Handbook of Solvents - George Wypych - ChemTech - Ventech!

1054 George Wypych
The acidity of benzene, toluene, xylenes, naphthas, and other aromatic hydrocarbons
is determined by the titration of a water extract with 0.01 N sodium hydroxide in the presence
of 0.5% phenolphthalein indicator solution. 4 The method is suitable for setting specifications,
internal quality control, and development of solvents. The result indicates the
potential corrosivity of solvent.
The acidity of solvents used in paint, varnish, and lacquer is determined by the titration
of solvent diluted with water (for water soluble solvents) or isopropyl alcohol or ethanol
(for water insoluble solvents) in proportion of 1:1. A water solution of 0.05 N sodium hydroxide
in the presence of 0.5% phenolphthalein indicator dissolved in ethanol or
isopropanol is used for titration. 5 The method is useful for determination of acidity below
0.05%. Acidity is a result of contamination or decomposition during storage, transportation
or manufacture. The method is used to assess compliance with specification.
Solvents which are depleted of stabilizers (amine or alpha epoxide) may become
acidic. The following method determines the combined effect of both alkaline (amine) and
neutral (usually epoxy) stabilizers. 6 The determination is done in two steps. First solvent is
mixed with hydrochlorination reagent (0.1 N HCl), then the excess is titrated with 0.1 N sodium
hydroxide in the presence of 0.1% bromophenyl blue as an indicator.
The total acidity of trichlorotrifluoroethane and other halocarbons is determined by titration
of a sample diluted with isopropanol with 0.01 N sodium hydroxide in isopropanol in
the presence of a 0.05% isopropanol solution of phenolphthalein as an indicator. 7 The
method is used for setting specifications and quality control.
15.1.2 AUTOIGNITION TEMPERATURE
The autoignition temperature can be determined by the hot and cold flame method. 8 Cool
flames occur in vapor-rich mixtures of hydrocarbons and oxygenated hydrocarbons in air.
The autoignition temperature is the spontaneous (self-ignition) temperature at which a substance
will produce a hot flame without an external ignition source. Autoignition occurs
when a hot flame inside a test flask suddenly appears accompanied by a sharp rise in temperature.
With cold flame ignition the temperature rise is gradual.
The test equipment shown in a schematic drawing in the method 8 consists of a test
flask, a furnace, a temperature controller, a syringe, a thermocouple and other auxiliary
parts. The measurement is performed in a dark room for optimum visual detection of cool
flames. The results are reported as ignition temperature, time lags (delay between sample
insertion and material ignition), and reaction threshold temperature (the lowest flask temperature
at which nonluminous pre-flame reactions (e.g., temperature rise) occur).
The results depend on the apparatus employed. The volume of vessel is especially critical.
A larger flask will tend to produce lower temperature results. The method is not designed
for materials which are solid at the measurement temperature or which undergo
exothermic decomposition.
15.1.3 BIODEGRADATION POTENTIAL
The method covers a screening procedure which assesses the anaerobic biodegradation of
organic materials. 9 The procedure converts organic substances into methane and carbon
dioxide which are measured by a gas volumetric pipette − part of the standard apparatus.
Other parts include, a biodegradation flask, a magnetic stirrer, a pressure transducer, a syringe,
and a water seal. The apparatus may be interfaced with a gas chromatograph to
determine quantities of the two gases.
The biodegradation process is conducted in a specially prepared medium inoculated
with sludge inoculum. The process occurs under the flow of a mixture of 70% nitrogen and
30% carbon dioxide to provide anaerobic conditions.