There exists a high demand to produce para-xylene and terephthalic acid from renewable biomass resources for use in the manufacture of clothing and plastics. Terephthalic acid is a precursor of polyethylene terephthalate (PET), which may be used to manufacture polyester fabrics. Terephthalic acid can be produced by oxidation of para-xylene.
Xylene is an aromatic hydrocarbon that occurs naturally in petroleum and coal tar. Commercial production of para-xylene is typically accomplished by catalytic reforming of petroleum derivatives. See e.g., U.S. Patent Application No. 2012/0029257. However, the use of petroleum-based feedstocks to commercially produce para-xylene (and hence terephthalic acid) generates greenhouse gas emissions and perpetuates reliance on petroleum resources.
Alternative methods to produce para-xylene from renewable biomass resources have been under investigation. Biomass containing cellulose and/or hemicellulose can be converted into DMF, and then DMF may be converted into para-xylene by Diels-Alder cycloaddition of ethylene. See e.g., U.S. Pat. No. 8,314,267; WO 2009/110402. The Diels-Alder conditions currently known in the art to produce para-xylene from cycloaddition of ethylene to DMF typically results in at least a portion of the DMF being converted into 2,5-hexanedione (HD), which generally polymerizes. Such a side reaction involving HD leads to a reduction of the selectivity to para-xylene. See e.g., Williams et al., ACS Catal. 2012, 2, 935-939; Do et al., ACS Catal. 2013, 3, 41-46.
Thus, what is needed in the art are alternative methods to produce para-xylene and terephthalic acid.