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Heterogeneous catalysts for hydrothermal liquefaction of lignocellulosic biomass. A review
No full textThe biomass conversion into more valuable fuels represents one of the most viable routes for the exploitation of this material. Hydrothermal liquefaction is currently considered one of the most efficient processes to convert wet biomass into a bio-crude, which however requires expensive upgrading treatments to be used as biofuel. The use of catalysts able to directly improve bio-crude yield and quality during the reaction is of fundamental importance to increase the overall process efficiency. Homogeneous alkaline catalysts are the most studied, but they are not recoverable at the end of the process and so cannot be reused. The use of heterogeneous catalysts allows to overcome this issue making the recovery and reuse possible, maintaining anyway high activity and selectivity in the bio-crude production. The aim of this review is to critically summarize the effect of heterogenous catalyst addition on the hydrothermal liquefaction of lignocellulosic biomass, looking specifically at the improvement in bio-crude yield and quality. On the basis of literature data about the effect of heterogeneous catalyst addition on bio-crude yield and quality in the hydrothermal liquefaction of lignocellulosic biomass, a common catalytic action was identified allowing to group the several catalysts into four classes (alkaline metal oxides, transition metals, lanthanides oxides and zeolites). The hydrodeoxygenation activity of the catalysts, their effect on bio-crude yield and quality and the operating conditions used are highlighted. The highest bio-crude yields are reported using transition metals and lanthanide oxides which are able to guarantee, at the same time, a high-quality bio-crude
Hydrothermal Liquefaction of Biomass using Waste Material as Catalyst: Effect on the Bio-crude Yield and Quality
No full textHydrothermal liquefaction (HTL) is one of the most promising technologies to produce valuable compounds from
biomass and waste. The use of water as solvent makes this process extremely convenient for high moisture
feedstock and also environmentally sustainable. However, the obtained product, the bio-crude, is not ready to
the end use, its oxygen content is quite high making the oil physically and chemically instable and thus difficult
to handle and store. The use of heterogeneous catalysts and hydrogen producers can improve the product
quality during the hydrothermal process being also easy to be separated and recirculated. In this work the use
of reduced red mud acting as hydrogen producer is tested in the hydrothermal process of oak wood. Red mud
is composed mainly by Fe2O3 that was reduced with the char produced by HTL and by a simulated syngas
which is obtained from char gasification. The reduced red mud was mixed with the biomass and fed into the
HTL batch reactor with variable red mud biomass ratio. The reduction temperature was optimized in order to
obtain zero valent Fe able to produce hydrogen reacting with water in HTL conditions. The tests were conducted
at 330 °C with a reaction time of 10 min. The obtained bio-crude was characterized with elemental analysis. The
results in terms of oil yield and quality were compared with those obtained with pure iron powder showing that
red mud can be used successfully as hydrogen producer in HTL process and recycled after its reduction with
char or syngas. The use of red mud leads to an increase of the oil yield of 20% with respect to the blank test
and looking at the oil composition the hydrogenation effect is evident, the amount of hydrogen increases while
the amount of oxygen decreases
New synthetic route for the production of mayenite support to enhance Ni resistance to coke deposition in the reforming of tar model compounds
No full textFour nickel/mayenite catalysts were synthesized. Mayenite was prepared from different precursors, namely boehmite (AlO(OH)) + Ca(NO3)2·4H2O and gibbsite + Ca(OH)2, for each couple a specific procedure was followed. The effect of the Ni addition method was also evaluated, comparing wet impregnation and direct inclusion of nickel precursor during mayenite preparation. The obtained catalysts were characterized by XRD, BET, SEM/EDS and TPR. The Ni/mayenite catalysts were tested in steam reforming of toluene and pyrocatechol, chosen as tar model compounds. The experiments were conducted in a fixed-bed lab-scale atmospheric reactor, evaluating carbon conversion, hydrogen selectivity and stability. Characterization of the spent catalysts after toluene steam reforming experiments by XRD and DTG-TPO were performed to assess structural changes and carbon deposition. Kinetic parameters of toluene steam reforming were determined for the different catalysts
Use of an innovative TGA apparatus for sampling the emissions generated by pyrolysis of plant assisted bio-remediation biomass
No full textPlant-assisted bioremediation (PABR) represents a green technique for the recovery and remediation of contaminated areas. The biomass produced by these crops is generally considered as a contaminated waste product and potentially harmful. Therefore, it is very important to characterize these biomasses aiming at understanding if they can be treated like traditional biomasses and it is possible to use them in energy conversion process (pyrolysis, gasification, etc.). In this work, the energy conversion processes is simulated through an innovative TGA-DTA analysis using PABR poplar pruning and the emissions are characterized to assess the distribution of the contaminants in the effluent. The TGA-DTA system is interfaced with a particulate filter and a bubbling system for capturing metals. To assess the potential of easily repeatable, small scale TGA-DTA analysis in predicting the main aspects of the gasification process, the results of the experiment are compared with those obtained using the same biomass in a lab-scale fluidized bed gasification (FBG) plant. This comparison showed a good agreement between laboratory tests and those conducted on the real system, confirming that the proposed instrumental apparatus represents an interesting predictive tool for determining the fate of the metals contained in biomass. The analysis also showed that Cd is completely concentrated in the bottom ashes, while as for the other metals, such as Mn, Fe, Cu, Zn, not negligible concentrations are found in the fugitive ashes, e.g. bubbling gases, and then specific metal trapping must be considered in case of PABR gasification
Lignin-enriched waste hydrothermal liquefaction with ZVMs and metal-supported Al2O3 catalyst
No full textHuge amount of technical lignin is produced in paper and pulp industries annually. In this article, lignin hydrothermal liquefaction (HTL) was conducted in the presence of zero valent metals (ZVMs): Zn, Fe, Ni and Co and metal-supported Al2O3 catalysts (Ni/Al2O3 , Fe/Al2O3 , Co/Al2O3 and Cu/Al2O3 ) in order to investigate the possibility to valorize this waste. The bio-crude yields of lignin HTL at 330 C for 60 min were 32.2% Fe > 29.8% Ni > 28.6% Zn > 26.5% blank > 25.4% Co. Fe and Zn act as hydrogen producer being oxidized by subcritical water; the hydrogen stabilized the lignin HTL intermediates, enhancing bio-crude yields which were further improved when Fe and Zn are combined with hydrogenation catalyst Ni/Al2O3 inducing an even higher bio-crude yield of 36.0 and 36.1%, respectively. The energy recovery of Fe + Ni/Al2O3 and Zn + Ni/Al2O3 tests reached 67.8% and 66.3%, significantly higher than 47.4% of blank test. Both ZVMs and metal-supported Al2O3 catalysts showed good demethoxylation function. Zn/Fe and water reaction environment was demonstrated to be promising substitution of high pressure gaseous hydrogen for lignin waste liquefaction process
Improved qualty bio-crude from hydrothermal liquefaction of oak wood assisted by zero-valent metals
No full textThe production of bio-fuels is becoming one of the biggest challenges of this decade. In this context, the interest on hydrothermal liquefaction (HTL) is continuously growing. In this work, the HTL of oak wood to produce a high-quality bio-crude is proposed. The effect of the use of zero-valent metals (ZVMs) as hydrogen producers (Fe and Zn) and hydrodeoxygenation catalysts (Ni and Co) on bio-crude quality is investigated. The tests were conducted at 330 °C in micro-batch reactors at different reaction times in the presence of ZVMs. Fe and Zn are oxidized by subcritical water producing active hydrogen, which is used to stabilize biomass fragments during the process and to be used in hydrodeoxygenation reactions in the presence of Ni and Co. The results show that the use of hydrogen producers significantly affects bio-crude yields, which increase by 20% with respect to the blank test when Fe is used. Furthermore, the synergic effect between the hydrogen producers (Fe and Zn) and the catalysts (Ni and Co) was tested. The results pointed out an enhancement of the bio-crude quality with an increase in the H/C ratio and a decrease in the O/C ratio, and also, looking at the bio-crude composition, the hydrogenation extent is clearly proven, for example, 2-cyclopenten-1-ones increase at the expense of furan derivatives
Syngas cleaning by chemical looping conversion of tars from hazelnut shells pyrolysis/gasification
No full textSyngas tars are responsible for clogging and corrosion of pipelines and equipments due to their high
condensation temperatures. At the same time, considering their energy content they cause a reduction in the
