Process Engineering for Scale-Up of Specialty Chemicals

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Scale-up of specialty chemicals encompasses various design methods through which a small lab process (typically at a gram scale) is enlarged to a large-scale process. The main objectives of scale-up activity at the Xerox Research Centre of Canada (XRCC) are: i) preparation of large quantities (typically 1000x lab scale) of materials having the same or similar chemical and physical properties of the material made at the small scale, and ii) delivery of a manufacturing-ready process. A reduction in unit manufacturing cost and improved quality are usually required and achieved on scale-up. Potential environmental and safety issues are adequately addressed at the engineering bench, before the process is scaled-up to the Pilot Plant. Process engineering plays a vital role in assuring an economical, robust, safe and environmentally friendly process for scale-up to manufacturing.

Scale-down before you scale-up

Our scale-up philosophy can be summarized as: “scale-down before scale-up” where the “scale-down” refers to scale-down of a manufacturing scale concept (Figure 1). This method assures that a newly engineered process is a scale-down replica of a manufacturing scale rather than a simple enlargement of a lab scale. Our process engineers are involved with every aspect of a new process scale-up, from preliminary project scoping, costing and commercial material sourcing, all the way to authoring a Standard Operating Procedure (SOP), a document describing in sufficient detail how a new process is to be run in the Pilot Plant.

We currently have a database with over 200 SOP's describing a variety of specialty chemical processes for preparation of: i) electronic-grade small molecules, ii) specialty electronic-grade polymers, and iii) custom composite materials. Some notable examples of specialty small molecule processes successfully commercialized include charge-transport molecules for xerography, as well as custom-made pigments and dyes for imaging applications. Examples of commercialized polymers include toner and carrier resins made either by suspension, emulsion, or polycondensation polymerization. An excellent example of a custom composite material scale-up is a chemical toner process (also known as emulsion/aggregation or EA toner process), pioneered at XRCC about 15 years ago and now widely adopted as the industry benchmark.

XRCC process engineers are involved with every aspect of a new process scale-up, from preliminary project scoping, costing and commercial material sourcing, all the way to authoring a Standard Operating Procedure (SOP), a document describing in sufficient detail how a new process is to be run in XRCC Pilot Plant. XRCC currently has a database with over 200 SOPs describing a variety of specialty chemical processes for preparation of: i) electronic-grade small molecules, ii) specialty electronic-grade polymers, and iii) custom composite materials. Some notable examples of specialty small molecule processes successfully commercialized include charge-transport molecules for xerography, as well as custom-made pigments and dyes for imaging applications. Examples of commercialized polymers include toner and carrier resins made either by suspension, emulsion, or polycondensation polymerization. An excellent example of a custom composite material scale-up is a chemical toner process (also known as emulsion/aggregation or EA toner process), pioneered at XRCC about 15 years ago and now widely adopted as the industry benchmark.

When speaking about a new process scale-up we can distinguish the following two scenarios:

Scale-up of straightforward reactions: Scale-up of some specialty chemical processes can directly benefit from using one of the 28 reactor systems in the Pilot Plant, ranging from 1 gal to 500 gal in scale as shown in Figure 2. In the case of a straight forward reaction (for eg. a reaction with a good yield, selectivity and throughput) a bench-scale sensitivity analysis followed by a pilot plant evaluation is usually sufficient to demonstrate feasibility of successful scale-up to manufacturing scale. An example is a scale-up of emulsion polymerization reaction for a custom latex synthesis.

Scale-up of complicated reactions: Scale-up of many reactions is not straight forward and variations in reaction rates and selectivity are observed as a function of operating scale. This is usually due to one of the following three reasons [1]: i)heat-transfer limitations, ii) mass transfer limitations, and iii) sensitivity to time of addition of a reactant and/or removal of a product in a semi-batch process. The way we approach scale-up of such, more complicated reactions, is by using modeling, design of experiments, and process optimization. All of our process engineers are Lean Six Sigma (LSS)trained and, as such, familiar with the design of experiments (DOE) approach to building semi-empirical models for scale-up at the engineering bench. In addition, we also have a Computational Fluid Dynamics (CFD) modeling capability that is used for visualization, exploration and optimization of more complex mixing designs. An example of CFD modeling employed for a continuous process engineering is shown in Figure 3. In addition, our Machine Shop is capable of designing and manufacturing mini-plant demonstration units “on a skid” such as the one shown in Figure 4.

One uniqueness of our process engineering is close interaction between chemists and chemical engineers during bench-scale process optimization and new process piloting in XRCC’s state-of-the-art Pilot Plant (26,000 ft2/2,400 m2). This allows process engineers rapid access to new reaction chemistries for new material designs or as a replacement for old and obsolete designs. A recent example is reengineering of a vintage Ullmann coupling reaction (using 0.8% w/w of Cu-based catalyst) to employ a modern Suzuki coupling reaction mechanism with a 0.02% w/w of Pd-based catalyst which resulted in productivity improvement and waste reduction for production of an electronic-grade small molecule.

Having a well-equipped and well trained Analytical Services and Characterization area as part of the Scale-up Engineering lab is crucial for rapid new QC method development and validation. Our analytical and material characterization capabilities include: HPLC, GPC, APC, DSC, TGA, HS-GC, C/H/N/S elemental analysis, ICP, NMR, TEM, SEM, in addition to various particle size and rheology measurements instruments and methods.

References

E. L. Paul, Design of Reaction Systems for Specialty Organic Chemicals, Chem. Eng. Sci., vol 43, No 8, pp.1773-1782, 1988.

Author: Marko Saban, P. Eng, Director, Engineering, Xerox Research Centre of Canada

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