*Alternatively, a tubular membrane system at higher capital costs                                

         The SAT process is a “perfect” replacement of carbonation and /or sulfitation  processes for production of plantation white sugar. Carbonation involves an environmental issue for disposal of carbonate cake, particularly for long term consideration. Sulfitation has been known for its serious problems with respect to process instability, operational difficulties, low sucrose yield due to high sucrose loss and poor product quality, including, but not limited to, high SO₂ contents and storage problems.

          With the SAT process a raw sugar mill can easily produce Very Low Color (VLC) sugar with color of 400 to 600 ICU and Ultra Low Color (ULC) sugar with color of 100 to 200 ICU. When VLC “raw sugar” is shipped for further refining, A refinery can eliminate affination and carbonation/ phosphatation processes. For ULC sugar, a refinery can eliminate all the processes before pan boiling with considerable operating cost saving. These advantages are illustrated in the following figure 2.

The  illustration clearly shows that refined sugar can also easily produce in a sugar mill by boiling ULC sugar one more time. As to be shown later in this presentation, a raw sugar mill can produce about 30% of its product as refined sugar without additional capital investment in boiling pans.

The SAT process will be perfect for a refinery attached to a raw sugar mill. In fact, when a ULC sugar is produced by the SAT process only some additional pans and drying equipment are needed to produce 100 % of refined sugar in the attached refinery.

Integration of sugar mill with refinery operation with SAT process (Figure 2)

Principle, Experiments, and Results

Factors affecting the color of white/refined sugar includes: purity and color of pan feed liquor, color types, polysaccharides, ash constituents, sugar crystal size and distribution, and boiling time. SAT process is designed / developed to reduce/minimize and improve or change these effect in order to produce white/refined sugar.

            Purity and color of feed liquor--The crystal sugar color is greatly affected by the color and purity of pan feed liquor. Generally crystallization removes between 90 to 96 % of color. The lower the color of feed liquor the better the sugar color. Sugar refining processes use affination (mechanical separation of color), carbonation, phosphatation, bone char, granular carbon and ion exchange resin to remove color before sugar boiling (crystallization) to produce white/refined sugar. Any or combination of above processes selected should perform the highest net color removal with minimum environmental problems. Unfortunately, except affination and crystallization, all other processes create environmental issue.  

The UF membranes used in the SAT process remove color with minimal effect on environmental quality as shown in the table below. The color removal ranges from 48% for raw sugar to 58% for affination syrup. The ability of SAT to remove color is essential to make white sugar from sugar mill. The maximum color of clarified cane juice entering the SAT system should not exceed 12,000 ICU.

The above data also indicate considerable improvement in purity due to non-sucrose removal by the SAT process. The increase in purity is as high as four points for affination syrup used in the study, most likely due to the presence of large quantity of macro-molecules and well dispersed fine particulates. The increase in clarified cane juice is expected to be less. The higher the purity of cane juice the easier it is to make white sugar. For the SAT process the cane juice should have a minimum purity of 85. Cane juice with low purity would contain large percentage of invert sugar, which would not only create color but also induce significant sucrose loss, particularly at low PH as practiced in sulfitation processes for production of plantation white. The following data evidences the tremendous sucrose loss due to sulfitation, up to 5%, due to low PH and high invert in the cane juice.

 % Sucrose loss at 80 °C, pH 5.0 of 65 brix sucrose solution spiked with  Fructose

 Color Types—To produce white/refined sugar, in addition to lessen the color of feed liquor, a survey of literature suggests a need for removal of colorants preferentially occluded in the crystal. Donovan and his coworker have concluded, in their study on preferential color occlusion in sugar crystal, that the higher molecular weight colorants, which can be separated by membrane, give much high color transfer into sugar crystal (2). Clarke and her coworkers has proposed that polysaccharide is part of the very high molecular weight color complex and is preferentially occluded in sugar crystal (3). Removal of these high molecular weight color and polysaccharide by a membrane system, which is part of the SAT system, should facilitate production of white/refined sugar from sugar mill. The following table shows the color and polysaccharide removal as a function of membrane molecular weight cut off limits. It should be noted that in general the % removal increase as the pore size of membrane decrease. Chou also reported similar findings (4).

Ash types—Carpenter reported (5) that ionic constituents in sugar solution would greatly influence the degree of color adsorption by adsorbents such as bone char and granular carbon. Colorants in a sugar solution with excess polyanions (EPA) has much less tendency to be adsorbed or picked up by adsorbents, particularly as the degree of conjugated double bond decrease as shown in his data. He did not advance his explanation for the phenomenon. Chou (4) advanced his reasoning in term of ionic strength of the solution and the degree of conjugated double bond of the adsorbents. Since the sugar crystal has no conjugated double bond, the adsorption/occlusion of colorants into the crystal should be minimal as the EPA is increased by addition of polyanions as processing aids. Some other reasonings can be found in the literature (6, 7). In the SAT process, polyanions are added as processing aids to increase EPA, and therefore minimize color occlusion into sugar crystals.

