's ion source. Because of the low voltage (5 volts) required in the quadrupole spectrometer, there is no voltage problem in the system, and no glow discharge back into the chro matograph. Total cost of the GC-MS setup is about $45,000. This doesn't include the Digital Equipment Corp. PDP8-L computer control system that Finnigan is using to operate the GC-MS com bination. Finnigan has used a Yarian-Aerograph Series 1700 gas chromatograph in the system. But Tom Conklin, Finnigan's marketing manager, points out that almost any gas chromatograph can be used in the system. APRIL 27, 1970 C&EN 69
