Optimization of hydrogen production from three reforming approaches of glycerol via using supercritical water with in situ CO2 separation

A pathway for hydrogen production from supercritical water reforming of glycerol integrated with in situ CO₂ removal was proposed and analyzed. The thermodynamic analysis carried out by the minimizing Gibbs free energy method of three glycerol reforming processes for hydrogen production was investigated in terms of equilibrium compositions and energy consumption using AspenPlus™ simulator. The effect of operating condition, i.e., temperature, pressure, steam to glycerol (S/G) ratio, calcium oxide to glycerol (CaO/G) ratio, air to glycerol (A/G) ratio, and nickel oxide to glycerol (NiO/G) ratio on the hydrogen production was investigated. The optimum operating conditions under maximum H₂ production were predicted at 450 °C (only steam reforming), 400 °C (for autothermal reforming and chemical looping reforming), 240 atm, S/G ratio of 40, CaO/G ratio of 2.5, A/G ratio of 1 (for autothermal reforming), and NiO/G ratio of 1 (for chemical looping reforming). Compared to three reforming processes, the steam reforming obtained the highest hydrogen purity and yield. Moreover, it was found that only autothermal reforming and chemical looping reforming were possible to operate under the thermal self-sufficient condition, which the hydrogen purity of chemical looping reforming (92.14%) was higher than that of autothermal reforming (52.98%). Under both the maximum H₂ production and thermal self-sufficient conditions, the amount of CO was found below 50 ppm for all reforming processes.     

A combined thermodynamic and experimental study on chemical‐looping ethanol reforming with carbon dioxide capture for hydrogen generation

Chemical‐looping ethanol reforming with carbon dioxide capture is proposed. It combines chemical‐looping reforming and carbon dioxide capture for pure hydrogen generation from ethanol with inherent separation of carbon dioxide. A thermal analysis of the process using NiO oxygen carrier is performed by simulating reactions using the Gibbs energy minimization method. The promising systems are investigated further with respect to temperature, NiO/C₂H₅OH molar ratio, CaO/C₂H₅OH molar ratio and pressure changes as well as possible carbon formation in the reformer. Favorable operation conditions in the presence of CaO are: pressures around 3 atm, reactor temperatures around 850 K, NiO/C₂H₅OH molar ratio = 3 and CaO/C₂H₅OH = 3. The H₂ yield and thermal efficiency with CaO addition are higher than that without CaO addition, showing that the addition of a CO₂ sorbent in the process increases the H₂ production. Copyright © 2012 John Wiley & Sons, Ltd.     

Methane decomposition kinetics and reaction rate over Ni/SiO2 nanocatalyst produced through co-precipitation cum modified Stöber method

Co-precipitation cum modified Stöber method was adopted to produce nano-Ni/SiO₂ (n-Ni/SiO₂) catalyst and conducted a series of methane decomposition kinetic experiments in a fixed bed pilot plant. Methane decomposition activity of n-Ni/SiO₂ catalyst was quantified by considering thermodynamic deposition of carbon at a temperature range of 550–650 °C and methane partial pressure from 0.2 to 0.8 atm. The utmost methane conversion of 18.87 mmol/g_cat min was obtained at 650 °C and methane partial pressure of 0.8 atm. The findings concluded that the enhancement occurred with carbon formation rate when increasing the methane partial pressure is very much evident at higher temperature such as 650 °C. However, the intensity in methane decomposition descending tendency was declined at lower reaction temperature. The effects of methane partial pressure and reaction temperature on the specific molar carbon formation rate were also examined. The calculated reaction order and activation energy were 1.40 and 61.1 kJ mol^?1, respectively. The kinetic experiments showed the existence of an optimum reaction condition to achieve the highest performance of n-Ni/SiO₂ catalyst in terms of methane decomposition rate. However, carbon accumulation ceases once complete catalyst deactivation occurred at certain reaction conditions such as high temperature and lower methane partial pressure. Virgin nanocatalyst and as-produced nanocarbons were studied with BET, XRD, and TEM.     

A pressurized ammonia-fed planar anode-supported solid oxide fuel cell at 1–5 atm and 750–850°C and its loaded short stability test

Ammonia is a useful energy carrier for solid oxide fuel cell (SOFC) with advantages over hydrogen. Understanding of the performance and stability of ammonia-fed SOFC operated at elevated pressure (p) is an important step towards the development of high-efficiency hybrid SOFC power system with micro gas turbine (MGT). This paper reports cell performance, electrochemical impedance spectra (EIS), and stability measurements of a pressurized ammonia-fed anode-supported SOFC at p = 1–5 atm and T = 750–850°C using a planar (50 × 50 mm²) single-full-cell (400 μm Ni-YSZ anode/3 μm YSZ electrolyte/12 μm LSC-GDC cathode). The full cell together with metallic frames and current collectors are sandwiched by a pair of rib-channel flow distributors (interconnectors) in a high-pressure testing facility. Results show that pressurization and increasing temperature enhance the ammonia-fed SOFC performance significantly having almost the same power densities as those of hydrogen/nitrogen-fed SOFC, as substantiated and explained by EIS data and an equivalence circuit model where the effects of p and T on ohmic, gas diffusion, and gas conversion impedances are shown. Moreover, the loaded short (10 h) stability tests at 700°C and 0.8 V for 1 atm/3 atm cases reveal no/little power degradation, where the microstructures without any crack within the scale of SEM observation and nearly the same element atomic percentages of Ni-YSZ anode surfaces from EDX spectra are found. These results suggest that the pressurized ammonia-fed SOFC is a promising candidate for the hybrid SOFC-MGT power generation.     

Hydrogen production by sorption enhanced steam reforming of oxygenated hydrocarbons (ethanol, glycerol, n-butanol and methanol): Thermodynamic modelling

Thermodynamic analysis of steam reforming of different oxygenated hydrocarbons (ethanol, glycerol, n-butanol and methanol) with and without CaO as CO₂ sorbent is carried out to determine favorable operating conditions to produce high-quality H₂ gas. The results indicate that the sorption enhanced steam reforming (SESR) is a fuel flexible and effective process to produce high-purity H₂ with low contents of CO, CO₂ and CH₄ in the temperature range of 723-873 K. In addition, the separation of CO₂ from the gas phase greatly inhibits carbon deposition at low and moderate temperatures. For all the oxygenated hydrocarbons investigated in this work, thermodynamic predictions indicate that high-purity hydrogen with CO content within 20 ppm required for proton exchange membrane fuel cell (PEMFC) applications can be directly produced by a single-step SESR process in the temperature range of 723-773 K at pressures of 3-5 atm. Thus, further processes involving water-gas shift (WGS) and preferential CO oxidation (COPROX) reactors are not necessary. In the case of ethanol and methanol, the theoretical findings of the present analysis are corroborated by experimental results from literature. In the other cases, the results could provide an indication of the starting point for experimental research. At P = 5 atm and T = 773 K, it is possible to obtain H₂ at concentrations over 97 mol% along with CO content around 10 ppm and a thermal efficiency greater than 76%. In order to achieve such a reformate composition, the optimized steam-to-fuel molar ratios are 6:1, 9:1, 12:1 and 4:1 for ethanol, glycerol, n-butanol and methanol, respectively, with CaO in the stoichiometric ratio to carbon atom.     

Thermodynamic analysis of H2 production by oxidative steam reforming of butanol-ethanol-water mixture recovered from Acetone:Butanol:Ethanol fermentation

Thermodynamic equilibrium analysis has been adopted for oxidative steam reforming of butanol-ethanol mixture (B-E) as renewable source obtained from Acetone:Butanol:Ethanol (ABE) fermentation to produce H₂ by using Gibbs free energy minimization method. The effects of pressure (1–10 atm), temperature (573–1473 K), steam/fuel molar feed ratio (f_O1 = 9 and 12), O₂/fuel molar feed ratio (f_O2 = 0–3), and B-E mixture compositions (50–90%B) on equilibrium compositions of H₂, CO, CO₂, CH₄, and carbon are performed. The maximum H₂ yield (65.456% for f_O2 = 0 and 58% for f_O2 = 0.75) has been achieved at f_O1 = 9, 90% B mixture, 1 atm, and 973 K. The yields of CO, CO₂, and CH₄ with respect to maximum H₂ are 53.390%, 44.384%, and 2.225% for f_O2 = 0, and 45.677%, 53.269%, and 1.053% for f_O2 = 0.75, respectively. Energy required per mol of H₂, thermal and exergy efficiencies for the process are also evaluated to utilize the potential of B–E mixture for H₂ production.     

In-depth study of the Ruddlesden-Popper LaxSr2−xMnO4±δ family as possible electrode materials for symmetrical SOFC

The Ruddlesden Popper (RP) manganites La_xSr_2?xMnO_4±δ with compositions 0.25 ≤ x ≤ 0.6 have been successfully synthesized as single phases by solid-state reaction in air. All those materials are not only stable in reducing atmosphere but they also maintain the K₂NiF₄-type structure with I4/mmm symmetry under redox cycling conditions with limited volume changes. The x = 0.5 phase was analyzed by in situ high temperature neutron powder diffraction (HTNPD), under flowing hydrogen, showing the formation of oxide-ion vacancies on the equatorial sites of the perovskite planes, during reduction process. The total electrical conductivity was optimized and found maximum for x = 0.5 with values of 35.6 S cm^?1 and 1.9 S cm^?1 at 800 °C in air and 3% H₂/Ar, respectively, what is judged to be sufficient for an active layer of symmetrical SOFC electrode. First Electrochemical Impedance Spectroscopy (EIS) measurements in both oxidizing and reducing conditions, using an YSZ electrolyte and a GDC buffer layer, are presented giving rise to promising values.     

Influence of MgO content as an additive on the performance of Ni/MgOSiO2 catalysts for the steam reforming of glycerol

Ni catalysts supported on MgOSiO₂ were assessed in the steam reforming reaction of glycerol for the study of the H₂ production and carbon deposition with different MgO contents as additives. The catalysts were prepared with commercial SiO₂ by the aqueous impregnation method and characterized by energy dispersive X-ray spectroscopy, specific surface area, X-ray diffraction, thermogravimetric analysis, X-ray diffraction in situ with O₂, temperature programmed reduction with H₂, X-ray diffraction in situ with H₂, temperature programmed desorption with H₂ and scanning electron microscopy. The glycerol steam reforming reaction took place at 600 °C for 5 h, with a water/glycerol molar ratio of 12/1 at 5 mLh^?1. N₂ was used as the carrier gas. The characterization of the samples showed the interaction of Ni with the support increases with the MgO addition, due to the formation of a NiMg silicate hydrate and MgNiO₂ solid solution; as a result, both metallic area and dispersion also increased. Catalytic results showed similar gaseous products yields (H₂, CH₄, CO and CO₂) for mixed-matrix catalysts, however, a lower carbon deposition on 10 wt%Ni catalyst supported on 30 wt%MgOSiO₂ was observed.     

Electrochemical performance assessment of low-temperature solid oxide fuel cell with YSZ-based and SDC-based electrolytes

In this work, solid oxide fuel cells (SOFCs) based on different electrolytes, i.e., the yttria-stabilized zirconia (YSZ) and the samaria-doped ceria (SDC), were investigated to study their performances at low-temperature operation. The predicted performance of both SOFCs was validated with the experimental results. The verified models were implemented to study the impact of operating conditions, i.e., cell temperature, pressure, thicknesses of cathode, anode, and electrolyte, on their performances. The decrease in the operating temperature from intermediate range (800–900 °C) to low range (550–650 °C) has a considerable effect on the performance of the YSZ-based SOFC as conventional type, which dropped from 0.67–1.40 W/cm² to 0.027–0.13 W/cm². Under the low operating temperature range, the performance of SDC-based SOFC was superior to that of the YSZ-based SOFC, due to the lower ohmic loss. Nevertheless, the SDC-based SOFC has higher concentration overpotentials than the YSZ-based SOFC. The concentration overpotentials of the SDC-based SOFC can be reduced by the thinner anode and cathode thicknesses. In addition, the SDC-based SOFC at low operating temperature with the pressurized operation could significantly improve its power density, about 20% at 2 bar, which was close to that of YSZ-based SOFC at intermediate temperature of 800 °C.     

Thermodynamic and experimental aspects on chemical looping reforming of ethanol for hydrogen production using a Cu‐based oxygen carrier

An investigation on the chemical looping reforming of ethanol process using Gibbs free energy minimization method was performed. It is found that the temperature, oxygen/ethanol molar ratio (OER), and pressure have pronounced influences on the product yields in chemical looping reforming of ethanol process. The ethanol conversion and H₂ yield are 100% and 2.25 mol mol^?1 ethanol, respectively, at 700 °C, OER of 1 and 1 atm. The higher temperatures promote H₂ and CO production, but the higher pressures and OERs have negative effect on the H₂ and CO generation. Favorable operation conditions are 1 atm, 700 °C, and OER = 1. The experimental tests were carried out in a fixed bed using a Cu‐based oxygen carrier prepared by impregnation method. Working at 1 atm, the H₂ concentration increased with an increase in temperature; however, it remained approximately with an increase in gas hourly space velocity. The H₂/CO molar ratio was between 3 and 5 in the period of 0–30 min at 1 atm and 700 °C. Copyright © 2013 John Wiley & Sons, Ltd.     

An energy and exergy analysis of the supercritical water reforming of glycerol for power production

As a continuation of a previous work, a conceptual design is proposed for reforming glycerol using supercritical water to produce maximum electrical power in an energy self-sufficient system. The scheme of the process is simulated after discussing some routes to achieve the aim. The selected way takes advantage of the huge pressure energy of reformate products just at the outlet of the reforming process. The expanded product gas is used as a fuel gas to provide the thermal energy required by the reforming process. The evaluation of the thermodynamic performance of the process is carried out by an energy and exergy analysis. As relevant outputs measurements of the process performance, the net work and exergetic efficiencies as well as the mole fraction and molar flow-rates of hydrogen obtained. Glycerol feed concentration in aqueous solution at which no external heat source is needed was obtained, both for pure and pretreated crude glycerol, at 800 °C and 240 atm. The effect of the main operating parameters has been investigated by sensitivity analysis to identify optimal conditions that maximize power production. In the exergy analysis, the thermodynamic efficiencies used for the overall process and for its individual units are suitably discussed. The computation has been made with the aid of AspenPlus™, using the predictive Soave-Redlich-Kwong equation of state as thermodynamic method in the simulation of the supercritical region. The next study in this series of glycerol reforming using SCW will aim to maximize hydrogen production, including the syngas purification, to generate electricity via fuel cells.     

Cycling stability of RNi5 (R = La,La+Ce) hydrides during the operation of metal hydride hydrogen compressor

