Batch reactor systems are used extensively in the pharmaceutical and fine chemical industries for the manufacture of small volume, high value products, in either dedicated or multipurpose production facilities.
Stable and reproducible operating conditions are of great importance in order to achieve the batch times, optimum yields and product purity required to satisfy commercial requirements and the relevant regulatory authorities (ie, the FDA).
The operating companies are required to notify the appropriate environment agency of the total emissions from their processes to the environment (ie VOCs).
When processing flammable solvents, it is standard practice to eliminate explosive mixtures by establishing and maintaining an inert atmosphere in the reactor.
Inert systems can be based on pressure balance or continuous flow. However when carrying out reactions at reflux, the inert flow should be reduced or eliminated in order to minimise volatile organic compounds (VOCs) emissions to the environment.
Some reactions involve the evolution of non-condensable compounds, which will become saturated with VOCs in proportion to the component vapour pressures at the overhead condenser exit temperature and pressure.
Adopting ‘rule of thumb’ methods for condenser sizing (ie condenser heat transfer area equal to reactor jacket or coil, heat transfer area) can result in under sizing of condensers when applied to multipurpose plant operations.
The traditional material used for multipurpose or pilot plants with corrosive processes has been a glass lined carbon steel reactor, graphite overhead condenser and PTFE lined carbon steel interconnecting pipework. This certainly applies where hydrogen chloride is involved in the process. However, Tantalum overhead condensers are being used to a greater extent on the final stages of pharmaceutical manufacture.
The major pharmaceuticals manufacturers have put in place the following directives regarding graphite heat exchangers for API production: on all the new API Production Facilities, graphite materials for the heat exchangers are not to be used due to potential contamination of product if the graphite or impregnant is chemically attacked.
On the existing API facilities, after the final filtration stage, graphite heat exchangers are to be replaced by Reactive Metal Heat Exchangers as soon as possible.
Carbone Lorraine has developed a fully welded gasket-free heat exchanger manufactured with a new material: Tantalum CL-Clad.
Tantalum is the most suitable reactive metal to comply with hot and corrosive fluids. Tantalum is a refractory and corrosion resistant metal to most acids to 200°C (Sulphuric, Hydrochloric, Acetic, Nitric). It is easily formed into common shapes and has a high thermal conductivity. Tantalum requires a high level of welding expertise, as it must be welded using an inert cover gas on all exposed surfaces. It is a high-end material whose price is expensive.
Carbone Lorraine has patented a new brazing process, CL-Clad in 2004. The new technology CL-Clad consists of brazing reactive metal sheets, (such as Tantalum, Titanium, Zirconium) on to steel. It is used in anti-corrosion equipment, notably columns and reactors, for the fine chemicals and pharmaceuticals industries. This new material will enable the customers to cut their maintenance costs, boost their production capacity and enhance the safety of their installations.
In collaboration with the in-house welded plate heat exchanger specialist, KAPP, Carbone Lorraine has reinforced all the synergies and developed a fully welded heat exchanger, Heatex made of Tantalum CL-Clad.
This new metallic Heatex overhead condenser has some key features that the API manufacturers can benefit from:
* Robustness: the Tantalum CL-Clad condenser does not require special handling and has an excellent resistance to thermal and mechanical shock.
* Easy-to-clean: with opening doors for the process side. Moreover, Tantalum CL-Clad highlights a very high efficient chemical cleaning by solvent reflux that is well suited to Batch Process.
* Very low maintenance requirements.
* Non-contamination design: due to ‘free gap’ plate design on process side
* Corrosion resistance: due to Tantalum on process side
* Optional sight glass: that allows easy control of the condensation or plates fouling.
One aspect of the KAPP Heatex design, that has been seen identified by API customers as a major advantage over the competition, is the ‘U’ plate design of welded plates. With the plates only welded to one tube-sheet, this allows for free thermal expansion of the plates, without stressing of the welds. On the batch duties carried out for API production, alternative designs, with plates welded to two fixed tube-sheets, can suffer from failure of the welds due to thermal expansion and contraction of the plates and hence stressing of the welds.
Another major advantage of the KAPP Heatex design of Welded Plate Heat Exchanger is that it can be designed to dimensionally match (including nozzle positions and supports) existing graphite cubic block heat exchangers, without the need for support or pipework changes. An additional advantage is that due to the higher thermal efficiency of the KAPP Heatex, the condensing performance can be greatly increased with a corresponding increase in production for the API plant.
The replacement of graphite heat exchangers has already been carried out, with great success, by a number of API customers, with Hastelloy and Stainless Steel versions of the Heatex. As replacement Heatex units were supplied, which matched exactly the original graphite units, the change over could be carried out quickly, keeping down-time to a minimum and the plant in operation.l
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Byron Boulby is with Carbone Lorraine – Chemical Equipment Division, Pagny-sur-Moselle, France. www.chem.carbonelorraine.com
