1. It may be because rhodium is a common catalyst that is widely used in chemical reactions. During the production of butanol, rhodium catalyst may be added to the reaction mixture to facilitate the reaction. However, at the end of the reaction, the catalyst pass is not completely consumed but remains in the reaction compound.
2. Rhodium is also a rare metal with high corrosion and heat resistance. Therefore, rhodium is often used in the manufacture of high-end electronic products chemical instruments and medical equipment, etc.. If rhodium is present in the catalysts used in the butan production process, these may be contaminated into the butanol during the production process, resulting in rhodium in the butanol residue.