energy efficiency of the conversion process. To overcome these drawbacks, the addition of a downstream
reactor to perform hot catalytic gas cleaning has been proposed. However, the occurrence of significant carbon
deposition and sulphide formation on the catalytically active surfaces can easily lead to early deactivation of the
catalyst. Chemical looping tar reforming is based on a solid material, known as oxygen carrier, that undergoes
two reactions steps: (1) reduction by interaction with the gas and tar streams; (2) regeneration by oxidation with
ambient air, which also involves the combustion of any deposits on the particle surface. In this work, the first
reaction step of the process is investigated in an integrated setup involving the pyrolysis or the gasification of
hazelnut shells and the reaction with the oxygen carrier for tar abatement. Two reactor configurations have been
considered: (1) single reactor, where the biomass and the oxygen carrier beds are loaded in series into the
same reactor; (2) two reactors, where the two beds are loaded into different reactors in series. Blank tests for
pyrolysis and gasification are also carried out for comparison. The results indicate that the two beds
configuration enables higher tar conversion (89% wt for pyrolysis and 75% wt for steam gasification), though
the presence of the oxygen carrier causes a reduction in the energy content of the syngas, especially in terms
of H2 concentration, which is reduced from around 34% to 21% mol for pyrolysis and from 28% to 21% mol for
steam gasification
Green hydrogen production using doped Fe2O3 foams
No full textHydrogen is the ideal energy vector to reduce our fossil-fuels dependency and diminish the climate change consequence. However, current production is still methane based. It is possible to produce hydrogen using bioethanol from the alcoholic fermentation of organic waste by chemical looping processes, but unfortunately current redox systems generate hydrogen with significant traces of CO. In the case of proton exchange membrane fuel cells (PEMFC), hydrogen must be highly purified to produce electricity. Here, high porosity interconnected Fe2O3 foams doped with 2 wt% Al2O3 were manufactured by the freeze-casting method, obtaining around 5.1 mmolH2·gsample−1 of highly pure hydrogen (<10 ppm of CO) consuming only 3.42 mmol of ethanol on each redox cycles, with no deactivation. This result shows the possibility of using an abundant and inexpensive raw material as the iron oxide to scale-up the direct pure H2 production and facilitates its use in the automotive sector
Co-treatment of plastics with subcritical water for valuable chemical and clean solid fuel production
No full textPlastic nylon 66, ethylene-vinyl acetate (EVA) and polyvinyl chloride (PVC) were treated in subcritical water to produce value-added liquid chemicals and clean solid fuels. A synergistic effect was found in the co-treatment of PVC and the other two plastic polymers. Nylon 66 was totally decomposed to water-soluble oligomers with the reaction at 330 °C for 45 min. The same condition was required for the complete hydrolysis of EVA to produce acetic acid and deacetylated solid fuel. The activation energy for nylon 66 and EVA hydrolysis were 99.30 and 146.46 kJ/mol, respectively. However, a relatively low temperature (250 °C) was adequate for PVC dechlorination (efficiency >80%). The hydrochloric acid released from PVC worked as the acidic catalyst, which significantly accelerated the hydrolysis of nylon 66 and EVA, consequently more moderate reaction conditions (250 °C for 60 min) are required. Co-treatment of PVC with other polymers by subcritical water showed a great perspective
In situ hydrodeoxygenation of guaiacol using magnetic catalysts and heterogeneous hydrogen producer
Get PDFThis research aims to figure out the effect of nickel, cobalt, iron powders and alumina-supported nickel catalyst on the hydrodeoxygenation (HDO) of guaiacol using zero-valent Zn as heterogenous hydrogen producer. The HDO tests are conducted at hydrothermal conditions in a batch micro reactor using equal amount of Zn and guaiacol feedstock, water to guaiacol ratio of 10, and catalyst load of 40 and 20 wt.% for metal powders and supported catalyst, respectively, with respect to the mass of guaiacol. Reaction time and temperature were set at 60 min and 300 oC. The fresh and exhausted supported catalysts were characterized by the XRD and SEM-EDX analyses. Among the tested commercial metal powders, Ni has the highest guaiacol conversion rate 51.3%, significantly higher than 11.8% of Fe and 20.0% of Co. Compared with metal powders, the alumina-supported nickel catalyst showed superior performance in terms of high conversion rate of 99.3% and high hydrodeoxygenation (HDO) and hydrodearomatization (HDA) efficiencies
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