I/EC A by B. F. Dudenbostel,
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INSTRUMENTATION K
B
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Jr., and Wm. Priestley,
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K
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Jr., Esso Research & Engineering
E Co.
Uniform, High Quality Production Exact measurements, replacing empirical tests in process control, promise marked savings in manufacturing cost
F R O M the farm to the chemical control laboratory, from whiskey manufacture to steel production, old time empirical tests employing the senses of feel, taste, sight, and smell are being replaced by exact physical and chemical composition data. To every manufacturer, the quality of his finished product is of utmost importance. In today's highly competitive market the product which has the highest and most consistent purity dominates the market. It has only been a few years since it was common practice in the dye industry to rely upon a person of exceptionally good color sense. In arriving at the exact shade desired, he would throw in a bucket of this and a bucket of that and if the shade were too light, a wad of chewing tobacco might be added. Today, an exact blending is carried out by mathematically adding the absorption spectra of the various dye components to produce a product with a specified spectrum. This replacement of the human senses has gone beyond laboratory testing and is finding its way into processing through the use of continuous analysis. These- analyses are in addition to those required for some of the newer chemical processes. In butadiene manufacture, for example, obviously the only quality control criterion can be an exact physical or chemical measurement of the butadiene purity. The "octane race" has resulted in development of several new processes for upgrading gasoline quality. One of the most important is the conversion of naphthenes and paraffins to aromatics. There are as many
names for this process as there are oil companies. The normal procedure for following this process would be by laboratory knock engine testing. Since aromatics are vastly different in many physical properties than the naphthenes and paraffins, such physical measurements as refractive index, gravity, ultraviolet and infrared absorption, and possibly mass spectrometric observations could be used to monitor the product on a continuous basis. In the fields of solvent manufacture and safety fuel production, the flash point is often critical. Exact and continuous determination of this property can be accomplished by use of continuous analyzers which
determine the critical low boiling constituents responsible for low flash points. This is exemplified by the lowering of the flash point of a relatively high boiling aromatic solvent through the inclusion of a lower boiling aromatic. A rapid continuous method could be the use of an ultraviolet or mass spectrometric continuous analyzer for the determination of the low boiling aromatic. In contrast to the determination of low boiling constituents, the opposite approach can be employed. For example, many of the motor gasolines marketed have a final boiling point specification of around 400° F. Naphthalene, which boils at 424° F., could be monitored by a continuous ultraviolet instrument to prevent
Figure 1. Percentage of readily available water in soils (measured by the soil moisture meter) and recommendations for irrigating VOL. 48, NO. 8
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the inclusion of high end point material in the product. This is possible since small amounts of naphthalene, easily detectable, distill overhead at temperatures considerably below its boiling point. On the farm, the farmer's "green thumb" has been replaced by a conductivity measurement of soil water content. It is well known that the quality and quantity of the crop can be materially raised by providing an adequate and constant supply of moisture. Today, thermal conductivity measurements of gypsum blocks buried a few inches below the ground surface are controlling sprinkling systems used for irrigation. Figure 1 shows the change in resistivity with per cent of readily available water. This not only ensures sufficient water for proper growth but also gives additional savings by elimination of excessive irrigations. The use of paraffin wax (wrapping paper, candles, milk cartons) requires that its oil content be at a specified level. In a wax from a given crude source, the oil which is removed has the same composition as the retained oil. As contrasted to the wax, this oil contains a high percentage of aromatic hydrocarbon s. Thus it is possible to monitor the oil content through the continuous measurement of a single wave length measurement at 230 millimicrons.
Feature
The relationship between this new measurement and the long elapsedtime oil content method is shown in Figure 2. The sight of dense white or yellow fumes issuing from many commercial operations has been a common sight in bygone years. A control of such operations depended largely on the rather insensitive nose of the plant operator. Today, air pollution is being controlled by exact determination of hydrogen sulfide, sulfur dioxide, and other contaminants through the use of continuous analyzers, such as the Titrilog. In the early years of the steel industry the temperature of the furnace melt was visually "guesstimated" by an operator. He relied on past experience in gaging temperature by the color of the melt. The advent of optical pyrometry replaced this approximation method with a much more accurate and reproducible one. In the medical field, administration of oxygen to a patient during an operation has been controlled by the complexion of the patient and other similar sensual observations. As stated in a previous Instrumentation article, a closed loop is now being employed with the sensing element being a carbon monoxide-carbon dioxide infrared analyzer. Many of the catalysts being used
Figure 2 . Continuous measurement of a single w a v e length monitors the oil content of paraffin waxes 52 A
INDUSTRIAL AND ENGINEERING CHEMISTRY
today must be regenerated. This is usually accomplished by burning off the carbon with air. If the admission of air is not carefully controlled, excessive temperatures are generated which can destroy the catalyst activity. Since this is a rapidly occurring phenomenon, the use of standard temperature measuring devices does hot give fast enough response. However, the presence of carbon monoxide in the regenerator exit gas in trace amounts is an excellent indication that excessive temperatures are being reached. Thus, through the use of infrared analyzers, it is possible to spot the temperature rise long before conventional thermocouple measurements are sensitive to that rise. A product which still relies on the senses for evaluation, for the first fewdrinks at least, is fermented spirits. Many of the products in this field depend on the exact reproduction of manufacturing steps and aging processes supplemented by taste evaluation by experts which have many years of training in the field. With the advent of vapor phase chromatography, it should be possible to analyze for these trace components which not only add to the bouquet and flavor but also those reaponsible for the "morning after" effect. This technique of vapor phase chromatography has been widely publicized in the literature and in scientific meetings. At the recent Dallas ACS meeting many papers were presented illustrating methods for determining trace quantities of components below 0.001%. While this philosophy may, in some cases, eliminate that rare and highly prized single bottle of wine, it has very definite advantages. In the years to come, the materials produced, both as intermediates and final products, will be of constant high purity. This should result in marked savings in manufacturing costs, since off-specification products will not have to be discarded, nor will exceedingly high grade materials need to be blended back to yield an average grade product. Correspondence concerning this column will be forwarded if addressed to the author,
% Editor, INDUSTRIAL AND ENGINEERING CHEMISTRY, 1155—16th St., N.W.,
Washington 6, D. C.
