Raschig Rings for Liquid Decolorization

Raschig rings have recently become popular tools to achieve liquid decolorization. Constructed of metal tubes of equal height and diameter, these Raschig rings can be loaded with metal oxides for increased surface area that promotes decolorization. Furthermore, this new type of Raschig ring has been reused 10 consecutive cycles without losing catalytic activity; an impressive feat considering regular forms of packing can often become wasteful processes in chemical production processes.

Fractional distillation uses tubes as an additional surface area for vapor to come into contact with condensed materials, increasing mixing and interaction in the column and thus decreasing pressure loss (delta p). Their increased surface area also allows for an appropriate number of theoretical plates but with lower hold up times and clog resistance than structured packings such as trays.

Raschig rings were successfully used for the oxidation of phenol in a semibatch basket reactor under mild reaction conditions for 8 h, producing excellent results with 100% conversion and 36-42% selectivity towards CO2. Fourier transform infrared analysis revealed that dye molecules were converted into sulfate, nitrate and nitrite molecules; further confirmation came via Fourier transform infrared analysis and ion chromatography analysis.

Results indicate that PP-Raschig rings exhibit efficient catalytic performance with excellent stability and reusability in oxidizing phenol through a Fenton process. The rings proved especially successful at up to 10 consecutive recyclings while maintaining structural and textural properties after 10 cycles of phenol oxidation.