•The catalyst particle size affects the carbon limits.•Carbon formation increases with particle size.•The precursor for carbon is methane at high temperature and CO at low temperature.
The effect of ...catalyst particle size on thermodynamic equilibrium of methane dry reforming and carbon formation has been studied through the Gibbs free energy minimization method taking into account the deviation of carbon formed from graphite Gibbs energy and its dependence on catalyst particle size. Methane and CO2 conversions are maximized at low pressure and high temperature, and a molar H2/CO ratio of 1 is obtained at 1100–1200K and 5–10bar. Carbon formation was found to increase with particle diameter, and carbon presence was noticed at conditions of high pressure/low temperature and high temperature/low pressure. Optimal operating conditions were found to be close to carbon limits, highlighting the need for active metal particle size to be less than 5–6nm to minimize coking. CO was identified as the precursor for carbon at low temperature, while CH4 was found to be the main precursor at high temperature.
•High Ni/Co ratio achieves higher activity.•Promotion with Ru improves stability, reducibility and coking.•Calcination affects stability of Co-Ru catalyst.•Synergetic effects in Ni/Co system due to ...hydrogen spillover.
This work studies the effect of Ni/Co ratio and calcination temperature on the performance of trimetallic Ni-Co-Ru catalysts supported on MgO-Al2O3. Higher activity was achieved with higher Ni/Co ratios, and the effect of calcination temperature on stability was small except for the bimetallic Co-Ru catalyst which showed different deactivation mechanisms at different calcination temperatures. A higher calcination temperature was generally associated with an increased coking rate due to elevated sintering, while a lower calcination temperature slightly improved the reducibility of the catalysts. Promoting the Ni-Co catalysts with Ru improved their stability and reducibility, but slightly compromised catalyst activity when calcined at high temperature. Coking rate was significantly reduced by Ru addition on the 7.5Ni 7.5Co sample. Excellent stability and the lowest coking rate were achieved at the expense of a slightly lowered activity with the 5Ni 10Co 0.25Ru catalyst calcined at 750 °C.
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•ECIG heating filament wires were found to have a strong catalytic effect.•Carbonyl formation chemistry is catalyzed at temperatures that are well below those expected during “dry ...puffing”.•New nichrome wires were the least reactive, but when aged they exhibited the highest reactivity.•Results suggest that catalysis by ECIG filaments may partially explain the wide ranges of carbonyls.
Carbonyls, a class of compounds strongly linked to pulmonary disease in smokers, are probably the most reported non-nicotine toxicants found in electronic cigarette (ECIG) aerosols. Reported emissions vary from negligible quantities to those far exceeding combustible cigarettes. Observations of high emissions are commonly attributed to “dry puffing”, whereby the ECIG heating filament runs dry of liquid and reaches temperatures that induce thermal degradation of the ECIG vapor components at the filament’s metal surface. Using a pyrolysis flow reactor, in this study we examined the potential role of surface chemistry in the formation of carbonyl compounds in ECIGs, and whether the different commercially available filament materials could potentially impact their toxicant emissions through catalysis. This information could inform nascent efforts to regulate the design of ECIGs for public health ends.
Nitrogen or air saturated with propylene glycol vapor was drawn through a temperature and residence-time controlled tubular quartz pyrolysis flow reactor in which nichrome, Kanthal, or stainless steel ECIG heating filament wires were inserted. A control condition with no inserted wire was also included. Concentrations of carbonyl products at the reactor outlet were measured as a function of temperature, heating filament wire material, and carrier gas composition (N2 vs air). Carbonyls were sampled using DNPH cartridges and analyzed by HPLC.
ECIG heating filament wires were found to have a strong catalytic effect. Carbonyl formation initiated at temperatures lower than 250 °C in the presence of the metallic wires, compared to 460 °C without them. Carbonyl formation was found to be a function of the material of construction, and whether the wire was new or aged. New nichrome wires were the least reactive, but when aged they exhibited the highest reactivity. Carbonyls were formed via dehydration or oxidation reactions of PG.
Carbonyl formation chemistry is catalyzed by commonly used ECIG heating filament materials, at temperatures that are well below those expected during “dry puffing”. The variability in the distribution and yield of carbonyl compounds across ECIG filament materials suggests that this heretofore unaccounted variable may partially explain the wide ranges reported in the literature to date. More importantly, it suggests that ECIG construction materials may be an important variable for regulations designed to protect public health.