Sugar crystal size and distribution— the sugar color, for a given weight of sugar product, increases with surface area due to the fact that about 15 to 30% of total color are on the outside of the crystal. To minimize sugar color, the SAT process requires a minimum of 0.65mm average sugar crystal size (MA) and a maximum of 35 coefficient of variation (CV) for its sugar products.

Boiling time--It is generally stated in the literature that ultrafiltration (UF.) treatment of sugar containing solutions improves the crystallization rate during boiling and therefore will subsequently increase vacuum pan capacities.  However, there is little specific data available in the literature on the subject.  Too many parameters affect sugar boil, for instance, boiling schemes.  The table below shows the increased rate of crystal growth achieved with juice treatment by the SAT process.

The SAT process provides benefits, in addition to color reduction, in the form of polysaccharide and other non-sucrose impurities removal.

For example, the treatment of affination syrup using the SAT process removed impurities as previously shown. It can be seen (see above table) that removal of polysaccharides and other impurities, which affect the rate of crystallization, did indeed improve the crystal growth rate by up to 49 %, 38 %, and 37 % for the first hour, second hour, and third hour, respectively.  The subsequent increase in crystal growth rate will increase the factory/plant capacity, reduce sucrose loss, and increase yield.

 The increased crystal growth rate can be attributed to a reduction in viscosity caused by the membrane ultrafiltration along with processing aid treatment.  It is well known that treating juice with U.F. and processing aids will give reduced viscosity.  The table below shows the reduction in viscosity up to 19% due to the SAT treatment. Since the viscosity is difficult to measure at 85 brix, they were measured at about 75 Brix.  It is expected that viscosity reduction would be significantly higher at 85 Brix, which is closer to the actual conditions in sugar boiling.

Pilot plant testing-- In essence, The SAT process uses (a) the membrane with right pore size to remove color, polysaccharide, and their complexes, after addition of processing aids, in order to reduce both feed liquor color and color transfer coefficient, and  (b) processing aids to increase EPA and to change the nature of colorants in order to reduce occlusion of sugar color into sugar crystal.

The experiment involved five scientists and engineers on three shifts/day basis for about two months. The clarified juice were first treated with processing aids and membrane filtered using a two gpm membrane pilot unit on site in Sterling Sugar Company of Louisiana. The treated clarified juice was then evaporated to 65 brix using an pilot evaporator on loan from ASI of Louisiana University of Louisiana (LSU). The concentrated syrup were then trucked to ASI of LSU and boiled/ crystallized using a pilot vacuum pan with nominal capacity of twenty gallons. The results are shown below. The data clearly indicate that white sugar with color ranging from 80 to 200 ICU can be produced from cane sugar factories.

White sugar produced with SAT process

           Benefits of the SAT process is shown in the following list

1.    Sparkling sugar with color of 85 minimum (ICU) meeting U. S. Food grade standard

2.    SO₂ less than 6 ppm

3.    Increase vacuum pan capacity by 30%

4.    Increase clarifier capacity by 15%  

5.    Reduce evaporator scale by up to 75%

6.    Reduce sucrose loss by up to 2%

7.    Excellent stability in storage

8.    Up to 90% Dextran removal

9.    An automated process

10.    No conventional sulfitation/carbonation/ flotation process facilitating  automation of mills to reduce manning, and consistent high process efficiency and products quality

11.    Ability to produce 30% of refined sugar without additional vacuum pan

12.    Operate in conjunction with the Cti process to produce white/refined sugar and value added sugarcane extract (antioxidant etc.)

            CONCLUSIONS

 Reported here is a new sugar processing method (SAT) providing an energy efficient and environmentally friendly process for production of white/refined sugar from cane sugar factories. The SAT process is a direct replacement of the sulfitation, carbonation, and Blanco Directo processes for plantation white sugar productions. 

The SAT process will: a) minimize color occlusion into sugar crystal during sugar boiling producing sugar product with color ranging from 80 to 200 ICU depending the need of the market ; b) reduce scale formation in the evaporation process by up to 75%; c) increase pan boiling capacity by 30%; d) increase primary clarifier capacity of 15 % by elimination of vacuum drum filtrate recycle; e) reduce sucrose loss by up to 2%; f) reduce sulfate/sulfite content of the sugar; and g) improve the storage stability of sugar products.

The crystallized ULC and VLC sugar products from the SAT process in raw sugar mills/factories can be used as food grade products for direct consumption as refined sugar, plantation white sugar, and other low purity refined sugar.  Application of the SAT process in raw sugar mills in conjunction with a sugar refinery can eliminate one or more of the various refining processes such as affination, carbonation, phosphatation, and/or granular carbon/bone char/ion exchange for decolorization.

In summary, the environmentally friendly SAT process can produce high quality food grade sugar products meeting customers’ needs with considerable savings in both capital and operating costs.

ACKNOWLEDGEMENT

 The authors are grateful to Sterling Sugars, Inc. (Franklin, LA) for facilities and support provided for this study and to Audubon Sugar Institute of Louisiana State University for the use of its facilities.

The authors’ sincere appreciation are extended to the Sugar Processing Research Institute (SPRI) group for analytical support including Dr. Linda Andrews, Mary An Godshall, Ronnie Triche, Sara Moore, Marie Kuebel, and Xavier Miranda.  

REFERENCES