Bits and Pieces, 21 Most authors of Bits and Pieces will make available listings andlor machine-readable versions of their o r o ~ ~ a mPlease s. ~~, read each description carefully t o determine compatibility with your own computing environment before requesting materials from any of the authors. Revised Guidelines for Authors of Bits and Pieces appeared in the December 1982 and December 1983 issues of the JOURNAL. Several programs described in this article and marked as such are available from Project SERAPHIM. If you do not already have a SERAPHIM Catalog, request one from: Dr. John W. Moore, Director, Project SERAPHIM, Department of Chemistry, Eastern Michigan University, Ypsilanti, MI 48197. ~~
Graphical Solution of Equations for Stirred-Tank Reactors in Series Pierre Chaignon, Jean-Pierre Caire, Patrick 0211 ENSEEG BP 75, Domaine Universitaire 38402 Saim Marlin #Heres, France Graphical solution methods are widely used in chemistry, particularly in the field of chemical engineering. These methods are often tedious when performed with arule and a pencil. Nevertheless, students need to handle them to get a good understanding of the problems. So we propose here a program using the graphical possibilities of microcomputers for solving a set of equations related to the study of a series of continuous, stirred-tank reactors. Consider the chemical elimination of a component A in a unit of N reactors in series having the same volume V. This unit is fed by a mixture with a flowrate F and a concentration Co for the species A which must be reduced at the outlet to the value CN.The rate of disappearance -rA of A (which depends only on the concentration CAof A) is known for several values of CA. The problem is to find the volume V of the reactors able to realize the desirrd operation. The material balance of component A for the ith>eactor is in the steady state FCi-I- FCC= V(-rA)i
(1)
Ci-I, C, being the inlet and outlet concentrations of A and ( - r ~ ) ; the reaction rate corresponding t o t h e concentration Ci. Defining the fractional conversion of A in the mixture leaving the i t h reactor hy mi =
[Co - CilICo
(2)
Equation (1)becomes
Figure 1. Plot of reciprocal of rate versus factional converslor latched area represents residence time for me ith reactor. From the kinetic data, (-PA) = F(CA),i t is easy to deduce the graph 1 4 - r ~ )versus A, u~ being the fractional conversion (Co - CA)/CA. In Figure 1, the residence time for the i t h reactor is represented by the hatched area Si. Hence for a series of N reactors, we have to determine the values a l , uz, . ..LYN-1 so that the areas corresponding to the residence times are equal for any reactor. This search is performed by successive tries. A large part of the program is devoted to the interactive dialogue as is usual in computer-assisted education. The student may call the detailed theory and the graphical method of solving. After the facultative introduction of operating and kinetic data, the program fits l / ( - r ~ )versus OlA/(l - a ~as) a polynom with a degree to be chosen by the user. Then the representative curve appears on the screen under a semi-graphical mode for abscissa values between 0 and N. A cross corresponding to a ~ -can I be moved on the right or the left side from the keyboard. After the selection of the s u ~ w s e dvalue of L Y N - 1 . the rectanrmlar area reoresentine the leiidenre time for the Nth reactor k drawnand its value is calculawd. Then two options are possible: 1) CN-I heing fixed, a new crass appears fcr a ~ - z and , the student repeats the previous step (and so on). When all the values of mi
have heen chosen, the equality of areas is checked with a given precision and the results are accepted or not. In case it should fail the graphical determination of the mi hegins at once (Fig. 2).
2) when a w l hm been chosen Is moving the cross, all the values
T being the residence time in any reactor. So the problem is described by the following set of equations
of u,me determined automatically f n m S and ~ if thecriterion on equality of areas is invalid, the student tries anocher u,+, value.
Such an approach seems to be very attractive for the students because i t is very cloqe to video games. The speed of 786
Journal of Chemical Education
Figure 2.TRS-80 screen display of reciprocal rate versus fractional conversion. Students select residence times by moving the cross along the horizontal axis.
comuutation and drawing incite the user to trv m a w solutions witha growing numher ol;reactors in order to improbe his skill. So when "ulavine" with the cornouter, the future enrineer will fmd very easily &at, for a given operation, an optimal solution exists because of the evolution of the volume with the number of reactors. Such an optimization would not be so carefully done by traditional means. This program is written in BASIC for aTRS80 Model I1and needs 9 Khytes of RAM. Documentation including a listing (with sample executions according to the several options) ran he obtained, free of charge, by writing to Ozil.
Employing Data Management Software for the Production and Searchina of Customized Mass Spectral ~ibraries Edward M. Gouge
Presbyterian College Clinton. SC 29325 Although a number of computerized mass spectral data hases are currently available (I),such factors as accessibility, size, specificity, andlor cost of the hases may make them inconvenient for use, particularly in institutions devoted mainly to teaching and less to research. T o overcome this problem a user may choose to create his own machine-based library for use with a microcomputer. This can he accomplished by writing a program that will, besides entering the spectral data, incoroorate a search alsorithm to scan the data for the ourowe of loc'ating a match to ;he spectrum of a n unknown cokp&nd (.2.) .Another uossihle anuroach to the creation of a soectral data hase is to employ commercially available data management (information management or electronic filing) software. A
-
As an aodication of the latter techniaue. we wish to describe .. the construction of a file of mass sl,c!&i4 data and a means of searchinr that file usinr PFS:FILE software. (PFS:FII.E , is a produ>t of software Publishing ~ o r ~ o r & i o n1901 Landings Drive. Mountain View. CA 94043.) This uarticular software, one i f several comm&cially available k~ectronic filing systems, has been developed for use with the Apple, IBM, COMPAQ, and Texas Instruments microcomputers. Data storage is accomplished by first designing a file form in which the data is to he inserted. Figure 3a shows the tailored form for each compound in our lihrarv. Information to the left of a colon in the f h m is designnted ks an item and is simply a descriptor awaiting information that will he inserted to the right ofthe colon. o he information indicated in the first two lines is self-explanatory., the last line is designed for the listing, in descending order, of the compound's five mle values of ereatest relative intensitv. this method of listine . (Althoueh . mass spectral data is particularly popular for small libraries containine comoounds with molecular weiehts less than 200. other teckiques (3) could be used.) A c o m 6 e t d form for one of the cumoounds in the lihrarv is shown in Fieure 3b and represents iata, taken with permission, from ref. (2). Although a t present our library is much smaller, simple calculations suggest that over 500 compounds could be catalogued on a single 5V-in.. single-sided. double-densitv, soft-sectored m i ~ i d i s k ~ m p 1 o the y i ~descrihed filing form. Using simple and easily executed commands, PFS:FILE allows such functions as form design, addition to and deletion from the file, and form redesign without loss of inserted information. The simplicity of spectral file construction and editing is matched by the ease of searching the file. Using information obtained from the mass spectrum of an unknown compound, a blank file form is filled withdata t o whatever extent is possible. These data would most typically be a combination of mle values of several of the more intense peaks and the molecular ion peak (inserted as the MW item), M+, although inserting the symbols, > or
