97e Intermediate Temperature Catalytic Reforming of Bio-Oil for Distributed Hydrogen Production
With the world's energy demands rapidly increasing, it is necessary to look to sources other than fossil fuels, preferably those that minimize greenhouse emissions. One such renewable source of energy is biomass, which has the added advantage of being a near-term source of hydrogen. While there are several potential routes to produce hydrogen from biomass thermally, given the near-term technical barriers to hydrogen storage and delivery, distributed technologies such that hydrogen is produced at or near the point of use are attractive. One such route is to first produce bio-oil via fast pyrolysis of biomass close to its source to create a higher energy-density product, then ship this bio-oil to its point of use where it can be reformed to hydrogen and carbon dioxide. This route is especially well suited for smaller-scale reforming plants located at hydrogen distribution sites such as filling stations. There is also the potential for automated operation of the conversion system. A system has been developed for volatilizing bio-oil with manageable carbon deposits using ultrasonic atomization and by modifying bio-oil properties, such as viscosity, by blending or reacting bio-oil with methanol. Non-catalytic partial oxidation of bio-oil is then used to achieve significant conversion to CO with minimal aromatic hydrocarbon formation by keeping the temperature at 650 C or less and oxygen levels low. The non-catalytic reactions occur primarily in the gas phase. However, some nonvolatile components of bio-oil present as aerosols may react heterogeneously. The product gas is passed over a packed bed of precious metal catalyst where further reforming as well as water gas shift reactions are accomplished completing the conversion to hydrogen. The approach described above requires significantly lower catalyst loadings than conventional catalytic steam reforming due to the significant conversion in the non-catalytic step. The goal is to reform and selectively oxidize the bio-oil and catalyze the water gas shift reaction without catalyzing methanation or oxidation of CO and H{sub 2}, thus attaining equilibrium levels of H{sub 2}, CO, H{sub 2}O, and CO{sub 2} at the exit of the catalyst bed. Experimental Bio-oil (mixed with varied amounts of methanol to reduce the viscosity and homogenize the bio-oil) or selected bio-oil components are introduced at a measured flow rate through the top of a vertical quartz reactor which is heated using a five zone furnace. The ultrasonic nozzle used to feed the reactants allows the bio-oil to flow down the center of the reactor at a low, steady flow rate. Additionally, the fine mist created by the nozzle allows for intimate mixing with oxygen and efficient heat transfer, providing optimal conditions to achieve high conversion at relatively low temperatures in the non-catalytic step thus reducing the required catalyst loading. Generation of the fine mist is especially important for providing good contact between non-volatile bio-oil components and oxygen. Oxygen and helium are also delivered at the top of the reactor via mass flow meters with the amount of oxygen being varied to maximize the yields of H{sub 2} and CO and the amount of helium being adjusted such that the gas phase residence time in the hot zone is {approx}0.3 and {approx}0.45 s for bio-oil and methanol experiments, respectively. A catalyst bed can be located at the bottom of the reactor tube. To date, catalyst screening experiments have used Engelhard noble metal catalysts. The catalysts used for these experiments were 0.5 % rhodium, ruthenium, platinum, and palladium (all supported on alumina). Experiments were performed using pure alumina as well. Both the catalyst type and the effect of oxygen and steam on the residual hydrocarbons and accumulated carbon containing particulates were investigated. The residence time before the catalyst is varied to determine the importance of the non-catalytic step and its potential effect on the required catalyst loading. Non-catalytic experiments (primarily homogeneous cracking) use a bed of quartz placed to capture any deposits that are formed in the volatilization and cracking zones. The inner reactor effluent is quenched by a flow of 10 SLPM He which serves to sweep the products quickly ({approx}0.03 s) to a triple quadrupole molecular beam mass spectrometer (MBMS) for analysis. The MBMS serves as a universal detector and allows for real time data collection. The study of pyrolysis by MBMS has been described previously. The dilution of the reactor effluent reduces the potential problems caused by matrix effects associated with the MBMS analysis. Argon is used as an internal standard in the quantitative analysis of all the major products (CO, CO{sub 2}, H{sub 2}, H{sub 2}O, and benzene) as well as any residual carbon, which is determined by subsequent oxidation of carbon (monitored as CO{sub 2}) after shutting off the feed and maintaining the oxygen/helium flow.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1021230
- Resource Relation:
- Conference: [Proceedings] Emerging Energy Frontiers in Research and Innovation. Topical Conference at the 2008 AIChE Sprint National Meeting, 6-10 April 2008, New Orleans, Louisiana
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
09 BIOMASS FUELS
BIOMASS
CARBON
CARBON DIOXIDE
CATALYTIC REFORMING
ENERGY DEMAND
ENERGY DENSITY
FLOW RATE
FOSSIL FUELS
GASOLINE SERVICE STATIONS
HEAT TRANSFER
HELIUM
HYDROGEN
HYDROGEN PRODUCTION
HYDROGEN STORAGE
MASS SPECTROMETERS
METHANOL
MOLECULAR BEAMS
OXIDATION
OXYGEN
PACKED BEDS
STEADY FLOW
ULTRASONIC WAVES
WATER GAS
Bioenergy