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In this work, effect of salt on cellulose pyrolysis behaviour using chemical percolation devolatilization (CPD) model has been investigated. The distributed activation energy model (DAEM) has been used to determine the kinetics of pure and NaCl-loaded cellulose pyrolysis in a thermogravimetric analyser (TGA). A number of these experiments were performed for a range of heating rates (5–100 °C min−1) and for different concentrations of NaCl in cellulose (0.25–2 mass/%) which showed a pronounced effect of salt on the primary pyrolysis reactions of cellulose. These data were then used in a two-component DAEM to calculate the kinetic parameters for the chemical percolation devolatilization model (CPD) for both pure and NaCl-loaded cellulose. The optimized kinetic parameters for the pure and NaCl-loaded cellulose were used in the CPD model, and the product yield was predicted. The CPD predictions showed that the fraction of gases and char in the pyrolysis products increased in the presence of salt. The amount of char for pure cellulose was 6.97% which increased to 16.4% in the presence of 0.25% NaCl. The amount of gases produced as a result of pure cellulose pyrolysis was 9.63% and this amount increased with addition of NaCl to 22.85% and then further increases with an increase in NaCl concentration. Amount of tar produced for pure cellulose was 83.4%, and this amount reduced to 60.7% with addition of 0.25% NaCl. The presence of NaCl accelerates cellulose decomposition and favours the formation of gases and char.

The effect of different reaction parameters helped in understanding the structure–property relationship in B-doped CNTs. A plausible reaction kinetic model and a reaction mechanism were proposed for the FCCVD synthesis of BCNTs.

Boron-doped carbon nanotubes (BCNTs) with varying B content (0–8 at%) were prepared by thermo-catalytic decomposition of ethanol in presence of boric acid at 1073 K. It was observed that hydrogen adsorption capacity improved to a critical B content of 3.86 at% and then decreased. Maximum hydrogen adsorption was found to be 0.497 wt% at 273 K and 16 bar with 3.86 at% of boron doping in CNTs. With the help of transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, it was found that in addition to dopant concentration, dopant bonding with carbon structures, crystallinity and defects play pivotal roles in determining the extent of hydrogen adsorption by BCNTs. The thermogravimetric studies revealed the oxidation stability of the BCNTs. The hydrogen adsorption kinetics was found to follow the pseudo-second-order model. The rate constant value was minimum for the BCNT with the highest hydrogen storage capacity.

Achieving greater control on crystallization to obtain desired crystal structure and morphology is a significant challenge in material synthesis. The highly stochastic nature of crystallization makes it necessary to conduct thorough experimental and computational investigations of crystalline materials. Polymorphic transformation, including hydrate formation during crystallization of potassium acid phthalate (KAP) is one such example. The hydrated form of crystals can appear during crystallization when water interacts strongly with functional groups of solute molecules, leading to its inclusion into the crystal lattice. Here, we show the temperature-dependent transformation of anhydrous KAP (form-I) to monohydrate KAP (form-II) crystal. Such polymorphic and associated morphological changes as a function of temperature and supersaturation are studied using in-situ hot-stage optical microscopy and validated with morphology domain analysis. While the measured growth rates and morphologies do not vary significantly with supersaturation, they show a stronger temperature dependence due to the formation of hydrated forms. The computational results uncover the previously unknown effect of temperature-dependent pH increase, which causes deprotonation of the carboxylic group leading to destabilization of [110] facets. The appearance of hydrated form seems to be due to temperature-induced pH changes. These results provide fundamental insights into the mechanism of hydrate transformations during cooling crystallization.

This paper illustrates the electrochemical exfoliation of graphite for the synthesis of graphene oxide (GO) with few layers. Innovative design and arrangement of electrodes were adopted, which allowed simultaneous exfoliation and re-exfoliation of graphite anode. Electrolyte having different molar concentrations of an aqueous solution of sulfuric acid (H2SO4) and pH offered successful exfoliation of graphite anode with a varying yield of GO. The addition of sodium hydroxide (NaOH) in the solution affected the exfoliation rate and the morphology of the GO sheets. The transition of GO sheets from clumping–scrolling–flat sheet edge rolling to nanoribbons was observed by the change of composition and pH of the electrolyte. GO sheets showed lateral dimensions ranging from 500 nm to 24 μm, and ribbons and scrolls were found to have dimensions up to 50 μm. With the help of transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, a mechanism of exfoliation has been proposed. In situ functionalization of graphene helped in imparting stability to the GO in solvents such as ethanol and water for more than 11 months. This study elaborates on the significance of solvated sulfate ions and provides a window of sulfate and hydroxyl ion combination for tuning of structural morphologies of GO.

