Reaction Inhibition as a Method for Preventing Thermal Runaway in Industrial Processes

Summary: In this work inhibitors were used to prevent runaway reactions during methylmethacrylate suspension polymerization processes. The main problem that may more frequently occur in chemical reactors, carrying out free radical polymerization reactions, is the loss of temperature control. The addition of an inhibitor during polymerization processes can be considered as a good method to stop or at the least slow down the reaction. In this work two inhibitors were used: hydroquinone and 1,4-benzoquinone in a series of polymerization experiments. In order to identify situations that can lead to a runaway reaction, an early warning detection system based on the divergence criterion was used. When this system signalled an alarm, small amounts of inhibitor were added to the reaction mixture. The results showed that hydroquinone and 1,4-benzoquinone behave slightly differently and the reactor temperature can be kept within safe limits.     

苯氧威 (C17H19NO4) 的热容和热力学性质

通过小样品精密自动绝热量热计测定了自己合成并提纯的苯氧威 (C₁₇H₁₉NO₄) 在79 ～ 360 K温区的低温摩尔热容。量热实验发现, 该化合物在320 ~ 330 K温区, 有一固 - 液熔化相变过程, 其熔化温度为（326.31±0.14）K, 摩尔熔化焓、摩尔熔化熵及化合物的纯度分别为：(26.98±0.04) kJ• mol^-1和（82.69 0.09）J•mol^-1•K^-1和 (99.53±0.01 )%。并计算出了80-360 K的热力学参数。用分步熔化法得到绝对纯化和物的熔点为326.60±0.06 K。用差示扫描量热 (DSC) 技术对该物质的固-液熔化过程作了进一步研究，结果与绝热量热法一致。     

Correlation Between Structure and Transport Properties of Polymeric Membranes for Immunoisolation

Laboratory-made asymmetric polyurethane membranes designed for immunoisolation were investigated. Two types of EK and ES membranes were prepared in different spinning conditions. The membrane structure was characterised by the skin pore radius measurements using differential scanning calorimetry (DSC). Diffusive transport properties of membranes were determined by in vitro method for albumin and creatinine. The scanning electron microscopy (SEM) was applied to study the morphology of membranes. It has been found that the DSC technique is a useful tool for the evaluation of pore radii in the skin layer for PU membranes. Calculated pore radii were in the range from 1.95 to 2.47 nm for the EK and ES types. A correlation between the skin pore radii and the transport properties was not found in this case of investigated membranes. However, the transport properties data can serve for the estimation of selectivity of membranes. Thus, the selectivity of membranes for solutes of various molecular size was estimated from the D _m/D _w ratio of diffusion coefficients for albumin and creatinine. The SEM micrographs reveal the finger-like internal structure of capillary membranes, as well as various skin thickness. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Analysis And Powder X-Ray Diffraction Study of Terpin: Evidence of a eutectic ‘hydrate/anhydrous form’

When the DSC analysis of different samples of terpin hydrate is carried out, a non identified small endotherm is observed at about 100°C, just before the melting endotherm. This phenomenon is detected whatever the experimental conditions are.After some trials, this endotherm was identified as an eutectic formed with terpin hydrate and desolvated terpin (17/83).The importance of the experimental conditions is preponderant. In an open pan, the desolvation occurs and the melting endotherm of the anhydrous form can be observed at 105°C. In a closed pan, no desolvation is detected and the melting endotherm at 120°C is that of the terpin hydrate.The eutectic exhibits a good compression ability and a fast dissolution. Its stability is correct. Its use in therapeutic tablets can be envisaged.The eutectic structure could be, more generally, favourable to compression owing to the isotropic texture of this particular solid state.This revised version was published online in November 2005 with corrections to the Cover Date.     

Investigation of Water-Based Emulsions: Surface and Film-Forming Properties

Summary: In the present study, reaction components such as emulsifiers, emulsifier combinations, and initiators were used for the particle stabilization of water-borne vinyl acetate - butyl acrylate copolymer latexes. The effects of these parameters on the colloidal film-forming properties of the vinyl acetate-co-butyl acrylate latex colloidal, physicochemical, surface, and film forming properties were investigated, in particular the aspect of their surface coating applications.     

DSC Analysis of the precipitation reactions in the alloy AA6082

The deformation introduced during the sample preparation had a high impact on the response of the alloy AA6082 to heating in the DSC cell. The DSC curve was strikingly different when DSC samples of this alloy were punched after the solution treatment. Dislocations introduced by punching have annihilated the quenched-in vacancies and have suppressed clustering initially. Dislocations have also provided heterogeneous nucleation sites for the GP-1 zones that readily grew to become stable nuclei for the β" phase owing to the enhanced atomic transport. β" as well as the β' precipitation kinetics were thus accelerated leading to a substantial change in the DSC peak arrangement. Deformation introduced during sample preparation by gentle grinding alone, on the other hand, did not suffice to alter the precipitation sequence, producing a DSC curve very similar to that obtained with samples punched before the solution treatment.     

