Process to prepare lower olefins

A process to prepare ethylene and propylene from a biomass feedstock wherein the process comprises the following steps:

• (a) a mild gasification of a torrefied biomass feedstock thereby obtaining a char and a gaseous fraction comprising hydrogen, carbon monoxide and a mixture of gaseous organic compounds;
• (b) a severe gasification of the gaseous fraction in the absence of the char to obtain a substantially tar-free syngas;
• (c) a Fischer-Tropsch reaction of the substantially tar-free syngas to obtain a first product mixture comprising of methane and C2+ aliphatic hydrocarbons,
• (d) a steam cracking reaction of all or part of the C2+ aliphatic hydrocarbons obtained in step (c) to obtain a second product mixture.

A process system to prepare ethylene and propylene from a biomass feedstock wherein the process configuration comprises the following units:

• (i) a mild gasification reactor unit in series with;
• (ii) a severe gasification reactor unit to produce a substantially tar-free syngas;
• (iii) a Fischer-Tropsch reactor unit for converting the substantially tar-free syngas to a first product mixture wherein the Fischer-Tropsch reactor unit comprises of a heterogeneous Fischer-Tropsch catalyst and an outlet for a first product mixture;
• (iv) a separation unit for separating the first product mixture into at least a FT gaseous fraction and a higher boiling FT C5+ fraction;
• (v) one or more furnaces for performing a steam cracking reaction wherein at least one furnace is suited to convert the entire FT C5+ fraction or a distillate of the FT C5+ fraction to a second product mixture;
• (vi) a separation train for isolating ethylene and propylene from the first product mixture and from the second product mixture.