Copper–Chlorine cycle has been identified as the most prospective among the low temperature thermochemical cycles for hydrogen production. The cycle consists of two thermal reaction steps, one electrochemical step and a physical separation step. The two thermal reaction steps, hydrolysis and thermolysis are carried out in series for water splitting and oxygen production, respectively. The solid product from hydrolysis step Cu2OCl2 enters the thermolysis step where it undergoes decomposition to CuCl and O2. In the present work, thermolysis experiments were carried out in a laboratory scale horizontal furnace reactor with CuO–CuCl2 equimolar mixture and Cu2OCl2 in the temperature range of 470–575 °C. Experiments in furnace reactor show that, under otherwise same conditions, similar conversions are obtained with Cu2OCl2 as well as with the equimolar mixture of CuO–CuCl2. It was also observed that the conversion increased with an increase in CuCl2 percentage in the reaction mixture. From the experimental data, an attempt has been made to provide insights into the reaction mechanism and kinetics. These results are expected to be useful for the design and scale-up of the thermolysis reactor.

A screw feeder is mainly used in industries for conveying and elevating granular materials. Despite having a simplistic design, the mechanics of conveying the material is quite complex. The flow behavior of particles in a screw feeder is influenced by its geometric and operating parameters. In this study, the authors focus on the change in flow behavior by changing these parameters, using the discrete element method (DEM) simulations software LIGGGHTS. The mass flow rate measurement and visual examination of the particle fill level in our experimental studies served as model validation. The simulations were conducted with monosized spherical particles, and a mass-based uniform distribution of particles, with diameters between 2 and 5 mm. A mass based uniform size distribution was considered to represent multisized biomass particles, with particle properties of a representative biomass being used. The simulations quantify the screw feeder performance in terms of mass flow rate, average particle speeds (axial, radial, and swirl), and average contact forces (normal and tangential). The average particle axial and radial speed increased and swirl speed decreased with increasing rotational speed. The increase in feed rate and flight pitch ratio enhances the average radial and swirl speed of particles. The swirl and radial speeds are highest for smallest particle diameter for all three varying parameters. The average normal and tangential contact forces increased with increasing rotational speed, particle feed rate and pitch flight ratio and was found highest for biggest particle diameter.

The purpose of this work was to establish the pyrolysis kinetics of agricultural biomass residues (mustard husk (MH), cotton stalk (CS), and groundnut shell (GNS)) using thermogravimetric analysis (TGA). TGA is carried out at different heating rates (5, 10, 30, and 50 K/min) under inert conditions in the temperature range of 303–1173 K. The iso-conversional methods of Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa were used to estimate the activation energy of the decomposition process. The Criado method, Coats-Redfern Method, and Direct Differential methods were used to model the kinetics, with the latter two methods providing a closer fit with the experimental data. The kinetics of thermal degradation were separately studied for three temperature zones represented as drying, active, and passive zones. The results of Coats-Redfern and Direct Differential methods showed that (i) the nth-order reaction model is applicable for all the samples with order of reaction in the active zone being around ~ 2.0–3.0, ~ 2.5–3.0, and ~ 3.0 for MH, CS, and GNS, respectively, and (ii) the D-3 model is applicable for all the samples in the passive zone.

Concentration solar power (CSP) systems convert solar radiation to heat and use heat engines to convert the heat to electricity. The solar receiver over which the solar radiation is concentrated and converted to heat is the most important part of the CSP. To attain maximum efficiency, the receiver in the CSP systems needs to be coated with an efficient selective solar absorber coating. In recent years, a lot of research has been focused on solar selective coatings. This has resulted in the synthesis of novel coatings that have high thermal and chemical stability, long term durability, and excellent solar selectivity making them suitable for solar thermal applications. This report reviews various solar selective coatings based on transition metals and their compounds. Various failure mechanisms are discussed in detail along with suggested prevention methods. Several thermal stability and durability tests are reported with their benefits and limitations. The effect of long-term durability on the levelized cost of coating is also discussed. Finally, we list some excellent systems and explore different ways of improving the thermal stability for SSCs, thus providing a reference for the design and optimization of new SSCs.

