Feedstock recycling of agriculture plastic film wastes by catalytic cracking

Feedstock recycling by catalytic cracking of a real plastic film waste from Almeria greenhouses (Spain) towards valuable hydrocarbon mixtures has been studied over several acid catalysts. The plastic film waste was mostly made up of ambient degraded low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) copolymer, the vinyl acetate content being around 4 wt.%. Nanocrystalline HZSM-5 zeolite (crystal size 60 nm) was the only catalyst capable of degrading completely the refuse at 420 °C despite using a very small amount of catalyst (plastic/catalyst mass ratio of 50). However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike it occurred with virgin LDPE, showed fairly close conversions to that of thermal cracking. Nanocrystalline HZSM-5 zeolite led to 60 wt.% selectivity towards C₁---C₅ hydrocarbons, mostly valuable C₃---C₅ olefins, what would improve the profitability of a future industrial recycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite was ascribed to its high content of strong external acid sites due to its nanometer dimension, which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline HZSM-5 can be regarded as a promising catalyst for a feasible feedstock recycling process by catalytic cracking.     

Hydrocarbon fuels produced by catalytic pyrolysis of hospital plastic wastes in a fluidizing cracking process

A mixture of post-consumer polyethylene/polypropylene/polystyrene (PE/PP/PS) with polyvinyl chloride (PVC) waste was pyrolyzed over cracking catalysts using a fluidizing reaction system operating isothermally at ambient pressure. The influences of catalyst types and reaction conditions including reaction temperatures, ratios of catalyst to plastic feed, flow rates of fluidizing gas and catalyst particle sizes were examined. Experiments carried out with various catalysts gave good yields of valuable hydrocarbons with differing selectivity in the final products dependent on reaction conditions. A model based on kinetic and mechanistic considerations associated with chemical reactions and catalyst deactivation in the acid-catalyzed degradation of plastics has been developed. The model gives a good representation of experimental results from the degradation of commingled plastic waste. The results of this study are useful for determining the effects of catalyst types and reaction conditions on both the product distribution and selectivity from hospital plastic waste, and especially for the utilization of post-use commercial FCC catalysts for producing valuable hydrocarbons in a fluidizing cracking process.     

Studies of Thermal Conductivity of Nano CaCO3/HIPS Composites by Unsteady State Technique and Simulation with Nielsen's Model

Differential scanning calorimeter (DSC) and thermal conductivity meter were used for measurement of thermal conductivity by unsteady state technique of the high impact polystyrene (HIPS) composites filled with 0.5, 1.5, and 2.5 wt.% of CaCO₃ nano particles. A comparison of experimental and theoretical values of (K _c /K _m) was done using MATLAB software fitting in Nielsen's model of thermal conductivity for polymers containing low limit of volume fraction. The packing fraction (Φ _max) and geometry and orientation dependent parameter (A) of the nanofiller were assumed as 0.10 and 100, respectively, which are most fitted for this model. The effect of nanosize on thermal conductivity was well predicted by plotting different values of thermal conductivity at various source temperatures. The violation of the theoretical values because of local molecular vibration at higher temperature is highlighted promisingly in the plots.     

The effect of Cr2O3 and P2O5 additions on the phase transformations during the formation of calcium sulfoaluminate C4A3S¯

The study describes the influence of chromium and phosphorus additions on the phase transformations during the formation of the calcium sulfoaluminate Ca₄Al₆SO₁₆ from CaCO₃-Al₂O₃-CaSO₄ mixtures. The temperatures of decarbonation reaction were measured by means of differential thermal analysis. The enthalpy variations at different heating temperatures were determined by isothermal calorimetry. The results show that the Cr₂O₃ and P₂O₅ additions lower the onset temperature of decarbonation. The energy requirement at high temperature of the doped mixtures is less, compared to that of mixtures without dopants. The formation of solid solutions is followed by X-ray diffraction. The higher concentrations of additives hinder the formation of the C₄A₃S¯ phase.     

Sulfate attack on cementitious materials containing limestone filler — A review

This review summarizes the results of sulfate performance in laboratory and field tests where limestone is used as a constituent of cement (PLC) or as a sand replacement where it is particularly beneficial to the properties of self compacting concretes (SCC).Laboratory studies on paste, mortar or concrete specimens exposed to Na₂SO₄ and MgSO₄ solutions in a wide range of concentrations at different temperatures as well as mixtures with different compositions, cement compositions and limestone proportions are considered in a conceptual analysis as for the resistance to external sulfate attack and, especially, thaumasite sulfate attack.A detailed analysis of environmental aggressiveness (concentration, temperature and pH), mixture composition and cement composition used in each study are presented for PLC and SCC. Reported field studies are also shown, only a few cases have used limestone filler in their composition. A conceptual graphical analysis is then proposed to relate the degree of surface deterioration and mineralogical composition of attacked surface to the main variables of external sulfate attack: water/cementitious material ratio, limestone content and C₃A content of the cement. Observation of graphical analysis clearly shows that deterioration by ESA is mainly governed by effective w/c ratio and C₃A content of the cement. Surface damage is controlled when low effective w/c ratio and low C₃A are used. In MgSO₄ solution, low temperatures increase the degree of deterioration. Thaumasite is the last attack stage in the different sulfate environments.     

