PRODUCTION Mass vs. Vapor Mass spectrometry and vapor phase chromatography grow more competitive in process applications MASS
SPECTROMETERS have come a
long way in 10 short years. From large, expensive, and complicated laboratory apparatus they have been developed to widely useful process monitoring instruments. But the promise of vapor phase chromatography for process control has undoubtedly slowed progress in mass spectrometers, says F. W. Karasek of Phillips Petroleum. Speaking at the 12th Annual Symposium on Instrumentation for Process Industries held at Texas A & M, Karasek points out that adapting an instrument as complex as a mass spectrometer from the laboratory to the plant is necessarily a slow and difficult process. But today, process mass spectrometers are overcoming the last major obstacle to more extensive plant use—explosionproofing. • Applications. The strongest recommendation for a process mass spectrometer is its great versatility coupled with its rapid analytical action. Major uses of process mass spectrometers fall into three categories: • Multicomponent monitoring. • Single component monitoring where a unique ion peak is available. • Group component monitoring where the^group contributes equally to an ion peak. A good example of an application combining all three categories is control of a plant recovering sulfur from sour gases. Usingothe mass spectrometer to obtain a sulfur material balance, losses of this material can ° be reduced. By monitoring sulfur in stack gases as hydrogen sulfide and sulfur dioxide, the amount of air used to convert hydrogen sulfide to sulfur dioxide may be controlled in the first step of the recovery process. (Formerly this airhydrogen sulfide ratio was found from chemical analysis of gases in the catalytic converter producing sulfur—a time consuming process.) Two unique ion peaks exist; mass 34 ion for hydrogen sulfide and mass 64 ion for sulfur dioxide. Sampling the stack gases gives complete analysis, or individual amounts of one component, i.e., sulfur dioxide, or total sulfur loss. Use on both feed gas and stack gas 70
C&EN
MAY
6,
1957
gives the material balance. In one test, for example, mass spectrometers o n a sulfur recovery plant led to a Tfo increase in efficiency, saving roughly five long tons of sulfur per day. • Vapor Chromatography. Much newer in process applications, vapor phase chromatography has been used for some continuous analyses. Its promise carries over from laboratory apparatus—generally simpler than laboratory mass spectrometers. This causes people to believe a vapor phase chromatographic process instrument
will be inexpensive, reliable, and have wide applicability, in addition to being simple. But, such may not b e the case, Karasek emphasizes. Mass spectrometry's problems have been explored much more, and difficulties are more obvious. However, even some phases of mass spectrometer operation and use still need development. One of these is data presentation. In its present form, information from the mass spectrometer is confusing to the operator and is unsuited for direct use in a control loop. Data presentation needs development s o that information is suitable for direct process control or use by plant operators. In its present state of development, vapor phase chromatography's major drawback for process use is probably its slow speed of response. Because of various process time lags, adequate control of many processes cannot be achieved unless an instrument possesses rapid response. Thus, in some cases, only the mass spectrometer is fast enough, says Karasek. •
Moss Spectrometry vs. Yopor Phase Chromatography for Process Instrumentation 1 Factor 1 Speed of Re1 sponse Data Pres1 entation
requires computation in certain cases
1
$10,000-$15,000
1
Instrument Cost Versatility
1
Calibration
1
Applicability
1
Complexity
1 Process Control 1
Mass Spectrometer 1 second or less
any component i n molecular weight range (to approx. 150) requires calibration for each component because of different sensitivities and spectra] patterns readily determined b y computation from known data mass selector tube, vacuum system, and data presentation are t h e complex components continuous monitoring, better suited for process control applications
Sensitivity
about 0 . 1 % . A. function of molecular structure
Stability
long term stability of approximately =t2%. May improve by automatic standardization
|
Vapor Phase Chromatograph 5 - 4 0 minutes; dependent on problem data usually can b e presented with little or n o calculation $3,000-$10,000
1 1 1 1 1 1 1
detectable components limited b y specific column; some components not detectable calibration simplified b y unique data provided
1 1 1 1 1 1
may require investigation of column materials and experimental parameters t o solve" specific problems programming and sampling are t h e complex components. Auxiliary gas supply necessary results less suitable for control applications, due t o time lag and iterative nature about 0.1% for low column retention time; less sensitive with increasing time appears to b e about ± 2 %
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Mathieson
SODA ASH is there YQU can't fool a dirty wall or a load of laundry if your chemical suppliers have fallen down in quality, it'll "all come out in the wash." That's why it pays to order your soda ash from Olin Mathieson. Mathieson Soda Ash comes from a maker with 60 years of success in maintaining the highest standards of consistency and purity. Mathieson has a soda ash grade to meet your specifications... and shipments from Wyandotte, Mich., Saltville, Va., and Lake Charles, La., assure you that your stocks will always be at the most efficient levels. Ask your Olin Mathieson representative to drop in soon. Get the interesting facts on a service that sells itself.
MATHIESON
when better cleansers are made
CHEMICALS
OLIN M A T H I E S O N CHEMICAL. CORPORATION I N D U S T R I A L . C H E M I C A L S D I V I S I O N . B A L T I M O R E 3. M D .
4722
INORGANICS: Ammonia Products · Muriatic Add
MATHIESON
Bicarbonate of Soda · Carbon Dioxide · Caustic Potash · Caustic Soda · Chlorine · Hydrazine and Derivatives · Hypochlorite Nitrate of Soda · Nitric Acid · Soda Ash · Sodium Chlorite Products · Sulphate of Alumina · Sulphur (Processed) · Sulphuric Add ORGANIC*: Ethylene Oxide · Ethylene Glycols · Polyethylene Glycols · Glycol Ether Solvents · Ethylene Dichloride · Dichloroethylether · Formaldehyde · Methanol Sodium Methylate · Hexamine · Ethylene Diamine · Polyamines · Ethanolamines · Trichlorophenol · Surfactants
MAY
6, 1957 C & E N
71
PRODUCTION
NEW HEAVY DUTY SOLUTION BALANCE with HANDWEIGHTRACK Another improvement on α fine balance! This handy weight carrier rack puts the attachment weights within easy reach of the operator. Bal ance is equipped with stainless steel platform and beams. Has self-aligning bearings.
TVA Demonstration Tennessee Valley Authority's Office of Chemical Engineering will hold pilot plant demonstrations of some of its latest developments in fertilizer tech nology June 18, 19, and 20, 1957. The demonstrations, to b e held at TVA's Wilson Dam Laboratories near Shef field, Ala., are aimed at showing how TVA's continuous ammoniator can be used to produce cheaper, better, or higher analysis fertilizers. TVA invites members of the fertilizer industry and other interested persons to attend. In charge of arrangements is J. H. Walthall, Director of Chemical Development, TVA, Wilson Dam, Ala.
• Cyanoethylated cotton fabric is now being produced by Tee-Pak, Inc., for use as shade covering for tobacco plants. Shade cloth can b e treated for a few cents per square yard, the com pany says, and is resistant to mold and rot. ' for complete information write for FREE bulletin •
SCMm&QR£ORjmiOW •;;.V.-·::·/·.: JOSO COMMERCE: AVE, UNION; NEW^JERSEY *•';>
plasticizer
MDMO for wire coating applications !
TYPICAL ELECTRICAL CHARACTERISTICS Dielect ic constant (ASTW, DI50-47T)
@ 60 cycles @ 1000 cycles
Power factor