Concentrating solar power is the most challenging and expensive yet highly efficient source of thermal energy from solar power. This is mainly due to the intermittency of the sun rays and expensive materials used to harness its energy. One of the main components adding to the cost is the solar selective absorber materials which are simply put spectrally selective coatings on a receiver system to capture maximum heat from the sun. These materials add to a large extent to the efficiency of converting the sun’s energy to thermal energy and in turn electricity. An ideal solar selective absorber possesses the property of absorbing maximum radiations in the solar spectrum and emit minimum in the thermal energy spectrum. In the current study, an inexpensive, simple and environment-friendly solar selective absorber is fabricated by a galvanic displacement reaction of copper nanoparticles on galvanised metal substrates. These copper nanoparticles have high absorptivity (0.8–0.9) by virtue of plasmon resonance property. The emissivity is low due to the highly reflective metal substrate. By varying size of the copper nanoparticles from 100 nm to 2 μm emissivity and absorptivity can be varied. However, achieving low emissivity and high absorptivity requires some optimising. The size depends on the concentration of precursor solution and immersion time of substrate. One of the remedies for controlling the deposition rate to tune the nanoparticle size and microstructure of deposited copper nanoparticle is by addition of a deposition inhibitor (e.g. Polyethylene glycol).

Direct Numerical Simulations (DNS) were carried out for a freely falling/rising rigid particle in an otherwise quiescent fluid, using a non-Lagrangian multiplier based fictitious domain (FD) method. Validation studies showed that the proposed FD based DNS are in good agreement with the existing experimental results in the transition regime of falling/rising spheres. Simulations done in the transitional regime (50 Γ = ρ p / ρ f ${\Gamma}={\rho }_{p}/{\rho }_{f}$ from 0.08 to 4), confirmed that (i) a falling spherical particle (Γ = 4) exhibits a helical trajectory in the range 270 1). Fast Fourier Transform (FFT) analysis characterized the presence of a bimodal frequency similar to that exhibited by flow past an isolated stationary bluff body.

In the present work, 3-D numerical simulations have been carried out to understand the flow patterns and heat transfer on the jacket side of a stirred vessel under mixed convection conditions. Vari...

Advanced thermo-chemical treatment in inert environment (also known as pyrolysis) of end of life tyres results into generation of oil, non-condensable gases and carbonized product termed as char. Solid char accounts to 35–45 wt% of the total products depending upon the process conditions. The present study is directed towards evaluating the suitability of tyre char for certain commercial applications. Char contains additives (inorganics) which are used to enhance certain properties of commercial tyres. Characterization of char confirms the presence of 19% inorganics that constitutes of elements such as Zn, S, Mg, Si and Ca. The other characterization techniques such as Raman, SEM and TGA have assisted in examining the surface characteristics and stability of tyre char. Raman analysis has emphasized on the presence of graphitized carbon structure with lesser defects. TGA analysis has showed suitable thermal stability at higher temperatures. The direct application of tyre char without further treatment has been undertaken based on these analyses. Char obtained from tyre pyrolysis was evaluated in Styrene Butadiene Rubber based compounding formulation at a dose of 50 parts per hundred gram of Rubber in comparison with a standard carbon black grade of Semi Reinforcing type of carbon black with equivalent dose. It was found that the increase in tensile strength and associated properties of vulcanization of char sample and the char can be utilized in rubber products formulation without any negative impact. Significant improvement was observed on tear strength properties while adding the char or carbon black which proves that there exists the reinforcing characteristics of the char like standard carbon black. Based on these studies, it has been concluded that there is need for further upgradation of tyre char for application in dyes, coatings and activated carbon industries.

Solid state decomposition studies of Low and High Density Polyethylene (LDPE and HDPE) have been carried out in the present work. Thermo-gravimetric analysis (TGA) is utilized to determine the degradation kinetics for pure plastic samples at different heating rates. The distribution of activation energy values and rates estimated using various Iso-conversional methods have been selected on basis of correlation coefficients. For LDPE, isoconversional method of Friedman and for HDPE Flynn Wall Ozawa methods are used to estimate the distribution of activation energies having their mean values as 256.5 and 257.2 kJ/mol respectively. The inputs from Isoconversional methods are used to determine decomposition behavior with Criado method. Model based studies performed with Criado method identifies the solid-state degradation follows contracting volume-sphere (R3) model based on lower statistical parameter values. The identified decomposition model is validated by Coats Redfern method which also results in lower statistical parameter values. This is further validated through a best fit of extent of reaction profile against temperature, substantiating the solid-state decomposition model followed by given plastic fractions.

Ibuprofen is widely used as an anti-inflammatory drug. Ibuprofen crystallized from non-polar hexane exhibits needle morphology, while from polar solvents, it exhibits a plate or polyhedral morpholo...

