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Title: Towards understanding fouling mechanisms in continuous crystallisation processes
Author: Mabbott, Fraser Adam
ISNI:       0000 0004 6422 6201
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2017
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Fouling involves the unwanted deposition and build-up of solid material on surfaces within a process. This problem is widely encountered in multiphase and solid phase processing in many industries including oil and gas, pharmaceutical and fine chemical manufacturing sectors. Although it is acknowledged to impact both batch and continuous processing methods it poses a particular challenge to the controlled operation of continuous crystallisation processes where extended operation under non-equilibrium conditions is required. Whilst the factors impacting on fouling have been proposed, there have been only a relatively limited number of studies into fouling mechanisms to date. With increased interest in deploying continuous crystallisation processes for pharmaceutical manufacturing, the motivation for this work was to develop an improved understanding of the influence of material properties and process conditions on fouling processes. In this work, a number of studies were conducted in which key materials and process parameters were investigated. These have included different materials of construction (MOCs), process conditions (flow, supersaturation, temperature gradients (ΔT)) and crystallising solutions (solute and solvent). Primary fouling studies were conducted using a small scale batch crystallisation setup to explore the influence on MOCs, supersaturation and agitation rate upon both bulk crystal nucleation and surface fouling of paracetamol. The prominent fouling mechanism was found to be particle deposition which was influenced by supersaturation, agitation rate, different MOCs and exposure time. Fouling is known to occur on heat exchange interfaces due to the localised supersaturation that can be generated e.g. in a plug flow continuous cooling crystalliser. A novel surface induced continuous crystallisation fouling assessment platform (C-FAP) was developed in conjunction with Cambridge Reactor Design (CRD). The C-FAP was evaluated as an assessment tool by exploring different MOCs and process conditions upon fouling and fouling mechanisms via in situ imaging and temperature measurement. The platform was characterised and used to explore surface induction mechanisms in which initiation and growth was strongly influenced by different MOCs, with stainless steel showing a greater tendency than PTFE, in addition to the degree of supersaturation. The temperature difference across the MOC interface (ΔTMOC) was demonstrated to influence nucleation and growth to varying extents. An ideal scenario would be to be able to predict or rule out unfavourable combinations of solute, solvent and MOC properties early in process design to avoid late stage problems. A screen was carried out to assess the potential to develop a multivariate predictive model for fouling propensity and fouling behaviour. The models provide insight into the most influential parameters comprising MOC, solute, solvent and process descriptors to steer subsequent experiments. The importance of MOC properties and process conditions was highlighted for all models. A variety of assessment tools were demonstrated within this work in which recommendations for fouling evaluation were provided in addition to methods to further develop fouling understanding.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral