A comparative process simulation study of CaCu looping involving post-combustion CO2 capture

This work presents a simulation study of several CaCu looping variants with CO₂ capture, aiming at both parameter optimization and exergy analysis of these CaCu looping systems. Three kinds of CaCu looping are considered: 1) carbonation–calcination/reduction–oxidation; 2) carbonation–oxidation–calcination/reduction and 3) carbonation/oxidation–calcination/reduction. A conventional Ca looping is also simulated for comparison. The influences of the calcination temperature on the mole fractions of CO₂ and CaO at the calciner outlet, the CaCO₃ flow rate on the carbonator performance and the Cu/Ca ratio on the calciner performance are analyzed. The second kind of CaCu looping has the highest carbonation conversion. At 1 × 10⁵ Pa and 820 °C, complete decomposition of CaCO₃ can be achieved in three CaCu looping systems, while the operation condition of 1 × 10⁵ Pa, 840 °C is required for the conventional Ca looping system. Furthermore, the Cu/Ca molar ratio of 5.13–5.19 is required for the CaCu looping. Exergy analyses show that the maximum exergy destruction occurs in the calciner for the four modes and the second CaCu looping system (i.e., carbonation–oxidation–calcination/reduction) performs the highest exergy efficiency, up to 65.04%, which is about 30% higher than that of the conventional Ca looping.     

Improving uncertainty evaluation of process models by using pedigree analysis. A case study on CO2 capture with monoethanolamine

This article aims to improve uncertainty evaluation of process models by combining a quantitative uncertainty evaluation method (data validation) with a qualitative uncertainty evaluation method (pedigree analysis). The approach is tested on a case study of monoethanolamine based postcombustion CO₂ capture from a coal power plant. Data validation was used to quantitatively assess the uncertainty of the inputs and outputs of the MEA model. Pedigree analysis was used to qualitatively assess the uncertainty in the current knowledge base on MEA carbon capture systems, the uncertainty in the MEA process model, and the uncertainty of the MEA model results. The pedigree review was done by 13 international experts in the field of postcombustion carbon capture with chemical solvents.The data validation showed that our MEA model is accurate in predicting specific reboiler duty, and CO₂ stream purity (4% and 1% difference respectively between model and pilot plant results), but in first instance it was less accurate in predicting liquid over gas ratio, and cooling water requirement (54% and 23% difference respectively between model and pilot plant results). The pedigree analysis complemented these results by showing that there was fairly high uncertainty in the thermodynamic, and chemistry submodels, as reflected in the low pedigree scores on most indicators. Therefore, the model was improved to better resemble pilot plant results.The results indicate that using a pedigree approach improved uncertainty evaluation in three ways. First, by highlighting sources of uncertainty that quantitative uncertainty analysis does not take into account, such as uncertainty in the knowledge base regarding a specific phenomenon. Second, by providing a systematic approach to uncertainty evaluation, thereby increasing the awareness of modeller and model user. And finally, by presenting the outcomes in easy to understand numerical scores and colours, improving the communication of model uncertainty. In combination with quantitative validation efforts, the pedigree approach can provide a strong method to gain deep insight into the strengths and weaknesses of a process model, and to communicate this to policy and decision-makers.     

气氛对低氮天然橡胶热降解的影响

采用热重分析(TG),研究了恒定升温速率下,低蛋白橡胶在氮气和空气气氛中的热降解行为,考察了反应气氛对降解速率、降解率和动力学参数的影响,分析了两者降解机理的可能差别。发现降解温度和降解率,氮气中均高于空气中;表观反应级数氮气中为2.0级,空气中为1.9级。     

Effect of cellulose crystallinity on the progress of thermal oxidative degradation of paper

Dynamic differential scanning calorimetry (DSC) using paper samples of different compositions has evidenced varying degrees of endothermic activity prior to the exothermic, oxidative decomposition of cellulose under static air. Whereas cotton cellulose papers displayed a significant endothermic activity, wood‐pulp papers showed a much less pronounced effect or no activity at all. DSC measurements using microcrystalline cellulose submitted to different extents of milling indicated that the observed endotherm is related to the degree of crystallinity of cellulose. Crystallinity decrease is accompanied by a decrease in the area of the endothermic peak. Thermal disruption of cellulose crystalline domains is therefore believed to be the reason for the appearance of an endotherm in the thermograms of paper. The higher degree of crystallinity of cotton cellulose in comparison to wood‐pulp cellulose accounts for the more pronounced endothermic activity observed for cotton papers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 61–66, 2000     

