Transport Processes and Separation Process Principles (Includes Unit Operations) Fourth Edition

13.9. REVERSE-OSMOSIS MEMBRANE PROCESSES

13.9A. Introduction

1. Introduction

To be useful for separation of different species, a membrane must allow passage of certain molecules and exclude or greatly restrict passage of others. In osmosis, a spontaneous transport of solvent occurs from a dilute solute or salt solution to a concentrated solute or salt solution across a semipermeable membrane which allows passage of the solvent but impedes passage of the salt solutes. In Fig. 13.9-1a, the solvent water normally flows through the semipermeable membrane to the salt solution. The levels of both liquids are the same as shown. The solvent flow can be reduced by exerting a pressure on the salt-solution side and membrane, as shown in Fig. 13.9-1b, until ...