Derivative Curves Research Articles

Parameters evaluation of fault-karst carbonate reservoirs with vertical beads-on-string structure based on bottom-hole pressure: Case studies in Shunbei Oilfield, Tarim Basin of Northwestern China

Tarim Basin newly discovered the fault-karst carbonate reservoirs, which are formed by the large-scale tectonic fault activities and multiple-stage karstification. Four kinds of mediums coexist in the reservoirs, including the large cave, vug, tectonic fracture and matrix. The tectonic fractures interconnect with large caves in series to form the vertical beads-on-string structure, which is the most common connection pattern in reservoirs. To provide a well test method for evaluating this type of structure, this work firstly presents a multi-fracture-region multi-cave-region series connection physical model by simplifying vertical beads-on-string structure. We consider four kinds of mediums in the proposed physical model, including large caves, small vugs, high-angle tectonic fracture and rock matrix. The fracture regions mainly contain fracture, vug and matrix mediums. The cave regions contain cave medium. The corresponding mathematical model is also developed, in which the flow in fracture regions obeys the Darcy’s law, while the flow in cave regions is assumed to obey free flow. Furthermore, the gravity is taken into account because the flow is along the vertical direction. Then the typical flow regimes are analyzed and sensitivity analysis is conducted on crucial parameters. Results indicate that (a) the typical feature of vertical beads-on-string structure on type curves is that the cave storage regimes and linear flow regimes alternately appear; (b) the type curves will exhibit the cave storage regimes with unit-slope pressure derivative for the existence of large caves, which is different from the inter-porosity flow regimes for the existence of the vugs (slope ≠ 1); (c) the gravity effect could lead to unit-slope pressure and pressure derivative curves, which can be regarded as closed boundary in a peculiar sense; (d) gravity effect is difficult to be observed from well test curves with about 2-weeks test duration in real application. Finally, two cases from Shunbei Oilfield are interpreted to illustrate the practicability and feasibility of proposed method.

Conformational stability as a quality attribute for the cell therapy raw material human serum albumin.

Although human serum albumin (HSA) has been used for many decades, there is still a lack of suitable quality control (QC) attributes. Its current use as a raw material in gene-, cell- and tissue-therapies requires more appropriate functionally-relevant quality attributes and methods. This study investigated the conformational stability of serum albumin using circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) for evaluating the thermal sensitivity, and quartz crystal microbalance-dissipation (QCM-D) and localized surface plasmon resonance (LSPR) for assessing the adsorption behavior. Different serum albumin samples were used, encompassing plasma-derived HSA (pHSA), recombinant octanoate-stabilized HSA (rHSA) and bovine serum albumin (BSA). The melting temperature (Tm) as well as the onset temperature (Tonset) were obtained from the derivative curves of the temperature gradient CD data at 222 nm. The results from DLS, as well as from real-time QCM-D and LSPR silica-adsorption kinetic profiles confirmed the relatively higher conformational stability of the octanoate (fatty acid) containing rHSA, while the additional negative charge resulted in a lower amount adsorbed to the silica surface compared to the non-stabilized HSA and BSA. Adsorption studies further revealed that BSA has a lower conformational stability and undergoes more extensive adsorption-induced spreading compared to the non-stabilized HSA. Collectively, the temperature-based (CD and DLS) as well as adsorption-based biosensor (QCM-D and LSPR) approaches gave congruent and discriminatory information about the conformational stability of different serum albumins, indicating that these techniques provide information on valuable QC attributes.

