In a Titanium Electric Heater Used to Maintain 110°C in a 60% Sorbitol Solution, How Does the Reducing Sugar Content (0.1% vs. 1%) Catalyze the Complexation of Titanium Ions and Accelerate General Corrosion?

Sorbitol solutions of 60% at 110°C are employed in pharmaceutical and food applications. Impurities in sorbitol such as reducing sugars (glucose, fructose) are capable of complexing titanium ions. At 0.1% reducing sugar, the titanium corrosion rate is 0.01–0.03 mm/year. The rate increases to 0.08–0.15 mm/year at 1.0% reducing sugar with the chelation of the Ti 4+ ions preventing the development of the passive film.

FIGURE 10. Reducing Sugar Content vs Quantitative Corrosion Rate

110 °C, 1,000 hr:

Reducing Sugar (%) Ti Release (ppm) Corrosion Rate (mm/year)Surface Appearance 0 (pure sorbitol)0.5–1 0.005–0.010 Bright 0.1 2–5 0.01–0.03Light etch 0.5 10-20 0.05-0.10 Etched
1.0 20-40 0.08-0.15 Uniform matte 2.0 40-80 0.15-0.25Deep etching
Effects of Temperature and Rate of Complexation

Temperature (°C) 1 % Corrosion Rate (mm/yr) – Reducing SugarActivation Energy (kJ/mol)
80 0.03–0.06 50 100 0.06–0.12 50 110 0.08–0.15 50 120 0.12–0.22 50
Sugar Control Guide Cut Down

Sugar Content Reduction (%) Recommended Action Expected Corrosion Rate (mm/year)
<0.2 None <0.03 0.2-0.5Accept with annual inspection 0.03–0.08
0.5–1.0 Use titanium grade 7 0.02–0.05 (grade 7)1.0 Purify sorbitol or lower temperature >0.08
Engineering Recommendation

Reducing sugar content of 60% sorbitol at 110°C must be less than 0.2%. For greater levels use titanium grade 7 or lower temperature to 100°C. The engineer controls the content of reducing sugars to prevent the increased titanium complexation and corrosion.