Transport Properties and Phase Behaviour in Binary and Ternary Ionic Liquid Electrolyte Systems of Interest in Lithium Batteries

A binary ionic liquid (IL) system based on a common cation, N‐methyl‐N‐propylpyrrolidinium (C₃mpyr⁺), and either bis(trifluoromethanesulfonyl)imide (NTf₂^?) or bis(fluorosulfonyl) imide (FSI^?) as the anion is explored over its entire composition range. Phase behavior, determined by DSC, shows the presence of a eutectic temperature at 247 K and composition around an anion ratio of 2:1 (FSI^?:NTf₂^?) with the phase diagram for this system proposed (under the thermal conditions used). Importantly for electrochemical devices, the single phase melting transition at the eutectic is well below ambient temperatures (247 K). To investigate the effect of such anion mixing on the lithium ion speciation, conductivity and PFG–NMR diffusion measurements were performed in both the binary IL system as well as the Li‐NTf₂‐containing ternary system. The addition of the lithium salt to the mixed IL system resulted in a decrease in conductivity, as is commonly observed in the single‐component IL systems. For a fixed lithium salt composition, both conductivity and ion diffusion have linear behaviour as a function of the anion ratio, however, the rate of change of the diffusion coefficient seems greater in the presence of lithium. From the application point of view, the addition of the FSI^? to the NTf₂^? IL results in a considerable increase in lithium ion diffusivity at room temperature and no evidence of additional complex ion behaviour.     

The Use of Adiabatic Calorimetry for the Process Analysis and Safety Evaluation in Free Radical Polymerization

Adiabatic calorimetry is a technique that has been introduced as an important approach to hazard evaluation of exothermically reactive systems. In this paper the free radical polymerization of methyl methacrylate (MMA) has been studied. One of the most important aspects of MMA polymerization is its exothermicity and autoaccelerating behaviour, these characteristics can generate the occurrence of a runaway reaction.In a runaway situation the reacting system is close to adiabatic behaviour because it is unable to eliminate the heat that is being generated. An even worse situation can be reproduced in the laboratory with the Phi-Tec pseudo-adiabatic calorimeter. Process design parameters that are usually calculated from thermodynamic data or using semiempirical rules, such as adiabatic temperature rise or maximum attainable pressure, can be directly determined.The existence of the ceiling temperature has been experimentally demonstrated.This revised version was published online in November 2005 with corrections to the Cover Date.     

On the Use of Differential Scanning Calorimetry for Thermal Hazard Assessment of New Chemistry: Avoiding Explosive Mistakes

Differential scanning calorimetry (DSC) is increasingly used as evidence to support a favourable safety profile of novel chemistry, or to highlight the need for caution. DSC enables preliminary assessment of the thermal hazards of a potentially energetic compound. However, unlike other standard characterisation methods, which have well defined formats for reporting data, the current reporting of DSC results for thermal hazard assessment has shown concerning trends. Around half of all results in 2019 did not include experimental details required to replicate the procedure. Furthermore, analysis for thermal hazard assessment is often only conducted in unsealed crucibles, which could lead to misleading results and dangerously incorrect conclusions. We highlight the specific issues with DSC analysis of hazardous compounds currently in the organic chemistry literature and provide simple “best practice” guidelines which will give chemists confidence in reported DSC results and the conclusions drawn from them.     

DSC Analysis of the Induction Period in the Vulcanisation of Rubber Compounds

Vulcanisation of rubber compounds was studied by DSC under isothermal and non-isothermal conditions. The parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained both from isothermal and non-isothermal measurements. A new method for obtaining the kinetic parameters from non-isothermal measurements, based on the dependence of onset temperature of vulcanisation peak on heating rate, is presented. Also, a procedure for the evaluation of temperature difference between the furnace and sample is proposed. It has been shown that the treatment of non-isothermal DSC measurements gives the kinetic parameters free of systematic errors. The new method can also be used for studying other reactions exhibiting the induction period. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystallization and melting of narrow composition distribution polyethylenes: Investigation and implications of crystal thickening