Hydraulic characteristics of a fractured crystalline basement aquifer in Nzhelele area, Limpopo Province, South Africa

Knowledge on hydraulic characteristics of fractured crystalline basement aquifers is limited resulting to lack of reliable information for effective groundwater management. This is crucial as these aquifers provide good sources of potable water in most rural communities. Heterogeneous nature of these aquifers requires detailed understanding and accurate estimation of hydraulic characteristics. This study estimated hydraulic characteristics of a fractured crystalline basement aquifer and inferred their influence on groundwater storage potential and flow. Aquifer Test Solver was used for automatic curve matching to identify appropriate aquifer models and test solutions for estimating hydraulic characteristics. Root-mean-square error (RMSE), mean absolute error (MAE) and correlation coefficient (R) were used to evaluate the performance of the fitted models. Plotted derivative curves were used to identify the presence of fracture dewatering in the aquifer. The R, RMSE and MAE ranged from 0.702 to 0.995, 0.31–3.45 m and 0.23 to 3.06 m, respectively. The fits between measured and estimated drawdowns were good and performance mostly acceptable and comparable to those of related studies. Storativity, transmissivity and hydraulic conductivity ranged from 0.0003 to 0.0680, 0.78 to 12.3 m2/day and 8.56 × 10−7 to 5.32 × 10−6 m/s, respectively. The storage potential of the aquifer varied from low to high, ability to transmit water per unit area was mostly medium though the ability to transmit water through its entire thickness was mostly low. The study area is dominated by leaky aquifer and fracture dewatering. Groundwater use should be monitored and managed effectively to avoid fracture dewatering and its associated risks.

Assessment of the thermal hazards and oxidization mechanism of coloured corn starch dust by TG–FTIR

Starch is widely used in industrial production and in every life, and an increasing number of accidents of starch dust burning and explosions are occurring and have caused serious casualties and economic losses. Previous studies on the oxidative properties and microscopic characterization of coloured corn starch dust have been less systematic than the present study. To prevent coloured corn starch dust explosion accidents more effectively, thermogravimetry and Fourier transform infrared spectroscopy were applied to study the oxidation characteristics of coloured corn starch dust. Seven characteristic temperatures were determined from the thermogravimetric curves and derivative thermogravimetric curves of coloured corn starch dust. The entire oxidation process of coloured corn starch dust was divided into five stages, and a 60% mass loss occurred in the rapid oxidation stage. Three iso-conversion methods were used to calculate the apparent activation energy (Ea) and pre-exponential factor (A) at different oxidation stages. The value of Ea was found to be related to the difficulty of the reaction, and it had a positive correlation with lnA. Six kinds of gases were detected during the oxidation process. The oxidation mechanism was further analysed by the macro and micro characterization of the oxidation process. The findings provide a theoretical basis for preventing and controlling explosion accidents that involve coloured corn starch dust.

Semi-analytical model for pumping tests in discretely fractured aquifers

In this paper, a novel semi-analytical model for pumping tests in discretely fractured aquifers with randomly distributed and finitely conductive fractures is presented to investigate the wellbore drawdown transient behaviour. An aquifer model and discrete fracture model are established. The flux and drawdown equivalent conditions in the Laplace space are applied in the fracture wall to couple the fluid flow in both systems. The advantage of the proposed semi-analytical model is that only fractures must be separated into segments, not the entire domain. Then, a matrix of the fracture segment in Laplace space can be built and solved by using Gauss's elimination method. A final solution for wellbore drawdown can be easily evaluated using the numerical Laplace inversion algorithm of Stehfest. The model is compared with a previous result of an extended well. The proposed model allows us to consider the problems of pumping tests in complex fracture networks, including parallel uncrossed fracture networks, arbitrary distribution non-intersected fracture networks, and intersected fracture networks with isolated fractures. In the past studies, some scholars have found that the drawdown or pressure derivative curve will present only one dip valley which looks like a V-shaped curve for the naturally fractured confined aquifer or reservoirs, and number of dip valleys are only related to porous media type. However, this study illustrates that the drawdown transient behaviour and the number of dip valleys are closely related to fracture density, fracture conductivity, fracture length, fracture orientation, fracture distribution, position of a pumping well, and the distance between the pumping well and fracture.