PA 1111的热降解过程和机理研究

通过热重分析研究了聚酰胺(PA)1111在N_2气氛中以不同升温速率时的热降解过程和机理。PA1111的热降解实验表明,PA 1111的热降解是一步过程,热降解温度为419.5℃。用Kinssinger和Flynn-Wall-Ozawa方法求得PA 1111的热降解表观活化能分别为239.3 kJ/mol和240.9 kJ/mol。用Coats-Redfern方法证明了PA 1111的热降解为减速机理。     

Studies of thermal oxidative degradation of polypropylene impact copolymer using the temperature rising elution fractionation method

Thermal oxidative degradation of polypropylene impact copolymer has been studied with its fractions obtained using the temperature rising elution fractionation method. The fractions were analyzed using ¹³C NMR, Fourier transform infrared and differential scanning calorimetry measurements, and the chemical structure, isotacticity, conformation and melting point were investigated. It is found that these fractions are composed of a homopolymer or a polymer blend of polypropylene, polyethylene and ethylene–propylene copolymer. The thermal oxidative degradation of each fraction was carried out at 130 °C, and the degradation progress was estimated by the change of molecular weight distribution (from gel permeation chromatography curves). The rate of degradation is found to be dominated by the content of tertiary C? H bonds (propylene unit) and the existence of 3₁ helix conformation corresponding to a crystalline polypropylene part in each fraction. The latter is more evident leading to the degradation reaction path with a lower activation energy. Copyright © 2007 Society of Chemical Industry     

Thermal oxidative degradation of bicomponent PP/PET fiber during thermal bonding process

The effects of the thermal bonding temperature, dwell time, and the type of mold materials on the thermal oxidative degradation of the PP sheath of bicomponent fibers were investigated using the Fourier Transform Infrared Spectra (FTIR) and Thermal Gravimetry/Differential Scanning Calorimetry (TG‐DSC) techniques. The samples were prepared on a new 3D nonwovens process based on air‐laying and through‐air thermal bonding. The fiber material was a commercial polypropylene (PP)/polyester (PET) (sheath/core) bicomponent staple fiber. The results reveal that ketone developed following β‐scission in the thermally bonded nonwovens. The level of thermal oxidative degradation increases with increase in the bonding temperature, dwell time, and the thermal conductivity of the mold material. Such thermal oxidative degradation led to the slight widening of the melting peaks of the fiber PP sheath in the thermally bonded nonwovens, and a slight decreasing of melting point compared with those of the as‐received fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 391–397, 2007     

F-12纤维热分解特性研究

采用热重方法研究杂环芳纶F-12纤维的热分解行为,非等温方法研究热分解反应动力学,利用分解反应动力学参数估算纤维在高温下的使用时间,并进一步分析热分解反应机理。结果表明:F-12纤维耐热性好,在空气和氮气气氛下开始分解温度分别为450℃和480℃;纤维可以在250℃以下长期使用;F-12纤维热分解反应的平均活化能是E=261.49±10 kJ/mol,指前因子A=(1.43×1017)±104min-1。     

New kinetic aspects on the mechanism of thermal oxidative degradation of polypropylenes with various tacticities

Thermal oxidative degradation behavior of polypropylene (PP) with different tacticities was studied based on the activation energy (ΔE) data obtained by thermogravimetric analysis (TGA). The ΔE value showed a negative proportion to the content of meso pentad fraction (mmmm) in all of isotactic PP (iPP) samples, and that of syndiotactic PP sample considerably deviated from this negative proportion relationship. Since the value of mmmm was directly related to polymer chain conformation, the ΔE value was thought to have close connection with the concentration of 3₁ helix conformation in the iPPs. The ΔE changes would be caused by the competition between uni- and bimolecular hydroperoxide decomposition, which was controlled by concentration and character of conformations of PPs.     

