Precision and accuracy in fluid and pressure control for parallel reactors
The key to success in small scale parallel reactor systems is to be able to test catalysts at exactly the same process conditions over multiple tests, and to translate these directly into commercial values. The two crucial ingredients for succeeding with that approach are both precision and accuracy. Interestingly, we often come across common misunderstandings or mix-ups of these two concepts. While accuracy is the closeness of a measured value to a known value, precision is the closeness of more measurements to each other as shown in the picture.
Translating these concepts into parallel testing systems, accuracy is provided by the total flow of a Massflow controller, while the precision is the equal distribution between the reactors to achieve a true parallel system. Since the early days of high-throughput parallel reactor systems, the flow distribution is based on the use of physical flow restrictors, e.g. narrow bore tubes (capillaries) In this way, a common feed flow can be distributed to parallel reactors. However, the use of capillaries poses its own challenges because it requires carefully chosen lengths for each capillary to ensure equal pressure drop so as to achieve a similar flow rate to each reactor channel. This can be cumbersome and implies a lot of manual labor work as each flow needs to be verified, preferably with the exact gas mixture.
Microfluidics – The easy way to precisely control your distribution
As is well known, in Flowrence, we make use of our proprietary high precision microfluidic flow distributor chips (see picture). Each microfluidic chip is tested in-house for a guaranteed flow distribution, with the precision between the channels guaranteed < 0.5%RSD.
The installation of a microfluidic distributor is a matter of minutes. Using the right pressure drop, the chip will give the user the best dynamic range and allows for great flexibility in types of feed and flow ranges. For further details on how to upgrade your current system with Microfluidics please contact us or read more in the Catalysis Insider July 2017 newsletter.
How to solve the issue of catalyst pressure drop influencing the feed distribution?
When long tests are to be executed, a common faced challenge is to guarantee the precision of the gas flow distribution over the duration of the test, when possible catalyst pressure drop effects or blockages in a reactor can occur over time. In traditional systems, the change in pressure drop over reactors will have a direct impact on the precision of the feed distribution as a higher reactor inlet pressure in one reactor will result in a decline in feed supply to that reactor, while other reactors will receive more flow. The resulting effects are even more pronounced at small scale testing. Such testing systems cannot compensate for this, which results in reduced testing precision.
Avantium has invented the individual Reactor Pressure Control – RPC – to overcome that problem. The RPC reactor pressure controller module allows accurate measurement and precise control of the individual reactor pressures to ensure an equal reactor inlet pressure between all reactors at all times as shown on the picture below. This is achieved by using the measured reactor inlet pressure and adjusting the control valve at the exit of each reactor to compensate for this with its patented technology (WO2014062055 and WO2014062056).
The benefit for the operator is twofold.
- If the pressure drop drifts during a test, the RPC can actively compensate for this to ensure an equal inlet pressure for each reactor, ensuring the continued precise functioning of the microfluidic gas distribution. This advantage is even greater in the case of low-pressure processes such as Oxidative Methane coupling or Reforming, because in such cases even small variations in reactor pressure can have a large impact on the yields of products.
- In addition, the RPC uniquely provides the user with a record of the pressure drop over each reactor at all times. This delivers important information about a potential plugging behavior.
Avantium’s microfluidics in combination with our RPC and Tinypressure are the tools to guarantee the most precise feed distribution in the industry. This allows our customers to distinguish even small catalysts activity differences, accurately and precisely required for the right decisions.