Infrared-spectrophotometric analysis of binary and ternary mixtures of liquid hydrocarbons Page: 4 of 23
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NACA AI No. 527
the spring and summer of 1944 to determine the suitability of a
modified, routine-model, infrared spectrophotometer for analyzing
synthetic liquid hydrocarbon mixtures. This instrument was reported
in reference 7 to be adequate for vapor mixtures. The investigation
consisted in analyses of synthetio binary and ternary mixtures of
liquid paraffinic, naphthenic, and aromatic hydrocarbons and also
included a study of some factors affecting aocuracy of the results.
Some details of the analytical methods employed have been omitted
from this report owing to the extensiveness of the available liter-
ature on the subject.
CONSTITOEJlS OF THE bIflES
The difficulty of spectrophotometrio analysis is affected by
the number of components, their molecular structure, and their
boiling points. As boiling points increase, temperature intervals
between adjacent-boiling compounds and the wavelength intervals
between bands in the infrared spectrum of each compound tend to
decrease. Separation by distillation and analysis based on the
spectra for mixtures that contain compounds with boiling points
above approximately 1000 C are difficult, and resulting analytical
errors may sometimes amount to more than 1 percent of the total
sample. Progress may nevertheless be expected in the successful
application of infrared methods.
Choice of hydrocarbons. - Components that form mixtures of
medium analytical difficulty were selected for trial analyses. The
compounds chosen for the present investigation were 2,2,3-trimethyl-
butane (triptane), .benzene, and cyclohexane. These hydrocarbons
represent typical paraffinic, aromatic, and napbthenioc components,
respectively, of an aviation-fuel cut that boils at approximately
80 C. The boiling point of the triptane is 80.90 C and the boiling
points of the other two hydrocarbons are within 1 of this temperature.
Purity of the samples. - Because all analyses presented
herein are in terms of the actual hydrocarbon samples (which were
regarded as pure),, the accuracy of these analyses relative to abso-
lutely pure compounds is affected by the purity of the samples used.
All samples were dehydrated, and a description of additional treat-
ment to reduce- errors caused by the presence of impurities is given
in the following paragraphs.
The sample of triptane was a middle fraction obtained by
distillation with a still of 40 theoretical plates from part of
a batch supplied by the General Motors Corporation. The batch. .
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Cleaves, Alden P. & Sherrick, Mildred E. Infrared-spectrophotometric analysis of binary and ternary mixtures of liquid hydrocarbons, report, August 1945; (https://digital.library.unt.edu/ark:/67531/metadc62303/m1/4/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.