Article pubs.acs.org/EF
Hydrocarbon Liquid Production from Biomass via Hot-Vapor-Filtered Fast Pyrolysis and Catalytic Hydroprocessing of the Bio-oil Douglas C. Elliott,*,† Huamin Wang,† Richard French,‡ Steve Deutch,‡ and Kristiina Iisa‡ †
Chemical and Biological Process Development, Pacific Northwest National Laboratory (PNNL), 902 Battelle Boulevard, Richland, Washington 99352, United States ‡ Thermochemical Process R&D and Biorefinery Analysis, National Renewable Energy Laboratory (NREL), 15013 Denver West Parkway, Golden, Colorado 80401, United States ABSTRACT: Hot-vapor-filtered bio-oils were produced from two different biomass feedstocks, oak and switchgrass, and the oils were evaluated in hydroprocessing tests for the production of liquid hydrocarbon products. Hot-vapor filtering reduced bio-oil yields and increased gas yields. The yields of fuel carbon as bio-oil were reduced by 10% by hot-vapor filtering for both feedstocks. The unfiltered bio-oils were evaluated alongside the filtered bio-oils using a fixed-bed catalytic hydrotreating test. These tests showed good processing results using a two-stage catalytic hydroprocessing strategy. Equal-sized catalyst beds, sulfided Ru on a C catalyst bed operated at 220 °C and sulfided CoMo on an Al2O3 catalyst bed operated at 400 °C were used with the entire reactor at 10 MPa operating pressure. The products from the four tests were similar. The light-oil-phase product was fully hydrotreated, so that nitrogen and sulfur were below the level of detection, while the residual oxygen ranged from 0.3 to 2.0%. The density of the products varied from 0.80 to 0.86 g/mL over the period of the test with a correlated change of the hydrogen/carbon atomic ratio from 1.79 to 1.57, suggesting some loss of catalyst activity through the test. These tests provided the data needed to assess the suite of liquid fuel products from the process and the activity of the catalyst in the relationship to the existing catalyst lifetime barrier for the technology.
■
chemical stabilizers13) treatment. Of less emphasis in the current research is physically stabilization of bio-oil, such as filtration. This study was formulated to assess the impact on the fuel conversion process and to determine if existing barriers, particularly the hydrotreating catalyst lifetime, can be mitigated through the use of physical stabilization, in this case, HVF. A woody and herbaceous biomass were selected as the feedstocks for this study. Hot-filtered bio-oils were produced in a fluidized-bed reactor at the National Renewable Energy Laboratory (NREL), and the impact of filtration on oil properties was assessed. The Pacific Northwest National Laboratory (PNNL) hydrotreated the hot-vapor-filtered pyrolysis oils in a bench-scale, continuous-flow, packed-bed catalytic reactor to validate the utility for the HVF for fastpyrolysis bio-oil and its impact on subsequent hydroprocessing to hydrocarbon fuels. This collaboration between NREL and PNNL leverages existing expertise to assess the impact of HVF at NREL4,7 on the hydrotreating process to produce liquid transportation fuels at PNNL.9,10
INTRODUCTION Fast pyrolysis of biomass is widely held to be a viable technology for the direct production of liquid fuels.1 The biooil product from such processes, however, is not of sufficient quality for direct use in internal combustion engines. Catalytic hydroprocessing has been developed to convert the highly oxygenated bio-oil into hydrocarbon liquids.2 The long-term operation of such systems has been challenging. Thermal instability of the bio-oil during the subsequent hydroprocessing, primarily in the preheating process steps, has been addressed by low-temperature hydrogenations.3 Alternatively, cleanup of the bio-oil to remove inorganic contaminants, which could act as catalysts for the thermally driven reactions, might be valuable. In addition, removal of the trace inorganics would facilitate long-term operations in the hydroprocessing reactors without catalyst fouling by inorganic deposits. Hot-vapor filtration (HVF) of the biomass fast-pyrolysis product has been studied at several institutions and found to effectively reduce trace element content in bio-oil by removal of char particulate.4−7 The HVF has been reported to affect the bio-oil yield,6,7 and there is also a reported change in the composition of the biooil.8 Such a change might affect the stability of the bio-oil in subsequent heating. The objective of this research was to evaluate physical stabilization of bio-oil, in this case, by HVF and its impact on catalytic upgrading to diesel, jet fuel, and gasoline. To date, the vast majority of research in hydrotreating stabilized bio-oil to produce liquid transportation fuels is centered on stabilizing bio-oils through chemical means, including condensed-phase (low-temperature hydroprocessing9,10 or thermal treatment11) or vapor-phase (catalytic pyrolysis12 or co-pyrolysis with © XXXX American Chemical Society
■
EXPERIMENTAL SECTION
Feedstocks. Commercial pelletized oak and switchgrass pellets from Idaho National Laboratory were knife-milled through a 0.5 mm screen and used without further sizing. Fast Pyrolysis and HVF. The feedstocks were pyrolyzed in the laboratory-built 5.0 cm (2 in.) inner diameter fluidized-bed reactor (2FBR) equipped with a glass condensation system (see Figure 1) to produce and collect the product bio-oils. The 2FBR was filled with Received: July 8, 2014 Revised: August 13, 2014
A
dx.doi.org/10.1021/ef501536j | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
Figure 1. Process flow diagram for a 5 cm fluidized-bed reactor with condensation system and gas measurement system. ∼300 g of 300−500 μm silica sand and fluidized with 14 L min−1 (standard) of nitrogen. The bed was indirectly heated by an electric furnace; the temperature was measured at three points vertically; and typically, there was