Pressure performance of multi-stage fractured horizontal well considering stress sensitivity and dual permeability in fractured gas reservoirs

Generally, the horizontal well multi-stage fracturing technology is widely used to enhance single well production of tight or ultra-low permeability gas reservoirs. The deformation of the rock pore structure makes the permeability of the reservoir impossible to be a constant. The pressure transient analysis mathematical model of the multi-stage fractured horizontal wells (MFHWs) with consideration of stress sensitivity, varying conductivity and dual-porosity dual-permeability (DPDP) is established. Laplace transformation, pressure drop superposition and Gaussian elimination are utilized to obtain the wellbore pressure solution of MFHWs. Comparison result reaches a good agreement by model validation. On the basis of pseudo-pressure derivative curve characteristics, eight flow regimes can be diagnosed, namely, well storage, skin affection, bi-linear flow, early linear flow, early radial flow, middle linear flow, inter-porosity flow and later radial flow regime. The influences of some vital parameters on pseudo-pressure and its derivative curve is discussed in detail. The proposed model can help engineers understand the pressure dynamic characteristic of the MFHWs with stress sensitivity, varying conductivity and DPDP performance.

Phase Transformation Mechanism and Microstructure Evolution of TC4 Alloy during Continuous Cooling

The effects of cooling rate on the microstructure and phase transformation mechanism of TC4 alloy during the continuous cooling of β phase region were studied by non-isothermal expansion method combined with microstructure observation. The phase transformation feature points at different cooling rates were obtained by the expansion curve and its first derivative curve. The characteristics of the phase transformation products in the corresponding phase transformation feature points were observed by optical microscopy (OM). The results show that with the increase of cooling rate (excluding water cooling), the nonlinearity of the expansion curve caused by phase transformation changes from one place to two, and the temperature corresponding to the peak value of the phase transformation rate curve also showed different changes. As the cooling rate increases, the microstructure sequentially underwent lamellar α, massive αm, and fine-needle α′ martensite. The phase transformation conditions of massive αm and α′ martensite are significantly different, and showed a competition trend between them. According to the phase transformation feature points and their corresponding microstructure, the continuous cooling diagram for TC4 β solution treatment was plotted.

Transient Pressure Analysis of Inclined Well in Continuous Triple-Porosity Reservoirs With Dual-Permeability Behavior

Inclined wells has recently been adopted to develop fractured-vuggy carbonate hydrocarbon reservoirs (FVCHRs) composed by matrix, fracture and vug system. Therefore, it is significant for us to describe pressure transient of inclined well for FVCHRs. In this paper, it is assumed that vug and fracture system connect with wellbore, and inter-porosity flow from vug to fracture system appears. Therefore, the pressure transient responses model of inclined well with triple-porosity dual-permeability behavior was built. The model is solved by employing Laplace integral transform and finite cosine Fourier transform. Real-domain solution of the model is obtained by Stehfest inversion algorithm. On the basis model of the published paper, the solution of the simplified model of this paper was validated with horizontal and vertical well of FVCHRs with triple-porosity dual-permeability behavior, and results reach a good agreement. Type curve, according to pressure derivative curve characteristic, can be divided into eight flow regimes, which includes wellbore storage, skin reflect, early vertical radial flow, top and bottom boundary reflection, linear flow, inter-porosity flow from vug to fracture, inter-porosity from matrix to vug and fracture and pseudo-radial flow regimes. The influence of some vital parameters (inclination angle, inter-porosity flow coefficient, well length and permeability ratio etc.) on dimensionless pressure and its derivative curves are discussed in detail. The presented model can be used to understand pressure transient response characteristic of inclined wells in FVCHRs with dual-permeability behavior.

Revising Transient-Pressure Solution for Vertical Well Intersected by a Partially Penetrating Fracture with Non-Darcy Flow Effect

