Ion Exchange Resins for Beet Sugar Refining

Ion Exchange resins are being used extensively in beet sugar refining operations for thin juice softening and chromatographic separation of beet molasses. There are many more opportunities to utilize ion exchange resins to improve refining operations, save costs, increase production capacity and solve environmental issues. Some of the current resin technologies for beet factories are described below. There are also many potential ion exchange resin applications in beet sugar refining.
 
Decalcification: Beet Sugar (Gryllus, NRS, Weak Catex)  
The carbonatation process leaves the juice with a significant amount of Ca⁺⁺ ions in solution that will precipitate and scale heat transfer surface, such as the thick juice evaporator or vacuum pans, resulting in increased energy costs and chemical boilout (descaling) costs. In addition to energy cost reduction, beet factories which employ molasses desugarization require a softened molasses to keep the chromatographic separation resin in the monovalent form.
 
The Gryllus process utilizes a strong acid cation resin in the monovalent form.  The divalent calcium and magnesium have a higher affinity for the resin and will exchange onto the resin which then simultaneously releases Na⁺ and/or K⁺ ions. After exhaustion with hardness the resin is regenerated back to the monovalent form with thick juice whose concentration of Na⁺ and K⁺ ions have increased through evaporation and can overcome the selectivity differences. The Ca⁺⁺ and Mg⁺⁺ which has been transferred back to the thick juice increases molasses exhaustion due to the lower melassigenic effect of these ions compared to Na⁺ or K⁺. This process results in no chemical usage, dilution or waste.
 
The NRS process also utilizes a strong acid cation resin in the monovalent form. The difference between NRS and Gryllus is in the regeneration. NRS utilizes NaOH in softened thin juice at a lower temperature to strip the Ca⁺⁺ ions off the resin. At the lower temperature, the Ca(OH)₂ forms a soluble complex with the sucrose which prevents the Ca(OH)₂ from precipitating until it is recycled back to carbonatation where the temperature is increased and the complex is broken and calcium precipitates as CaCO₃. This process results in no dilution or waste.
 
The Weak Catex process utilizes a weak acid cation resin in the H⁺ form to remove hardness. Initially, the H⁺ ions on the resin are exchanged by the K⁺ and Na⁺ ions in the thin juice, which are subsequently exchanged by the Ca⁺⁺ and Mg⁺⁺ ions which have a higher selectivity for the resin. Regeneration is accomplished with H₂SO₄ and the regenerant effluent containing CaSO₄ used as a pulp pressing aid.

Recommended Products: C100S, C150S, C160S, C104EPlus, SSTC80S

Quentin Process: 
To achieve maximum molasses exhaustion (minimum sucrose purity) sometimes the B-green syrup is passed through a strong acid cation resin in the Mg⁺⁺ ion form. Due to the high concentration of Na⁺ and K⁺ ions present in the syrup, the resin will exchange the Mg⁺⁺ for the Na⁺ and K⁺ ions. The Mg⁺⁺ ions are less melassigenic than Na⁺ and K⁺, so their presence reduces the solubility of sucrose, allowing more sugar to be crystallized. Upon exhaustion, the resin is regenerated with a MgCl₂ solution to convert the resin to the Mg⁺⁺ form for more syrup treatment.

Recommended Products: C160S

Chromatographic Separation of Molasses: 
Since approximately 15% of the sucrose in the beets leaves the factory in the molasses, there is a strong financial incentive to recover this sugar by using a Chromatographic Separation resin to separate the sucrose from the non-sugars. Additionally, the molasses contains a significant concentration of betaine, a valuable amino acid, which can also be separated using the same resin. As the molasses passes through the resin, the salts will be ionically excluded from entering inside the resin beads along with large molecule color bodies. These will exit the separator first. The sucrose will diffuse into the resin beads and will be eluted out with water. This delays the passage of the sucrose in the column. The betaine is further retarded by interaction with the resin. Three separate cuts of the effluent can be taken, a salt fraction (raffinate), a sucrose fraction (extract) and a betaine fraction. In a coupled loop separator, the first separator will make just a betaine cut and the second will make a sucrose cut. Over 90% of the sucrose in the molasses can be recovered for evaporation and crystallization.

Recommended Products: PCR642K
 
Decolorization of Thick Juice or Extract: 
Late in the beet campaign as the beets deteriorate in the piles, the color of the thick juice produced in the factory increases. A strong base anion resin in the Cl^- form can be used to reduce the thick juice color, saving energy in crystallization and increasing white sugar production. Since many of the color bodies in molasses are small, they will pass through the resin bed during desugarization at the same rate as the sucrose and exit the column in the extract cut. Those color bodies are readily removed with a strong base anion resin.

Recommended Products: A502PS, A860S
 
Demineralization of Thin Juice or Extract: 
Thin juice or extract can be decolorized and demineralized to a water white liquid sugar or invert solution using ion exchange resins. However, the chemical cost of removing the large salt and amino acid load rarely justifies the process.

Recommended Products: C115E, A500SPlus
 
Sucrose Inversion: 
When producing a liquid invert solution from sucrose, the inversion process can be accomplished by passage through a strong acid cation resin in the H⁺ form. The invert will contain less impurities and ash compared to inversion with direct acid addition and neutralization. The degree of inversion in controlled with residence time and temperature.