Zeolitization of mineral wastes by molten-salt method: NaOH–KNO3 system

Salt-thermal method exhibits several features such as high production yield, large-scale conversion, low elemental loss, and environmentally benign nature. This study has investigated the optimization of the NaOH–KNO₃ system for the zeolitization of fly ash and elucidated the characteristics of the resulting zeolitic materials. The following are the optimal reaction conditions for zeolitization of fly ash in NaOH–KNO₃ system: a temperature of 250 °C, 0.3–0.5 weight ratio of NaOH/KNO₃ and 0.7–1.4 weight ratio of KNO₃/fly ash. The NaOH–KNO₃ system is also confirmed for facile zeolitization of anthracite briquette, kaolinite, and pumice. The NaOH–KNO₃ system is likely to result in KNO₃ occlusion or/and trapping. Because KNO₃ supplies two plant nutrients, the zeolitic materials synthesized by the NaOH–KNO₃ system could be used in agriculture as soil conditioners and fertilizer additives. It is clearly shown in this study that KNO₃ could be employed in place of NaNO₃ in the salt-thermal method with a potential use of the product as soil conditioner and fertilizer.     

Studies on Mechanical,Thermal, and Flame Retarding Properties of Polybutadiene Rubber (PBR) Nanocomposites

An effect of nanosize CaCO₃ on physical, mechanical, thermal and flame retarding properties of PBR was compared with commercial CaCO₃ and fly ash filled PBR. CaCO₃ at the rate of 9, 15, and 21 nm were added in polybutadiene rubber (PBR) at 4, 8 and 12 wt.% separately. Properties such as swelling index, specific gravity, tensile strength, Young's modulus, elongation at break, modulus at 300% elongation, glass transition temperature, decomposition temperature, flame retardency, hardness, and abrasion resistances were determined. The swelling index decreased and specific gravity increased with reduction in particle size of fillers in PBR composites. There was significant improvement in physical, mechanical, thermal and flame-retarding properties of PBR composites due to a reduction in the particle size of fillers. Maximum improvement in mechanical and flame retarding properties was observed at 8 wt.% of filler loading. This increment in properties was more pronounced in 9 nm size CaCO₃. The results were not appreciable above 8 wt.% loading of nano fillers because of agglomeration of nanoparticles. In addition, an attempt was made to consider some thermodynamically aspects of resulting system. The cross-linkage density has been assessed by Flory-Rehner equation in which free energy was increased with increase in filler content.     

Formation of NOx precursors during the pyrolysis of coal and biomass. Part V. Pyrolysis of a sewage sludge

A sewage sludge sample from a wastewater treatment plant in China was pyrolysed in a fluidised-bed/fixed-bed reactor and in a fluidised-bed/tubular reactor. HCN was found to be the main NO_x precursor, representing up to about 80% of the nitrogen present in the sludge. The thermal cracking of volatiles is the main route of HCN formation. NH₃ was also an important NO_x precursor formed during the pyrolysis of the sewage sludge. The experimental results indicate that there are at least two distinctive stages of NH₃ formation during the pyrolysis of the sewage sludge at a fast heating rate. The formation of NH₃ at temperatures lower than 400-500 °C is at least partly due to the amino structures in the sludge. The reactions of volatiles in the gas phase make negligible contributions to the observed NH₃ yield.     

Formation mechanism of barium titanate by thermal decomposition of barium titanyl oxalate

This study examined the formation mechanism of BaTiO₃ from the thermal decomposition of barium titanyl oxalate. A significant amount of O₂ evolution near 357 and 720 °C was observed by gas chromatography/mass spectroscopy, except for the previously known H₂O, CO₂, CO evolution. The metastable Ba₂Ti₂O₅CO₃(CO₂) intermediate phase seemed to be transformed mainly to Ba₂Ti₂O₅CO₃, while a certain amount of crystalline BaCO₃ and amorphous Ti-rich phase were formed simultaneously at 450-600 °C in air. A modification of the decomposition mechanism reported by Gopalakrishnamurthy et al. was proposed based on the experimental findings.     

Preparation and characterization of CeO2/TiO2 nanoparticles by flame spray pyrolysis

Nanocrystalline TiO₂, CeO₂ and CeO₂-doped TiO₂ have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N₂-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO₂ and CeO₂-doped TiO₂ nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO₂. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce^3+/4+ in the TiO₂ matrix, which generated an n-type impurity band.     

