Passage IV

When an oil is exposed to air, small amounts of reactive peroxides can form in the oil. If the peroxide concentration reaches a certain level, the oil will rapidly decompose to form acidic organic compounds such as formic acid.Scientists use an accelerated oxidation apparatus, AOA, to model this process on a short time scale (see diagram).

A 3 g oil sample is heated to a certain temperature. Starting at time = 0 min, dry air is bubbled through the sample at a constant rate. The flow of air carries organic acids produced in the sample into the flask containing water. The conductivity (ease of electric flow) of the water is monitored. The conductivity of the water stays relatively constant until the oil rapidly decomposes. As the oil rapidly decomposes, the conductivity sharply increases. The length of time from 0 min until this increase occurs is the induction period.

Biodiesels are renewable fuel oils typically made from soybeans. Scientists did 3 experiments to study 4 biodiesels (BD1-BD4). BD2 was a 50/50 mixture of BD1 and BD4 by volume.

Experiment 1

The induction period was determined for fresh samples of BD1-BD4 at 4 temperatures (see Figure 1).

Experiment 2

The induction period was determined for fresh samples of BD1-BD4 at 110^oC. Each sample contained 1 of 4 antioxidants at a concentration of 500 mg/kg (see Figure 2). Antioxidants are compounds that can inhibit the decomposition of oils exposed to air.

Experiment 3

The induction period was determined for fresh samples of BD1-BD4 at 110℃. Each sample contained a different concentration of the antioxidant TBHQ (see Figure 3).