Progress 01/01/01 to 12/31/05
Outputs
Cane white sugar production involves a complex system of extraction, purification and crystallization in two separate processing steps: from cane sugar to raw sugar in raw sugar mills; and from raw sugar to refined sugar in sugar refineries. This separation is due to the presence of specific impurities in sugar juice, mainly high molecular colorants that have a high affinity for sugar crystals. Therefore, if these compounds are not properly removed in sugar mills the raw sugar product has a residual color without the characteristics of a white sugar. There are advantages to producing white sugar directly in the sugar mill, avoiding the refining process. Attempts have been made to apply new technologies such as membrane filtration. This technology is promising, but it is not usually economically viable for this purpose. In our novel approach, clarified juice is decolorized with granular activated carbon (GAC) in two columns in series, followed by demineralization and/or
softening. During 2005 season a pilot plant was installed in one Louisiana sugar mill to decolorize and soften the clarified syrup. GAC was placed in two columns of 15 and 30 L capacity. The first column is a guard column to protect the second column from suspended solids carried over with the juice. Before the second column, juice was contacted with hydrogen peroxide. After passage through the GAC columns, juice was treated with cationic and anionic resins in a mixed bed column, in order to remove hardness in solution and reduce juice color. The installation worked continuously for two months with clarified juice at a flow rate of 1 BV/h (on total carbon). Average composition of clarified juice was: Brix 14.3; color 9 070 IU, turbidity 212 NTU, ash 3.5 g/100 g solids, pH 7.2. Average composition of final treated liquor was: Brix 13.9; color 1 680 IU; turbidity 165 NTU, ash 4.0 g/100 g solids; pH 6.0. A reduction of 81.4 % in juice color was obtained (75.6 % on carbon columns and 24.1
% on resins). A turbidity decrease of 22.1 % and hardness (calcium and magnesium) reduction of 88.5 % was observed. After each five day cycle, carbon was washed and regenerated using a special chemical regeneration. Resin cycles varied between three and four days. After each cycle, resins were washed with condensate water followed by regeneration with NaCl and NaOH. In the new regeneration process developed in ASI, a special solvent regeneration is used. Normally in the sugar industry GAC is regenerated at high temperature in special kilns. In the process we developed, regeneration is performed using a solution with solvents and other chemicals. The high regeneration capacity of this process will allow the application of GAC in the sugar industry without requiring the expense of a regeneration kiln.
Impacts
From these results it appears that the proposed decolorization process (granular activated carbon and ion exchange resins) is efficient enough to process clarified juice to white sugar directly in raw sugar mills.
Publications
- Patent application serial number 11/260,069. PW Rein et al.(2005) "Direct production of white sugar from sugarcane juice or sugar beet juice". Provisional patent serial no 60/717,410. LSM Bento et al.(2005) "Process for chemical regeneration of activated carbon".
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Progress 01/01/04 to 12/31/04
Outputs
Work on the effect of treatment of clarified juice with different adsorbents on a lab scale was completed and resulted in an MS dissertation in chemical engineering being awarded. The work was taken further in a pilot plant at St James mill. The color results comparing the feed color to the final product color showed that 80 to 90% decolorization could be achieved. Although more samples are still to be analyzed, the results are very promising even with minor setbacks occurring. The main problem encountered was the failure of the peristaltic pump tubing with prolonged use. This problem improved by changing the pump head and the peristaltic tubing but the tubing still required frequent changing. Other problems encountered were associated with the blocking of various thin tubes. Also, when an increased throughput was passed through the column a larger pressure drop was witnessed across the bed. This could be attributed to increased mud deposition, which was experienced
at low flow-rates when large amounts of mud were present in the feed cane. Crystallization tests are to be performed on syrup, which was concentrated and collected using a small evaporator. Approximately 20 gallons of syrup were collected and will enable ion exchange work and other treatments to be performed on the product at a later stage. Low temperature regenerations were used to clean the column once fouled. The regenerations were performed every 7-10 days. The cleaning stages included a high up-flow water wash, an acidic treatment and then a series of alkaline washes. Various concentrations and flow-rates were tried during the regenerations as well as different regenerant temperatures. The patenting of this process is being pursued.
