CHAPTER 15

STANDARDIZATION IN MICROPROCESS ENGINEERING

ALEXIS BAZZANELLA

15.1 INTRODUCTION

A large variety of components and equipment for microprocess engineering is nowadays offered by different manufacturers and suppliers all over the world. Although this clearly demonstrates the advances and evolution of this technology, it presents particular challenges and/or opportunities for both manufacturers and users. From a manufacturer’s perspective, a portfolio of different components (e.g., reactors, mixers, etc.) offers the possibility of designing and constructing standar- dized elements to be used in different components. The repeated use of such elements in different components increases the manufacturing lot of identical parts and is an effective means to reduce manufacturing costs. This is, in particular, relevant for toolboxes containing different components with identical footprint, connectors, and housing. In such cases, microstructured elements can be designed as inlays of an otherwise standardized housing, which can be produced in higher numbers. Figure 15.1 gives an example of this approach; several microprocess engineering toolboxes are commercially available.

From a user’s perspective, the availability of a wide variety of components holds the possibility of matching a selected piece of equipment to the physicochemical requirements of the intended chemical process. Parameters such as material selection, required mixing time, heat dissipation capability, residence time, pressure, tempera- ture, or viscosity can be defined or determined and provide a basis for selecting the most appropriate equipment for a given process step. Subsequently, for example, lab-scale plants for process development can be erected using appropriate equipment pieces for the different process steps. This scenario is usually supported by the commercially offered toolboxes and systems, which allow the more or less rapid

Microchemical Engineering in Practice. Edited by Thomas R. Dietrich Copyright 0 2009 John Wiley & Sons, Inc.

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350 STANDARDIZATION IN MICROPROCESS ENGINEERING

FIGURE 15.1 of the modular microreaction system (courtesy Ehrfeld Mikrotechnik BTS).

Standardized heat exchanger module with microstructured inlay; component

set-up of different modules to a complete system, including, for example, sensors, pumps and other actuators, and control instrumentation.

However, it is generally much more difficult or even prohibitive to couple components from different suppliers due to the lack of compatibility of components in terms of connectivity. This results from not only the large variety of used fluidic connectors (e.g., Swagelok, UNF threads, and HPLC fittings) but also different component geometries, sealing approaches, materials, and mechanical requirements. Although this problem can, in principal, be circumvented by using different fluid adapters and tubing, the resulting connectors have a rather large hold-up compared to the connected microstructured components, and the process of building the set-up is time-consuming and tedious.

Toolbox and system manufacturers have partly reacted to customers’ demands to couple components from other suppliers to their systems by providing “gateways” based on adapter modules or by specifically designed modules to adopt OEM equipment. However, these measures are far from a desirable generic and flexible approach to component connectivity.

Subsequently, first steps toward the vision of flexibly constructed microplants using different microstructured components irrespective of the origin are described. These are based on the MicroChemTec initiative in Germany.

15.2 THE MICROCHEMTEC STANDARDIZATION INITIATIVE

The strategic research project Modular Micro Chemical Engineering (MicroChemTec [ 11) was a standardization initiative funded by the German Ministry of Education and Research. This project, running from October 2001 to January 2005, aimed to establish a uniform standard and modular approach to microstructured process technology, thus providing a solution to the connectivity problem of different

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microstructured components. The project, conducted by research institutes with expertise in microprocess engineering such as IMM and Forschungszentrum Karlsruhe, was steered by a large panel of industrial experts that included both equip- ment manufacturers and representatives of the chemical and pharmaceutical appli- cation sectors. Three years of research and development resulted in a manufacturer-spanning toolbox of compatible microprocess components provided by different manufacturers. The core concept of the project was a modular fluidic con- nection system, the backbone, which allows both commercial and demonstration-type microstructured devices to be coupled in all three dimensions in a flexible and easy manner. Micro heat exchangers, reactors, and mixers of different manufacturers are surface-mounted onto this backbone. Standardized interfaces ensure that devices can be exchanged easily, for example, to evaluate different types of mixers. In addition, the project targeted the integration of sensors and control equipment.