The principle purpose of this work is to formulate an accurate mathematical model to evaluate the transient pressure behavior of a well intercepted by a partially penetrating vertical fracture (PPVF) with non-Darcy flow effect. Fracture conductivity is taken into account by coupling the three-dimensional flow in reservoir and the two-dimensional flow within fracture; the Barree-Conway model is incorporated into the model to analyze non-Darcy flow behavior in fracture, which leads to the nonlinearity of the governing equations. A high-effective iterative algorithm using a combined technique of fracture-panel discretization and dimension transform is developed to render the nonlinear equations amenable to analytical linear treatment. On the basis of the solutions, the pressure response and its derivative type curves were generated to identify the evolution of flow regimes with time. Furthermore, the influences of fracture conductivity, penetration ratio, and non-Darcy characteristic parameters on pressure response are investigated. The results show that PPVF exhibits five typical flow regimes, and analytical solutions for each flow regime are similar to that for a fully penetrating vertical fracture (FPVF) that can be correlated with the penetration ratio and apparent conductivity. The non-Darcy flow effect is found to have more significant effect on the low and moderate conductivity, especially in early-stage flow regimes. When the penetration ratio is smaller than 0.5, the pressure behavior exhibit a more remarkable variation with penetration ratio. This study provides a better insight into understanding the influence of non-Darcy flow on flow regime identification.

Effect of Stress-Sensitive Fracture Conductivity on Transient Pressure Behavior for a Multi-Well Pad With Multistage Fractures in a Naturally Fractured Tight Reservoir

This paper presents a semianalytical solution for evaluating transient pressure behavior of a multi-well pad with multistage fractures in a naturally fractured tight reservoir by considering the stress-sensitive effect imposed by both natural and hydraulic fractures. More specifically, the model pertaining to matrix/natural fractures is considered as a dual-porosity continuum, while its analytical flow model can be obtained by use of a slab-source function in the Laplace domain. The hydraulic fracture model is solved by discretizing each fracture into small segments to describe the flow behavior, while stress sensitivity in both the natural fracture (NF) subsystem and hydraulic fracture (HF) subsystem has been taken into account. To validate the newly developed semianalytical model, its solution has been obtained and compared with those of a commercial numerical simulator. By generating the type curves, there may exhibit eight flow regimes: pure wellbore storage, skin effect transition flow, linear flow regime within HFs, early radial flow, biradial flow, transition flow, pseudo-steady diffusion, and the late-time pseudo-radial flow. Furthermore, late-time flow regimes are found to be significantly distorted by the multi-well pressure interference. The smaller the well-rate ratio is, the more distorted the pressure and pressure derivative curves will be. In addition, well spacing and fracture length are found to dominate the flow behavior when multi-well pressure interference occurs. As the well spacing is decreased, the fracture length is increased, and thus occurrence of multi-well pressure interference is initiated earlier. Permeability moduli of NFs and HFs impose no impact on the multi-well pressure interference; however, it can distort flow regimes, leading to a severe distortion of pressure and pressure derivative curves. Similarly, the effect of HF permeability modulus on the flow in a hydraulic fracture, the minimum fracture conductivity is another key factor affecting the “hump” on the pressure curve. As the crossflow coefficient is increased, flow exchange between matrix and NFs is increased. With an increase in the storage ratio, flow exchange lasts longer and the second “dip” on the pressure curve becomes deeper.

Pressure Performance of Highly Deviated Well in Low Permeability Carbonate Gas Reservoir Using a Composite Model

It is commonly believed that matrix and natural fractures randomly distribute in carbonate gas reservoirs. In order to increase the effective connected area to the storage space as much as possible, highly deviated wells are widely used for development. Although there have been some studies on the composite model for highly deviated wells, they have not considered the effects of stress sensitivity and threshold pressure gradient in a dual-porosity gas reservoir. In this paper, a semi-analytical composite model for low permeability carbonate gas reservoir was established to study the effect of non-Darcy flow. By employing source function, Fourier transform and the perturbation method, the pressure performance and typical well test curves were obtained. Eight flow regimes were identified, and their characteristics were discussed. As a result, it can be concluded that the effects of stress sensitivity and threshold pressure gradient would make pseudo-pressure and derivative curves rise, which is the characteristic of non-Darcy flow to determine whether there is stress sensitivity or threshold pressure gradient.

Synthesis, characterization, thermodynamics and thermal degradation kinetics of imine-linked polymers

A series of new imine-linked polymers reveal variations of aliphatic and aromatic linkers were synthesized via Schiff base co-condensation polymerization and fully characterized. The polymers are classified as 1,4- and 1,6-based polymers according to their preparation methodology, which depicted by the polymerization of thiophene-based aryl aldehydes with1,4-butanediamine and 1,6-hexanediamine, respectively. The interpretation of their thermal stability from the thermal gravimetric analysis and the first derivative (TGA-DTG) curves have indicated that the variation in the contents of the aryl-aldehydes and the length of the linker are significantly affect the thermal stability behavior. For example, the polymer prepared via the connection of ter-thiophene-aldehyde with 1,4-butanediamine (1,4-TIP) has shown higher thermal stability, higher char residue content, higher limited oxygen index (LOI = 32) than the polymer prepared by bi-thiophene-phenyl-aldehyde (1,4-F2IP) in the same manner. Furthermore, 1,4-TIP has shown the highest LOI value over all polymers and thus, can be considered as a flame-retardant polymer. However, an inverse relation has been observed upon the inclusion of 1,6-hexanediamine with the same aryl-aldehydes. Further insight into the TGA curves was performed by applying well-known fitting models: Coats-Redfren (CR), Arrhenius, Briodo, and Horowitz-Metzeger for the determination and comparison of the activation energy (Ea) values upon degradation process. The CR-method was further used for the determination of the kinetic triplet parameters (Ea), reaction order (n) and pre-exponential factor (A) and thermodynamic parameters include entropy, the heat of enthalpy, and Gibbs free energy of the polymers. All these methods support the fact that the degradation mechanism follows first-order kinetics, thermodynamically favored and the higher thermal stability polymer requires higher (Ea) for thermal degradation.

Kinetic mechanism of magnesium production by silicothermic reduction of CaO·MgO in vacuum

Abstract The investigation of silicothermic reduction of CaO·MgO was carried out using a self-developed thermogravimetric analysis (TGA) instrument under vacuum and high temperature conditions. The TG data of pellets prepared with calcined dolomite, ferrosilicon and fluorite were determined at the heating rates of 1.5, 2.0, 2.5 and 3.0 °C/min in 5 Pa vacuum at 300–1400 °C, respectively. Model-free analysis and model-based analysis were applied for simulating the kinetic mechanism. By analyzing the characteristics of the initial and final reaction temperatures of TG curve, ratio of half-width of derivative TG curve and kinetic parameters, a conclusion was made that the most probable mechanism function is the first order formal chemical reaction with activation energy of 233.42 kJ/mol and pre-exponential factor of 5.14×1010 s−1. This study provides the basic data of dynamics of silicothermic magnesium production under vacuum conditions.

Excogitation and Assessment of Curcumin-Vitamin E Self-assembly PEGylated Nanoparticles by the Route of Oral Administration

Curcumin (CUR) has attracted wide research interests due to its abundant bioactivities and potential advantages in cancer treatment. But the poor water solubility, instability, and quick metabolization and elimination after oral administration severely restrict the efficacy and further clinical application of CUR. Derivation is an approach often used to improve the druggability of active ingredients, so the study aim to prepare a CUR derivate with better stability, satisfactory pharmacokinetics, and inherent self-assembled ability in contrast with CUR. The derivate was designed and evaluated in vitro and in vivo. Vitamin E (VE) was used to perform the esterification reaction with CUR, and the cytotoxicity of derivative CUR-VE ester on MCF-7 tumor cells was similar to CUR. Besides the better stability in simulated gastric and intestinal fluid, plasma and liver homogenate, the self-assembly CUR-VE nanoparticles were fabricated by feasible and controllable nanoprecipitation method. The Transmission Electron Microscope (TEM) showed CUR-VE NPs were spherical with an average particle size of 172.9 nm, and drug loading was up to 93%. CUR-VE NPs exhibited a sustained-release behavior and fitted to Fick's diffusion mechanism. Differential Scanning Calorimeter (DSC), X-ray Powder Diffractometer (XRPD) and Fourier Transform Infrared Spectrometer (FTIR) declared no crystalline substances were formed, and the self-assembly process of CUR-VE relied on driving forces including van der Waals forces, hydrogen bonding forces, intermolecular forces. In pharmacokinetics, Cmax and AUC0-∞ of CUR-VE NPs by the route of oral administration were (104.69 ± 40.72) ng/mL and (3496.92 ± 1088.93) ng/mL∗h, which were about three times and 18 times more compared with CUR. The eliminated half-time of CUR-VE extended to 28 h ascribed to the outstanding stability and surface PEGylation of NPs. It prompted that appropriately PEGylated NPs via oral administration was beneficial to prolong systemic circulation similar to intravenous PEGylated NPs.In summary, the study provides a convenient way to fabricate the self-assembled CUR-VE NPs qualified with high drug loading, satisfactory stability and desired pharmacokinetics. CUR-VE has the potent advantage to be an ideal substitute for CUR in the future of healthcare and clinical application.