This work investigates the design of optimal tri-generation systems for heat, power and water production via multiple fuel selections, thus aiming to reduce the reliance on fossil fuel consumption. ...Generally speaking, tri-generation systems are associated with high levels of carbon dioxide emissions to meet energy and water production requirements. Hence, a shift towards more renewable energy sources can assist in partially reducing the environmental damage associated with standard tri-generation operations. Since the switch from fossil fuels to renewable energy is very costly, hybrid energy systems were found an appealing solution that could allow a gradual reduction of carbon emissions. Hence, the novelty aspect of this work is the ability to generate cost-effective tri-generation systems that incorporate optimal hybrid energy selections and utility generation routes, subject to specific net carbon reduction targets (NCRT). As such, four different energy sources (natural gas, biomass, municipal solid waste (MSW) and Concentrated Solar Power (CSP) were investigated, together with five different routes for steam expansion and electricity production using a Mixed Integer Nonlinear Program (MINLP), including technical, economic and environmental constraints. In order to study the effect of different fuel selections, energy production operations, and water production routes on the performance of tri-generation systems, data from three different desalination plants (located in USA, Cyprus and Qatar) were used. The results obtained show that energy requirements for desalination greatly affects the order of selection of energy sources. In general, biomass was identified as the best alternative to replace natural gas at NCRT values below 40%. On the other hand, MSW incineration using grate-fired and fluidized bed boilers became more desirable for steam production when higher NCRT values were utilized. The water production costs (WPC) of a standalone CSP system integrated with each of the studied plants, having a feedwater salinity of 33.5, 41.8 and 45 g/L, were estimated at 1.739, 2.233 and 2.67 USD/m3, respectively. In addition, an average incremental increase of 5.5% in the WPC has been observed during seasons that provide the lowest solar availability values.
Ethanol gasification of waste tires was investigated against pyrolysis in the presence of H-β zeolite and γ-Al2O3 catalysts. Non-catalytic gasification gave a much higher gas yield of 45.2% in ...comparison to a pyrolysis gas yield of 29% and increased the hydrogen content of the gas. Using a catalyst increased the gas yield during both pyrolysis and gasification from 29% to 34–35% and 50–52%, respectively. γ-Al2O3 was found to be more effective at catalyzing secondary pyrolysis reactions such as cracking, dehydrogenation, aromatization, and cyclization, especially when coupled with the excessive free radicals produced during ethanol gasification, resulting in a gas with 35 mol% hydrogen. H-β was found to enhance the formation of light alkenes such as propylene and ethylene during pyrolysis and gasification, respectively. The resultant syngas is suitable for use either as an energy alternative, or as feedstock for Fischer-Tropsch synthesis for the production of higher hydrocarbons.
•Catalytic gasification of scrap tires with ethanol increases gas yield to 50–52%.•Gasification with γ-Al2O3 catalyst enhances production of hydrogen.•Gasification with H-β zeolite enhances production of ethylene.•Thermal gasification produces gas with H2/CO ratio suitable for Fischer-Tropsch and methanol synthesis.
The performance of catalysts used for the dry reforming of methane can strongly depend on the selection of active metals, supports and promoters. This work studies their effects on the activity and ...stability of selected catalysts. Designing an economically viable catalyst that maintains high catalytic activity and stability can be achieved by exploiting the synergic effects of combining noble and/or non-noble metals to form highly active and stable bi- and tri-metallic catalysts. Perovskite type catalysts can also constitute a potent and cost effective substituent. Metal oxide supports with surface Lewis base sites are able to reduce carbon formation and yield a greater stability to the catalyst, while noble metal promoters have proven to increase both catalyst activity and stability. Moreover, a successful metal-support-promoter combination should lead to higher metal-support interacrtion, lower reduction temperature and enhancement of the anti-coking and anti-amalgamation properties of the catalyst. However, the effect of each parameter on the overall performance of the catalyst is usually complex, and the catalyst designer is often faced with a tradeoff between activity, stability and ease of activation. Based on the review carried out on various studies, it is concluded that a catalyst design must take into consideration not only the separate effects of the active metal, support and promoter, but should also include the combined and mutual interactions of these components.
Zinc-promoted nickel catalysts on Ultra-Stable Y (USY) zeolite support are tested for their efficacy towards methane pyrolysis. The un-promoted catalyst obtained a conversion of 65.8%, which dropped ...to 57.3% at the end of the experiment. However, addition of 5 wt% Zn promoter increased the conversion to 67.7%, with no discernible loss in activity after 60 h on-stream. XPS analysis indicated evidence of electronic interaction between the Ni and Zn metals, and the addition of Zn caused a reduction in the metal-support interactions of the catalyst as revealed in TPR and XRD analyses. The catalytic activity of the 50Ni–5Zn/USY also remained completely stable for 60 h even after the operating temperature was increased to 650 °C and the partial pressure of methane in the inlet increased to 80%, at a High gas hour space velocity of 120 L/gcat.h. Analysis of the spent 50Ni–5Zn/USY catalyst revealed the presence of Ni–Zn carbides that may have contributed to the increase in activity, as well as the formation of large quantities of highly graphitic and ordered multi-walled carbon nanotubes produced by the tip-growth mechanism which have been shown to prolong catalyst lifetime on-stream.
•Electronic interactions between Ni and Zn enhanced catalytic activity.•Zinc catalyst doping weakened metal-support interaction and increased NiO particle size.•5% zinc loading raised methane conversion to 67.7% which remained stable for 60 h.•Addition of Zn increased the degree of carbon graphitization.•The observed tip growth carbon mechanism improved catalyst stability.
