Evaporation concentration of liquids

Liquids (tomato juice, plum juice, apple juice, coffee ext.) are concd. by causing the liquid to flow along in contact with a selectively permeable layer formed in situ by accumulation of easily renewable hydrophilic material and maintaining a gaseous phase of a low H2O vapor pressure on the other side of the selectively permeable layer, thereby causing H2O to be removed. Thus, coffee ext. obtained by the extn. of ground roasted coffee beans with hot H2O was dehydrated in a diffusion app. A diffusion cell consists of 2 sheets of fine wire gauze, stretched in a rectangular frame parallel to and at a distance of 1.5 mm. from each other. The frame of each cell is provided on one side with a means to introduce the liquid evenly between the sheets and on the other side with a means to withdraw the liquid evenly. The coffee ext. was fed to the diffusion cells by an adjustable dosing pump. The liquid flowing in the cells was recirculated by a centrifugal pump. Under the influence of the cohesion forces of the liquid and the applied vacuum between the gauzes (of 10 cm. H2O), the av. thickness of the liquid film was 1 mm.; the liquid content of the diffusion cell/m.2 surface amounted to 0.5 l. The temp. of the ext. was 20 Deg, the concn. 10% by wt. of dry substance, and the feed rate was 104 kg. liquid/hr. After the desired slight subatm. pressure of the liquid between the gauzes was obtained, an air current at 100 Deg was conducted along the cells. By the dehydrating action of the air an extremely thin membrane of dried coffee ext. was quickly formed in the gauze. The temp. of the ext. in the diffusion cell was 60 Deg. The discharge rate was 29 kg. liquid/hr. with a dry substance content of 35.7% by wt.; the diffusion capacity/m.2 surface of the cell amounted to 5 kg. H2O/hr. Drawings illustrating the diffusion app. are given. [on SciFinder (R)]