Chemical composition and stability of renewable hydrocarbon products generated from a hydropyrolysis vapor upgrading process

Abstract

Catalytic hydropyrolysis is an emerging and promising technology for producing cellulosic biofuels. Ex situ catalytic hydropyrolysis offers additional benefits of operational flexibility and catalyst performance. The unique feature of a two-step ex situ hydropyrolysis vapor upgrading process has been demonstrated for the first time using a double fluidized-bed reactor system. Product distribution (35.2–46.7% C5+ organic yield on a carbon basis) and oxygen content of the organic liquid product (2–17 wt%) can be tailored by adjusting process conditions. Nuclear magnetic resonance spectroscopy and gas chromatography–mass spectrometry were used to identify oxygen functionalities and representative species in the organic liquid products. The structural information was further related to product stability, a key property pertaining to product storage, transportation, and processing. Unlike pyrolysis oil, the products contained minimal amounts of reactive oxygenates (e.g., aldehydes, acids, sugars, and other multifunctional oxygenates) that could cause stability issues. As a result, the products were stable in storage at 40 °C for 2 months. Further thermal stability tests show that all of the products were more stable than pyrolysis oil and soybean oil at elevated temperatures. The products with 6 wt% oxygen or less showed high thermal stability (behaving much like a petroleum distillate hydrotreater feed in the tests) and possessed low total acid number (<1 mg KOH per g), indicating good petroleum refinery compatibility.