Case Study

Quality control of the final product requires a large and varied number of chemi­cal analyses to evaluate the physical and chemical parameters in comparison with quality standards, usually established by regulatory legislation. Table 7 shows the specifications and analytical methods for the quality control of ethanol, an impor­tant Brazilian biofuel.

Table 6 Examples of analytical techniques widely used in analyses of chemical composition of raw materials for biofuels

Raw material

Parameter

Analytical technique

Reference

Sugarcane for 1G ethanol production

Content of sugars

HPLC-refractive index detectora

Shuo and Aita (2013)

Vegetable oils for bio­diesel production

Content of fatty acids and esters

GC-flame ionization detectorb

Meher et al. (2006)

Bioenergy crops

Molecular

characteristics

Near-infrared

spectroscopy

Everard et al. (2012)

Lignocellulosic

residues

Energy content

Differential scanning calorimetry

Chang et al. (2011)

aHPLC High performance liquid chromatography; bGC Gas chromatography

Table 7 Some analytical parameters for the quality of Brazilian ethanol (anhydrous and hydrated) for fuel use (Brazilian National Agency of Petroleum, Natural Gas and Biofuels 2008)

Parameter

Unity

Specification

Anhydrous

.

Hydrated

Method

Technique

Acidity (max.)

mg L-1

30

30

ASTMa D7795

Volumetry

pH

6-8

ASTM D6423

Electrochemistry

(direct

potentiometry)

Residues (max.)

mg 100 mL-1

5

5

ASTM E1690-08

Gravimetry

Chloride content (max.)

mg kg-1

1

1

ASTM D7328

Ion chromatog­raphy

Ethanol content (min.)

% v/v

98

94.5

ASTM D5501

GC-flame ioniza­tion detectorb

Sulfate content (max.)

mg kg-1

4

4

ASTM D7328

Ion chromatog­raphy

Iron content (max.)

mg kg-1

5

5

ASTM D6647

Atomic absorption spectrometry

aASTM American society for testing and materials; bGC Gas chromatography

These data highlight the large number of techniques required to ensure ethanol quality, from classical techniques (volumetry, gravimetry, and direct potentiometry) to instrumental techniques (ion chromatography, GC-flame ionization detector, and AAS). The method for each analytical technique needs to be rigorously and systematically applied in order to enable accurate comparison between samples and to accurately assess the quality of the sample.

Figure 8 shows a flowchart for the use of AAS for quality control of ethanol. AAS is a rapid technique for the determination of the presence and concentration of several metals and some nonmetals. Nevertheless, preparation steps require attention because this step will release the analyte into the solution to be meas­ured. If not all of the species is released into the solution, inaccurate results will be obtained. The analytical result could be obtained as a concentration (mg kg-1 or mg L-1) or as a mass percentage in a certain volume (% m/v), depending on the individual’s interest or standard regulation.

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