The Compressibility Chart and the Ideal Reduced Volume EDWARD F. OBERT Northwestern Techrzological Institute, Evanston, 111.
T
H E generalized compressibility chart is a useful tool for predicting the properties of gases or gas mixtures with acceptable accuracy for most engineering purposes. However, the chart is awkward to use when volume is one of the known properties and either pressure or temperature is unknown, because the answer must be found by trial and error. T o remedy this condition, the ideal critical volume proposed by Su ( d ) allows ideal reduced volume lines t o be incorporated as a part of the compressibility chart. The ideal critical volume is defined: VEi
=
R Tc -
=
Ur’
-
Vaatual
(2)
Uci
ZRT __ =
2-= x-T. R T, -
(3)
PT
P4
where T , and p , are defined in the usual manner:
T Tr = jjio
pr =
-PPc
(4)
Equation 3 shows that the ideal reduced volume, vr’, is a function of Tp and p r . This is the relationship implied by Su (8) as a modified law of corresponding states.
PO
Then the ideal reduced volume is as shown in Equation 2.
1.20
1.10
1.00
0.90
+ae0
N a
0 I- 0.70 0
Lf
>-
!=
2
0.60
m
v) v)
w
a n
030
5 0
0 0.40
0.30
020
OJO
05
1.0
IS
Z.0
Z.5
3 .O
3.5
4.0
4.5
s.0
5.6
REDUCED PRESSURE, p, Figure 1.
Compressibility Chart
2185
6.0
6.6
7.0
2186
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 1 has been constructed from the charts of Su ( 2 ) and Dodge (1) and the ideal reduced volume defined by Equation 3; t,he compressibility factor from the chart will correlate experimental values for most gases within a n average deviation of 2%. This chart is useful because trial and error solutions can be eliminated and, also, interpolation of the chart is improved. For example, an intermediate T’, line can be added to the chart by finding tho intersections Of this line with the 2.r‘ and Pr lines* The accuracy of t.he construction is adequate for most purposes.
urfural
Vol. 40, No. 11.
Interpolation between w lines is made by select,ing various points along the T , line until Equation 3 is satisfied. LITERATURE ClTED
(1) Dodge, B. F.. “Chemical Engineering Thermodynamics,” g g . 161. 162, Kew York. McCran~-HillBook Co., 1944. ( 2 ) Su,G. J., IXD. ENG.CIIEM.,38,803 (1946). RECEIVED September 11, 1947. -4 copy of Figure 1 (11 X 17 inches) and a similar print of the high pressure region can be obtained by x\.rriting t o the author.
enyhydrazone as Chemical oftener for GR-S d
J
J . C. AJIBELASG, G. E. P. S\IITM, J R . , h N D G. W. GOTTSCHALK Firestone Tire & Rubber Company, Akron, Ohio
In the development of new processing aids for synthetic rubbers, it has been discovered that the phenylhydrazones of furfural and of certain aromatic aldehydes show high activitj as chemical softeners for GR-S. The p-bromophenylhydrazone and the 1-naphthylhydrazone of furfural are also active softeners. while thep-nitrophenylhydrazone is not. The phenylhydrazones of various additional aldehides and ketones are either inert or show a stiffening action under comparable conditions. Furfural phenylhydrazone may be used effectively in two general procedures, (a)by incorporating the hydrazone into the GR-S polymer on the mill and either storing for 2 weeks a t room temperature or by oven heating for a shorter period of time, or (b) by dispersing the furfural phenjlhydrazone in G K - S latex so that, after coagulation, drying of the polymer and softening take place simultaneously. Air appears necessar) for the softener to function. No softening was
observed w-hen the polymer-hydrazone mixture was dried in vacuo after coagulation of the latex. Tread compounds of increased plasticity ma> be prepared from the furfurai phenylhydrazone-softened polymers, especially after the furfural phenj lhydrazone has been incorporated into the latex and the softening obtained during the suhsequent drying period. It has been found that stiff, nonprocesbible, high Mooney polymers (ML4/212 = 75 to 180) may be softened to equal regular GR-S of specification Mooney (\IL4/212 = 45 t o 5 5 ) in processing characteristics, yet the v ulcaniaates retain many of the superior properties of the high-hZooney rubber, such as higher aged tensile, elongation, and crack-growth resistance. Thus plasticization and improved processibility of these polymers and stocks have been achieved without any additional operation other than t h a t of mixing the furfural phenylhydrazone dispersion into the latex.
d.
Most chemical softcners are thought to be either oxidizing agents or oxidation catalysts which promote the specific oxidation reactions of rubber so important in the breakdown of rubber on thc mill. The subject has been reviewed recently by Davis (3,4 ) , in describing a new class of catalytic plasticizers for GR-S and disulfides. natural rubber-via., the o,o’-diaeylaminodiphenyl GR-S, being less reactive t.han natural rubber toward oxygen (25) might be expected to require more active chemical softeners, higher concentrations, or more severe working condit,ions. Thus, while hydrazones in general have been reported to have weak to moderately strong plasticizing action (55) in natural rubber, the authors found that only a few monoarylhydrazones of certain aromatic and heterocyclic aldehydes were effective in GR-S. While p-nitrophenylhydrazine and as-phenylmethylhydrasine were reported to be plasticizers for natural rubber (Sf?), their furfural derivatives proved to be inert in GR-S. Ketone phenylhydrazones appeared to be either inert in GR-S, as in the case of benzophenone phenylhgdrazone, or t o be stiffeners, as, for example, acetophenone phenylhydrazone. Both of t’hese were mentioned by Gumlich (16) as softeners for a butadiene-styrene copolymer, which, however, might not show all the properties o f GR-S. Furfural phenylhydrazone in the aut’hors’ investigations proved to be one 01 the most active chemical soft.eners for GR-S.
YXCDk: rubber,, nst,ui’al or syiithetic, before mixing with pigments or fabrication into useful articles, must be plasticized. While natural rubber is readily plasticized by a milling operation, GR-S type synthetic rubber does not respond as readily to mechanical breakdown. Hence, the synthetic rubber must be modified during polymerization to give a relatively soft polymer with some loss of properties in the vulcanized product, or else the tough unmodified polymer must be: (a) mixed with rehtively large amounts of plasticizing oils in compounding, ( b ) plasticized thermally, or (c) plasticized by chemical means. Substances m-hich, when added in low concentrations to a polymer, bring about a marked increase in plasticity may be defined as “chemical softeners.” They are distinguished from solvent and lubricant type plasticizers by the characteristic that much smaller amounts of the chemical type are required for a given degree of plasticization. Their activity is assumed to be due to chemical reaction with the polymer or t’o a catalysis of t h e , breakdown reactions of the polymer molecules. Chemical softeners for natural rubber have been known for some time (2f) ; these include hydrazine derivatives, especially phenylhydrazine (a, 6, 10, 28, 3-5, 36, 38), aromatic and heterocyclic thiols (9, 16, 18, 37, 40) and their salts (3f, S 2 ) , monothiocarboxylic acids and their derivatives (5, 19, 23, 24, $7, ,$I), aromatic nitroso compounds (12, 39),and acyl peroxides (SO).
