Thermal Pretreatment Temperature Research Articles

Effect of thermal pretreatment on the surface structure of PtSn/SiO2 catalyst and its performance in acetic acid hydrogenation

The effect of thermal pretreatment on the active sites and catalytic performances of PtSn/SiO2 catalyst in acetic acid (AcOH) hydrogenation was investigated in this article. The catalysts were characterized by N2 physical adsorption, X-ray diffraction, transmission electron microscopy, pyridine Fourier-transform infrared spectra, and H2-O2 titration on its physicochemical properties. The results showed that Pt species were formed primarily in crystalline structure and no PtSnx alloy was observed. Meanwhile, with the increment of thermal pretreatment temperature, Pt dispersion showed a decreasing trend due to the aggregation of Pt particles. Simultaneously, the amount of Lewis acid sites was remarkably influenced by such thermal pretreatment owning to the consequent physicochemical property variation of Sn species. Interestingly, the catalytic activity showed the similar variation trend with that of Lewis acid sites, confirming the important roles of Lewis acid sites in AcOH hydrogenation. Moreover, a balancing effect between exposed Pt and Lewis acid sites was obtained, resulting in the superior catalytic performance in AcOH hydrogenation.

Colour stability of oil-heat treated black locust and poplar wood during short-term UV radiation

Abstract Black locust (Robinia pseudoacacia L) samples with high extractive content and poplar (Populus × euramericana cv. Pannonia) samples with low extractive content were chosen for the test. The specimens were thermally treated at 160 and 200 °C in sunflower oil for 2, 4, and 6 h then irradiated by a strong UV emitter mercury lamp up to 36 h. The effects of thermal treatment and UV radiation were monitored by colour measurement. The results indicated that the extractives play an important role in the photodegradation of oil-heat treated wood. Thermal treatments reduced the lightness change effect of photodegradation. The oil-heat treated black locust samples showed similar photodegradation properties independently on the thermal pre-treatment time and temperature. The redness of oil-heat treated black locust samples hardly changed during UV radiation proving the photostability of the thermally modified extractives. The redness change of poplar samples caused by UV radiation was partly determined by the temperature of thermal treatment (darkening and lightening also happened). The yellow colour change of the investigated samples showed that the lignin of thermally modified wood undergoes similar photodegradation as that of the untreated natural wood.

Effects of thermal pretreatment on the biomethane yield and hydrolysis rate of kitchen waste

In this study, batch tests were performed to evaluate the effects of different thermal pretreatment temperatures (55–160°C) and durations (15–120min) on the anaerobic digestion of kitchen waste (KW). Two commonly used approaches, namely the modified Gompertz model and the approach developed by Koch and Drewes, were applied to assess the effects of the different pretreatment parameters on the biomethane yield, lag time and hydrolysis rate constant via data fitting. The subsequent anaerobic digestion of KW pretreated at 55–120°C presented greater efficiency, and longer treatment durations resulted in increased methane production and higher hydrolysis rate constants. These findings were obtained due to the lower nutrient loss observed in KW treated at lower temperature treatments compared with that found with higher temperature treatments. In general, the effects of thermal pretreatment on the lag phase and hydrolysis rate differed depending on the treatment parameters leading to the variations in the KW compositions. The soundness of the two model results was evaluated, and higher statistical indicators (R2) were found with the modified Gompertz model than with the approach developed by Koch and Drewes.

Kinetics of combined thermal pretreatment and anaerobic digestion of waste activated sludge from sugar and pulp industry

The purpose of this work was to evaluate the effects of thermal pretreatment temperature (from 100°C to 200°C) and time (15–60min) on the characteristics and the anaerobic biodegradability of wasted activated sludge from sugar and pulp mills. Reaction Curve model and First-order kinetics were used to obtain a better understanding of the data from the anaerobic biodegradability tests. Sludge characteristics and methane production prior and after thermal pretreatment confirmed that temperature exerted the major influence on sludge solubilization and biodegradability. The optimal methane yield (182mlCH4/gVSFeed) and ultimate methane production rate (72.1mlCH4/gVSFeedd) was obtained at 165°C for 30min. However, the negative effects of melanoidins and Amadori compounds appeared and the rising trend of biodegradability reversed at 200°C. The growth rate of methane yield topped out at 476% at 100°C, and the maximum methane yield (range from 28.9 to 72.1mlCH4/gVSFeedd) were also observed at the first day, showing the radical kinetics improvement after pretreatment. This remarkable initial methane yield was attributed to the raising share of the rapidly biodegradable organics generated in thermal pretreatment, which were estimated with methane yield percentage of day 3. Both Reaction Curve model and First-order kinetics fitted with the experimental data well, and a Simplified Reaction Curve model without lag time provides a feasible tool to estimate methane yield of the rapidly biodegradable substrates.

Thermal granulation of U3O8 powder using a rotary voloxidizer

The thermal granulation of U3O8 powder using a rotary voloxidizer was investigated in terms of the initial particle bed motion such as slumping and rolling, thermal pretreatment (voloxidation) temperature and time, and the rotational speed in slumping motion. The granules, particles of larger than 1mm, were obtained directly from fine particles of U3O8 by only heating and rotating the reaction chamber. With respect to the initial particle bed motion, the yield of granules of above 1mm in slumping motion was higher than that in rolling motion. A rolling motion was changed into a slumping motion with high slumping frequency by formation of granules from fine particles. Granule yield significantly increased with an increase in the thermal pretreatment temperature and time of up to 10h. As the rotational speed of the reaction chamber in the case of the initial particle bed showing a slumping motion increased, the granule yield increased from 81.5% to 88.7%. However, a rotational speed of 2rpm provided an effective density, crushing strength, and circularity of the granules.

Development of CaO-based sorbent doped with mineral rejects–bauxite-tailings in cyclic CO2 capture

A highly efficient CaO-based sorbent, using inexpensive materials (CaCO3) and mineral rejects (bauxite-tailings) as reactants, was tested for carbonation conversions for 15 carbonation/calcination cycles in a thermogravimetric analyzer (TGA). The morphology was investigated by scanning electron microscopy (SEM) and the phase composition was determined by X-ray diffraction (XRD). Effects of different bauxite-tailings (BTs)/CaO ratios and thermal pretreatment temperatures on carbonation conversion were investigated in this study. The sorbent doped with 5% BTs (calcined at 900°C for 3h) showed superior cyclic stability during 50 carbonation/calcination cycles (being >42% conversions after 50 cycles). Mayenite (Ca12Al14O33) in the CaO-based sorbents doped with BTs is responsible for the favorable performance. It can provide a stable framework inhibiting sintering over multiple cycles. In addition, this study may offer the possibility of recycling the BTs from aluminum manufacture.

Effective pathogen removal by low temperature thermal pre-treatment and anaerobic digestion for Class A biosolids production from sewage sludge

Production of Class A biosolids depends mainly on the effective control of thermotolerant coliforms and Salmonella spp. Thermal pre-treatment followed by anaerobic mesophilic digestion may be a simpler and more sustainable option to accomplish this compared with other process arrangements. In this work, removal and inactivation of thermotolerant coliforms and Salmonella spp. in waste municipal sludge were studied at three thermal pre-treatment conditions in batch tests (60, 70 and 80 °C). Effective removal was obtained with 70 °C and one-hour pre-treatment, but reactivation of both pathogens was noticed in the following step using an anaerobic mesophilic digester. Predictive microbial decay models (Weibull and sigmoidal-empirical) were used for fitting the experimental data. The sigmoidal-empirical model showed better results at the final counts, suggesting thermal adaptation of some microbial subpopulations. In order to overcome this unexpected result, the influence of the cooling phase was also studied applying three different conditions. For effective treatment, a fast cooling step (in this case, an ice-bath with sodium chloride) should follow thermal pre-treatment (70 °C and 60 min). At these conditions, no reactivation or re-growth of both pathogen indicators were seen during the following 48 h under anaerobic mesophilic digestion.

Effects of Thermal Pretreatment Temperature on the Solubilization Characteristics of Dairy Manure for Dry Anaerobic Digestion

The effect of thermal pretreatment conditions on hydrolysis characteristics of dairy manure and sawdust mixtures has been evaluated. Thermal pretreatment temperature varied between 35 and <TEX>$120^{\circ}C$</TEX> and the period of the treatment changed between 30 and 1440min (24h). As thermal pretreatment temperature and duration increased, organic material solublization rates were improved. Maximum solubilizations of chemical oxygen demand (SCOD), carbohydrates, and volatile fatty acids(VFAs) were observed when dairy manure treated for one day at <TEX>$120^{\circ}C$</TEX>. Although one day treatment duration at <TEX>$120^{\circ}C$</TEX> showed the highest SCOD, soluble carbohydrates, and VFAs concentration, its hydrolysis rate was only about 12%. The results reveal that the thermal pretreatment conditions tried in this study are not enough to solubilize the organic matter contained in dairy manure and sawdust mixtures. In order to maximize hydrolysis performance, the further research needs to determine the factors influences on organic material solubilization in addition to thermal pretreatment temperature and duration.

Low temperature microwave and conventional heating pre-treatments to improve sludge anaerobic biodegradability

This paper presents the results of lab-scale experiments on low temperature thermal pre-treatment (less than 100 °C) prior to anaerobic digestion of sewage sludge. Two heating ways, microwave heating (MH) and conventional heating (CH), and two types of sludge, primary and waste activated sludge, were compared under the same experimental conditions. The degree of solubilisation produced by MH and CH up to 72, 82 and 93 °C was firstly estimated. For both types of heating, increase in soluble chemical oxygen demand (COD) caused by the pre-treatment was about 14% on waste activated sludge and only 3% on primary sludge. The final temperature of 72 °C resulted as the most cost-effective in terms of additional soluble COD per unit of energy required. Subsequently, five series of biochemical methane potential mesophilic assays were run in 120 mL serum bottles on sludge samples pre-treated at 72 °C. When compared with control reaction vessels, no significant differences were noticed in net methane production of pre-treated primary sludge, whereas a relevant increase occurred regarding the pre-treated waste activated sludge. It was also observed that the trend of methane content in biogas during the batch tests can be described by a second order polynomial.

Biodiesel production with nanotubular sodium titanate as a catalyst

Sodium titanate nanotubes (STNT) with a chemical formula Na2Ti3O7·nH2O were synthesized and tested as a heterogeneous catalyst in the transesterification of soybean oil with methanol. The catalyst was characterized by N2 physisorption, powder XRD, scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM) and CO2 temperature-programmed desorption (CO2-TPD). It was found that the prepared catalyst had nanotubular structure, high sodium content (10.3wt.%) and attractive textural characteristics (surface area around 200m2/g and total pore volume of 0.61cm3/g). The influence of the catalyst's loading, methanol to oil molar ratio, reaction time and temperature on the biodiesel yield was investigated. High biodiesel yields (97–100%) were obtained with the STNT catalyst at 8h reaction time at methanol reflux temperature with 1–2wt.% of the catalyst and 40:1 methanol:oil molar ratio. Increase in the reaction temperature to 100–120°C had a positive effect on the biodiesel yield. In this case, 99–100% yields were obtained with a lower catalyst loading (∼1wt.%) and methanol to oil molar ratio (20:1). In addition, it was found that the STNT catalyst does not require high temperature thermal pre-treatment (activation) before the transesterification reaction. The reuse of the same catalyst in the transesterification reaction three times showed a decrease of about 10% in the catalytic activity.

Controlling Co-support interaction in Co/MWCNTs catalysts and catalytic performance for hydrogen production via NH3 decomposition

The influence of thermal treatment in hydrogen and nitrogen atmosphere of Co precursors in Co/MWCNTs system on the catalyst structure and catalytic activities in NH3 decomposition were studied. The cobalt-support interaction in cobalt supported on MWCNTs was controlled by varying the temperature of thermal treatment of Co precursor and reaction media. Due to the interaction of cobalt species with multi wall carbon nanotubes (MWCNTs), the Co/MWCNTs catalysts after pretreatment in nitrogen exhibited higher catalytic activity for NH3 decomposition comparing to that observed after hydrogen pretreatment of the sample. Cobalt dispersion in MWCNTs-supported catalysts was found to be a function of thermal pretreatment temperatures. The studied samples were characterized by X-ray diffraction, HRTEM, thermo gravimetric analysis, temperature programmed reduction and temperature programmed desorption

Gold-supported tin dioxide nanocatalysts for low temperature CO oxidation: preparation, characterization and DRIFTS study

A series of gold-supported tin dioxide (Au/SnO2) nanocatalysts were prepared by a deposition–precipitation method using SnO2 powders prepared by the sol–gel dialytic processes as supports, and were characterized by means of XRD and XPS techniques. The catalytic properties of the prepared Au/SnO2 nanocatalysts were evaluated by low-temperature carbon monoxide oxidation using a microreactor-GC system. The results showed that the catalytic behavior of the Au/SnO2 system was remarkably influenced by the deposition pH, the reaction solution concentration and the thermal pretreatment temperature of the catalyst. The DRIFTS study results indicated that CO adsorbed on the Au/SnO2 catalyst reacted with support surface lattice oxygens and hydroxyl groups to form oxidation products, i.e., CO2–, HCOO–, CO32–, HCO3– and CO2, and the gas phase oxygen acted as an activator for the reaction of CO with support surface lattice oxygens and hydroxyl groups.