Particle dispersion behaviour in a solid liquid fluidised system leads to interesting outcomes such as mixing and segregation which are often quantified by an empirical dispersion coefficient. The present study aims at providing a better estimation of particle dispersion behaviour from a fundamental definition analogous to diffusion coefficient. By tracking a tracer particle using high speed image analysis, fluctuating velocity components (Vi/) were determined in a solid-liquid fluidised bed comprising glass particles (dS = 8 mm, ρS = 2230 kg m−3) and water as a fluidising medium. Both inter-particle and particle-wall collisions were determined from the time varying jerk data. The particle mean-free path (λ) was then estimated as a distance between two successive peaks in the jerk profile. Finally, dispersion efficient D was computed based on the product of λ and V. Estimated dispersion coefficients were compared with the available correlations and reasonable agreement was obtained.

In this study, we have developed a novel model to include the spatial heterogeneity for the combustion of volatiles in the presence of oxygen inside a biomass cookstove (BCS). Three-dimensional com...

Hydrolysis of CuCl₂ is the water splitting step of the Cu–Cl thermochemical cycle, where CuCl₂ reacts with steam to produce Cu₂OCl₂ and HCl. In the present work, this gas–solid reaction was investigated to understand the mechanism and kinetics. Experiments were conducted in a semibatch fluidized bed reactor to study the effect of temperature (275–375 °C), steam mole fraction (0.4–0.9), and reaction time (0–3 h). The challenges due to the hygroscopic nature of the reactant, product agglomeration, and multiple side reactions to achieve smooth and consistent reactor performance were overcome by the addition of inert additives during fluidization. The analysis of the mechanism showed that the desired product Cu₂OCl₂ is formed initially and further undergoes decomposition to CuO and CuCl₂. Also, with increasing temperatures, the yield of Cu₂OCl₂ decreases because of the formation of CuCl from reactant decomposition. The results indicate that a minimum steam mole fraction of 0.5 is required to prevent the formation of side product CuCl in the temperature range of 300–325 °C. The minimum steam requirement for maximum yield to Cu₂OCl₂ was found to increase with increase in temperature.

The annular centrifugal extractor is one of the robust stage-wise solvent extraction contactors. In a multistage operation, failure of any single stage leads to the stoppage of the entire annular c...

Boron and nitrogen codoped carbon nanotubes (B,N-CNTs) were synthesized by floating catalyst chemical vapor deposition (FCCVD) using ethanol, ferrocene, boric acid and imidazole as carbon source, catalyst, boron and nitrogen precursors, respectively. The samples were analyzed using transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis and X-ray photoemission spectroscopy. 1.5 at% B and 1.34 at% N could be doped in the resultant structure, which has higher length (few μm) with higher thermal stability (621 °C). At pressure 16 bar, hydrogen adsorption for B,N-CNTs was found to be 1.96 and 0.35 wt% at 77 K and 303 K, respectively. Hydrogen storage as function of time was also reported for both the cases. The adsorption process follow pseudo second order kinetics. The present study reveals that the codoping of CNTs aid in tuning properties of CNTs for hydrogen storage application.

Screw feeders and conveyors are mainly used in industries like minerals, agriculture, chemicals, pharmaceuticals, pigments, plastics, cement, sands, and food processing for transporting and mixing the granular materials. The system looks mechanically simple but the physics of particle transport in the system is complex; problems like bridging and blockage may be observed in the operation. A comprehensive understanding is required to study the granular flow behavior in screw feeders and conveyors. Hence, this extensive review has been prepared on granular flow behavior, transportation and mixing occurring in screw feeders and conveyors, via experimental, theoretical and discrete element method (DEM) approaches.

This review presents a systematic analysis of the published literature on flow regime mapping and effects of external disturbances for flow past a single stationary sphere. Various experimental and numerical investigations have been performed over the past years on such flows over a wide range of Re. The first part of this review (Tiwari et al. [ 1 ]) explained the methodologies to carry out these investigations and the statistical tools used for analyzing the flow behavior. This part presents the findings on the flow parameters such as pressure and force coefficients, Reynolds stresses, velocity and vorticity. Also, the physical significance of wake structures and their contribution in enhancing/ reducing the turbulence and mixing in the flow has been elaborated. According to the available findings from the published literature a regime map has been presented to categorize the flow into eight different regimes. The effect of disturbances such as the presence of walls, surrounding particles, free surface, stratification and external perturbations on these flow regimes have also been covered in brief. In this review a coherent presentation has been made on transitional journey of flow past an isolated stationary single sphere from creeping flow to highly turbulent regimes. In addition to this, a short section has been included to show the significance of detailed knowledge of a rather fundamental issue of flow past a sphere in designing and optimizing some process equipment such as a packed bed and a fluidized bed reactor.