Separation of copper from cobalt in sulphate solutions by using CaCO3

Lime neutralization is widely used to precipitate heavy metals including copper and cobalt from wastewater. Limestone (calcium carbonate: CaCO₃) is too stable to be used directly for this purpose. Grinding of CaCO₃ in the solutions of copper and cobalt sulphate was conducted to raise its reactivity. During the mechanochemical activation, CaCO₃ reacted with copper sulphate but not significantly with cobalt sulphate and this phenomenon allowed an easy separation of copper from cobalt. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of the Co(II) ions remained in aqueous solution.     

Use of different limestone and chalk powders in self-compacting concrete

This paper presents a study on the use of different types of limestone and chalk powders as fillers in self-compacting concrete (SCC) and their effects on superplasticizer demand and the strength properties of concrete mixes. It was found that all the different limestone and chalk powders selected could be used successfully for producing SCC mixes, although modest adjustments of superplasticizer dosage were necessary. Generally, higher superplasticizer dosages were required for SCC using chalk powder than for that using limestone powder. The fineness of the powders had little effect on the superplasticizer demand. The compressive strength of the SCC mixes containing the limestone and chalk powders was significantly greater than that of the conventional vibrated reference concrete at the same water/cement ratio, particularly at early ages.     

The experimental investigation of concrete carbonation depth

Phenolphthalein indicator has traditionally been used to determine the depth of carbonation in concrete. This investigation uses the thermalgravimetric analysis (TGA) method, which tests the concentration distribution of Ca(OH)₂ and CaCO₃, while the X-ray diffraction analysis (XRDA) tests the intensity distribution of Ca(OH)₂ and CaCO₃. The Fourier transformation infrared spectroscopy (FTIR) test method detects the presence of C-O in concrete samples as a basis for determining the presence of CaCO₃. Concrete specimens were prepared and subjected to accelerated carbonation under conditions of 23 °C temperature, 70% RH and 20% concentration of CO₂. The test results of TGA and XRDA indicate that there exist a sharp carbonation front. Three zones of carbonation were identified according to the degree of carbonation and pH in the pore solutions. The TGA, XRDA and FTIR results showed the depth of carbonation front is twice of that determined from phenolphthalein indicator.     

Effects of the Treatment of Al(OH)3 by a Silane Coupling Agent on the Tensile Properties of PVC/Al(OH)3 Composite

The present work deals with the study of a composite based on poly(vinyl chloride) (PVC) and aluminum hydroxide (Al(OH)₃) which is treated with different concentrations of the silane coupling agent N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

The composites containing untreated Al(OH)₃ and those treated with the coupling agent were prepared by melt mixing using a two-roll mill.

Analysis of the treated filler by means of Fourier Transform Infrared spectroscopy (FTIR) showed the formation of oligoaminosilanes resulting from the condensation of the silane coupling agent.

The tensile properties of the PVC/Al(OH)₃ composite reflected the effect of the addition of the mineral filler and also the influence of the chemical treatment on the interfacial adhesion. The incorporation of aluminum hydroxide into PVC resulted in an increase of Young's modulus and the yield stress.

From the calculation of a parameter B which was used to quantify the state of adhesion between the polymeric matrix and the filler, it was concluded that the surface chemical treatment of the filler with the silane coupling agent leads to higher reinforcement as a result of the interfacial interactions developed between PVC and Al(OH)_3.     

In situ fabrication of spherical porous tin oxide via a spray pyrolysis technique

Spherical porous tin oxide was fabricated via a spray pyrolysis technique. TEM revealed that the primary SnO₂ crystals had an average size of 5-10 nm. Good interconnection between SnO₂ crystals is also observed. The electrochemical measurements showed that the spherical porous SnO₂ samples have excellent cyclability, which can deliver a reversible capacity of 410 mAh/g for up to 50 cycles as a negative electrode for lithium batteries. Our approach for enhancing the structural stability of tin oxide is to incorporate spherical porous structures as a buffer zone to alleviate the volume expansion of the tin oxide anode during lithiation/delithiation.     

Preparation of ultrafine calcium carbonate particles with micropore dispersion method

Ultrafine particles of CaCO₃ were synthesized by dispersing the mixture of CO₂ and N₂ into the Ca(OH)₂/H₂O slurry with a micropore-plate. Because the micropore is micrometers scale, process of momentum transfer, mass transfer and reaction was significantly enhanced. The carbonation process of Ca(OH)₂/H₂O system was monitored with pH and conductivity. Operation conditions were investigated on the specific surface area of particles, such as initial slurry concentration and volume, gas flowrate and concentration, and temperature. The crystal structure of particles was characterized with BET, IR, TEM, SEM, etc. Results showed ultrafine particles were calcite with general shape of cube, whose size was about 40 nm and specific surface area was more than 25 m²/g. This preparation method is easy to operate.     

