Operating Strategies for the Oxidative Steam Reforming (OSR) of Raw Bio-oil in a Continuous Two-step System (original) (raw)
Related papers
Steam Reforming of Raw Bio-oil in a Fluidized Bed Reactor with Prior Separation of Pyrolytic Lignin
Energy & Fuels, 2013
The effect that operating conditions (temperature, steam/carbon molar ratio, and space-velocity) have on the steam reforming of raw bio-oil has been studied in a two-step reaction unit. In the first step (operated at 500°C), a carbonaceous solid (pyrolytic lignin) deposits by repolymerization of certain bio-oil components, and the remaining volatiles are reformed in the second step (fluidized bed reactor) on a Ni/La 2 O 3 −αAl 2 O 3 catalyst. Under suitable reforming conditions (700°C, S/C = 9, space-velocity = 8000 h −1 ), the yields of H 2 and CO were 95% and 6%, respectively. Catalyst deactivation was very low, whereby the H 2 yield decreased by only 2% over 100 min of reaction. By using dolomite as adsorbent in the reforming reactor, CO 2 was effectively captured, and the raw bio-oil was reformed at 600°C without adding water (S/C = 1.1), thus avoiding its vaporization cost. The yields of H 2 and CO were 80−82% and 1%, respectively, for a space-velocity (G C1 HSV) of 7000 h −1 and catalyst/ dolomite ratio of 0.25, although a high yield of CH 4 (7%) was obtained due to the cracking capacity of the dolomite. The coke content on the catalyst was high (7.7 wt % in 2 h) because of the limited gasification of coke precursors under the operating conditions (low temperature and low S/C ratio) used in the process with CO 2 capture.
International Journal of Hydrogen Energy, 2014
The aim of the present work is to produce hydrogen from biomass through bio-oil. Two possible upgrading routes are compared: catalytic and non-catalytic steam reforming of bio-oils. The main originality of the paper is to cover all the steps involved in both routes: the fast pyrolysis step to produce the bio-oils, the water extraction for obtaining the bio-oil aqueous fractions and the final steam reforming of the liquids. Two reactors were used in the first pyrolysis step to produce bio-oils from the same wood feedstock: a fluidized bed and a spouted bed. The mass balances and the compositions of both batches of bio-oils and aqueous fractions were in good agreement between both processes. Carboxylic acids, alcohols, aldehydes, ketones, furans, sugars and aromatics were the main compounds detected and quantified. In the steam reforming experiments, catalytic and non-catalytic processes were tested and compared to produce a hydrogen-rich gas from the bio-oils and the aqueous fractions. Moreover, two different catalytic reactors were tested in the catalytic process (a fixed and a fluidized bed). Under the experimental conditions tested, the H 2 yields were as follows: catalytic steam reforming of the aqueous fractions in fixed bed (0.17 g H 2 /g organics) > non-catalytic steam reforming of the bio-oils (0.14 g H 2 /g organics) > non-catalytic steam reforming of the aqueous fractions (0.13 g H 2 /g organics) > catalytic steam reforming of the aqueous fractions in fluidized bed (0.07 g H 2 /g organics). These different H 2 yields are a consequence of the different temperatures used in the reforming processes (650 C and 1400 C for the catalytic and the non-catalytic, respectively) as well as the high spatial velocity employed in the catalytic tests, which was not sufficiently low to reach equilibrium in the fluidized bed reactor.
Fuel, 2018
Hydrogen-rich gas production by steam reforming (SR) of the raw bio-oil was studied in a continuous two-step system, with the first unit of thermal treatment (at 500°C) used for retaining the pyrolytic lignin. The remaining volatile stream was reformed in the second unit (fluidized bed reactor) over a Ni/La 2 O 3-αAl 2 O 3 catalyst at 700°C. The effect of space-time (0.04-0.38 g catalyst h/g bio-oil) and steam-to-carbon ratio (S/C) (1.5-6) on bio-oil conversion and product yields was assessed. Temperature programmed oxidation (TPO) was used to analyze the coke deposited on the Ni/La 2 O 3-αAl 2 O 3 catalyst. It was found that a raise in both the space-time and the S/C ratio contribute to increasing the H 2 yield and to decreasing that of CO, CH 4 and C 2-C 4 hydrocarbons. Catalyst deactivation is highly attenuated by raising space-time because of the lower deposition of encapsulating coke, which is directly related to the concentration of bio-oil oxygenates in the reaction medium. Space-time does not affect the formation of filamentous coke (less responsible for deactivation). The S/C ratio has less influence on total coke content than space time. For 700°C, 0.38 g catalyst h/g bio-oil and S/C = 6, a hydrogen-rich gaseous stream (66 vol% H 2) is obtained, with the H 2 yield being 93% based on the bio-oil entering the catalytic reactor (or 87% based on the raw bio-oil fed into the two-step system), which decreases to 70% after 7 h time on stream as a consequence of the low catalyst deactivation. (3) Under usual operating conditions, the H 2 yield obtained is lower than the stoichiometric maximum because of side reactions, such as thermal decomposition of bio-oil oxygenates (Eq. (4)), methanation (Eqs. (5) and (6)), Boudouard reaction (Eq. (7)), and thermal decomposition of CH 4 (Eq. (8)). These reactions lead to the formation of byproducts (CO, CO 2 , CH 4 and light hydrocarbons) and to carbon (coke)
Catalysts
The present review focuses on the production of renewable hydrogen through the catalytic steam reforming of bio-oil, the liquid product of the fast pyrolysis of biomass. Although in theory the process is capable of producing high yields of hydrogen, in practice, certain technological issues require radical improvements before its commercialization. Herein, we illustrate the fundamental knowledge behind the technology of the steam reforming of bio-oil and critically discuss the major factors influencing the reforming process such as the feedstock composition, the reactor design, the reaction temperature and pressure, the steam to carbon ratio and the hour space velocity. We also emphasize the latest research for the best suited reforming catalysts among the specific groups of noble metal, transition metal, bimetallic and perovskite type catalysts. The effect of the catalyst preparation method and the technological obstacle of catalytic deactivation due to coke deposition, metal sinte...
