The output of the downstream detectors during a transient resulting from a step change \\-as not pure sine waves. The outputs cannot be interpreted simply tiuring the transient. Therefore the period of the sine ware generator must be less than the probable frequency of input sample composition changes. The key to reducing the responRe time of the continuous gas chromatograph is to increase the sine wave generator frequency and proportionately reduce the column lengths. Carter (1964) suggests that by using AO-cycle-per-minute frequencies and columns about 0.8 inch long, the transient response could be reduced to about 4 seconds. Reduction to Practice
The present continuous gas chromatograph is an experimental apparatus, designed to test the principle. To use it in monitoring a process stream, it would be necessary to provide a special-purpose computer to detect phase and conipute coniposition automatically. This would replace reading the digital phasenieter visually and transferring the measurements to a general-purpose digital computer to calculate coniposition. Probably the best way to conipute composition automatically will be to make an analog device which automatically amplitude-modulates and then surlis an externally generated electrical set of sine waves corresponding to the pure cornponent’ sine waves to give a set of mixture sine waves that match the output sine waves of the detectors. I t will also probably be desirable to use input frequencies 10 to 20 times the input frequency of the prototype and to decrease colwiin segments to 1/’10 to 1/20 of their present length. This is expected to reduce the transient response to a step change in sample input from the preseiit 30 to 40 seconds to 1.5 to 4 seconds. It would also simplify phase det’ectioii or comparison, because higher frequency electric signals are easier to work with. The continuous gas chromatograph should be applicable to sample systems \vhich have no more than six major coinponeiits and which give measurably different phases with an attenuation factor, (3?~, greater than 0.2 in an isothermal
chromatographic column. I n its present form it is not suitable for assaying trace quantities. -111 coinponents to be measured should be present a t 5% concentration or more. Acknowledgment
The authors express appreciation to J. 0. Hougen for much valuable advice and assistance and to J. S.Staiitoii for designing aiid assembling the digital phaseineter. Nomenclature
Aj
peutlomole fraction of j t h component concentration of n-component sample gay, grani-mole>/cu em c j = pseudomolar concentration of j t h component, grammole./cu cin t = time, sec Zk = distance of kth dot$ ristreani detector from column inlet, it =
c = paeudomolar
GREEKLETTI,: RS a l k = phase of j t h component sine wave a t kth downstream detector relative t o inlet, radians 0 , a = ratio of aniplitutle of j t h component sine wave a t kth donnstreani detector relative to its amplitude a t inlet @k = phase of sum of pure componeiit sine waves a t kth dowistream detector, radians w = angular velocity of piston nioveinent literature Cited
Carter, 1). E. ( t o 3Iolisairto C o . ) , Belg. Patent 616,066 (Oct. 5 , 10821; I-. S.Patent 3,236,092(Feb. 22, 1966). Carter, 1). E., “Cotitiiiuous Gas Chromatography,” U S c . dissertation, \Tashitigtoti 1,-tiiversity, 1964. Fraade, 1).J., PdrolCheni.Eng. 36 ( 1 2 ) ) 54 (1964). Hiratsukn, S., Ichikana, A . , Bu/I. Chon. Sac. Japan 40, 2303 (1967). Perry,, l
