Steam reforming of propionic acid: Thermodynamic analysis of a model compound for hydrogen production from bio-oil

The thermodynamic equilibrium of steam reforming of propionic acid (HPAc) as a bio-oil model compound was studied over a wide range of reaction conditions (T = 500–900 °C, P = 1–10 bar and H₂O/HPAc = 0–4 mol/mol) using non-stoichiometric equilibrium models. The effect of operating conditions on equilibrium conversion, product composition and coke formation was studied. The equilibrium calculations indicate nearly complete conversion of propionic acid under these conditions. Additionally, carbon and methane formation are unfavorable at high temperatures and high steam to carbon (S/C) ratios. The hydrogen yield versus S/C ratio passes a maximum, the value and position of which depends on temperature. The thermodynamic equilibrium results for HPAc fit favorably with experimental data for real bio-oil steam reforming under same reaction conditions.     

Hydrogen production from bio-oil: A thermodynamic analysis of sorption-enhanced chemical looping steam reforming

The steam reforming of pyrolysis bio-oil is one proposed route to low carbon hydrogen production, which may be enhanced by combination with advanced steam reforming techniques. The advanced reforming of bio-oil is investigated via a thermodynamic analysis based on the minimisation of Gibbs Energy. Conventional steam reforming (C-SR) is assessed alongside sorption-enhanced steam reforming (SE-SR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR). The selected CO₂ sorbent is CaO(s) and oxygen transfer material (OTM) is Ni/NiO. PEFB bio-oil is modelled as a surrogate mixture and two common model compounds, acetic acid and furfural, are also considered. A process comparison highlights the advantages of sorption-enhancement and chemical looping, including improved purity and yield, and reductions in carbon deposition and process net energy balance.The operating regime of SE-CLSR is evaluated in order to assess the impact of S/C ratio, NiO/C ratio, CaO/C ratio and temperature. Autothermal operation can be achieved for S/C ratios between 1 and 3. In autothermal operation at 30 bar, S/C ratio of 2 gives a yield of 11.8 wt%, and hydrogen purity of 96.9 mol%. Alternatively, if autothermal operation is not a priority, the yield can be improved by reducing the quantity of OTM. The thermodynamic analysis highlights the role of advanced reforming techniques in enhancing the potential of bio-oil as a source of hydrogen.     

A thermodynamic equilibrium analysis of hydrogen and synthesis gas production from steam reforming of acetic acid and acetone blends as bio-oil model compounds

Thermodynamic analysis of steam reforming of blends of two model oxygenates, acetic acid and acetone, representing carboxylic acids and ketones in bio-oil is performed to investigate the effects of their potential interactions on hydrogen yield, synthesis gas composition and progress of reaction network. The results show that both acetic acid and acetone reach complete conversion at all operating conditions. Higher S/C molar ratio results in higher H₂ and CO₂ yields for both acetic acid and acetone. With the increase in pressure, H₂ and CO yields are diminished whereas CH₄ and CO₂ yields are enhanced. H₂ and CO₂ yields increase with the decrease in acetone concentration in the feed blend. CO and CH₄ production are affected adversely for acetic acid rich blends. The maximum H₂ yield values are 75.54%, 78.34%, 80.09%, 81.78% and 84.17% at 700 °C for acetic acid/acetone blends of 0.0/1.0, 0.3/0.7, 0.5/0.5, 0.7/0.3 and 1.0/0.0, respectively.     

