Temperatures, industrial heat from acid recovery

Of greater industrial utility is the zinc chloride process that has been extensively used in Europe. In this, 0.5 to 4 parts of zinc chloride in the form of a concentrated solution are mixed with one part of pulverized peat or sawdust. In some operations, hydrochloric or phosphoric acid is also added. After drying, the mixture is heated in a brick-lined rotary kiln at 600° to 700° C—although temperatures from 400° to 900° C are also reported. The finished carbon is washed with water and acid, and provision is made for recovery and re-use of the zinc salts.1 4 15,16... 

An example is the recovery and purification of amino acids via crystallization. Here, the solubility of the amino acid can be influenced by a number of methods (1) lowering the temperature, (2) evaporating the solvent, (3) selective removal of the solvent by means of membranes techniques, and (4) by using a water-miscible cosolvent such as lower alcohols and acetone. In the last of these, which is close to industrial practice, work is lost at a large number of places. Unequal quality of heat input (at a high T level) and recovery (at a low T level) and incomplete solvent recovery from the mother liquor increase lost work and, less obviously, incomplete recovery contributes to lost work as well. This is shown schematically in Fig. 7. Considering option 3, work is lost to force the solvent (wa-... 

---