by Joe Bonem
Essentially all research and/or development work is done with the goal to eventually commercialize the product or process so that it may:
• Create increased profits or turn a money losing venture into one that makes a profit.
• Create a new chemical or modification of an existing chemical that can increase company profitability.
• Create a pharmaceutical drug which can extend life, cure diseases or make life more comfortable.
Regardless of a successful laboratory product or process demonstration, there will almost always be a step to expand the production from laboratory size quantities to commercial sized quantities. This step is referred to as ‘scaleup’. There may be multiple scaleups involved in going from laboratory sized production and/or process to a fully commercial venture.
The term scaleup is well known in the chemical/refining, food and pharmaceutical industries. However it has multiple meanings such as:
• Scaling up from bench scale equipment to a pilot plant.
• Scaling up from bench scale equipment to commercial size equipment.
• Scaling up from pilot plant equipment to commercial size equipment.
• Scaling up from a small commercial sized plant to a large commercial plant.
• Scaling up a single piece of equipment such as an indirect heated dryer or extruder.
• Scaling up from bench scale studies to use a new catalyst and/or new additive in either a pilot plant or commercial plant.
Each of these scaleup steps requires an outlay of money and also involves some risk. When considering scaleup to commercial plants the outlay of money can be significant. In addition, the building of a commercial plant often involves a commitment to supplying product to a customer at a specific time. Thus the importance of the scaleup becomes obvious.
When considering the current chemical engineering academic environment and the wide diversity of chemical engineering employment opportunities, the areas of process development and process scaleup are often overlooked. This often leaves the chemical engineer assigned to develop a new process struggling with how to proceed. Given the importance of scaleup, the risks of an improper scaleup can be classified into the following categories:
• Type of equipment –The type of equipment used in a commercial plant will likely be significantly different from that used in a bench scale experiment. For example, a chemist at a major producer of polypropylene used a coke bottle to polymerise propylene. Another example might be the use of bench scale ovens to simulate additive stability versus the use of high shear commercial processing equipment.
• Size of equipment – Determining the equipment size often involves a change in type of equipment. For example, bench scale polymerisations are often conducted in a batch process where each catalyst particle has the same amount of residence time. In a commercial design, it is almost always desirable to have a continuous flow reactor. In this case each catalyst particle has a different residence time. This factor by itself will increase the residence time requirements in the commercial plant relative to the bench scale.
• Thermal characteristics – While the basic thermodynamics don’t change as the process is scaled up, the change in equipment dimensions may change characteristics such as A/V ratio, heat transfer coefficient or fouling of heat transfer surfaces. In addition, if the degree of reaction is increased, the amount of heat that must be removed will also increase. Often in bench scale operations, there is no apparent heat of reaction. However, 85 to 90 % of reactions have a significant heat of reaction and most of these reactions are exothermic.
• Safety – As processes are scaled up, the amount of explosive material increases in proportion to the volume of the vessels being utilised. This can impact the safety of the commercial process in at least four ways:
1. The size of a vapour cloud formed if a vessel leak occurs will be larger and the probability of finding an ignition source will increase.
2. The probability of an unconfined vapour cloud explosion increases as the amount of material increases when going from pilot plant size to commercial size.
3. The probability of a temperature ‘run away’ in a reactor increases as the A/V ratio decreases.
4. If the material in the vessels is toxic, there is a greater toxicity risk.
• Recycle -- Essentially all bench scale and many pilot plant designs do not have capability to recycle. Thus these processes do not have the capability to determine the impact of impurities or inerts that might buildup in a commercial sized plant with recycle capabilities. If recycle facilities are not provided in the bench scale or pilot plant, they can be simulated with computer algorithms. However, it will often be necessary to make an assessment regarding what inerts, impurities or reaction by products might be present in the recycle streams.
• CAPEX and OPEX – To confirm that a research project is really of value, economics must be considered. The economics can be developed from the Capital Investment (CAPEX) and the Operating Cost (OPEX). The development of these economics will avoid the risk of going ahead with a research project that will not be financially attractive. While it can be argued that this step cannot be taken until the basic research is finished, if one uses a minimal amount of bench scale data and first principles of engineering, values of CAPEX and OPEX can be determined with sufficient accuracy to make a decision about proceeding with the research.
In summary, scaleup involves both a preliminary assessment of the CAPEX and OPEX based on a limited amount of bench scale data and a careful assessment of the various unit operations involved. These assessments can often be done by use of bench scale data and first principles of engineering. A forthcoming book will present more details on this subject.