Optimization of two bio-oil steam reforming processes for hydrogen production based on thermodynamic analysis

Thermodynamics of hydrogen production from conventional steam reforming (C-SR) and sorption-enhanced steam reforming (SE-SR) of bio-oil was performed under different conditions including reforming temperature, S/C ratio (the mole ratio of steam to carbon in the bio-oil), operating pressure and CaO/C ratio (the mole ratio of CaO to carbon in the bio-oil). Increasing temperature and S/C ratio, and decreasing the operating pressure were favorable to improve the hydrogen yield. Compared to C-SR, SE-SR had the significant advantage of higher hydrogen yield at lower desirable temperature, and showed a significant suppression for carbon formation. However excess CaO (CaO/C > 1) almost had no additional contribution to hydrogen production. Aimed to achieve the maximum utilization of bio-oil with as little energy consumption as possible, the influences of temperature and S/C ratio on the reforming performance (energy requirements and bio-oil consumption per unit volume of hydrogen produced, Q_D/H2 (kJ/Nm³) and Y_Bio-oil/H2 (kg/Nm³)) were comprehensively evaluated using matrix analysis while ensuring the highest hydrogen yield as possible. The optimal operating parameters were confirmed at 650 °C, S/C = 2 for C-SR; and 550 °C, S/C = 2 for SE-SR. Under their respective optimal conditions, the Y_Bio-oil/H2 of SE-SR is significant decreased, by 18.50% compared to that of C-SR, although the Q_D/H2 was slightly increased, just by 7.55%.     

Hydrogen production from a model bio-oil/bio-glycerol mixture through steam reforming using Zeolite L supported catalysts

Zeolite L featuring different size and shape (nanocrystals and discs), with and without alkaline metal exchange (Cs or Na), was used as catalyst support in bio-oil/bio-glycerol mixture Steam Reforming (SR). Zeolites were modified with CeO₂ to improve support properties before the impregnation of nickel. Then, prepared catalysts were tested in SR of a multi-component synthetic bio-oil/bio-glycerol mixture at 1073 and 973 K, under atmospheric pressure and using a Steam to Carbon (S/C) ratio of 5.0. Activity tests showed that catalysts deactivated during the experiments at 973 K. In addition, the sodium exchange produced the sintering of the Zeolite L crystals. Thus, Na containing catalysts produced low conversions and hydrogen yields lower than 30%. On the other hand, Cs containing catalysts resulted in slightly lower hydrogen yields than the supports without this metallic cation. Regarding the morphology of the zeolites, the ones with disc shape were the most active for bio-oil SR purposes producing hydrogen yields close to 80% in the first reaction stage at 1073 K and hydrogen yields close to the 50% at the last reaction stage at 1073 K.     

Carbon deposition behavior in steam reforming of bio-oil model compound for hydrogen production

Catalyst deactivation caused by coke formation is a bottleneck in steam reforming of bio-oil for hydrogen production. The investigation of carbon deposition behavior can make a contribution to the improvement of catalyst and the knowledge of reaction mechanism. In this paper, m-cresol (C₇H₈O, one of the organic compounds present in bio-oil) was chosen as model compound. The experiment was carried out on a commercial Ni/MgO catalyst. As a comparative test, m-cresol decomposition showed carbon deposition can be formed more easily under higher temperature. In steam reforming process, for the competition of carbon deposition and carbon elimination, a peak value of coking formation rate was obtained in a broad range of temperature (575–900 °C). The increase of steam to carbon ratio can favor the carbon elimination. Final coking formation rate curve was determined under optimal reaction conditions and the results showed the severity of carbon deposition maintained a very low level during the entire reaction time. Based on the distribution of reforming products, high temperature and sufficient water feeding can favor the carbon conversion from solid and liquid phase to gaseous phase. Unreacted m-cresol is the main organic compound detected in liquid condensate. Some secondary reactions can be deduced through the other compounds detected. The carbon deposition state on catalyst surface can be in the form of nanofiber, but their concrete shapes can be different due to different reaction conditions.     

Optimization of bio-oil steam reforming process by thermodynamic analysis

A straightforward thermodynamic analysis of bio-oil steam reforming was carried out in the context of hydrogen and syngas production, employing Gibbs energy minimization method to determine equilibrium composition and global reaction heat. The bio-oil model compound was a mixture of acetic acid, phenol, and acetone. The effects of process variables, such as temperature and inlet S/C molar ratio, were investigated over a wide range of conditions. Thermodynamic analysis was performed using the software Aspen Plus v.11. It was identified the best operational conditions that could maximize syngas and further hydrogen production considering energy efficiency. The optimum production of hydrogen is 2.28 mol per carbon mole at S/C = 10 and 850 K, and syngas is 2.37 mol per carbon mole at S/C = 10 and 900 K. It has been demonstrated that the equilibrium calculations can be used to simulate these steam reforming reactions, given the catalyst's behavior.     

Sustainable hydrogen production from steam reforming of bio-oil model compound based on carbon deposition/elimination

Steam reforming of crude bio-oil or some heavy component present in bio-oil is a great challenge for sustainable hydrogen production due to the extensive coke formation and catalyst deactivation. Catalyst regeneration will be an unavoidable operation in this process. In this paper, m-cresol (a model compound derived from bio-oil) was steam reformed on commercial Ni-based catalyst. Two conventional carbon elimination methods for coked catalyst were applied and the results showed that sustainable hydrogen production can be obtained based on carbon deposition/elimination. The carbon deposition can be gasified easily under certain temperature. The activity of regenerated catalyst samples can be nearly recovered as the fresh ones. Under the reaction conditions of 850 °C and steam to carbon ratio 5:1, >66% hydrogen mole fraction, >81% hydrogen yield, and >97% carbon conversion can be achieved based on regenerated catalyst. Catalyst characterization indicated that the loss of active metal can be considered as the main reason for tiny activity drop. Ni redispersion and Fe contamination may be another two factors that influence catalyst activity.     

Hydrogen production from catalytic steam reforming of biomass pyrolysis oil or bio-oil derivatives: A review

Steam reforming of biomass pyrolysis oil or bio-oil derivatives is one of the attractive approaches for hydrogen production. The current research focused on the development of promising catalysts with favorable catalytic activity and high coke resistance. Noble metal such as Rh has been proven to achieve promising reforming reaction efficiencies. However, Ni has attracted considerable attention owing to its stability, cost effectiveness, and good activity in breaking C–C and C–H bonds. Nevertheless, Ni-based catalysts have serious carbon deposition problems arising from chemical poisoning, metal sintering, and poor metal dispersion. This paper attempted to review the current trends in catalyst development considering the aspects of supports, metals, and promoters as an effort to find possible solutions for the limitations of Ni-based catalysts. The present review also covered the current understanding on the reaction mechanisms as well as the future prospects in the field of steam reforming catalysts.     

Hydrogen production via catalytic steam reforming of the aqueous fraction of bio-oil using nickel-based coprecipitated catalysts

Hydrogen production was studied in the catalytic steam reforming of a synthetic and a real aqueous fraction of bio-oil. Ni/Al coprecipitated catalysts with varying nickel content (23, 28 and 33 relative atomic %) were prepared by an increasing pH technique and tested during 2 h under different experimental conditions in a small bench scale fixed bed setup. The 28% Ni catalyst yielded a more stable performance over time (steam-to-carbon molar ratio, S/C = 5.58) at 650 °C and a catalyst weight/organic flow rate (W/m_org) ratio of 1.7 g catalyst min/g organic. Using the synthetic aqueous fraction as feed, almost complete overall carbon conversion to gas and hydrogen yields close to equilibrium could be obtained with the 28% Ni catalyst throughout. Up to 63% of overall carbon conversion to gas and an overall hydrogen yield of 0.09 g/g organic could be achieved when using the real aqueous fraction of bio-oil, but the catalyst performance showed a decay with time after 20 min of reaction due to severe coke deposition. Increasing the W/m_org ratio up to 5 g catalyst min/g organic yielded a more stable catalyst performance throughout, but overall carbon conversion to gas did not surpass 83% and the overall hydrogen yield was only ca. 77% of the thermodynamic equilibrium. Increasing reaction temperatures (600–800 °C) up to 750 °C enhanced the overall carbon conversion to gas and the overall yield to hydrogen. However, at 800 °C the catalyst performance was slightly worse, as a result of an increase in thermal cracking reactions leading to an increased formation of carbon deposits.     

