In addition to economic benefits, maintaining the final product’s quality was a key consideration. Residual (unconsumed) bisulphite was measured at specific points in the fermentor drop curves for each additive during the engineering study. Unconsumed bisulphite not only represents chemical waste but can also contribute to yeast stress and increase the risk of sulphate carryover into the final ethanol product. A significant reduction in freight costs was also observed with Voxout 70C. Its calculated freight cost was 77% lower than that of SBS and 42% lower than that of ABS. Biodiesel Biodiesel ranks just below bioethanol in production scale. It is used widely in diesel blending in Europe, the US, and Indonesia, which together account for more than two- thirds of worldwide production. Driven by policy mandates and climate goals, biodiesel output is expected to expand worldwide, especially in the transport sector. The primary feedstock used in biodiesel production varies across regions, but vegetable oils remain the dominant source globally. Palm oil, soybean oil, and rapeseed oil are among the most commonly used, while waste oils such as used cooking oil and animal fats also contribute significantly. In the US and Brazil, soybean oil is the leading feedstock, with growing interest in alternatives like animal fats and recycled oils. In Asia, palm oil is the primary input. Meanwhile, while the EU currently relies heavily on agricultural crops, especially rapeseed oil, it is leading a shift toward non-food and waste- based feedstocks to enhance sustainability.
100 160 140 180 120 200
Chemical cost (k€/year) Residual bisulphite (ppm)
60 80 20 40
0
ABS
SBS
VOXOUT® 70C
commodity ABS and sodium bisulphite (SBS) as comparative scrubber additives. The goal was to determine which chemical could best meet the permitted acetaldehyde levels while also evaluating other performance criteria. Testing was conducted over complete fermentor drop cycles for each additive, ensuring that operations were as consistent as possible. During these tests, several key factors were assessed, including compliance reliability, application cost, residual bisulphite levels, the impact on yeast viability, sulphur content in the final product, and the overall value provided by each chemistry. The results demonstrated that the use of Voxout 70C resulted in the lowest average levels of residual bisulphite, with other benefits including lower overall chemical costs and reduced freight expenses. Comparative results based on use cost, product performance, and average residual bisulphite are summarised in Figure 3 . Figure 3 Performance comparison of various chemistries
Acid or base washing
Waste oil / fat
Free fatty acid proprocessing
Acid
Biodiesel
Methanol
Neutralisation & settling
Phase separation
Fatty acid methyl ester distillation
Transesteri cation reactor
Methanol recovery
Methanol & water
Oil / Fat
Base catalyst
Unreacted oil fat
Methanol
Methanol & water
Salt removal
Glycerin methanol separation
Glycerin & water
Salt
Figure 4 Simplified biodiesel transesterification process flow scheme
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