Thermal oxidative and photo‐oxidative degradation of polytetrahydrofuran studied using 1H NMR, 13C NMR and GPC

The products and mechanism of the thermal oxidative degradation at 180 °C and the photo‐oxidative degradation at 40 °C of polytetrahydrofuran have been investigated using ¹H NMR, ¹³C NMR and GPC. The NMR analysis was assisted by the use of DEPT ¹³C spectra, two‐dimensional NMR spectroscopy (COSY, HMQC and HMBC) and chemical shift simulation software. The NMR spectra of both thermally and photolytically degraded samples were similar showing that the degradation mechanisms were similar. GPC indicated that both chain scission, leading to lower molar mass products, and chain extension, leading to higher molar mass products, occurred initially. NMR analysis of the initial soluble degraded polymers showed that chain scission resulted in formate, aldehyde, propyl ether, butyl ether and propanoyl chain ends, and in‐chain ester groups were also formed. For longer periods of degradation, crosslinked gels were formed but these were not amenable to detailed structural characterisation by high‐resolution NMR to determine the crosslink mechanism. Copyright © 2004 Society of Chemical Industry     

A study of the products and mechanism of the thermal oxidative degradation of poly(ethylene oxide) using 1H and 13C 1‐D and 2‐D NMR

The products and mechanism of the thermal oxidative degradation of poly(ethylene oxide) at 150 °C have been analysed using ¹H and ¹³C 1‐D and 2‐D NMR spectroscopy, including COSY, HMQC, HMBC and DOSY techniques. Peaks from methanoate ester chain ends (in the majority), in‐chain esters, peroxy groups, acetal links and ethanoyl chain ends have been assigned. Two small molecule degradation products, 2‐hydroxyethyl methanoate and ethylene glycol dimethanoate have been identified. Copyright © 2004 Society of Chemical Industry     

Synthesis and thermal oxidative degradation of a novel amorphous polyamide/nanoclay nanocomposite

A novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X-ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactant with phenyl groups was delaminated in the polymer matrix, resulting in well-dispersed morphologies even at high montmorillonite content. Thermal oxidation behavior of the polymer nanocomposites was studied by thermogravimetric analysis (TGA), and the chemical evolution in the solid residue was monitored by elemental analysis and Fourier transform infrared spectroscopy (FTIR). TGA results showed that the addition of well-dispersed organoclay resulted in a substantial increase (30 °C) in the onset degradation temperature of the nanocomposites as compared to the homopolymer. Elemental analysis on the solid residue indicated that the presence of nanoclay resulted in char formation with greater thermal stability. FTIR spectra showed that thermal degradation in air occurred via both oxidative and non-oxidative mechanisms simultaneously. In the homopolymer, the oxidative mechanism was more dominant. However, with the addition of well-dispersed organoclay, the non-oxidative pathway became more significant. Hence the presence of delaminated nanoclay layers could effectively retard thermo-oxidative degradation of the amorphous polymer by constraining the polymer chains and slowing down the rate of oxygen diffusion through the nanocomposites, but it was not as effective in hindering the non-oxidative degradation reaction pathway.     

Macerals in bituminous coals and the coking process: Part 1: Effect of basic coal properties on the process of thermal degradation

Bituminous coals produced in the Ostrava—Karviná coal basin show considerable variation in their maceral composition and rank. In order to explain the significance of the petrographic composition, structure and chemical parameters in coal degradation processes, a large number of coal samples was investigated. From the relationships obtained, the behaviour of macerals during these processes is discussed. It is found that isometamorphic vitrinites are characterized by a distinctive behaviour affected to a first approximation by the atomic ratios C/H and C/O. Inertinite, despite its occasional significantly higher volatile matter, does not yield an appreciable amount of fused material.     

Thermal oxidative degradation kinetics of PP and PP/mg (OH)2 flame‐retardant composites

The thermal stability and thermal oxidative degradation kinetics of polypropylene (PP) and flame‐retardant PP composites filled with untreated and treated magnesium hydroxide (MH) in air were studied by thermogravimetric analysis (TGA). The effect of the heating rate in dynamic measurements (5°C–30°C/min) on kinetic parameters such as activation energy was also investigated. The Kissinger and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy for the degradation of neat PP and flame‐retardant PP composites. The results of TGA showed that the addition of untreated or treated MH improved the thermal oxidative stability of PP in air. The kinetic results showed that the apparent activation energy for degradation of flame‐retardant PP composites was much higher than that of neat PP, suggesting that the flame retardant used in this work had a great effect on the mechanisms of pyrolysis and combustion of PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1978–1984, 2007     

Assignment of 1H NMR spectrum and investigation of oxidative degradation of poly(ethylenimine) using 1H and 13C 1‐D and 2‐D NMR

