(120b) Pyrolysis and Etherification Process for Advanced Diesel Blendstocks

The integration of fast pyrolysis, mild hydrogenation, and etherification has been evaluated to produce a renewable diesel blendstock from woody biomass. Predictive models indicate that many ethers, which might be produced from components in pyrolysis oils, would have good blendstock characteristics, such as enhanced cetane and reduced sooting, at the expense of an energy density that is lower than petroleum diesel.

A techno-economic analysis (TEA) and a life cycle analysis (LCA) have been conducted for the integrated process. A simulation was created using Aspen Plus^®, and data for fast pyrolysis at 500 °C was used for the base case. Thermodynamic properties of hydrogenation and etherification model compounds were estimated using Density Functional Theory (DFT). The results from the process simulation were used to estimate the capital and operating costs for a plant that processes 2,000 dry metric tons per day of forest residues. The well-to-wheels LCA was developed using Argonne’s GREET 2019 software to assess the environmental sustainability of producing the renewable diesel fuel blendstock.

The TEA determined that diesel blendstock products with a lower heating value of 24 MJ/kg might be produced from forest residues at a minimum selling price of $2.95/ Diesel Gallon Equivalent (DGE). The requirement to remove a lower amount of oxygen from the pyrolysis oil, compared to complete hydrodeoxygenation, means that reforming of non-condensable gases from the pyrolysis reactor provides sufficient hydrogen for the mild hydrotreating reactor. Temperature effects on the pyrolysis oil composition and yields predict that the MFSP might be reduced to $2.61 per DGE at lower pyrolysis temperatures. The reduction in MFSP is due to the enriched composition of phenols and furans in pyrolysis oils produced at lower temperatures. The well-to-wheels LCA analysis indicates that the renewable diesel blendstock would have a 93% reduction in fossil fuel use and a 93% reduction in greenhouse gas emissions relative to petroleum diesel.