Overview
ISO 1388-10:1981 - "Ethanol for industrial use - Methods of test - Part 10: Estimation of hydrocarbons content - Distillation method" (first edition, 1981) specifies a laboratory distillation procedure for evaluating hydrocarbon contamination in industrial ethanol. The method is based on distilling a measured test portion in the presence of water, extracting the distillate with a saturated sodium chloride solution, and measuring the volume of the insoluble hydrocarbon layer.
Key procedural elements described in the standard include the use of a Hempel fractionating column coupled to a Liebig condenser, a 4 000 ml round-bottom distillation flask, and a graduated evaluation tube for direct reading of hydrocarbon volume. The method requires collection of the initial distillate (approximately 13 ml), addition of saturated NaCl, separation of layers and reading the volume of the upper hydrocarbon layer. An empirical diagram (figure 3 in the standard) converts the measured layer volume to percentage (v/v) hydrocarbons - the diagram reflects that hydrocarbon distillation is not strictly proportional to concentration and that not all hydrocarbons distill in the first 13 ml.
This part of ISO 1388 should be read in conjunction with ISO 1388/1 (general provisions) and uses analytical-grade reagents and distilled or equivalent-quality water.
Key Topics
- Scope and principle: Distillation in presence of water, salt-saturated extraction, volumetric reading of insoluble hydrocarbons.
- Apparatus: Hempel fractionating column (230 mm packing height), Liebig condenser with extension, 4 000 ml distillation flask, graduated evaluation tube (as per figures).
- Sampling: Laboratory sample size indicated in the text (1 500 ml sample portion, taken per ISO 1388/1 guidance).
- Procedure controls: Maintain distillation rate (not exceeding ~30 drops/min), collect initial distillate to the marked volume (~13 ml), mix gently to separate layers without inverting the tube.
- Result expression: Use the empirical diagram provided to convert measured upper-layer volume to percentage (v/v) hydrocarbons.
Applications
This test method provides practical value for:
- Quality control of industrial ethanol production and incoming raw material inspection.
- Process monitoring where hydrocarbon carryover or contamination must be tracked.
- Batch release and routine laboratory testing in chemical and fuel-related industries.
- Comparative assessments when referenced alongside other ISO 1388 parts for a comprehensive ethanol test program.
Advantages:
- Simple volumetric endpoint that is straightforward to implement in a standard laboratory.
- Uses commonly available glassware (Hempel column, Liebig condenser) and standard reagents (saturated sodium chloride solution).
Related Standards
For implementation, laboratories should consult the full text of ISO 1388-10:1981 for figures, exact apparatus dimensions, safety guidance and the empirical diagram for converting measured volumes to % (v/v) hydrocarbons.
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