The effect of cake filtration behaviour and washing on the cake microstructure

Cake filtration is a popular solid-liquid separation unit operation in many manufacturing processes utilized by the catalyst, mining, wastewater treatment, oil exploration, petroleum, dye and pigment, pharmaceutical and food industries. In this kind of filtration, gravity, pressure or vacuum driven flow of the particulate solid suspension through a permeable medium causes the separation of the solids from the filtrate which passes through the medium. A filter cake formed from the solid particles builds up over time on the filter medium. Although cake filtration is an established process, it is still largely empirical as it is difficult to predict the actual rate of filter cake formation and the required pressure drop or flow rate and their evolution over time. In this study, filtration experiments were conducted by using a benchtop Nutsche filter device and slurries containing nonporous glass beads or porous catalyst materials (Fine Catapal A, Fine Alumina and Zeolite Y). The objective of this thesis is to identify key material properties and operating conditions influencing cake filtration behavior and to relate these parameters to observed trends in filtration behavior. Unlike other studies on cake filtration, the research mapped the filter cake microstructure, specifically, the variation in particle size distribution and bulk density at different axial locations along the filter cake. Moreover, the filtration of porous catalyst materials has received limited attention in the literature yet is highly industrially relevant. Specific aims include: (i) Relating primary properties of particles to filtration behavior and filter cake properties, for model nonporous and porous catalyst materials; (ii) Examining the influence of operating conditions on filtration behavior; (iii) Investigating the effect of washing on filter cake microstructure and cake resistance.Results show that conventional models such as the Carman-Kozeny equation and the Ergun equation give reasonable correlations of the cake permeability with void fraction for nonporous glass beads and for most porous catalyst materials if the internal particle porosity is neglected. Fine Alumina exhibited contrasting behavior to the other materials, where high void fraction was accompanied by low permeability. The ratio of air to water permeability decreased with particle diameter, which is consistent with previous work in the literature. Operating conditions such as an added waiting time, the slurry pH, the mixture of two particle sizes, and material batch variability also influenced the resulting cake permeability and filtration time. Unique observations of changes in the cake microstructure during recycling of the filtrate and cake washing were presented, for 1-20 micron diameter glass beads, a model nonporous material. The fraction of fine particles was found to be more similar among layers after recycling and washing than before recycling. In general, the middle layers of the cake have the highest bulk density and the cake is more uniform in density after recycling and washing. The effectiveness of washing was evaluated for Zeolite Y and showed agreement with existing models. Moreover, nano-CT images of 1-20 micron diameter glass bead filter cakes of regular filtration runs show the details of porosity and voids of the filter cakes. The results of this investigation provide new fundamental insights into the cake filtration process. Acknowledgements First, I would like to express my deepest appreciation and gratitude to my advisor, Prof. Nina C Shapley, for her great support, encouragement, and patience through the last years. I would also like to extend my sincere thanks to my defense committee members for their time and efforts. I am deeply grateful to Prof. Benjamin J. Glasser, Dr.William G. Borghard and Dr. Thomas English, for their valuable suggestions and support to this project. I must also thank my group members for their help during the project period: Dr. Kristin G. Steeley, Tulsi Char and Alex Lubarsky. I would like to thank David Mest for his help in doing some experiments at Evonik. Also, Special thanks to the members of the Chemical and Biochemical Engineering at Rutgers who helped me in finishing my degree. I especially would like to thank my husband, my children and my other family members at my home country for their continued support. Finally, special thanks to the soul of the one who is really made me reach this point in my life, my father.Ph.D.Includes bibliographical reference