15.2.1 The Backbone Concept: Fluidic Platform for Surface-Mount Microstructured Components

The backbone concept is based on the idea of a standardized fluidic bus system, in which the flow is passed through a central spine. Figure 15.2 shows a microplant with different component modules connected via the backbone. The backbone consists of individual blocks with a defined footprint and standardized fluid con- nectors at defined positions. Microstructured components, such as micromixers, micro heat exchangers, miniaturized pumps, etc., with fluid connectors matching the backbone can be surface-mounted to one or more backbone elements, depending on their size.

FIGURE 15.2 Microplant based on the MicroChemTec backbone concept.

352 STANDARDIZATION IN MICROPROCESS ENGINEERING

The backbone thus provides fluid paths between different modules and the inte- gration of heating/cooling fluids. Modules are always connected via the backbone and not directly to each other. The fluidic connectors of the modules and the back- bone are complementary and follow a defined system of flow inlets and outlets. This is essential to achieve full compatibility and to ensure that different components with identical functionality can be exchanged without compromising the flow path scheme of the microplant.

15.2.2 Backbone Elements

The backbone consists of several cubic backbone elements, each following a footprint of 45 mm. As depicted in Fig. 15.3, the backbone blocks are modular components, each incorporating a number of pipes and housing parts. For the fluidic connections, three types of pipes are available: a straight pipe, an elbow, and a T-piece. These stan- dard pipes are sufficient to build up all required fluid connections between the backbone and surface-mount module. Three different pipe diameters allow for different flow rates and throughputs, corresponding to the capabilities and requirements of the modules attached. This way, volume flows up to 100 L/h are feasible in the microplant.

The individual backbone blocks are connected by screwing the front plates of two blocks using appropriate seals. This way, the backbone is built up. Figure 15.4 sche- matically shows the front plate and top views of a backbone block. The front plates can accommodate up to four pipes, thus allowing four fluids to be conveyed in parallel in one backbone. The top plate has eight optional positions to accommodate pipes to be coupled to the microstructured module. These eight optional fluid ports allow the con- nection to modules of different functionality (e.g., mixing, and heat exchange), which require, respectively, different number and position of fluid inlets and outlets.

In addition to the standard backbone, full block elements of different materials with channels can be used for different applications. Ceramic or PEEK (polyether ether ketone) blocks can be employed to achieve the thermal decoupling of adjacent process steps in the microplant at a different temperature level. Stainless steel blocks can be used as heat exchanger modules, in which cooling or heating fluids are

FIGURE 15.3 (a) Assembled backbone element. (b) Backbone parts: housing and piping elements.

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Front plate view: 4 fluid connections

d = Top view: 8 potential fluid ports d =

FIGURE 15.4 fluid ports.

Schematic depiction of a backbone block, indicating the different optional

provided in one or more channels. Figure 15.5 shows a PTFE (polytetrafluoro- ethylene) backbone block for thermal decoupling and its use in a microplant includ- ing process steps at different temperatures.

15.2.3 Compatibility of Modules

The particular standardization effort of the MicroChemTec project included the rationale of the connection interface between the backbone blocks and the manufac- turers’ microstructured modules. This required the predefinition of the geometry and function of the fluid ports (inlets and outlets) as described subsequently. The com- patibility of equipment modules to the backbone is achieved either by designing the module to directly match the position and geometry of the fluid ports to the back- bone interface, or by using an adapter plate to adjust such a position and geometry. Examples of both cases are depicted in Fig. 15.6. The redesign of modules to match the standardization specifications is more complex and costly, but is the preferential option in terms of reliability and hold-up, as adapters cause more sealed fluid connec- tions and additional volume.

In order to achieve the compatibility of a large number of modules from different manufacturers without imposing too many restrictions on the module design, the module size is not limited to the backbone block footprint of 45 mm x 45 mm. Depending on the size, modules can be coupled to one, two, or more backbone blocks. In Fig. 15.6, for instance, module (a) is coupled to two backbone blocks, while module (b) is coupled to one backbone block.