Formation of NOx precursors during the pyrolysis of coal and biomass. Part VI. Effects of gas atmosphere on the formation of NH3 and HCN

Our results indicate that the gas atmosphere surrounding coal/char particles can greatly affect the formation of NH₃ and HCN through its influence on the availability of H radicals. Based on our results, it is believed that the chemisorption of CO₂ on the nascent char surface can consume H radicals or block the access of N-sites by H radicals for the formation of NH₃ and HCN. For the chars whose thermal cracking generates little H radicals, the gasification of char by CO₂ can also generate additional H radicals, enhancing the formation of NH₃. However, even gasification of char in CO₂ at 950 °C does not lead to the formation of HCN. The oxidation of coal with 4% O₂ at low temperatures (400-600 °C) leads to the formation of HCN as well as NH₃ due to the enhanced formation of (H) radicals. The gasification of coal with 15% H₂O drastically enhances the formation of NH₃ due to the greatly enhanced availability of H as an intermediate between the reactions of H₂O and char. These results support our reaction mechanisms proposed previously, emphasising the importance of H on the formation of NH₃ and HCN during pyrolysis, which can also be extended to the conversion of coal-N during gasification.     

Steam reforming of liquid hydrocarbon fuels for micro-fuel cells. Pre-reforming of model jet fuels over supported metal catalysts

The present work deals with pre-reforming of logistic hydrocarbon fuel (jet fuel) as a part of an integrated approach to developing an on-board fuel reformer for use in a micro-solid-oxide fuel cell system. The purpose of doing pre-reforming is to ensure carbon-free reformulation of JP-8 jet fuel into hydrogen and carbon monoxide for use in a micro-solid-oxide fuel cell. Several model jet fuels have been tested for the pre-reforming at low temperature (450–550 °C) in a lab-scale reforming reactor. Proper temperature control and pre-mixing of feed fuels and steam have been found to be important for the prevention of coke formation prior to pre-reforming. Both noble metal and base-metal catalysts have been prepared and tested. As compared with an Al₂O₃-supported Ni catalyst, supported Rh catalysts show not only high activity but also high resistance to deactivation due to carbon formation. Removal of residual Cl⁻ from Rh/CeO₂–Al₂O₃ improves the metal dispersion and the pre-reforming activity. The reformates from the current pre-reformer contain mainly CH₄, CO, H₂, in which CH₄ can be further converted to H₂ and CO by subsequent main-reforming.     

Effect of Nano CaCO<Subscript>3</Subscript> on thermal properties of Styrene Butadiene Rubber (SBR)

Styrene butadiene rubber (SBR) as matrix was reinforced separately with 9, 15 and 21 nm sizes of CaCO₃, which were synthesized by matrix mediated growth technique. The mixing and compounding was done on two-roll mill and sheets were prepared in compression molding machine. The effect of nature and loading of nano CaCO₃ on these rubber nanocomposites was investigated thoroughly by different characterizations such as DSC, TGA, XRD, and mechanical properties. An appreciable increase in glass transition temperature has been observed from DSC study. 9 nm sizes of CaCO₃/SBR composites show more increment in Tg as compared to pristine SBR as well as different sizes of CaCO₃ filled SBR. This increment in Tg is due to restricted mobility of nano CaCO₃ filled SBR nanocomposites. XRD study of nanocomposites showed that nano CaCO₃ dispersed uniformly throughout the matrix because of the small peak at lower 2θ. This uniform dispersion of nano CaCO₃ contributes towards the higher mechanical properties of rubber composites. From TGA study, it was observed that as the size of CaCO₃ reduces the thermal stability increases as compared to pristine SBR. The other results of these rubber nanocomposites were compared with commercial CaCO₃ filled SBR. Partly this research paper has been presented in International conference on ‘RubberChem 2006, Dec 5–6, 2006, Munich, Germany.     

Properties of biomineralized (CaCO3) PVP-CMC hydrogel with reference to its cytotoxicity

The authors focus on properties of biomineralized (CaCO₃) PVP-CMC hydrogel (designated as I–X) including cytotoxicity assay using primary mouse embryonic fibroblasts. The biomineralized samples (VII–X) showed >80% cell viability, was selected for further characterizations. FTIR and XRD indicate deposition of CaCO₃ within the PVP-CMC hydrogel matrix, SEM shows changes in morphology and pore diameter (VII and VIII: 1–12 µm; IX: 10–70 µm; X: 70–170 µm), TGA determines the decomposition scenario of CaCO₃, and tensile strength of samples (VII–X) ranged between 0.04 and 1.0 GPa, which practically corresponds to the modulus of cancellous bone.