According to one or more embodiments described herein, a process for producing propylene, the process comprising at least partially metathesizing a first portion of a first stream to form a first metathesis-reaction product, at least partially cracking the first metathesis-reaction product to form a cracking-reaction product, the cracking reaction product comprising propylene and ethylene, at least partially separating ethylene from at least the cracking reaction product to form a first recycle stream, combining the first recycle stream with a second portion of the first stream to a form a mixed stream, and at least partially metathesizing the mixed stream to from a second metathesis-reaction product. In embodiments, the second metathesis-reaction product may comprise propylene, the first stream may comprise butene, and the first recycle stream may comprise ethylene.