The effects of operating conditions (temperature, residence time, and water contents) of hydrothermal carbonization (HTC) of spent mushroom compost (SMC) waste on the hydrochars (HCs) and liquid ...effluent characteristics were experimentally revised and ranked in increasing order: residence time < dilution factor < temperature. HTC upgraded the energy capabilities by doubling their heating values and increasing their fixed carbon contents four times. HTC also enhanced the soil amendment characteristics of SMC feedstock in terms of increasing the adsorption polar heads concentration, enriching its calcium and heavy metals contents after a thorough inorganic contents evaluation, doubling the surface area and increasing the pore size by a factor of five. When compared against biocoal from torrefaction in another study, HCs contained less toxic oxygenated compounds and had an 11% higher HHV at lower temperature (i.e. lower energy cost). On the other hand, HCs showed higher surface area (25 m2/g at 250 °C in HTC compared to 16 m2/g at 550 °C in pyrolysis), close adsorption characteristic, and comparable energy capabilities (22.72 MJ/kg at 700 °Cs in pyrolysis compared to 20.7 MJ/kg at 250 °C in HTC) to pyrolysis at significantly lower temperature. GCMS along with UV were used to verify the reviewed degradation mechanism and evaluate the effect of process parameters on this mechanism and on the composition and toxicity of the HTC liquid effluent. They showed that acetic and formic acids, ethanol, phenol, and acetaldehyde were the major compounds that had resulted from the degradation of cellulose, hemicellulose, and lignin. Their concentrations increased with temperature and residence time, but was dependent on temperature in the case of increasing the dilution factor. Nevertheless, HTC degradation enhanced the total acids-phenols concentration in the liquid effluent by 700%.
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•HTC upgraded the energy capabilities and soil amendment characteristic of SMC.•HC competed with biochar and biocoal in soil amendment and energy production.•Process parameters ranked as temperature > dilution factor > residence time.•A detailed degradation mechanism for the liquid phase was developed.•HTC produced a liquid phase affluent with acids, alcohols, ketones and phenols.
In this study, pyrolysis is suggested as an environmentally and economically sustainable treatment for pharmaceutical waste within the context of circular economy. Low temperature pyrolysis was ...conducted on immediate release tablets containing 500 mg paracetamol, with the liquid and gas products analyzed using GC-MS (gas chromatography-mass spectroscopy). The pyrolytic behavior of the pharmaceutical product was studied through kinetic and thermodynamic analysis. The data obtained by thermogravimetric analysis (TGA) were used to estimate the activation energy (E) and the pre-exponential factor (A) through isoconversional models of Kissenger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO), and The thermodynamic parameters were determined. The average E values for the pyrolysis of the drug product using KAS and FWO methods were found to be 125.9 and 128.8 kJ.mol−1, respectively. The GC-MS results showed that the most abundant component of the pyrolysis liquid was the active pharmaceutical ingredient (paracetamol), along with other compounds, including long-chain alkanes and acids while the pyrolysis gas consisted mainly of light hydrocarbons, including CO, CO2, CH4, and ethylene. Both the gaseous and liquid pyrolysis products may be repurposed, as the active pharmaceutical ingredient (API) may be recycled to produce new tablets, and the other compounds may be utilized as fuel or chemical feedstock.
•Used low temperature pyrolysis for pharmaceutical waste treatment of paracetamol.•Determined paracetamol pyrolysis activation energy and pre-exponential factor.•Pyrolysis product liquid recovery was rich in paracetamol.•Pyrolysis product gas consists of light hydrocarbons suitable as energy feed.•Low temperature pyrolysis has potential as circular pharma waste treatment approach.
Pyrolysis is a well-known thermochemical process used to treat various types of solid waste that is often associated with an intensive energy demand. To this date, the heat source for pyrolysis has ...been mainly through burning fossil fuels (e.g. coal or natural gas) or via electric heating. As a result, pyrolysis is still considered an economically unattractive solid waste management technique. One environmentally-attractive solution would be to integrate solar thermal energy, via concentrated solar power (CSP) systems, into the pyrolysis process to reduce its dependency on fossil fuel.
In the current work, we investigate the pyrolysis of waste tires integrated with CSP using linear Fresnel reflectors (LFRs) technology. The heat transfer fluid (HTF) is heated to elevated temperatures of 520 °C to provide the necessary thermal energy for the pyrolysis reactor operating at 550 °C. Using System Advisor Model (SAM) integrated with the Aspen Plus® tire pyrolysis flowsheet proved that solar energy in Lebanon can provide on average 47.14% of the annual energy demands of the pyrolysis reactor. Energy savings can decrease on average to 26.6% in winter season and increase to 60.8% in the summer.
•Aspen Plus model used for Tire pyrolysis process.•System Advisor Model (SAM) applied to design solar concentrator plant.•Integrated approach to study annual energy demands/savings.•Simulations showed that energy savings vary from 26.6% in winter to 60.8% in summer.
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