The effect of internal droplet crystallisation on the drying process of Alpha Olefin Sulfonate

Aims:

The research aims to establish correlations between surfactant phase behaviour (AOS) and the solid-state structure of the dried droplet, with the latter strongly influencing product performance. New insights regarding structure-performance relationships will be determined that enable the controlled design of spray dried products.

Project objectives include:

Develop methods to study single droplet and multiple droplets drying with the purpose of demonstrating consistency at different processing scales.

Determine the relationship between the components of alpha olefin sulphonate and the drying process.

Demonstrate use of the single droplet drying method to determine the surfactant phase evolution during droplet drying.

Develop correlations that enable the predictability of spray drying performance at scale.

Methodology Proposed:

Droplet drying: Two methods of drying will be considered: i) single droplet drying using levitating/filament droplet apparatus and ii) lab-scale (L) spray drying column. These methods will be used to determine the role of process parameters (temperature, air flow rate, drop size, surfactant concentration) on the resultant structure of the dried surfactant droplet. The single droplet apparatus will enable structure characterization during drying, with the end-state correlated to that observed in the spray drying column. Principal component analysis will be undertaken to determine the overriding factors that are influencing the drying process.

Surfactant chemistry: The phase behaviour and relationship of isomers, impurities and additional components will be investigated and their role within the system analysed to deepen understanding of the chemistry. The relationship between solid-state structure, particle morphology and performance will be correlated.

Materials characterization: SAXS will be used to study surfactant structure during droplet drying as the material crystallizes to form the solid-state structure. Surfactant phases will be further interrogated using cross-polarized microscopy, and the liquid and solid phases studied using SEM, particle size analysis, rheology and dissolution testing.

Model development: Working within the parameter space, empirical/theoretical models will be developed to enable the prediction of the spray drying performance at scale, linking the physicochemical and process parameters to achieve the desired solid-state structure for optimal product performance.

Potential Impact of Proposed Project (up to 200 Words)

Provide detail regarding significance of the proposed project in terms of its potential for either industrial and/or economic/societal impact

While many materials are spray dried, little is known about the phase transitions that occur when surfactant-laden droplets are dried to form the final product. It is hypothesized that those phase transitions are sensitive to the physicochemical properties of the system, and through greater insight, better control on the drying process and the final solid-state structure can be achieved. Currently only the input and output properties are measured, but with knowledge of the structural phase changes, system parameters can be tuned to deliver optimal product performance, ensuring product consistency, reducing waste, and eliminating the need for substantial trial-and-error activities to begin spray drying projects.

Expected Deliverables:

A better understanding of surfactant phase structure on drying kinetics and resultant solid-state structure.

A method to follow from single drop to spray dried that is repeatable for other surfactants.

A new mechanistic model, which would act as a predictive tool for large-scale spray drying operations.

The CDT in Molecules to Product has the potential to make a real impact as a consequence of the transformative nature of the underpinning 'design and supply' paradigm. Through the exploitation of the generated scientific knowledge, a new approach to the product development lifecycle will be developed. This know-how will impact significantly on productivity, consistency and performance within the speciality chemicals, home and personal care (HPC), fast moving consumer goods (FMCG), food and beverage, and pharma/biopharma sectors.
UK manufacturing is facing a major challenge from competitor countries such as China that are not constrained by fixed manufacturing assets, consequently they can make products more efficiently and at significantly lower operational costs. For example, the biggest competition for some well recognised 'high-end' brands is from 'own-brand' products (simple formulations that are significantly cheaper). For UK companies to compete in the global market, there is a real need to differentiate themselves from the low-cost competition, hence the need for uncopiable or IP protected, enhanced product performance, higher productivity and greater consistency. The CDT is well placed to contribute to addressing this shift in focus though its research activities, with the PGR students serving as ambassadors for this change. The CDT will thus contribute to the sustainability of UK manufacturing and economic prosperity.
The route to ensuring industry will benefit from the 'paradigm' is through the PGR students who will be highly employable as a result of their unique skills-set. This is a result of the CDT research and training programme addressing a major gap identified by industry during the co-creation of the CDT. Resulting absorptive capacity is thus significant. In addition to their core skills, the PGR students will learn new ones enabling them to work across disciplinary boundaries with a detailed understanding of the chemicals-continuum. Importantly, they will also be trained in innovation and enterprise enabling them to challenge the current status quo of 'development and manufacture' and become future leaders.
The outputs of the research projects will be collated into a structured database. This will significantly increase the impact and reach of the research, as well as ensuring the CDT outputs have a long-term transformative effect. Through this route, the industrial partners will benefit from the knowledge generated from across the totality of the product development lifecycle. The database will additionally provide the foundations from which 'benchmark processes' are tackled demonstrating the benefits of the new approach to transitioning from molecules to product.
The impact of the CDT training will be significantly wider than the CDT itself. By offering modules as Continuing Professional Development courses to industry, current employees in chemical-related sectors will have the opportunity to up-skill in new and emerging areas. The modules will also be made available to other CDTs, will serve as part of company graduate programmes and contribute to further learning opportunities for those seeking professional accreditation as Chartered Chemical Engineers.
The CDT, through public engagement activities, will serve as a platform to raise awareness of the scientific and technical challenges that underpin many of the items they rely on in daily life. For example, fast moving consumer goods including laundry products, toiletries, greener herbicides, over-the-counter drugs and processed foods. Activities will include public debates and local and national STEM events. All events will have two-way engagement to encourage the general public to think what the research could mean for them. Additionally these activities will provide the opportunity to dispel the myths around STEM in terms of career opportunities and to promote it as an activity to be embraced by all thereby contributing to the ED&I agenda.