Ultimate Yield of Solvent Extraction of Coal Calculation from Rate of Extraction H.G. LANDAU AND R. S. ASBURY Coal Research Laboratory, Cernegie Institute of Technology, Pittsburgh, Pa.
This method is purely empirical; its justification is that experimental values plotted in this way do fall on a straight line with the exception of small values of t as noted. This has been verified on runs with aniline and tetrahydronapthalene made in this laboratory, in addition to the benzene runs shown in Figure 1; on the data of Peters and Cremer (S), using benzene; and on the data of Gryaznov (d), using an alcoholbenzene mixture. Any statement as to whether or not there exists an ultimate maximum yield, calculable in this way, for any and all solvents must depend on the accumulation and examination of additional experimental evidence.
I
N THE course of an investigation of the extraction of a Pittsburgh seam coal with various organic solvents under pressure, it became necessary to find a method for comparing the yield of extract with any solvent or any coal. From results obtained in long runs i t appeared that there was a limiting value for yield of extract which would not be exceeded, no matter how long the extraction was continued. On this basis a simple method was chosen. Yield of extract, y, was plotted against the reciprocal of time, l/t, and the curves were extrapolated to infinite time; that is, l / t = 0. Values for yield at infinite time were then used for comparison with similar values from other solvents (1). Recently it has been found possible to improve this method for estimating the ultimate yield. The new method consists of plotting values of time, t, against time divided by yield, t/y. When the values were plotted in this way, they lay on a straight line, except those for small values of t. If the equation of this line is written as t =
b(t/y)
450
400 350 v)
300
a
-u
3 250
0 I
where a and b are constants to be determined from the data, then dividing by t,
- 200 2 I50 I-
and for t =
, 1 = b/y;
that is,
100 50
y = b 2
For p-coal:
t = -46.2 For 16-20 mesh coal: t = -26.0
4
6
8
1
0
1
TIME DIVIDED BY YIELD
This means that the slope of the line gives the ultimate yield of extract. Figure 1 shows how closely the experimental values for two long runs a t 260' C. may be fitted by such a line; these runs are extractions of p-coal for 302 hours and of 16-20 mesh coal for 446 hours using benzene; only the values of time greater than 32 hours are plotted. The lines on the plot have the following equations:
FIGURE1
I n fitting a straight line to results plotted in this way, we are expressing the relation between yield and time by the equation Y = bt/(t
+ 30.1 t / g + 20.6 t / Y
+ a)
This relation seems to fit very well for the later portions of the run, after the very rapid initial extraction. However, a single equation of this form does not hold for the entire run, and this form of relation is not proposed as expressing the time dependence of yield of extract, except during the later stages of the extraction.
The values for ultimate yield obtained from the slope of the lines in this way are 30.1 per cent for p-coal and 20.6 per cent for 16-20 mesh coal, compared with values of 29.0 and 21.5 per cent obtained by the previous method. Although these values are not significantly different, the present method has the advantage of requiring no extrapolation beyond the experimental data. It can be used on much shorter runs where extrapolation would not be justifiable.
Literature Cited (1) Asbury, R. S., IND. ENG.CHEM.,26, 1301 (1934); 28, 687 (1936). (2) Gryaznov, N. S.,Khim. T ~ e r d o g oTopliva, 7, 225 (1938). (3) Peters and Cremer, Angew. Chem., 47, 576 (1934). RECEIVED November 9, 1937.
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