Process simulation of hydrogen production from bio-oil using iCON

This work aims to investigate the feasibility of upgrading bio-oil into hydrogen via steam reforming and water shift reactions using conceptual design and simulation approaches. In the simulation work using PETRONAS iCON software, it is assumed that the aqueous fraction of bio-oil comprises of 67% acetic acid, 16.5% acetone, and 16.5% ethylene glycol. It is observed that increment in temperature and the amount of steam supplied in the steam reformer increase the hydrogen production until a certain extent. Meanwhile, opposite effect on hydrogen production is observed for both the temperature and steam used in the shift reactor. The overall conversion predicted for the process is 84% at operating temperatures and pressures for the steam reformer and shift reactor of 650 and 200°C, and 1 and 17 bar, respectively, and at the molar steam-to-carbon ratio (S:C) of 6.5. The results are compared and showed good agreement with those from published simulation and experimental work. Positive preliminary economic potential was obtained for the process developed, that is, USD 5.56 × 10⁶/year.     

Renewable hydrogen production via steam reforming of simulated bio-oil over Ni-based catalysts

The production of hydrogen via steam reforming (SR) of simulated bio-oil (glycerol, syringol, n-butanol, m-xylene, m-cresol, and furfural) was investigated over Ni/CeO₂-Al₂O₃ and Me-Ni/CeO₂-Al₂O₃ (Me = Rh, Ru) catalysts. Monometallic (Ni) and bimetallic (Rh-Ni and Ru-Ni) catalysts were prepared by the wetness impregnation technique of the CeO₂-Al₂O₃ support previously synthesized by the surfactant-assisted co-precipitation method. The as-prepared powders were systematically characterized by N₂-physisorption, XRD, H₂-TPR, and TEM measurements to analyze their structure, morphology, and reducibility properties. Experiments were performed in a continuous fixed-bed reactor at atmospheric pressure, temperature of 800 °C, steam to carbon (S/C) ratio of 5, and WHSV of 21.15 h⁻¹. Then, the temperature was decreased to 700 °C and increased afterwards to 800 °C. After the experiments TPO and TEM analysis were performed on the spent catalysts to check any evidence of catalyst deactivation. The results showed that the incorporation of noble metal (Ru or Rh) promoter positively affected the activity of the Ni/CeO₂-Al₂O₃ catalysts by enhancing the reducibility of Ni²⁺ species. Ni-based catalyst deactivated under the studied conditions, whereas Ru- and mainly Rh-promoted systems showed increased resistance to carbon deposition by favouring the gasification of adsorbed carbon species. Between all tested catalysts, the Rh-Ni/CeO₂-Al₂O₃ provided the highest H₂ yield and coking-resistance in SR of simulated bio-oil.     

Thermodynamic analysis of aqueous phase reforming of three model compounds in bio-oil for hydrogen production

