From a commercial standpoint, flow chemistry is the preferred method over batch chemistry. These systems require less space, make better use of raw materials and produce a much higher volume of consistent products. Continuous flow systems are cost-effective and becoming increasingly popular in the manufacture of pharmaceuticals, creating faster reactions with better yields.
Granted there is more complexity in setting up a continuous system as compared to batch but once that work is done, the payback is substantial. For continuous flow systems, that would mean having the pumps set up correctly and calibrated, valving is correct and the automated system’s logic has been pre-approved. However, if one is dosing a batch system with a totalizer then the steps are almost the same in terms of set up. Pumping is only an issue if materials of construction are not correct or solids are generated in situ. (However, both of these are known quantities prior to commercialization and should not influence the process.)
One major item to be considered in comparing batch vs continuous flow is that the surface area to volume ratio of batch is an order of magnitude LESS than continuous. What this means is that the temperature difference between the heating or cooling fluid is much LESS for a continuous system vs batch. If the heat, Q, for both is the same then and increase in Area, A, means that ΔT (delta T) can decrease. That is because:
Q = U x A x ΔT where Q = Heat removal in BTU/Hr or Kcal A = Surface Area in square feet or square meters U = Heat transfer coefficient in BTU/square feet-Hr-oF or Kcal/square meter-Hr-oC ΔT = oF or oC Also, for the engineers, the heat transfer coefficient, U, will be greater in a continuous system than a stirred tank, further lowering the ΔT in a continuous system.
Thus, any byproduct formation that could occur in a heated system in batch due to the larger temperature gradient at the wall is almost eliminated. (Engineers refer to this occurring in the film attached to the reactor wall). Also, for cooling operations, the coolant is at a much HIGHER temperature for continuous ones because the system does not have to compensate for the smaller heat transfer area characteristic of batch systems in order to get the heat out. Many batch systems have very low temperature cooling (-20oC or lower) requirements and that is because they have to get the heat out and need the higher temperature driving force.
Thus, the long term benefits of continuous flow systems far outweigh batch systems where economics, quality and safety are the primary drivers for consideration as opposed to the known comfort of batch ones.
Sentinel has over 30 years of experience developing custom chemistry systems for the pharmaceutical industry. We engineer flow chemistry processes and reactors designed to improve your bottom line, with automated production methods to ensure the mixtures produced are consistent and safe for the end-user. If you would like to know more about our products and how we can design a system that is suited to your needs, send us a request for more information or call our team today.
As a distributor and fabricator of high-purity equipment, Sentinel Process Systems helps solve a variety of process challenges facing the high-purity manufacturing industry. With a large portfolio of partners and a high level of industry expertise, we help our customers overcome process difficulties and optimize operations quickly and conveniently.