Introduction
Historically, mini-plants have utilized oil-sealed rotary vane vacuum pumps as a vacuum source because they provide relatively high flow rates and because they can reach relatively deep vacuum levels, such as 10-3 mbar. The same can be said of kilo labs. However, rotary vane pumps also include several critical disadvantages which make their use in pilot plants and kilo labs suboptimal. Most notably, these disadvantages include significant maintenance requirements in terms of both time and material costs. By switching from an oil pump to an oil-free technology such as a diaphragm pump, there are significant benefits to be realized. These benefits include better process control, chemical resistant wetted materials, and significantly reduced maintenance.
DSM Nutritional Products has worked with VACUUBRAND GMBH to realize these benefits in its miniplant technical center in Sisseln, Switzerland. DSM Nutritional Products converts pure ingredients into formulations suitable for commercial use as additives in food (ice cream, beverages), pharmaceutical products (tablets, capsules), feed (cube, premixes), and cosmetics. It falls to researchers in DSM’s Kaiseraugst, Switzerland facility to develop methodologies which ensure that the product has the necessary bioavailability, stability, and solubility characteristics. The team in Sisseln, Switzerland is then responsible for scaling this process from research-scale to pilot-scale while simultaneously optimizing the process.
DSM operates “mini-plants” to optimize process parameters. (Similar facilities may be called “pilot plants”or “kilo labs”in other parts of the world.) Plants of this scale may also be used to produce small quantities of product, though DSM does not use its Sisseln mini-plant technical center in this way. Instead, the technical team in Sisseln operates a pilot plant (what may be called a micro plant in other parts of the world), in parallel with its mini-plant facilities, to supply product for application testing and further R&D work. In order to optimize processes to meet quality and efficacy standards, DSM makes use of the latest production technologies in their mini-plant facilities. Consequently, DSM has updated their vacuum supply in recent years. In this case, DSM’s goal was to replace oil-sealed rotary vane pumps with an oil-free alternative in its mini-plant operations where technically feasible.
DSM’s Initial Analysis
The technicians at DSM worked with counterparts at VACUUBRAND to analyze if it would be feasible for DSM to convert to VACUUBRAND’s line of chemical-resistant diaphragm pumps. DSM’s teams identified two critical factors for this project:
• The operating vacuum for most applications is in the range of 1 mbar – 500 mbar. Diaphragm pumps are well suited to providing vacuum in this range, often referred to as the “rough vacuum range.” Certain high vacuum processes like short path distillation require the deeper vacuum provided by rotary vane pumps.
• Once the mini-plant set-up has been evacuated down to the operating vacuum level, the expected pumping speed (i.e., flow) is expected to be minimal. Because most of the process vapors condense before reaching the pump, the pumping speed requirement is driven by residual process vapors and system leaks.
Both observations favored a switch from rotary vane pumps to oil-free diaphragm pumps. Since the operating vacuum level is within the capabilities of a diaphragm pump, it was clearly possible to use a diaphragm pump to meet the operating vacuum specifications. On the other hand, the initial system leakage was found to be substantial enough that oversized (rotary vane) pumps were needed. DSM’s analysis of the pumping speed requirements showed that by reducing system leaks, the necessary flow capacity of the pump would also be well within the rated pumping speeds of diaphragm pump technology. A diaphragm vacuum pump, with its low maintenance requirement and chemical-resistant construction, could be used.