Impacts
The production of edible sugars directly in sugar mills is an opportunity to diversify mill production with high added value products. The results of this study (product characteristics and production schemes) will show the value to the industry or individual mill of direct production of direct consumption sugars. For a mill processing 1 million tons of cane /yr, the potential benefit in terms of increased revenue is considered to be 3 cents/lb, or $6 million/yr.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Research on the effect of membrane treatment and ion exchange treatment on Louisiana juices was undertaken. Two different strategies for producing white sugar directly have been identified and are under investigation. The WSM process is being examined with funding from Calgon Carbon and an alternative cheaper process is being investigated which gives better color removal. The patenting of this process is under investigation.
Impacts
A direct production of white sugar process could increase the Louisiana sugar mills' revenue by over $90 million per year
Publications
- Broadhurst, H. A. and Rein, P.W. (2003). Modeling Adsorption of Cane Sugar Solution Colorant in Packed-bed Ion Exchange. Am. Inst. Chem. Eng. J. 49, 10, 2519-2532.
- Broadhurst, H.A., and Rein, P.W. (2003). Deconvolution of GPC chromatograms of sugar solutions. Zuckerindustrie 127, 3, 96-99.
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Progress 01/01/02 to 12/31/02
Outputs
An investigation into the products of various color formation mechanisms was undertaken. Color was formed in the laboratory by alkaline degradation, caramelization, the Maillard reactions, and exposure to iron in an attempt to replicate color formation in the factory. Samples were analyzed with HPLC gel permeation chromatography (GPC), using a differential refractometer to detect concentration in series with an absorbance detector set to 420nm to detect color. GPC produces concentration and color profiles as a function of molecular weight, which enables the effects of these formation mechanisms to be compared. Molecular weight ranges were chosen for the characteristic products of each mechanism. Fractions corresponding to these molecular weight ranges were collected from repeated GPC runs. Fourier-Transform Infrared (FTIR) spectrometry was conducted as a preliminary functional analysis. Gel Permeation Chromatography (GPC) of sugar solutions yields chromatograms
containing overlapping peaks. Further separation or deconvolution may be performed using a mathematical treatment after the GPC analysis by representing the chromatogram as a number of Gaussian distributions. A deconvolution technique using nonlinear least-squares optimization was developed that allows for accurate quantification of GPC chromatograms. The removal of cane sugar solution colorant by packed-bed exchangers was modeled using a linear driving force adsorption model. Three resins were investigated: a strong acid cation, a weak-base anion and a standard sugar industry strong-base anion decolorizing resin. Batch testing of the resins produced linear isotherms, indicating that the colorant is dilute. Results from column testing showed that a plug-flow model with a constant linear isotherm was sufficient in all cases except the SAC resin. The SAC adsorption parameter decreased sharply as the pH increased, causing colorant to be desorbed from the resin. This situation must be
avoided if optimal decolorization is to be achieved. Decolorization trails using granular carbon and ion exchange were undertaken as part of the work being done to produce white sugar directly in a raw sugar mill.
Impacts
Fundamental information on the nature and behavior of colorants in raw sugar cane mills is being produced. This is providing a better understanding of how white sugar may be produced directly in a cane sugar mill. This could have a significant impact on the profitability of sugar mills, leading to the production of a product of much greater value.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
The removal of color from cane juice using a strong cation followed by a weak base resin, with a polishing step using a decolorising resin is under investigation. A GPC (gel permeation chromatography) system to characterise colorants by molecular weight has been set up and calibrated. The behaviour of different colorants in the 3 column system is being studied. A mathematical model has been formulated to model the adsorption of different molecular weight colorants. Colorants are being identified by sophisticated techniques with the assistance of the LSU Chemistry Department. The effectiveness of ultrafiltration and nanofiltration membranes in removing color has been assessed by treating juice with these membranes and boiling sugar from the juices.
Impacts
Information is being obtained on how to produce white sugar directly in a raw sugar mill, by-passing the refining step. This should have a beneficial financial effect for the cane sugar producers.
Publications
- No publications reported this period
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