Processes and compositions for Organic Rankine Cycles for generating mechanical energy from heat

A process for recovering heat from a heat source and generating mechanical energy, comprising the steps of:

• (a) compressing a first working fluid in liquid phase to a pressure above said first working fluid's critical pressure;
• (b) passing said first working fluid from Step (a) through a heat exchanger or a fluid heater and heating said first working fluid to a temperature that is higher or lower than the critical temperature of said first working fluid, wherein said heat exchanger or said fluid heater is in communication with said heat source that supplies said heat;
• (c) removing at least a portion of the heated said first working fluid from said heat exchanger fluid heater;
• (d) passing said at least a portion of the heated said first working fluid to an expander, wherein at least portion of said heat is converted into mechanical energy, and wherein the pressure on said at least a portion of the heated said first working fluid is reduced to below the critical pressure of said first working fluid, thereby rendering said at least a portion of the heated said first working fluid to a first working fluid vapor or a first working fluid mixture of vapor and liquid;
• (e) passing said first working fluid vapor or said first working fluid mixture of vapor and liquid from said expander to a condenser, wherein said first working fluid vapor or said first working fluid mixture of vapor and liquid is fully condensed to the first working fluid in liquid phase;
• wherein said first working fluid consists of HFO-1336mzz-Z;
• and wherein the working fluid in step (a) is compressed to a pressure within the range from 3 MPa to 6 MPa and said expander in step (d) operates at an inlet temperature of 200° C. to 400° C.