Mechanism of removal of undesirable residual amylase, insoluble starch, and select colorants from refinery streams by powdered activated carbons

Authors: Lima, Isabel; Eggleston, Gillian; SARIR, EMMANUEL - Carboua International; DONADO, CARLOS - Carboua International; THOMPSON, JACK - Lsr Refinery, Llc; St Cyr, Eldwin

Submitted to: International Sugar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2016
Publication Date: 5/17/2016
Citation: Lima, I., Eggleston, G., Sarir, E., Donado, C.A., Thompson, J., Cyr, E.S. 2016. Mechanism of removal of undesirable residual amylase, insoluble starch, and select colorants from refinery streams by powdered activated carbons. International Sugar Journal. 118(1409):352-362.

Interpretive Summary: Refineries use both high and very high temperature stable amylases that have been developed for much harsher processing conditions in their processes. As a consequence, they appear in white refined sugars and urgently need to be inactivated both at the sugar factory and refinery. Powdered activated carbon (PAC) has been shown to effectively reduce amylase, as well as impurities such as starch and various colorants from sugar syrups. Mechanisms for the performance of these powdered activated carbons in simultaneously removing multiple impurities with different physical characteristics were suggested to further improve the effective use of the PAC as well as their complementarity with the existing purification processes at the factory and refinery. Further studies are now warranted to investigate the use of high performance PAC as a tool to remove residual amylase, select colorants, and insoluble starch at the large-scale.

Technical Abstract: There is a need in the world-wide sugar industry to find a practical and economical solution to remove or inactivate residual alpha-amylase that are high temperature stable from factory or refinery streams. A survey of refineries that used amylase and had activated carbon systems for decolorization, revealed they did not have any customer complaints for residual amylase. Five commercial, high performance powdered activated carbons (PAC) were investigated for their ability to remove residual amylase as well as other impurities. Removal of the residual amylase protein by PAC was dependent on its surface area as well as mixing (retention) time. A select, high performance PAC (RFM-JH™) with high surface area (1764 m2/g) performed the best and, because this PAC also had the largest particle size characteristics (mean particle size ~274 µm), it was also the easiest to filter after use. Activated carbon also had the additional benefit of removing color, and RFM-JH™ preferentially removed cane derived flavonoid and phenolic colorants at pH 9 over process formed color at pH 4, which is opposite of color removal by the refinery phosphatation-clarification process and thus complementary. The dose of RFM-JH™ was more critical than retention time with respect to color removal. RFM-JH™ also consistently removed undesirable insoluble starch from raw sugar syrups and refinery liquors. A tentative mechanism for the removal of impurities is provided. Further studies are now warranted to investigate the use of high performance PAC as a tool to remove residual amylase, select colorants, and insoluble starch at the large-scale.