Thermodynamic analysis with Gibbs free energy minimization was performed for aqueous phase reforming of methanol, acetic acid, and ethylene glycol as model compounds for hydrogen production from bio-oil. The effects of the temperature (340-660 K) and pressure ratio Psys/PH₂O (0.1-2.0) on the selectivity of H₂ and CH₄, formation of solid carbon, and conversion of model compounds were analyzed. The influences of CaO and O₂ addition on the formation of H₂, CH₄, and CO₂ in the gas phase and solid phase carbon, CaCO₃, and Ca(OH)₂ were also investigated. With methanation and carbon formation, the conversion of the model compounds was >99.99% with no carbon formation, and methanation was thermodynamically favored over hydrogen production. H₂ selectivity was greatly improved when methanation was suppressed, but most of the inlet model compounds formed solid carbon. After suppressing both methanation and carbon formation, aqueous phase reforming of methanol, acetic acid and ethylene glycol at 500 K and with Psys/PH₂O = 1.1 gave H₂ selectivity of 74.98%, 66.64% and 71.38%, respectively. These were similar to the maximum stoichiometric hydrogen selectivity of 75.00% (methanol), 66.67% (acetic acid), and 71.43% (ethylene glycol). At 500 K and 2.90 MPa, as the molar ratio of CaO/BMCs increased, the normalized variation in H₂ increased and that for CH₄ decreased. Formation of solid carbon was effectively suppressed by addition of O₂, but this was at the expense of H₂ formation. With the O₂/BMCs molar ratio regulated at 1.0, oxidation and CO₂ capture increased the normalized variation in H₂ to 33.33% (methanol), 50.00% (acetic acid), and 60.00% (ethylene glycol), and the formation of solid carbon decreased to zero.     

Study of bio-oil and bio-char production from algae by slow pyrolysis

This study examined bio-oil and bio-char fuel produced from Spirulina Sp. by slow pyrolysis. A thermogravimetric analyser (TGA) was used to investigate the pyrolytic characteristics and essential components of algae. It was found that the temperature for the maximum degradation, 322 °C, is lower than that of other biomass. With our fixed-bed reactor, 125 g of dried Spirulina Sp. algae was fed under a nitrogen atmosphere until the temperature reached a set temperature between 450 and 600 °C. It was found that the suitable temperature to obtain bio-char and bio-oil were at approximately 500 and 550 °C respectively. The bio-oil components were identified by a gas chromatography/mass spectrometry (GC–MS). The saturated functional carbon of the bio-oil was in a range of heavy naphtha, kerosene and diesel oil. The energy consumption ratio (ECR) of bio-oil and bio-char was calculated, and the net energy output was positive. The ECR had an average value of 0.49.     

Hydrogen production by steam reforming of bio-oil/bio-ethanol mixtures in a continuous thermal-catalytic process

The feasibility of the steam reforming of bio-oil aqueous fraction and bio-ethanol mixtures has been studied in a continuous process with two in-line steps: thermal step at 300 °C (for the controlled deposition of pyrolytic lignin during the heating of the bio-oil/bio-ethanol feed) followed by steam reforming in a fluidized bed reactor on a Ni/α-Al₂O₃ catalyst. The effect of bio-ethanol content in the feed has been analyzed in both the thermal and reforming steps, and the suitable range of operating conditions (temperature and space-time) has been determined for obtaining a high and steady hydrogen yield. Higher ethanol content in the mixture feed improves the reaction indices and reduces coke deposition. Operating conditions of 700 °C and space-times higher than 0.23 g_catalyst h (g_bio-oil+EtOH)⁻¹ are suitable for attaining almost fully conversion of oxygenates (bio-oil and ethanol) and hydrogen yields above 93%, with low catalyst deactivation.     

Characterization of bio-oil and its sub-fractions from pyrolysis of Scenedesmus dimorphus

In the present study, microalgae Scenedesmus dimorphus was reported for pyrolysis in a fixed-bed reactor to determine the effects of temperature on products yield and the chemical compositions of the liquid and solid products. Experiments were carried out at a temperature range of 300–600 °C with heating rate of 40 °C/min and nitrogen flow rate of 100 ml/min. The yield of bio-oil was found to be maximum (39.6%) at the temperature of 500 °C and was further fractionated into n-hexane, toluene, ethyl acetate and methanol sub-fractions by using liquid column chromatography. Various characteristics of bio-oil and its sub-fractions were determined by ¹H NMR, FTIR and GC–MS. The biochar produced as a co-product can be a potential soil amendment with multiple benefits including soil fertility and C-sequestration. The present investigation suggests the suitability of Scenedesmus dimorphus as a potential feedstock for exploitation of energy and biomaterials through pyrolytic conversion.     