The ¹H NMR spectrum of poly(ethylenimine) (PEI) has been assigned using two‐dimensional NMR correlation with the previously established assignment of the ¹³C spectrum. The oxidative thermal and UV degradation of PEI has been studied using mass loss measurements, and NMR and Fourier transform infrared spectroscopy. Analysis of the spectra of the degradation products shows that the degradation process may readily be monitored, particularly by ¹³C NMR. The major products are formamide and other amide groups which may be understood in terms of chain scission and dehydration reactions of hydroperoxides. Copyright © 2006 Society of Chemical Industry     

Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

The use of hydrogen peroxide (H₂O₂) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO₂ powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H₂O₂/UV, TiO₂/UV, and H₂O₂/TiO₂/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H₂O₂ concentrations on photodegradation process were examined. It was shown that photodegradation using H₂O₂/TiO₂/UV process was much more effective than using either H₂O₂/UV or TiO₂/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10⁻⁴ min⁻¹ by direct photolysis to 1.4 × 10⁻² min⁻¹ using H₂O₂/TiO₂/UV process. The role of H₂O₂ on such enhanced photodegradation of phenol in aqueous solution was finally discussed.     

The impact of cupric ion on thermo‐oxidative degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in air was studied using thermogravimetric and differential thermal analyses in the temperature range 30–600 °C. The impact of cupric ion on the thermo‐oxidative degradation of chitosan was investigated. Fourier transform infrared and X‐ray diffraction analyses were utilized to determine the microstructure of the chitosan–cupric ion compounds. Kinetic parameters such as activation energy, pre‐exponential factor, Gibbs energy, and enthalpy and entropy of activation were determined using the Coats–Redfern equation. The results show that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a two‐stage reaction. The impact of cupric ion on the thermo‐oxidative degradation of chitosan is significant, and all thermodynamic parameters indicate that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a non‐spontaneous process and proceeds via a mechanism involving nucleation and growth, with an Avrami–Erofeev function (A₄) with the integral form [?ln(1 ? α)]⁴. Copyright © 2010 Society of Chemical Industry     

Degradation of high barrier ethylene–vinyl alcohol copolymer under mild thermal‐oxidative conditions studied by thermal analysis and infrared spectroscopy

A study of the thermal‐oxidative degradation of a high barrier ethylene–vinyl alcohol copolymer with 32 mol% of ethylene (EVOH) has been carried out by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier‐transform infrared spectroscopy (FTIR) under mild temperature conditions above melting. It was found that time exposures of up to 11 h at temperatures between 9 and 33 °C above the EVOH melting point resulted in polymer weight losses of up to 3.6% with colour formation. The weight loss was faster at short times and slowed down with increasing exposure time. DSC showed a small decrease in crystallinity and melting point, melting‐peak broadening and a slight increase in the glass transition temperature of the samples subjected to the more severe thermal‐oxidative treatment. The FTIR experiments showed transformation of the vinyl alcohol hydroxyl groups into carbonyl groups and creation of double bonds. Changes in degradation kinetics and perhaps in mechanisms are thought to occur with increasing exposure time. Moreover, FTIR measurements suggest that transformation of the hydroxyl groups leads to a weakening of the overall hydrogen bonding strength in the degraded samples, and therefore a reduction in intermolecular cohesion can be anticipated. © 2001 Society of Chemical Industry     

Information technology support in the chemical process design life cycle

Information technology has been becoming increasingly important in all areas of engineering during the last few years. Much of the progress achieved in chemical engineering would not have been possible without the enabling methods and tools provided by information technology. This trend will continue in the future but most likely with a considerably wider scope. While individual software tools and services have been in focus until recently, their integration into engineering work processes is an emerging and challenging area of research and development. This contribution attempts to highlight state of the art and future trends in supporting the activities during the life cycle of a chemical process by means of information technology. Emphasis will be largely on the process and plant design process rather than on procurement, manufacturing, and distribution of materials in the supply chain.     

The oxidative degradation of styrenic copolymers: A comparison of photoproducts formation under natural and accelerated conditions

Natural and accelerated weathering of polystyrene and high‐impact polystyrene were carried out in the present investigation. The structural changes in the polymer samples were characterized by using FTIR spectroscopy, tensile strength testing, and SEM spectroscopy. The natural exposure was conducted throughout the year. Rates of photooxidation were determined by measuring the evaluation in hydroxyl and carbonyl regions. The surface deterioration was revealed from SEM micrographs. The drop in tensile strength was also monitored. A correlation between natural and artificial weathering was considered for lifetime prediction in a short exposure time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1676–1682, 2002