This work presents results of the experimental studies (XRD, SEM, PCT) of hydride forming intermetallides used in the first (LaNi₅) and the second (La_0.5Ce_0.5Ni₅) stages of industrial-scale metal hydride hydrogen compressor providing H₂ compression from 3.5 to 150 atm with the productivity about 10 Nm³/h. During the operation, both materials underwent 18,180 hydrogenation/dehydrogenation (h/d) cycles which included H₂ absorption at the pressure of 3.5 atm (LaNi₅) and 35–38 atm (La_0.5Ce_0.5Ni₅) at T = 15–20 °C followed by H₂ desorption at the pressure of 35–38 atm (LaNi₅) and 150 atm (La_0.5Ce_0.5Ni₅) at T = 150–160 °C. It was found that the observed ～30% drop of the productivity of the compressor by the end of its operation is associated with a degradation of the first stage hydride material (LaNi₅) under conditions specified above. The cycling resulted in the appearance of Ni and LaH_2+x phases in addition to the parent intermetallide. In turn, the cycled LaNi₅ exhibited more than 20% lower hydrogen storage capacity than the alloy at the beginning of the cycling; the cycling was also found to result in a noticeable sloping of initially flat plateau. Conversely, the degradation effects in La_0.5Ce_0.5Ni₅ were found to be much less pronounced, in spite of the higher operating H₂ pressures. The observed effect was associated with the decrease of thermodynamic driving force (TDF) of AB₅ disproportionation in H₂ when substituting La with Ce.     

Performance analysis and optimization of a trigeneration process consisting of a proton-conducting solid oxide fuel cell and a LiBr absorption chiller

In this work, the trigeneration system, consisting of a proton-conducting solid oxide fuel cell (SOFC–H⁺) and a single-stage LiBr absorption chiller, was proposed. The SOFC–H⁺ and single-stage LiBr absorption chiller models were developed through Aspen Plus V10. From the sensitivity analysis, the results show that increases in temperature and fuel utilization can improve the performance of the SOFC–H⁺. Conversely, the air to fuel (A/F) molar ratio and pressure negatively affect the electrical efficiency and overall system efficiency. In the case of the absorption chiller, the coefficient of performance was increased and made stable according to a constant value when the generator temperature was increased from 90 to 100 °C. When the optimization was performed, it was found that the SOFC–H⁺ should be operated at 700 °C and 10 bar with fuel utilization of 0.8 and A/F molar ratio of 2 to achieve a maximum overall efficiency of 93.34%. For the energy and exergy analysis, a combined heat and power SOFC–H⁺ was found to have the highest energy and exergy efficiencies, followed by the trigeneration process. This indicates that the integration of the SOFC–H⁺ and LiBr absorption chiller is possible to efficiently produce electricity, heating and cooling.     

Thermodynamic analysis of hydrogen production via glycerol steam reforming with CO2 adsorption

Thermodynamic equilibrium for glycerol steam reforming to hydrogen with carbon dioxide capture was investigated using Gibbs free energy minimization method. Potential advantage of using CaO as CO₂ adsorbent is to generate hydrogen-rich gas without a water gas shift (WGS) reactor for proton exchange membrane fuel cell (PEMFC) application. The optimal operation conditions are at 900 K, the water-to-glycerol molar ratio of 4, the CaO-to-glycerol molar ratio of 10 and atmospheric pressure. Under the optimal conditions, complete glycerol conversion and 96.80% H₂ and 0.73% CO concentration could be achieved with no coke. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in glycerol steam reforming with or without CO₂ separation. Glycerol steam reforming with CO₂ adsorption has the higher energy efficiency than that without adsorption under the same reaction conditions.     

Effects of sulfur poisoning on degradation phenomena in oxygen electrodes of solid oxide electrolysis cells and solid oxide fuel cells

The durabilities of a single solid oxide electrolysis cell (SOEC) and a solid oxide fuel cell (SOFC) operating at 0.3 A cm^?2 and 973 K under different air supply conditions were investigated. In the SOEC, S penetration was observed mainly at the gadolinium-doped ceria (CGO) electrolyte/lanthanum strontium cobalt oxide (LSC) oxygen electrode interface. In contrast, during SOFC operation, S was distributed widely within the LSC. The reaction governing S penetration into the LSC is an oxidizing one. Thus, it is likely that the high oxygen partial pressure at the CGO electrolyte/LSC oxygen electrode interface accelerated the penetration of S. When air was supplied using an activated carbon filter during SOEC operation, the degradation rate decreased to 0.6% kh^?1 within 3000 h. Finally, the results of accelerated tests performed using air containing 0.2 ppm SO₂ suggested that the effect of S poisoning was greater during SOEC operation than during SOFC operation.     

