Methods are provided for refining natural oil feedstocks. The methods comprise reacting the feedstock in the presence of a metathesis catalyst under conditions sufficient to form a metathesized product comprising olefins and esters. In certain embodiments, the methods further comprise separating the olefins from the esters in the metathesized product. In certain embodiments, the methods further comprise hydrogenating the olefins under conditions sufficient to form a fuel composition. In certain embodiments, the methods further comprise transesterifying the esters in the presence of an alcohol to form a transesterified product.

Systems and processes for the production of a high purity isobutylene stream, a high purity isooctene stream or for the co-production of a high purity isobutylene and a high purity isooctene. The systems and processes advantageously process mixed C4 hydrocarbon streams via etherification, back cracking, isomerization, and/or dimerization, along with various separation systems, to produce the desired high purity streams.