Design and operation of a scaled-up pilot plant for the removal of sugar beet extract colorants using powdered activated carbons

Authors: Lima, Isabel; Clayton Iii, Charles; Tir, Annie; Wierdak, Andrew; PARKER, CRAIG - British Sugar Ltd; SARIR, EMMANUEL - Carboua International; EGGLESTON, GILLIAN - Audubon Sugar Institute

Submitted to: Sugar Tech
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2020
Publication Date: 1/1/2021
Citation: Lima, I.M., Clayton, C., Tir, A., Wierdak, A., Parker, C., Sarir, E., Eggleston, G. 2021. Design and operation of a scaled-up pilot plant for the removal of sugar beet extract colorants using powdered activated carbons. Sugar Tech. 23(1):167-177. https://doi.org/10.1007/s12355-020-00812-3.
DOI: https://doi.org/10.1007/s12355-020-00812-3

Interpretive Summary: A pilot scale filtration unit has been modified and operated at the Southern Regional Research Center of the United States Department of Agriculture in New Orleans, LA, for scaled up trials to test the efficacy of powdered activated carbon in the removal of color impurities from sugar beet extract (SBE). This extract is obtained as a by-product of sugar beet processing. Particularly, molasses is subjected to simulated moving bed chromatography to extract high-value betaine. Additional sucrose can be recovered by recycling the resulting high color SBE from the chromatography system back into the crystallization unit. Color compounds, when present in large amounts, can make this process unfeasible. One method of reducing color as well as other impurities, prior to further processing into white refined sugar, is the application of high surface area powdered activated carbon (PAC). Pilot plant trials were undertaken to determine the feasibility of using PAC to adsorb both natural and process-induced colorants from SBE. Experiments were performed using a batch decolorization process to maximize color removal and determine optimal distribution of PAC as either a body feed or a filter pre-coat. With initial colors at 4,275±114, 4,256±223 and 4,774±157 IU for pH4, 7 and 9, respectively, a target of 50% color removal was achieved using 4,000 ppm of PAC, with a recommended distribution of 75% as pre-coat in the filter and 25% as body feed in the process feed tank. A 50/50 distribution of PAC also reached the target rate of color removal. A merry-go-round experiment was undertaken to simulate a semi-continuous process in order to achieve continuous color removal over time. Overall, PAC performance was slightly better for the removal of native sugar beet colorants than colorants produced during processing. Addition of PAC did not lead to significant sucrose losses nor affect the pH of beet extract.

Technical Abstract: A pilot scale filtration unit has been modified and operated at the Southern Regional Research Center of the United States Department of Agriculture in New Orleans, LA, for scaled up trials to test the efficacy of powdered activated carbon in the removal of color impurities from sugar beet extract (SBE). This extract is obtained as a by-product of sugar beet processing. Particularly, molasses is subjected to simulated moving bed chromatography to extract high-value betaine. Additional sucrose can be recovered by recycling the resulting high color SBE from the chromatography system back into the crystallization unit. Color compounds, when present in large amounts, can make this process unfeasible. One method of reducing color as well as other impurities, prior to further processing into white refined sugar, is the application of high surface area powdered activated carbon (PAC). Pilot plant trials were undertaken to determine the feasibility of using PAC to adsorb both natural and process-induced colorants from SBE. Experiments were performed using a batch decolorization process to maximize color removal and determine optimal distribution of PAC as either a body feed or a filter pre-coat. With initial colors at 4,275±114, 4,256±223 and 4,774±157 IU for pH4, 7 and 9, respectively, a target of 50% color removal was achieved using 4,000 ppm of PAC, with a recommended distribution of 75% as pre-coat in the filter and 25% as body feed in the process feed tank. A 50/50 distribution of PAC also reached the target rate of color removal. A merry-go-round experiment was undertaken to simulate a semi-continuous process in order to achieve continuous color removal over time. Overall, PAC performance was slightly better for the removal of native sugar beet colorants than colorants produced during processing. Addition of PAC did not lead to significant sucrose losses nor affect the pH of beet extract.