Paz Chiavarino - Axion Energy
In August 2012, Axion Energy planned a back to back inventory replacement for the FCC unit incorporating cat-naphtha sulfur additive from Grace Davison. The main objective at that moment was reaching a legal limit of 50 ppm total sulfur in the gasoline pool by maximizing cat-naphtha volume and minimizing alkylate imports.
Before entering the unit with the new additive, a base case of study was performed. With that information, Grace Davison’s technical support group developed mathematical expressions which allowed estimations for sulfur removal efficiency taking into account distillation curves, specific gravity and sulfur content in feedstock. In addition most operating variables were tracked, in order to understand how the severity of the cracking reactions, conversion, temperatures and C/O ratio works with sulfur reduction.
Cut-Point data from the main fractionator tower was also collected, understanding than the higher FBP of the product, the more difficult the sulfur reduction of species such as benzothiophenes is to achieve. Progressive effects were seen while content of sulfur additive was increasing in equilibrium catalyst inventory. 25 to 30% drop in total sulfur of cat-naphtha was reached, with events of 40-45% at maximum severity in the unit. Some unexpected additional reductions were seen in LPG (propane and butane production before entering caustic treatment) getting margin improvements in spent caustic handling.