Submitted to: Association for the Advancement of Industrial Crops Conference
Publication Type: Abstract only
Publication Acceptance Date: 7/29/2004
Publication Date: 9/23/2004
Citation: Evangelista, R.L. 2004. Partial dehulling of milkweed seeds for oil extraction. Association for the Advancement of Industrial Crops Conference. Interpretive Summary:
Technical Abstract: Oil-bearing seeds are usually dehulled whenever appropriate. Dehulling increases throughput of the oil extraction equipment resulting from reduced material to be processed. Removing the hulls reduces the amount of pigments and waxes that get expressed with the oil, thus improving oil quality. The low bulk density of milkweed seeds is largely due to the paper-thin husk (wing) around the edges of the flat seeds. The presence of wings also contributes to the seeds' poor flow characteristics. In addition, the light wings that get detached during handling create dust problems. This study explored the feasibility of removing the wings from milkweed seeds to reduce the material going into oil extraction, to improve material flow, and to minimize dust during processing. Seeds were hand fractionated to determine the weight fractions and oil contents of wings, hulls, and cotyledons. One-kg batches of seeds with 4%, 7% and 10% moisture contents (MC) were processed through an impact type huller at 1250 rpm and 1700 rpm impeller speeds. The material from the huller was screened using standard testing sieves No. 8, 10, 12, 14, 18 and 25. The weight, moisture and oil contents of each fraction were determined. Two 100-kg batches were processed using the suitable seed moisture and impeller speed combination previously identified. The wing, hull, and cotyledon accounted for 12.2%, 51.2%, and 36.5% of the seed weight, respectively. Oil contents (dry basis) were 1.9% in wings, 9.0% in hulls, and 41.1% in cotyledons. Seeds with 4% MC and processed at 1250 rpm generated 22% fines fraction (smaller than 14 mesh) which contained 13% of the total oil. At 1700 rpm, the fines fraction increased to 42% and contained 35% of the total oil. Also, seeds with 7% MC cannot withstand higher impeller speed. Nearly 25% fines fraction with 15% of the total oil was produced. Three seed moisture and huller speed combinations (7%-1250 rpm, 10%-1250 rpm, and 10%-1700 rpm) produced the least oil losses (6.4-6.8%) in about 20% of fines. Two 100-kg batches of whole seeds with 8.5% MC were dewinged at 1250 rpm. Seeds with wings still attached were recycled to the huller until all the seeds were dewinged. After the third pass through the huller, the recycled material was reduced to mostly pod hulls. About 88% of the total material was dewinged seeds with an oil content of 24% and bulk density of 276 g/L. The discard fraction (fines and light fractions) had an oil content of 7.7%. Seed wings were effectively removed by using an impact type huller. Suitable seed moisture content and impeller speed combinations were 7%-1250 rpm and 10%-1700 rpm. Removing the seed wings reduced the weight by 12%, increased oil content by 11%, increased the bulk density by 52%, and reduced seed volume by 40% while losing less than 5% of the total oil. The significant decrease in seed volume will bring about a large increase in throughput of the oil extraction equipment.