(83ah) Universal Micro-Reactors Made of Glass for Applications to Study the Reaction Kinetics

the reaction kinetics

Thomas Frank, Little Things Factory GmbH, 98693 Ilmenau/ Germany

Di Zhi, University of Technology Ilmenau/ Germany

Introduction

Micro-reactors for the chemical reactions in general have a volume of a few milliliters. The dwell correspond to the reaction time. In conventional terms the reaction time is for a variety of compounds in the area of fractions of a second to a few minutes. Although the reaction times in the second area are very suitable for micro-reactors, essentially bring us prolonged problems. Because of the long dwell , at acceptable flow rates, the micro-reactors must be refined with an extremly large innervolume. In order to avoid this, we should to try to accelerate the reaction speed. The following three variables affect the response rate particularly strong.

Concentration: The higher the concentration of the reactant, the more likely it is that particles mix with the appropriate energy.

Temperature: The higher the temperature, the more particles just require the minimum energy or more.

Surface: The larger the surface, the greater the reactive surface is mixing.

Process intensification in glass micro-reaktors

By the use of micro-reactors these variables can be moved to the direction of higher response rate, particularly well succeed in this highly exothermetic reactions. However, many endothermic reactions at extreme reaction conditions are still to be investigated. Especially for the study of reaction kinetics of micro-reactors were developed, what permit the reaction temeratures up to 1000°C and pressures up to 200 bar. The micro-reactors consist of fusion bonded borosilicate glass( maximum operating temperature 450°C) or quartz glass( operating temperature 1000°C). The structures are produced by micro-abrasive compressed air rays, Figure 1 shows a SEM micrograph of a jet structure, as they are used for a micro mixer. Ports and temperature control prepare the largest problems at the extreme process conditions. When teflon tubing used align themselves with high temperatures and pressures, there are still problems at 1000°C even clamping ring joints made up of stainless steel(eg. WNr. 1.4571) in combination with metal pipes. The task can be resolved by micro-reactors with a cold(up to 200°C)  and a hot(450 °C - 1000°C)  zone. It is possible to implement hot and cold zones, conditionally due to the low heat conductivity of glass, l_Glas » 1,2-1,5 1,2 W(mK)^?1. Additionally, the reaction can be intensified by microwave for metalfree. The reactor can be also operated in a Ultrasound cleaning bath. This has been particularly proved its worth, which the particle afflicted reactions are as a measure to antifouling.

Due to continuous record of mechanical energy the particles have no time to agglomerating.

The figure 2 shows two micro-reactors made up of borosilicate glass.

The figure 2 at top display us a reactor with integrated tempering and the thermostat is directly connected. Through the four outputs the samples can to be taken according to various dwell so as the turnover to assess. In particularly low or high temperatures the direct temperature will be affected. The  reactor will be tempered direct in a bath or on a hot plate. Only the reaction field is heated, the ports remain largely cold due to the low heat conductivity in the glass and the optional cooling. The distance between the ports and the warm reaction field is chosen  in such a way that feed line and sealing material thermally not overloaded.