(241f) Development of Microstructured Reactors and a Following Continuous Work-up System for Liquid/liquid Reactions for Use in Polycondensation

In the German public funded BMBF project POKOMI (Förderkennzeichen 16SV1981) the synthesis of OLED materials by the Suzuki-Polycondensation using microreactor technology is investigated. Within the scope of this project IMM focus on one hand on the development, realization, characterization and application of suited microstructured reactors for biphasic liquid/liquid reactions and on the other hand also on the establishment of a pilot scaled (2-3 L/h) following continuous work-up system.

The Suzuki reactions are conventionally carried out in a liquid-liquid biphasic solvent system as a batch process. In the scope the POKOMI project a continuous process was established.

In order to ensure mass transfer in biphasic reactions a sufficient interfacial area is required. In the considered case the two phase system is not stable and therefore coalescence comes into play. In order to overcome this issue two different reactor concepts were developed. The first concept based on the repeated breakage of the droplets. The so called redispersion microractor [1] consists of exchangeable redispersion units which are separated by multi-channels and an observation window which allows the investigation of the flow patterns. A ternary biphasic solvent consisting toluene, 1,4-dioxane and water has been used for the determination of the reactor performance. Thereby the specific interfacial area was estimated. Depending on the flow rate a specific interfacial area between 1000-1600 m2/m3 was formed.

As a second concept a metal foam filled tube reactor was developed. The metal foam is used as a form of static mixer. Due to the special combination of chemical, mechanical and physical properties metal foams are already used for a wide range of applications, for example heat exchangers [2]. The microstructure of the used open-cell metal foam provides a very high porosity (60-98 %) which leads to low pressure drop. As a test reaction the palladium catalyzed Suzuki cross coupling of phenylboronic acid and 4-bromotoulene was carried out. A conversion of 30% within 10 min was achieved. Based on these first findings, a metal foam filled tube reactor was developed as a kind of milli process technology counterpart of the laboratory microreactor. The metal foam is used as a form of static mixer. The microstructure of the used open-cell metal foam provides a very high porosity (60-98 %) which leads to low pressure drop. At a pressure between 7-14 bars, a TON of 424 and a TOF of 121 h-1 was achieved for the Suzuki coupling. Furthermore, the results of the polycondensation reaction performed in the tube reactor will be reported.

To come to a complete continuous process it was necessary to develop a continuous working work-up system following the microstructured reactor. The realized set-up consists of a phase separator to remove the aqueous phase and two wash steps including again phase separation. Phase separation thereby is realized by gravity driven mini-settlers with a volume of 246 mL for each settler. The developed washing unit is suited for total flow rates between 1.8 and 6 L/h. The testing of the mixer-settler system was so far restricted to practical issues regarding to the continous coupling of the single purification steps so that no negative interference establishes. It could be in particular proven that a stable and time-independent filling and discharging of the settler occurs without any flooding or draining effects. Also, the dynamic operation during system start-up has been investigated, especially concerning the filling of the siphon.

[1] Hessel, V., Rothstock, S., Agar, D.W., Jadhavrao, P., Löb, P., Werner, B., in: Conference proceedings, 2007, AIChE spring national meeting: April 22-27, 2007, Houston. ? New York: AIChE, 2007, 74d.

[2] Boomsma, K., Poulikakos, D., Zwick, F., Mechanics of Materials 35 (2003), 1161-1176.