Application of PAT Probes in Aluminum Phosphate Adjuvant Manufacturing

Abstract

Purpose: This study is focused on monitoring process parameters and quality attributes of aluminum phosphate (AlPO₄) using multiple in-line probes incorporated into an industrial-scale adjuvant suspension manufacturing unit.

Methods: The manufacturing of aluminum adjuvant suspension was monitored at manufacturing scale using conductivity, turbidity, infrared, and particle sizing and count probes to follow the continuous evolution of particle formation and size distribution, and the reaction kinetics during the synthesis of AlPO₄.

Results: The data showed that AlPO₄ forms large particles at the early stages of mixing, followed by a decrease in size and then stabilization towards the later stages of mixing and pH adjustment. The results provided a complementary view of process events and assisted in optimizing several parameters, e.g., flow rate of reactants AlCl₃ and Na₃PO₄ solutions, mixing rate, pH, and conductivity of AlPO₄, as well as adjuvant quality attribute such as particle size, thus streamlining and shortening the process development stage.

Conclusion: The results of this study showed the usefulness of the in-line probes to automate continuous assessment of AlPO₄ batch-to-batch consistency during in-house adjuvant production at the industrial scale.

Keywords: aluminum phosphate adjuvant (AlPO4); automated unit of operation; conductivity; focused beam reflectance measurement (FBRM); infrared sensor; particle size distribution (PSD); process analytical technology (PAT); turbidity.