lntroduction

In the manufacture of high quality dental products, a concentrate is frequently used which is manufactured by removing methylene chloride from a solution containing methacrylic acid and other ingredients.

In the manufacture of this concentrate, one of the principal processing problems to overcome is to eliminate polymerization reactions which readily take place at temperatures between 122 and 140^oF, resulting in the production of extremely viscous product which adheres to the walls of the equipment.

A single tube climbing film evaporator operating under vacuum and on a once through basis is an ideal method of overcoming this problem. A particular feature of the climbing film evaporator is the very low residence time of materials in the heating zone making it particularly suitable for use with heat sensitive materials. By operating under vacuum conditions, the boiling point of the feedstock and concentrate are reduced sufficiently to virtually eliminate all polymerization reactions.

For larger processes, multi-tube climbing film evaporators are also available from QVF Process Systems.

Process Description

A single calandria tube climbing film evaporator is illustrated in above diagram. In it, a batch of 100 liters of the methacrylic acid feedstock is typically concentrated using a feed-flowrate in the order of 0.6 to 0.8 l/min. Methylene chloride is then evaporated at the rate of 0.25 to 0.35 l/min from this feedstock when operating with a steam pressure of 5 psig and under a vacuum of approximately 7 psia.

Features of the CFE

The climbing film evaporator is extremely well suited to the concentration of heat sensitive, low viscosity feedstocks. Residence times are extremely short and operating temperatures can be substantially reduced through the use of vacuum.

CFE's fabricated in borosilicate glass are particularly suited to pharmaceutical and food applications - for example, the concentration of milk or fruit juices - as, due to the inert nature of the glass, product contamination is negligible.

The unit can be operated on a 'once through' basis or, alternatively, the concentrate can be recycled for further concentration.

This Process Profile supersedes all previous issues.

QVF Process Systems pursues a policy of continuous product improvement. We therefore reserve the right to alter any product or process as described and illustrated.