In any case, the position and function of fluid ports with respect to the backbone have to be maintained, to keep full compatibility. This is schematically depicted in

3% STANDARDIZATION IN MICROPROCESS ENGINEERING

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Backbone central axis [rnm]

FIGURE 15.5 different temperature levels [ 2 ] .

Use and effect of a thermal insulating backbone block in microplant with

FIGURE 15.6 Backbone compatible modules: (a), heat exchanger with standardized fluid ports (Forschungszentrum Karlsruhe); (b), glas micromixer with steel adapter plate (Little Things Factory).

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Module for one backbone block backbone blocks

Module for two Reactor ~~T~ Mixer

Heat Exchanger

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FIGURE 15.7 fluid inlets and outlets is mandatory to ensure full compatibility with the backbone.

Allocation of fluid ports for different equipment modules: The systematic of

Fig. 15.7 for three types of modules connected to one or two backbone blocks, respectively. Fluid inlets and outlets occur at defined positions, the allocation depend- ing on the type and function of the module. A very simple reactor possesses one inlet and one outlet at predefined positions. These two standard ports are used in every module for conveying reaction medium from the backbone into the module and back into the backbone. A mixer has an additional inlet for the second fluid; a heat exchanger has both an additional inlet and outlet for the heating/cooling fluid. This fluid port allocation is mandatory to ensure that a module at a given position on the backbone can be exchanged by another module of identical function without compromising the fluid distribution in the backbone.

15.2.4 Building a Microplant Based on the Backbone

Based on the schematic flow diagram of the process, the construction of a microplant starts with the selection of appropriate standardized modules meeting the respective process requirements (manufacturers specifications or experimental characterization). Subsequently, a schematic piping and installation plan is created for the microplant that is then used to build up the backbone. Finally, the modules are surface-mounted to the backbone and peripheric equipment is installed. Figure 15.8 shows a microplant for the sulfonation of toluene with gaseous SO3, one of four demonstration plants that were erected and extensively tested during the MicroChemTec project for the proof- of-concept of the toolbox. This plant consists of 10 modules from 7 different

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FIGURE 15.8 Microplant for the sulfonation of toluene with gaseous SO,; the microplant includes the following modules: microgear pumps (HNP Mikrosysteme), heat exchanger (Forschungszentrum Karlsruhe), microfalling film reactor (IMM Mainz), micromixer and microheat exchanger (Little Things Factory), residence time module (CPC GmbH), microreac- tor (mikroglas chemtech), and sampling valves (Swagelok).

manufacturers. Furthermore, several sensors (temperature, pressure, and mass flow controllers) and a control unit have been integrated (not depicted here).

15.3 CONCLUSION AND OUTLOOK

Standardization is a common step in the development process that transform a new technology into a mature one. In this sense, the MicroChemTec initiative is a first step toward the vision of truly compatible modules irrespective of the manufacturer. With the more widespread implementation of microprocess engineering as a tool of process development, the further harmonization of systems and toolboxes for lab applications across manufacturers can be expected, driven by customers’ demand for high flexibility. Related standardization initiatives such as the new sampling/sensor initiative (NeSSI) [3] aimed at the modularization and miniaturiza- tion of process analyzer sample system components have to be taken into account or may even be harmonized with standardization activities in microprocess engineering.

In the future, the standardization of fluid connectors and industry-accepted standards on how to rationally connect and distribute fluid streams-in particular, between components of different characteristic dimensions-will become an increa- singly important issue for the implementation of microstructured components in industrial pilot plants and on the production level. Accordingly, current research and development activities with respect to industry-scale microstructured equipment for high tonnages, and subsequent concepts of equaling-up and scaling-out of microstructures will finally lead to corresponding standardization efforts on the plant level.

BIBLIOGRAPHY 357

BIBLIOGRAPHY

1. Web site: http://www.microchemtec.de, DECHEMA e.V., Frankfurt, Germany. 2. A. Miiller, et al. (2005). Chemical Engineering Journal, 107(1-3): 205-214. 3. Web site: http://www.cpac.washington.edu/NeSSI/NeSSI.htm. Center for Process Analy-

tical Chemistry, University of Washington.