Thermodynamic study of the supercritical water reforming of glycerol

Hydrogen can be produced by steam reforming, partial oxidation, autothermal, or aqueous-phase reforming processes using various noble metal based catalysts, but also by supercritical water (SCW) reforming. Using AspenPlus™, a systematic thermodynamic analysis of glycerol reforming using supercritical water has been carried out by the total Gibbs free energy minimization method, which computes the equilibrium composition of synthesis gas (syngas). The predictive Soave-Redlich-Kwong equation of state (EOS) has been used as thermodynamic method in the simulation of the supercritical region, after evaluating it against other EOS methods. A sensitivity analysis has been conducted on supercritical water reforming of pure and pretreated crude glycerol, as obtained from biodiesel production. The effect of the main operating parameters (temperature, concentration of glycerol feed, glycerol purity in the feed of crude glycerol, and pressure) aimed to the hydrogen production has been investigated in the reforming process, by obtaining the mole fraction and molar flow-rate of components in syngas, as well as the hydrogen yield. Selectivity to the different compounds has been also calculated. By this way, the thermodynamic favorable operating conditions at which glycerol may be converted into hydrogen by SCW reforming have been identified. The simulation results agree well with some few experimental data from the literature. This study is the first of a series addressed to glycerol reforming using SCW.     

Biohydrogen production from Imperata cylindrica bio-oil using non-stoichiometric and thermodynamic model

This paper presents a non-stoichiometric and thermodynamic model for steam reforming of Imperata cylindrica bio-oil for biohydrogen production. Thermodynamic analyses of major bio-oil components such as formic acid, propanoic acid, oleic acid, hexadecanoic acid and octanol produced from fast pyrolysis of I. cylindrica was examined. Sensitivity analyses of the operating conditions; temperature (100–1000 °C), pressure (1–10 atm) and steam to fuel ratio (1–10) were determined. The results showed an increase in biohydrogen yield with increasing temperature although the effect of pressure was negligible. Furthermore, increase in steam to fuel ratio favoured biohydrogen production. Maximum yield of 60 ± 10% at 500–810 °C temperature range and steam to fuel ratio 5–9 was obtained for formic acid, propanoic acid and octanol. The heavier components hexadecanoic and oleic acid maximum hydrogen yield are 40% (740 °C and S/F = 9) and 43% (810 °C and S/F = 8) respectively. However, the effect of pressure on biohydrogen yield at the selected reforming temperatures was negligible. Overall, the results of the study demonstrate that the non-stoichiometry and thermodynamic model can successfully predict biohydrogen yield as well as the composition of gas mixtures from the gasification and steam reforming of bio-oil from biomass resources. This will serve as a useful guide for further experimental works and process development.     

Enhanced ethanol steam reforming by CO2 absorption using CaO,CaO*MgO or Na2ZrO3

This paper presents results of thermodynamic analysis and experimental evaluation of hydrogen production by steam reforming of ethanol (SRE) combined with CO₂ absorption using a mixture of a solid absorbent (CaO, CaO*MgO and Na₂ZrO₃) and a Ni/Al₂O₃ catalyst. Thermodynamic analysis results indicate that a maximum of 69.5% H₂ (dry basis) is feasible at 1 atm, H₂O/C₂H₅OH = 6 (molar ratio) and T = 600 °C. whereas, the addition of a CO₂ absorbent at 1 atm, T = 600 °C and H₂O/C₂H₅OH/Absorbent = 6:1:2.5, produced a H₂ concentration of 96.6, 94.1, and 92.2% using CaO, CaO*MgO, and Na₂ZrO₃, respectively. SRE experimental evaluation achieved a maximum of 60% H₂. While combining SRE and a CO₂ absorbent exhibited a concentration of 96, 94, and 90% employing CaO, CaO*MgO, and Na₂ZrO₃, respectively at 1 atm, T = 600 °C, SV = 414 h⁻¹ and H₂O/C₂H₅OH/absorbent = 6:1:2.5 (molar ratio).     

