From Miniplants to pilot plants

Dr. Hans Bernd Kuhnhen, Mike Cartlidge

In the seventies the installation of an industrial plant was unthinkable without prior process development with a pilot plant. Nowadays, the Miniplant technique supplies reliable process parameters, which contribute to an accelerated reliable process development. In earlier times pilot plants were even built for teaching and demonstration tasks, which was disadvantageous because of the high throughput. In addition, they proved to be uneconomical and caused high expenditure for waste disposal.

The main benefits of the Miniplant technique are:

l low costs for investments, personnel, operation and disposal,

l modular construction permitting easy modification to suit changing requirements,

l supply of reproducible measurements,

l evaluation of the experimental results in comparison with theoretically acquired results, and finally

l the process scale-up.

The Miniplant technology cannot be applied when solid particles need to be processed or if the required sensors cannot be made smaller.

The majority of Miniplants are basically made from the chemically resistant borosilicate glass 3.3 in conjunction with highly chemically resistant plastic materials, such as PTFE, special metals and alloys (Fig. 1). The transparency of the glass allows the actual chemical process to be observed. The Miniplants have to be constructed in a clearly arranged, functional and hard-wearing manner. The modular construction permits the versatile application of this technique as well as quick and easy modifications for adapting to new processes.

Major importance is attached to robust and safe glass flange connections. The flat safety buttress end with its fire-polished surface minimises undue mechanical or thermal stress in the glass. Its groove locates the PTFE seals.

Couplings are available in a variety of materials, and are extremely easy to assemble in conjunction with the preformed insert made of injection-moulded plastic. The tried-and-tested articulation joint adds flexibility to the inherent stability of the standardised flat-end safety flange. This flat-end flange permits glass components to be connected to components made of other materials and possibly even constructed with different flange ends.

As well as pipelines manufactured from glass and stainless steel, PTFE tubing is especially used for product and vacuum lines. Even the measuring probes are easily fitted thanks to the use of threaded glass screws. Metal fittings are used for special requirements and operating conditions.

Due to the low heat input and the disadvantageous ratio of surface to volume, insula-tion is a very important aspect. Glass components are insulated by means of high-vacuum jackets.

Valves manufactured from other materials have also been developed. They are unique, owing to their compact dimensions and their construction principle which ensures a low dead volume. The high integrity of the seals in these valves and tubes is a further contribution to exact operation and safety for the operator and the environment.

The universal unit shown here can be easily adapted to different basic processing methods, such as reaction, distillation, rectification, extraction and absorption. Short start-up and equilibration periods are required as well as exact, reproducible measurements. The unit consists of glass components which are integrated in a structure accessible from all sides. The structure accommodates the apparatus as well as measuring and control units. The safety tray incorporated at the base serves as a catchment area for any spillage. The reaction vessel with flat-end flanges is heated by a thermostat, which should be equipped with a cooling device for exothermic reactions. To determine the heat balance, the throughput of the heating liquid and the temperature difference between the inlet and outlet nozzles of the vessel are measured. To reduce heat loss from the column, the latter is insulated by a silver-plated, high-vacuum jacket. The head condenser can be operated by tap water or preferably by a cooling unit. In this case, moreover, the heat balance can be determined by the throughput and the temperature difference at the condenser. For vacuum operation, a diaphragm pump with a phase separator at the inlet and a condensing part at the outlet, can easily be connected to the outlet of the unit’s condenser.

The control system, which is a flexible two-stage system, offers an ideal solution forsafe process control and data acquisition. The independently working first stage consists of self-optimising control units with RS422 interfaces, which are linked to a programmable process control system. All the process parameters for start-up, normal running and shut down are stored in this system. These parameters can be pre-set and read from the control system by a PC-based process visualisation unit in the second stage, which also includes data handling.

The PC visualisation unit in the laboratory usually runs under Windows 3.11. Windows ’95 is even more effective for achieving safe operation. There are almost no limits to the variety of configurations and programming options offered by the software.

Finally, the number of exact process para-meters that can be determined and the extent to which the automation is required for constant, safe operation are dependent on the selected measuring sensors and on the available data.

The cryogenic reaction unit is one example of the continuous transition from Miniplants to pilot plants (Fig. 2). The industrially manufactured product is often required to have a low volume and a high value, and at some stage during the production process cold reactions, usually in the upper -70’s °C, need to take place. In addition, this same unit must be able to operate at high temperatures. The researchers and manufacturers working on this product were looking for an independent reactor to accomplish this task for volumes between 10 l and 200 l. This cryogenic reactor is normally installed in pilot plants and in chemical scale-up facilities. Its specifications also include:

l -80 °C to +150 °C operation within the reactor,

l reactor capacities of 10 to 300 l,

l rapid cool-down rates,

l accurately controlled steady-state opera-tion,

l computer control/data acquisition/alarm system,

l integral heat/chill facility,

l excellent corrosion resistance,

l straightforward cleaning.

Reliability, cleanliness and safety were all key elements during the development of this product. The use of borosilicate glass 3.3 and virgin white PTFE as standard construction materials for all wetted parts ensures maximum corrosion resistance, inertness to a very range of chemicals, ease of cleaning and visual monitoring of process indicators. The combination of pilot plant technology and these highly corrosion-resistant materials and equipment has resulted in the successful development and supply of a hybrid low/high-temperature reactor unit. The reactor, supported within a stainless steel heating/cooling bath, is fully independent with an integral heat/chill system requiring only electricity and nitrogen to operate. The heat-transfer oil is cooled via an internal cooling unit using liquid nitrogen, so that the cooling-down process is fast. The liquid nitrogen is stored and delivered by a self-pressurising mobile Dewar or via bulk storage. It is exhausted to atmosphere/vent. To ensure high operating temperatures the heat-transfer oil is heated using flameproof immersion heaters. The heat transfer is maximised by use of agitators within the oil.

The cryogenic reactor and its ancillary equipment meets the requirements of international standards, including CGMP. This reactor is used to control rapid reactions and to protect thermally sensitive products in an inert environment, enabling valuable products to be manufactured more safely and more predictably.

QVF Glastechnik

Fax: ++49/611/26 16 91

Further information cpp 204