A sorption-expansion process is disclosed that recovers waste energy contained in a fluid stream, such as hot water from a power plant. The sorption-expansion system includes sorbent beds which are selectively coupled to an expander. The expander could be a reciprocating engine, scroll, turbine, or other style. A sorbent bed with absorbed/adsorbed working fluid at high pressure operates in a desorption mode and provides the working fluid to the expander while another sorbent bed receives absorbs/adsorbs the expanded, low-pressure working fluid from the expander. With four sorbent beds, while first and second beds are active in sorption and desorption, a third bed is heated (by a source such as via waste energy) and a fourth additional bed is cooled via a coolant stream. The beds are switched between modes by valves that fluidly couple the sorbent beds with the expander, the hot fluid, and the cold fluid.