Semi-analytical modeling of transient pressure behaviour for fractured horizontal wells in a tight formation with fractal-like discrete fracture network

In this work, theoretical models have been formulated, validated, and applied to evaluate transient pressure behaviour of a horizontal well with fractal-like multistage fractures in a tight formation. A coupled matrix-fracture flow model is proposed based on the superposition principle. More specifically, a slab source function was developed to describe the transient fluid flow behaviour from matrix to fracture, while a numerical solution was derived to describe the fluid flow behaviour in the complex fracture network. Then, a semi-analytical method is applied to solve such coupled models by discretizing hydraulic fracture into small segments. Furthermore, type curves are generated to examine the effect of the fractal fracture network. Sensitivity analysis of some major parameters (e.g., iteration number, deviation angle, and branch number) has been conducted to investigate their effects on the transient pressure responses. It is found that the fractal fracture network will greatly affect the transient pressure behaviour. The deviation of the pressure derivative curve from the case with the traditional bi-wing fracture can be used to quantify the complexity and the conductivity of the fracture network, while the existence of the complex fracture network will greatly improve the well performance in the intermediate time period.

Thermomagnetometric analysis of nickel–zinc ferrites

In this paper, magnetic phase transitions of nickel–zinc ferrites (Ni1−xZnxFe2O4) with a zinc content of 0 ≤ xZn ≤ 0.7 were studied using the thermomagnetometric method, which is a thermogravimetric analysis with a constant magnetic field applied. The studied ferrites were made from oxide powders using ceramic technology. The Curie point was determined from the derivative thermogravimetric curve in the region of magnetic phase transition. The Curie temperature calibration curve was obtained against the degree of doping of nickel ferrite with zinc to detect the magnetic phases by the Curie temperature. Thermal analysis of multicomponent magnetic mixtures that consist of nickel–zinc ferrites with different zinc contents was performed. The dependence of the change in mass during magnetic phase transition on the mass content of the magnetic phase in the ferrite mixture was revealed.

Effects of Shellac Treatment on Wood Hygroscopicity, Dimensional Stability and Thermostability

Dimensional stability proves to be an important factor affecting the quality of wooden products. As a sort of crude and thermoplastic resin, shellac excreted by lac insects demonstrates water-repellent and environmental-friendly features. The research impregnated shellac with wood at room temperature and with a vacuum-pressure procedure. Efforts were made to examine how shellac treatment affected the dimensional stability, moisture absorption, chemical structure, thermostability, as well as morphological characteristics of wood. Results indicated that shellac treatment was a type of efficient solution useful in the enhancement of the dimensional stability of wood. Shellac solution had good permeability in the wood, and the weight percentage gain reached 13.01% after impregnation. The swelling coefficients of treated wood in the tangential and radial directions decreased by 20.13% and 24.12%, respectively, indicating that impregnation could improve wood dimensional stability. The moisture absorption of shellac-treated wood was reduced by 38.15% under 20 °C and 65% relative humidity. Moreover, shellac treatment significantly modified wood structure, although there were no drastic changes in the spectra. Specimens for shellac treatment ran across two decomposition peaks at 350 and 390 °C, and specimens in the control group saw one more common derivative thermogravimetric curve when the sharp peak approached 355 °C. After impregnation of shellac into wood, the shellac blocked pits and hardened on the intrinsic layer of the wood for fear of hygroscopicity. The practice was applicable to a variety of wood products, such as buildings, furniture, and landscape architecture.

Pressure Transient Analysis for Sandstone Reservoir by Using Saphir

This work is discussed how to differentiate between two tricky models for sand stone formation by using the pressure transient analysis PTA for three Wells which are distributed in south, middle and north of X field. In the derivative curve these two models have the same sequence of flow regime which are by hump, first radial flow regime, transition hump and then late radial flow regime. The parameter Kappa (K) played the most important key to select the type of reservoir model and differentiate between the two models in PTA. In the middle and south of the field, this parameter has a value close to one at well no. Rt-16 & Rt-18, which means that the system behaves as dual porosity. On the other hand, Kappa has a value of around (0.74) in Rt-17 to represent a double permeability system but without cross flow between two layers due to the small value of Lamda.

Isokinetic analysis on the oxidation of Jurassic coal: a case study of samples from Xinjiang, China

Jurassic coal samples from Liuhuanggou (LHG) and Wudong (WD) coal mines, Xinjiang Province, China, were selected for oxidative thermal energy experiments. A temperature-programmed experimental system measured the variation of gaseous products and the changes in thermal energy release with temperature. Thermokinetic parameters, namely the apparent activation energy (Ea) and pre-exponential factor (A), of the coal samples for four heating rates were determined using a thermogravimetric analyser. During the low-temperature oxidation stage, two samples had temperature curves characterised by their production levels of the index gas (CO); the temperature changes were approximately equal, but the critical temperatures differed. The WD sample produced less CO gas. However, the maximum and minimum exothermic strengths of the two samples had some similarities to the temperature change curves. The characteristic temperatures for the coal samples were discovered using different heating rates. For the WD sample, the characteristic temperature varied according to the heating rate, and the thermogravimetry (TG) and derivative TG curves of the samples lagged with an increase in the heating rate. The characteristic temperatures of the sample increased with the increase in the heating rate. Isokinetic analysis (the Flynn–Wall–Ozawa and the Kissinger–Akahira–Sunose models) was used to calculate the thermokinetic parameters of the sample. The range of the heating rates was 2 to 15 °C min−1 for oxygen concentration of 21 vol%, and the Ea of the samples decreased with the increase in the heating rate.

Thermochemical Conversion of Sugarcane Bagasse: Composition, Reaction Kinetics, and Characterisation of By-Products

Sugarcane bagasse pyrolysis is an effective way of producing renewable and sustainable energy. A combined study on characterisation of primary and secondary by-products of sugarcane towards the effective use of bagasse as an energy feedstock and biochar is not yet available in the existing literature. This study is an attempt to bridge this gap and to understand the complete valorisation potential of sugarcane bagasse and its by-products. In this study, the elemental, structural, and compositional analyses of sugarcane bagasse collected from various sources were carried out, and their thermal decomposition behaviour under pyrolysis conditions was investigated using thermogravimetric data. The composition of all sugarcane bagasse samples showed remarkable similarity, except for the presence of high soluble sugars in two of the six samples. The hemicellulose content in the lignocellulosic bagasse samples was found to have a distinct thermal decomposition pattern, resulting in deconvolved derivative thermogravimetric curves with peaks centred at around 300 °C. A detailed analysis of the thermogravimetric data indicated a complex multi-step thermal degradation behaviour for bagasse under pyrolysis conditions. The pyrolysis reaction kinetics of sugarcane bagasse were developed by using iso-conversional and model-fitting methods. Further, SEM–EDS analysis revealed that the biochar obtained from bagasse fast pyrolysis experiments was predominantly siliceous. X-ray diffraction studies on biochar indicated that there were no crystalline phases, even at pyrolysis temperature of 700 °C.