by R. F. Wall, Monsanto Chemical Co.
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Instrumentation for Process Development Continuous analytical instruments are useful for process development from laboratory to bench scale to pilot plant. Flexibility is desirable to follow variables during scale-up
PROGESS development in pilot plant and bench unit, where information rather than a product is the major objective, offers on opportunity for application of advanced instrumentation and use of specialized instrumentation techniques, with the possibility of greater returns than appears to have been realized. This work is characterized by a wide range of operating conditions and frequent equipment changes and process revisions. The process is being developed, and relationships between variables are unknown and are being determined. More rather than less control and analyses will be needed as compared to the final production plant. The manpower used in process development is expensive. The initial laboratory project will have at least one technical man and usually more, plus technician assistance, and this phase of the project may last from several months to several years. A small flow controller is better than a needle valve, and a continuous gas chromatograph superior to an occasional laboratory analysis. Very often relatively simple control gadgetry will permit a run to proceed overnight unattended. The technical man can perform technical work rather than constantly adjusting manually controlled equipment. Process development really becomes expensive when the move to the pilot plant takes place. Engineering and supervision add to the
technical personnel requirements. Shift operation requires a staff of operators. Pilot plant operation may require nearly as many personnel as the full scale production plant and many operating costs may not be far different. Raw materials may comprise a considerable expense. Intensive instrumentation of bench and pilot plant units with advanced environmental and analytical controls can provide more accurate and complete information in a minimum experimental time, plus smoother operation of the unit. Project time may be reduced by one third to one half. Direct savings are thus possible, to pay for extensive instrumentation and provide substantial savings in research costs. Reduction of project time may be extremely valuable and justify advanced instrumentation, even though it brings no direct saving in research costs. Several years are usually required to develop a research idea into commercial production. Advanced instrumentation for process development may save time over the entire project, as a result of being on the market months to years earlier, and give a marked competitive advantage, quicker returns from invested capital, and possibly an overall reduction in total project cost. The value in simply reducing the time required to go from idea to marketable product may easily be overlooked. I/EC
Planning Is Key to Effective Use of Instrumentation
The key to effective use of advanced instrumentation for process development is careful planning, with decisive experiments designed to obtain direct information rather than a mass of data to be statistically resolved. Statistics should be a tool, not a substitute for planning. Instrumentation enables more precise control of systems and direct measurement of results. Easier operation is convenient but not very important, unless it also improves the speed, accuracy, and/or completeness of obtaining information. The marked increase in research expense involved in going from laboratory to bench scale to pilot plant indicates that it is very desirable to get as complete information as possible from each step before proceeding to the next scale up, and to instrument as completely as required for this objective. The justification for intensive instrumentation of the bench unit may be in the pilot plant. Production plants are too often operated under exploratory conditions during an extended startup period, to obtain information that could far better have been obtained during the pilot plant phases. It is particularly cosdy to use the production plant to do development work on the process after it has been built. The pilot plant should be fully instrumented to obtain all the informaORKBOOK FEATURES
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tion possible. The pilot plant is an excellent place to work out control problems and process problems, and to develop the best control methods for the final plant. Intensive instrumentation of a process development project is not always indicated, or may not be practical. A study of catalyst life may require a rather definite time, whether or not automatic controls or process analysis instrumentation are used. Unfortunately, control or analysis equipment for some systems may not be available. The objective should be to use all of the available instrumentation that will be of value and no more. Each instrument should save more than it costs, and/or reduce total project time. Control equipment suitable for research and pilot plant operations is becoming much more available, with a better selection of materials and more versatility. Convenient changes of control characteristics are often required in pilot plant operation. These small scale processes have much less material in process and can deviate from control much faster than a larger plant. Precise fast-acting controls are required. Instrumentation can be selected that can go from the bench reactor to the pilot plant, and on into the production plant if desired. An excellent resume of pilot plant instrumentation was presented in three articles in I / E C [45, 1836-52 (1953)], with a review of equipment, application techniques, and preferred practices. New control equipment has become available since then, and a number of manufacturers are specializing in control equipment sized for pilot plant and bench work, with conveniently replaceable trim that provides the necessary versatility. A diversity of materials to meet almost any requirement is available. All this new equipment is helpful to complete and effective instrumentation of bench units and pilot plant, but the techniques of application plus a lot of ingenuity are required in addition. Pilot plant and bench scale units are much more subject to corrosion, erosion, fouling, and plugging, and so forth, than the larger units of a major plant, and instrumentation must be devised with particular attention to these effects.
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Process analysis equipment is being used in process development work to an increasing degree. The high cost of analyzers is a major obstacle to more extensive use, for one or two analyzers could dominate the equipment cost of a small unit. Pilot plant and bench reactor units require flexible analytical equipment. Stream compositions are often changed radically with very brief notice, and interest may shift rapidly between streams and from one component to another. Versatile equipment that can be used on succeeding projects is desirable and much more readily justified. Infrared analyzers have been used for process development projects, with good results. They are not easily changed from one analysis to another and a change of range may present some difficulty, which limits their applicability. The use of infrared has been restricted by the lack of versatility and difficulty of changing either analysis or range. The continuous infrared analysis facilitates automatic control. Mass spectrometry has had appreciable use in pilot plant and bench reactor problems. The mass spectrometer is completely versatile in application; it can handle any sample stream that can be obtained in the vapor state. The problem of mass spectrometry application lies in interpretation of the composite spectra. Calculation of the analysis may be tedious and time-consuming, if the spectra overlap seriously, as with mixed hydrocarbon streams. The most successful pilot plant use of mass spectrometry has been where unique peaks provide satisfactory direct analysis, or at most require only relatively simple computations. In these cases the mass spectrometer is very fast, easily calibrated, and can be very rapidly changed from one stream or one analysis to another. An excellent illustration of the value of stream analysis and mass spectrometry in process development [IND. ENG.
CHEM. 46,
1400
(1954)] de-
scribes the development of the Wulff acetylene process. The mass spectrometer, though versatile, is not yet a fully developed process analyzer, and probably operates best under pilot plant conditions, where adequate attention can be given.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Gas chromatography seems excellently adapted to pilot plant and bench reactor work. The gas chromatograph is versatile and can be relatively easily changed from one analysis problem to another. It is reasonably priced, and therefore much easier to justify. The process chromatograph is a rugged instrument and easily maintained ; a minimum of skill and training is required. A change of analysis may require a change of column, which can easily be made. A little time may be required to develop a column suitable for an application ; however, a background of experience is being developed, so that this is becoming largely a matter of selection. Occasionally a chromatographic analysis may require more time than is desirable without back-flushing or multiple column techniques. These methods add to the versatility of gas chromatography and seem to make almost any analysis practical. T h e chromatograph results can be interpreted directly without calculation, and the multicomponent nature of the analysis is very helpful in exploratory process development work. Full instrumentation of a pilot plant or bench unit can provide smoother operation of that unit, and make available more complete and accurate information, facilitating and accelerating the process development. Complete instrumentation can offer an opportunity of working out control problems and developing operating methods for the production plant, and make the plant startup both easier and quicker. Perhaps the greatest potential of instrumentation throughout process development is in getting the idea into an operating production plant in a minimum time. Effective process development instrumentation is best accomplished through inclusion of instrumentation in information-centered project planning.
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