Bifunctional Ni–CaO catalysts modified with CeO2 and inert Ca12Al14O33 for sorption-enhanced steam reforming of ethanol

In this work, sorption-enhanced steam reforming of ethanol (SE-SRE) process was studied using Ni–CaO-based bifunctional catalysts modified with Ca₁₂Al₁₄O₃₃ (mayenite) and CeO₂. The CaO and CaO/Ca₁₂Al₁₄O₃₃ sorbents were synthesized by a sol-gel method and, subsequently, CeO₂ and Ni were added by the incipient wetness impregnation method. These materials were characterized by BET surface area, thermogravimetric analysis (TGA), in situ X-ray diffraction (XRD), and in situ X-ray absorption near edge structuare (XANES). In addition, the catalysts were tested on 10 cycles of SE-SRE reaction and regeneration. In general, the characterization results revealed an inverse relationship between average crystallite size of CaO and CO₂ sorption capacity. By the in situ XRD/XANES, the addition of the mayenite reduced by half the average crystallite size of CaO and increased the interaction between support and active phase. As a consequence, the catalyst containing mayenite (NiCaAl) showed the best CO₂ capture uptake and stability, which could be justified mitigation of the CaO sintering effect by the inert material presence. Great stability was also observed in the catalytic tests, since the duration of the pre-breakthrough stage for NiCaAl and for the catalyst containing maynite and ceria (NiCaAlCe) remained constant over the reaction cycles. In terms of hydrogen production, NiCaAl catalyst showed the highest H₂ molar fraction during the pre- (90%) and post-breakthrough. The CeO₂ addition slightly favored the methane formation, although did not bring significant benefits in the CO₂ capture and catalytic performance. Therefore, NiCaAl showed the best CO₂ capture capacity and stability, which led to the best SE-SRE performance.     

Enhancing the aromatic hydrocarbon yield from the catalytic copyrolysis of xylan and LDPE with a dual-catalytic-stage combined CaO/HZSM-5 catalyst

The high concentration of oxygenated compounds in pyrolytic products prohibits the conversion of hemicellulose to important biofuels and chemicals via fast pyrolysis. Herein CaO and HZSM-5 was developed to convert xylan and LDPE to valuable hydrocarbons by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and elucidate the reaction mechanism were also investigated in detail. The results indicated that xylan/LDPE copyrolysis was more complicated than pyrolysis of the individual components. LDPE hindered the thermal decomposition and aromatic hydrocarbon formation from xylan at temperatures under 350 °C and had a synergistic effect at high temperatures. 50% LDPE was proven to be more beneficial than other percentages for the formation of monocyclic aromatic hydrocarbons. Simultaneously, the addition of CaO/HZSM-5 significantly reduced the reaction Ea and increased the reaction rate. CaO can effectively improve the deoxygenation and aromatization reaction, enhancing the yield and selectivity of aromatics to a certain extent. The maximum yield of hydrocarbons (96.01%), mono-aromatic hydrocarbons (88.53%) and S_BTXE (85.79%) were obtained at a CaO/HZSM-5 ratio of 1:2, a pyrolysis temperature of 450 °C, a catalytic temperature of 550 °C, a catalyst dose of 1:2 and a xylan-to-LDPE ratio of 1:1 via an ex situ process. The system was dominated by toluene, xylene and alkyl benzene. Diels-Alder reactions of furans and hydrocarbon pool mechanism of nonfuranic compounds improved aromatic formation. This study provides a fundamental for recovering energy and chemicals from pyrolysis of hemicellulose.