Steam Reforming of Biomass Pyrolysis Oil: A Review
International Journal of Chemical Reactor Engineering, 2019
The steam reforming of biomass pyrolysis oil is a well-established means of producing the more useful bio-hydrogen. Bio-oil has a comparatively low heating value, incomplete volatility and acidity, hence upgrading to a more useful product is required. Over the years, the experimental conditions of the process have been studied extensively in the domain of catalysis and process variable optimisation. Sorption enhancement is now being applied to the system to improve the purity of the hydrogen stream. Lifecycle analyses has revealed that bio-hydrogen offers considerable reductions in energy consumption compared to fossil fuel-derived hydrogen. Also, green-house-gas savings from the process can also be as high as 54.5 %. Unfortunately, techno-economic analyses have elucidated that bio-hydrogen production is still hampered by high production costs. Research endeavours in steam reforming of biomass bio-oil is done with an eye for developing added value products that can complement, subst...
Catalytic Steam Reforming of Bio-Oil to Hydrogen Rich Gas
2013
Bio-oil is a liquid produced by pyrolysis of biomass and its main advantage compared with biomass is an up to ten times higher energy density. This entails lower transportation costs associated with the utilization of biomass for production of energy and fuels. Nevertheless, the bio-oil has a low heating value and high content of oxygen, which makes it unsuited for direct utilization in engines. One prospective technology for upgrading of bio-oil is steam reforming (SR), which can be used to produce H2 for upgrading of bio-oil through hydrodeoxygenation or synthesis gas for processes like the Fischer-Tropsch synthesis. In the SR of bio-oil or biooil model compounds high degrees of conversion and high yields of H2 can be achieved, but stability with time-on-stream is rarely achieved. The deactivation is mainly due to carbon deposition and is one of the major hurdles in the SR of bio-oil. There are two main pathways to minimize carbon deposition in steam reforming; either through opti...
Energy & Fuels, 2010
Bio-oil reforming to produce hydrogen could be an attractive option for sustainable hydrogen. Hydrogen production via catalytic steam reforming of bio-oil in a fluidized-bed reactor was studied in this paper. The optimum conditions on hydrogen production were obtained at 700°C, steam/carbon mole ratio (S/C) of 17, and weight hourly space velocity (WHSV) of 0.4 h -1 . In addition, the reason for catalyst deactivation in a fluidized-bed reactor was investigated. The fresh and deactivation catalysts were analyzed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), which showed that the carbon deposition is not the main reason for catalyst deactivation. The main reason for fresh catalyst deactivation was the NiO grain sintered on the supporter surface.
Steam Reforming of the Bio-Oil Aqueous Fraction in a Fluidized Bed Reactor with in Situ CO 2 Capture
Industrial & Engineering Chemistry Research, 2013
The effect of CO 2 capture in hydrogen production by steam reforming of the bio-oil aqueous fraction was studied. The reforming and cracking activity of the adsorbent (dolomite) and the relationship between these reactions and those corresponding to the catalyst (reforming and water gas shift (WGS)) were considered. The experiments were conducted in a two-step system with the first step at 300°C for pyrolytic lignin retention. The remaining volatiles were reformed in a subsequent fluidized bed reactor on a Ni/La 2 O 3 −α-Al 2 O 3 catalyst. A suitable balance was stricken between the reforming and WGS reactions, on the one side, and the cracking and coke formation reactions, on the other side, at 600°C for catalyst/ dolomite mass ratios ≥0.17. At this temperature and space-time of 0.45 g catalyst h (g bio-oil) −1 , bio-oil was fully converted and the H 2 yield was around 99% throughout the CO 2 capture step. Catalyst deactivation was very low because the cracking hydrocarbon products (coke precursors) were reformed.
Catalytic steam reforming of bio-oil
International Journal of Hydrogen Energy, 2012
Hydrogen and synthesis gas can be produced in an environmentally friendly and sustainable way through steam reforming (SR) of bio-oil and this review presents the stateof-the-art of SR of bio-oil and model compounds hereof. The possible reactions, which can occur in the SR process and the influence of operating conditions will be presented along with the catalysts and processes investigated in the literature. Several catalytic systems with Ni, Ru, or Rh can achieve good performance with respect to initial conversion and yield of hydrogen, but the main problem is that the catalysts are not stable over longer periods of operation (>100 h) due to carbon deposition. Support materials consisting of a mixture of basic oxides and alumina have shown the potential for low carbon formation and promotion with K is beneficial with respect to both activity and carbon formation. Promising results have been obtained in both fluidized and fixed bed reactors, but the coke formation appears to be less significant in fluidized beds. The addition of O 2 to the system can decrease the coke formation and provide autothermal conditions at the expense of a lower H 2 and CO-yield. The SR of bio-oil is still in an early stage of development and far from industrial application mainly due the short lifetime of the catalysts, but there are also other aspects of the process which need clarification. Future investigations in SR of bio-oil could be to find a sulfur tolerant and stable catalyst, or to investigate if a prereformer concept, which should be less prone to deactivation by carbon, is suitable for the SR of bio-oil.