Sugar Decolorization

In everyday life, it is almost certain that we need sugar, whether it is white crystal sugar for direct consumption or industrial refined crystal sugar that is not consumed directly. According to BPS data, Indonesia’s sugar consumption in 2021 is 5.1 million tons, consist of 2.8 million tons of white crystal sugar and 2.3 million tons of industrial (refined) crystal sugar. Approximately 1.1 million tons were supplied by private sugar mills, about 0.9 million tons were produced by state-owned sugar mills, and the shortfall of 3.1 million tons had to be met by imports. Very much isn’t it?

Then what is the difference between ordinary white crystal sugar and refined crystal sugar? Refined crystal sugar has a higher purity level and low SO₂ content so that it meets the requirements for the food and beverage processing and pharmaceutical industries. The purification process is also slightly different, white crystal sugar uses a sulfitation process, while refined sugar uses a carbonation process. In addition, due to the higher purity level, currently the raw materials that can meet the requirements for refined sugar production generally use imported raw sugar.

The process of producing refined crystal sugar from raw sugar varies depending on the specifications of use for the related industry, but in general terms are as follows:

• Affination    : washing raw sugar so that the molasses is reduced and the colour decreases by 35-50%
• Carbonation             : clarification process to remove non-sugar impurities
• Filtration                   : the process of separating the sediment and the clean filtrate
• Decolorization          : the process of removing colour with ion exchange resin
• Evaporation              : the process of evaporation of water in the fine liquor
• Crystallization           : the process of crystallization of sugar
• Dryer & Cooler         : drying and cooling process to separate crystals and solutions
• Packaging                 : the process of packaging refined crystal sugar

Colour content in raw sugar is determined by the content of impurities in the form of colour pigments such as carotene, tannin, chlorophyll, flavonoids, xanthophylls and anthocyanins. The whiteness level of sugar is measured by the ICUMSA (International Commission for Uniform Methods of Sugar Analysis) standard. The smaller the ICUMSA value in the International Unit (IU) scale, the whiter the sugar, for example as follows:

• Raw Sugar                                 : ICUMSA value 600 – 1200 IU
• White Crystal Sugar (GKP) 2  : ICUMSA value 201 – 300 IU
• White Crystal Sugar (GKP) 1  : ICUMSA value 81 – 200 IU
• Refined sugar grade 2              : ICUMSA value 46 – 80 IU
• Refined sugar grade 1              : ICUMSA value < 45 IU

So, it is quite clear that to get a low ICUMSA value, a process of decreasing the colour content of raw sugar is needed. For example, if our raw sugar has an ICUMSA value of 600 IU, then the affination process will reduce the colour content by 35 – 50% to 300 – 390 IU. Furthermore, the carbonation process will reduce 40-50% of the colour content to 150-254 IU. After filtration, the sugar decolorization process will reduce 60-70% of the colour content to 45-102 IU. Finally, the crystallization process and centrifugal separation will reduce the colour content by 90 – 95% to < 45 IU, according to the criteria of grade 1 refined sugar.

Sugar Decolorization with Ion Exchange Resin (IER) is basically an ion exchange process like the Demin Plant that we discussed in the previous article, except that Sugar Decolorization uses a special resin, namely a strong base anionic (SBA) resin with a macroporous matrix. Why? Since sugar impurities in the final process are generally anionic and hydrophobic, two colour reduction mechanisms are expected to work, namely ion exchange and hydrophobic interactions between resin and impurities.

There are 2 kinds of SBA resin used in Sugar Decolorization:

• Acrylic Anion Resin          : max. ICUMSA inlet 2000 IU, low selectivity
• Styrenic Anion Resin       : max. ICUMSA inlet 800 IU, high selectivity

For the selection of the resin sequence or configuration depending on the desired ICUMSA inlet and ICUMSA outlet values, namely:

• Acrylic – Acrylic                : highest efficiency, but ICUMSA outlets are still relatively high
• Acrylic – Styrenic              : low ICUMSA outlet, longer Styrenic resin life
• Styrenic – Styrenic           : feasible if ICUMSA inlet is not too high

Like other Demin Plants, Sugar Decolorization resins operate under certain conditions, such as a typical cycle time of 24 – 72 hours, a maximum temperature of 80°C, a minimum bed depth of 1000 mm and a service flow rate of 2 – 4 BV/hour. The regenerant chemical used is 10% NaCl and 0.2% NaOH with a flow rate of 2 BV/hour and a contact time of 45-60 minutes.

Beta Pramesti Asia has experience in developing an Ion Exchange Sugar Decolorization system for a refined sugar factory in Indonesia. For more details about Sugar Decolorization, please contact and discuss further with our engineering team. So, hopefully you find this useful and see you in the next article.