Chip-based reactors

GP 1] [R 10] Conversion rates over platinum catalyst were determined in a chip-based reactor [56]. In the temperature range from 180 to 310 °C rates from 0 to... 

Microreactors belong to the family of sfructured reactors as well (Figure 6). Current microfabrication techniques allow fabrication of small structured catalytic reactors (8). The versatile fabrication possibilities for chip-based reactors have led to the simultaneous development of sfructured and unstructured reactors (9,10), but in the final analysis, the structured version was usually favored. 

A silicon-chip-based reactor was applied for the Fischer-Tropsch synthesis using an iron catalyst [77]. The chips had outer dimensions of 1 X3cm with channel dimensions of 5 or 100 pm width at 50-100 pm depth. The reaction was carried out at a H2/CO ratio of 3, and flow rates of 0.4 std. cm min between 200 and 250 °C. Conversions between 50 and 70% were found after 12 h activation of the catalyst under reaction conditions. 

To fulfill such requirements, attempts have been made in the past decade by researchers working on peptide mapping and proteomics through development of immobilized microfluidic enzymatic reactors. Microfluidic enzymatic microreactors are an alternative to in-solution method employing immobilization of proteases on microchaimels of chip-based reactors or surfaces of capillaries. The microreactors that enable proteolytic digestion by enzymes immobilized on solid supports are also referred to as immobilized enzyme reactors, IMERs. The great potential of IMERS for proteomic applications comprise rapid and enhance... 

Biocatalytic reactions performed using immobilized enzyme microreactors under continuous flow mode have been found effective for hydrolysis reactions [121,158-161], with the enzyme either trapped in the matrix [159], covalently linked to modified surface wall [160,121], enzymes entrapped in hydrogels [162], or enzymes immobilized on monolith [179]. The experimental setup consists of either chip-type microreactors with activated chaimel walls where enzymes bind, enzymes that bind to beads, enzymes entrapped in the matrix, enzymes adsorbed in nanoporous materials, and most recently, nanosprings as supports for immobilized enzymes in chip-based reactors, or enzyme immobilized monolith reactors, where support is packed inside a capillary tube (Table 10.4). 

Micro Total Analysis Systems (pTAS) are chip-based micro-channel systems that serve for complete analytics. The word Total refers to the monolithic system character of the devices, integrating a multitude of miniature functional elements with minimal dead volumes. The main fields of application are related to biology, pharmacology, and analytical chemistry. Detailed applications of pTAS systems are given in Section 1.9.8. Recently, pTAS developments have strongly influenced the performance of organic syntheses by micro flow (see, e.g., [29]). By this, an overlap with the micro-reactor world was made, which probably will increase more and more. 

Miniaturizing a conventional-flow screening system (macro-scale system) to a chip-based system comprises a number of changes, such as flow rates, reagent supply, and the material. While the conventional system with the open tubular reactors is restricted to polymer reactors, the choice of materials for the chip is... 

Without being itself a screening device, the reactor of Jensen et al. [6, 42, 43] also has to be mentioned because they opened up a completely new field in catalysis by combining MEMS (micro-electro-mechanical systems) technology with a chip-based catalytic reactor (Fig. 4.10). A mixing-tee was equipped with heaters and temperature and flow sensors, thus giving on-stream information about the reaction conditions. 

A chip-based integrated precolumn microreactor with 1 nl reaction volume has been explored by Jacobson et al. [67]. The reactor is operated in a continuous manner by electrokinetically mixing of sample (amino acids) and reagent (o-phthaldialdehyde) streams. The reaction time is adjusted via the respective flow velocities. By switching of potentials, small plugs of the reaction product were injected into a 15.4 mm separation channel in a gated injection scheme (< 1.8% RSD in peak area). The separation efficiency achieved was relatively poor, however, electrokinetic control of reaction time (and yield) permitted to monitor the kinetics of the derivatization under pseudo first-order conditions. A similar integrated precolumn reactor operated in a stopped flow mode has been described by Harrison et al. [68]. 

This simple reactor concept is based on a microstructured silicon chip (Figure 3.18) covered by a Pyrex-glass plate by anodic bonding [73, 74]. The silicon microstructure comprises, in addition to inlet and outlet structures, a multi-channel array. Only the Pyrex-glass plate acts as cover and inlet and outlet streams interface the silicon chip from the rear. 

The design of the Pd-membrane reactor was based on the chip design of reactor [R 10]. The membrane is a composite of three layers, silicon nitride, silicon oxide and palladium. The first two layers are perforated and function as structural support for the latter. They serve also for electrical insulation of the Pd film from the integrated temperature-sensing and heater element. The latter is needed to set the temperature as one parameter that determines the hydrogen flow. 

GP 11] [R 19] No qualitative differences between the reaction performance of a wire-based silicon-chip and a quartz-shell micro reactor were observed [9]. 

The silicon chip reactor was compressed between a top plate, for direct observation of the flows, gaskets with punched holes and a base plate with all fluid connections [13,14]. Thermocouples inserted between the two plates were located next to the micro reactor. A third inlet served for reaction quenching by introducing an inert gas such as nitrogen. Generally, heat removal is facilitated by the special reactor arrangement acting as a heat sink. 

Reactor type Dual-channel micro reactor Base plate material of interfacing chip housing Silicon stainless steel... 

We have demonstrated the feasibility of miniaturized MS assays by converting the cathepsin B assay described in Section 5.2.2 to a chip format, using the same substrate and products for the MS-based readout [27]. The assay set-up is identical to the format described in Fig. 5.1. The advantages of chips as micro reactors over fused silica capillaries are in their compactness, strength, greater degrees of freedom in design and material, and the presence of hair-pin curves to increase the diffusion rate. 

So far, only a few reports have been dedicated solely to this topic. The available ones most often were developed for chip devices based on control concepts known from micro electronics. Although the concepts are probably not directly transferable to micro structured reactors of larger size, they may nonetheless serve as describing generic paths for how to approach the problem. 

---