Optimization and characterization studies on bio-oil production from palm shell by pyrolysis using response surface methodology

In this work palm shell waste was pyrolyzed to produces bio-oil. The effects of several parameters on the pyrolysis efficiency were tested to identify the optimal bio-oil production conditions. The tested parameters include temperature, N₂ flow rate, feed-stock particle size, and reaction time. The experiments were conducted using a fix-bed reactor. The efficient response surface methodology (RSM), with a central composite design (CCD), were used for modeling and optimization the process parameters. The results showed that the second-order polynomial equation explains adequately the non-linear nature of the modeled response. An R² value of 0.9337 indicates a sufficient adjustment of the model with the experimental data. The optimal conditions found to be at the temperature of 500 °C, N₂ flow rate of 2 L/min, particle size of 2 mm and reaction time of 60 min and yield of bio-oil was approximately obtained 46.4 wt %. In addition, Fourier Transform infra-red (FT-IR) spectroscopy and gas chromatography/mass spectrometry (GC-MS) were used to characterize the gained bio-oil under the optimum condition.     

Thermodynamic analysis of hydrogen production via steam reforming of selected components of aqueous bio-oil fraction

This work presents thermodynamics analysis of hydrogen production via steam reforming of bio-oil components. The model compounds, acetic acid, ethylene glycol and acetone, representatives of the major classes of components present in the aqueous fraction of bio-oil were used for the study. The equilibrium product compositions were investigated in a broad range of conditions like temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm). Any of the three model compounds can be fully reformed even at low temperatures producing hydrogen with maximum yield ranging from 80% to 90% at 900 K. Steam to fuel ratio positively affect the hydrogen content over the entire range of temperature studied. Conversely, higher pressure decreases the hydrogen yield. The formation of solid carbon (graphite) does not constitute a problem provided that reforming temperatures higher than 600 K and steam to fuel ratios higher than 4 for acetic acid and ethylene glycol and 6 for acetone are to be used. Thermal decomposition of the bio-oil components is thermodynamically feasible, forming a mixture containing _C(s)${\mathrm{C}}_{(\mathrm{s})}$, CH₄, H₂, CO, CO₂, and H₂O at various proportions depending on the specific nature of the compound and the temperature. Material and energy balances of complete reforming system demonstrated that the production of 1 kmol/s hydrogen from bio-oil steam reforming requires almost the same amount of energy as with natural gas reforming.     

Catalytic steam reforming of bio-oil

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 state-of-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.     

Mechanistic study of bio-oil catalytic steam reforming for hydrogen production: Acetic acid decomposition

To clarify the understanding of the mechanism of bio-oil catalytic steam reforming, we selected acetic acid as a typical bio-oil model compound to study its detailed behavior in decomposition over an active stepped Ni surface by density functional theory calculations. The adsorption geometries and energies of various intermediates were reported. Linear correlations between the adsorption energy and the number of hydrogen atoms removed for CH_xCOOH, CH_xCOO, and CH_x species (x = 1–3) were found, with increments of ?1.56, ?0.81, and ?1.80 eV, respectively. Thirty-seven possible elementary reactions of acetic acid decomposition were proposed, and their activation energies, reaction energies, rate constants, and equilibrium constants were calculated. Acetic acid dissociation likely started via α-carbon dehydrogenation, OH dehydrogenation, and dehydroxylation. Combined with microkinetic modeling, the most preferable decomposition pathway was suggested as CH₃COOH → CH₃CO → CO + CH₃. The rate-determining step was CH₃COOH dehydroxylation to CH₃CO with an activation energy of 0.68 eV and a rate constant of 3.82 × 10⁸ s^?1. The formation of CH₃COO was dominant at high temperatures, whereas its decomposition occurred with difficulty.