A gas-solid-liquid separator and settler (HCS) was designed and tested in a pilot plant to determine the optimal dimensions and best operating conditions for the new solid alkylation process. The HCS uses a hot hydrogen stream to reduce density and viscosity, vaporize a part of hydrocarbons, and preheat a solid. Different geometries were tested, and underflow and overflow streams were characterized; different calibrated sensors determine the flow pattern, radial and axial velocities, particle size distribution, temperature, and pressure. Separation efficiencies depend upon the inlet slurry flow rate and temperature, cone length, hydrogen flow rate and temperature, solid content, and particle size distributions. The best gas, solid, and liquid separation was observed for a base case set of dimensions and operating conditions that produce less than 20 kHz of vibration at the tail pipe and less than 20 kPa of the delta of pressure in the steady state. Effects of hydrogen are discussed.