Effect of pretreatment temperature on the yield and properties of bio-oils obtained from the auger pyrolysis of Douglas fir wood

This paper investigates the effect of thermal pretreatment temperatures between 200 and 370°C on the yield and composition of products (bio-charm gasm water and organics) obtained when Douglas-fir wood was subsequently pyrolyzed in an auger reactor at 500°C. The yield of products was reported for the pretreatment and pyrolysis steps separately, and for the two steps added. The maximum yield of bio-oils achieved without pretreatment was close to 59mass%. A decrease in total liquid yield was observed when the biomass was pretreated at 300°C. At higher temperatures, the yields of Douglas-fir primary degradation products (lignin oligomers, anhydrosugars and alkylated and methoxylated phenols) decreased. The overall water yield increased gradually to 14mass% at a pretreatment temperature of 290°C. The yield of lignin oligomers also decreased as the pretreatment temperature increased. A drastic reduction in the yield of methoxylated phenols derived from guaiacyl (G) was observed when the biomass was pretreated at temperatures over 300°C. This drastic reduction in the yield of methoxylated lignin derivatives can be explained by the formation of liquid intermediates that facilitate the formation of ionic species, enhancing dehydration reactions leading to the production of o-quinone methide intermediates critical for bio-char formation.

Effect of low temperature thermal pre-treatment on the solubilization of organic matter, pathogen inactivation and mesophilic anaerobic digestion of poultry sludge

Treatment of poultry industry effluents produces wastewater sludge with high levels of organic compounds and pathogenic microorganisms. In this research, the thermal pre-treatment of poultry slaughterhouse sludge (PSS) was evaluated for low temperatures in combination with different exposure times as a pre-hydrolysis strategy to improve the anaerobic digestion process. Organic compounds solubilization and inactivation of pathogenic microorganisms were evaluated after treatment at 70, 80 or 90°C for 30, 60 or 90 min. The results showed that 90°C and 90 min were the most efficient conditions for solubilization of the organic compounds (10%). In addition, the bacteria populations and the more resistant structures, such as helminth eggs (HE), were completely inactivated. Finally, the thermal pre-treatment applied to the sludge increased methane yield by 52% and reduced hydraulic retention time (HRT) by 52%.

Techno-economic evaluation of ultrasound and thermal pretreatments for enhanced anaerobic digestion of municipal waste activated sludge

To enhance the anaerobic digestion of municipal waste-activated sludge (WAS), ultrasound, thermal, and ultrasound+thermal (combined) pretreatments were conducted using three ultrasound specific energy inputs (1000, 5000, and 10,000kJ/kg TSS) and three thermal pretreatment temperatures (50, 70 and 90°C). Prior to anaerobic digestion, combined pretreatments significantly improved volatile suspended solid (VSS) reduction by 29–38%. The largest increase in methane production (30%) was observed after 30min of 90°C pretreatment followed by 10,000kJ/kg TSS ultrasound pretreatment. Combined pretreatments improved the dimethyl sulfide (DMS) removal efficiency by 42–72% but did not show any further improvement in hydrogen sulfide (H2S) removal when compared with ultrasound and thermal pretreatments alone. Economic analysis showed that combined pretreatments with 1000kJ/kg TSS specific energy and differing thermal pretreatments (50–90°C) can reduce operating costs by $44–66/ton dry solid when compared to conventional anaerobic digestion without pretreatments.

Effect of thermal treatment on sintering and strength of ceramics from hydroxyapatite nanopowders

The effect of thermal prehistory of hydroxyapatite powders synthesized by precipitation from aqueous solutions on sintering and strength of ceramics produced on their basis was investigated. After synthesis, the initial powders underwent thermal treatment in the temperature range from 400 up to 1000°C, which resulted in the change from a needle-like morphology to a hexagonal one, whereas the individual particle size increased from 15 to 200 nm. Sintering was performed under continuous heating conditions with isothermal soaking at a maximum temperature of 1200°C. It was established that the activity of powders in sintering depends on the temperature of thermal pretreatment. The existence of a maximum at 700°C on the dependence of the ceramic strength on temperature is caused by competing effects of the residual porosity and granule size on the sample strength.

Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on Spark Plasma Sintering of transparent alumina

A slurry of α-Al 2O 3 was doped with Mg, Zr and La nitrates or chlorides, in various amounts in the range 150–500 wt ppm and then freeze-dried to produce nanosized doped powder (∼150 nm). The powder was sintered by SPS to yield transparent polycrystalline alpha alumina. The influence of the nature of the doping element and the starting salt, the thermal treatment before sintering and the sintering temperature on the transparency of the ceramics were investigated. The transparency of the ceramics of nanosized Al 2O 3 was shown to depend mainly on the way the powder was prepared, the nature of the doping salt also had an effect. Finally, a high real inline transmittance, reaching 48.1% was achieved after optimization.

Influences of thermal pretreatment temperature and solvent on the organosilane modification of Al 13-intercalated/Al-pillared montmorillonite

The grafting reactions between 3-aminopropyltriethoxysilane and Al 13-intercalated/Al-pillared montmorillonites thermally pretreated at different temperatures were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis and nitrogen adsorption–desorption isotherms. The porous structures and the grafting degree of the organosilane modified Al 13-intercalated/Al-pillared montmorillonite products are significantly affected by the solvents. The product prepared in anhydrous ethanol has high specific surface area (~ 160 m 2 g − 1 ) and larger porous volume (0.134 cm 3 g − 1 ) but low degree of grafting modification, while the one prepared in cyclohexane has a high loading amount of silane (2.02 mmol g − 1 ) but low surface area (7 m 2 g − 1 ). Thermal treatment affects the grafting process by both reducing the water content in the interlayer space of the pillared montmorillonite and causing the transformation of the interlayer Al compounds from polycations to oxides. The hydrolyzed 3-aminopropyltriethoxysilane is mainly grafted onto the surface of the interlayer Al Keggin ions and/or Al oxides. This study demonstrates the functionalization of pillared clay to form inorganic–organic hybrid material that combines the high porosity of inorganic pillared clay and the lipophilicity of organoclay by adjusting the solvents and the pretreatment conditions, enabling potential applications in adsorption and environmental restoration.

Tailoring the synthesis of supported Pd catalysts towards desired structure and size of metal particles

In a systematic study, the influence of different preparation parameters on phase composition and size of metal crystallites and particles in Pd-Cu/TiO(2) and Pd-Sb/TiO(2) catalyst materials has been explored. Temperature and atmosphere of thermal pretreatment (pure He or 10% H(2)/He), nature of metal precursors (chlorides, nitrates or acetates) as well as of ammonium additives (ammonium sulfate, nitrate, carbonate) and urea were varied with the aim of tailoring the synthesis procedure for the preferential formation of metal particles with similar size and structure as observed recently in active catalysts after long-term equilibration under catalytic reaction conditions in acetoxylation of toluene to benzylacetate. Among the metal precursors and additives, the chloride metal precursors and (NH(4))(2)SO(4) were most suitable. Upon thermal pretreatment of Pd-Sb or Pd-Cu precursors, chloroamine complexes of Pd and Cu are formed, which decompose above 220 degrees C to metallic phases independent of the atmosphere. In He, metallic Pd particles were formed with both the co-components. In H(2)/He flow, Pd-Cu precursors were converted to core-shell particles with a Cu shell and a Pd core, while Sb(1)Pd(1) and Sb(7)Pd(20) alloy phases were formed in the presence of Sb. Metal crystallites of about 40 nm agglomerate to particles of up to 150 nm in He and to even larger size in H(2)/He.

Dielectric Response and Analysis of Structural Evolution of NaA Zeolite with High Pretreatment Temperature

Dielectric relaxation spectroscopy (DRS) was carried out on hydrated NaA zeolite (LTA) with various high pretreatment temperatures (PT), and the effect of thermal treatment on crystal structure was characterized by X-ray diffraction analysis (XRD). A dielectric relaxation about 10 5 Hz was found to be closely related to the integrity of the pore framework, and the decreased relaxation increment was attributed to the structural evolution of LTA. The critical temperature (CT), where the crystal structure of LTA starts to essentially change, was jointly determined by DRS and XRD. Comprehensive investigation of the relaxation mechanism and time indicated symmetrical shrinkage of pore channels at thermal PT below CT. The Hanai method was used to calculate the dielectric properties of LTA particles and aqueous medium. The invariant permittivity of particles indicated the thermal stabilization of polarization distribution of sodium ions, and the decreased particle conductivity with PT increasing to CT reflected the negative effect of thermal pretreatment on the mobility of sodium ions. The abnormal conductivities of particles and medium indicated prior sintering on the pore's surface at the beginning of crystal structure transition.