The crystal structure produced during the isothermal crystallization of polyethylene (PE) copolymers with a broad range of comonomer concentrations was determined by the measurement of the melting endotherms directly after crystallization. PE copolymers with higher concentrations of short‐chain branches (≥10 branches per 1000 total carbon atoms) exhibited strong resistance to crystal thickening during isothermal crystallization. Negligible thickening, estimated to be only about 0.1 nm in 10 min of isothermal crystallization, was observed. The side‐chain branches apparently acted as limiting points of chain incorporation into the crystals, which exhibited great resistance to the modification of their position, that is, crystal thickening. Even with long periods (up to 8 h) of isothermal storage, crystal thickening was very small or negligible, about 0.3 nm. The crystal thickness was calculated from differential scanning calorimetry data. The behavior of copolymers with lower branching concentrations and the unbranched PE homopolymer was quite different from that of the copolymers with higher branching. Polymers with low or no branching exhibited the initial crystallization of a thinner crystal population, which thickened substantially with increasing time. The thickening observed for these lower or unbranched polymers was an order of magnitude larger, that is, 1.6–2.0 nm in 10 min of isothermal crystallization. Copolymers with higher concentrations of branching had relatively short sequence lengths of ethylene units between branch points, and this resulted in strong control over the crystal thickness by the branch points and great resistance to crystal thickening, even with long times of isothermal crystallization. Copolymers with low concentrations of branching had relatively long sequence lengths of ethylene units between branch points, and this resulted in little control over the crystal thickness by the branch points and rapid crystal thickening upon isothermal crystallization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 235–246, 2003     

DSC曲线各特征点的物理意义以及相变热焓的广义Speil公式的推导

按目前差示扫描量热法（DSC）公认的Gray－Speil理论，由于对实际的过程过于简化，以致不能很好地解释DSC曲线上的每个特征点；就相变前后试样的热容量发生改变的普遍情况下，如何定量计算相变潜热，目前尚未有严格的计算理论。本文对差示扫描量热法的基本理论做了一些较深入的探索，通过考虑容器及试样内存在温度梯度这一实际情况，成功地解释了实际DSC曲线上各个特征点具体的物理意义，并就相变前后试样的热容量发生变化且热容量是温度的函数这一普遍情况，推广出广义的Speil公式和热焓计算的普遍法则，得到了与实验更加接近的结果。     

胶粉在改性沥青中的物化行为分析

生产胶粉改性沥青(CRMA)是实现废橡胶资源化利用及减轻环境污染的有效途径。为了研究胶粉在沥青中的物理及化学行为,采用邻苯二甲酸二丁酯(DBP)模拟沥青的轻组分,将胶粉置入DBP中,在175℃下,反应1.5 h后分离胶粉与轻组分,对轻组分进行气相色谱与质谱联用(GC-MS)分析,讨论胶粉与轻组分发生的物理化学作用;对不同条件下制备的胶粉改性沥青分离胶粉后进行红外光谱(IR)和差示扫描量热(DSC)分析,研究橡胶改性沥青中的官能团变化和热力学特性。结果表明,分离胶粉后的DBP中存在19种检出物,除含量最高的DBP外,其余物质均为胶粉浸出物或与轻组分的反应产物,即胶粉在轻组分中发生了复杂的物理化学反应。胶粉沥青样品中的—CH_2和C=C双键等特征官能团吸收峰大幅增强,橡胶分子在沥青中发生断链降解释放出小分子物质溶于沥青组分发挥改性作用;195℃、1.5 h和175℃、3.0 h制备的沥青样品DSC谱线出现了强烈的吸热峰,即处理温度过高或时间过长,可能发生胶粉过度降解、胶粉团聚或沥青老化行为,使胶粉改性沥青的物化状态发生改变,导致性能劣化。从胶粉物化变化的角度,建议制备胶粉改性沥青时,胶粉掺量(质量分数)应在20%左右,处理温度不高于195℃,处理时间不超过1.5 h。     

A study of thermal crystallization in glassy Se80Te20 and Se80In20 using DSC technique

Different methods have been used by various workers to determine the activation energy of thermal crystallization (E_c) in chalcogenide glasses using non-isothermal DSC data. In the present work, the crystallization kinetics of two important binary alloys Se₈₀Te₂₀ and Se₈₀In₂₀ is studied using non-isothermal DSC data. DSC scans of these alloys have been taken at five different heating rates. The values of activation energy of crystallization (E_c) have been determined by four different methods, i.e., Kissinger's method, Matusita-Sakka method, Augis-Bennett's method and Ozawa's method, have been used to calculate E_c. The results obtained have been compared with each other to see the effect of using different methods in the determination of E_c.     

Pyrolysis Analysis and Kinetics of Crude Oils

This research presents the results of an experimental study on the determination of pyrolysis behaviour and kinetics of six crude oils by differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). Crude oil pyrolysis indicated two main temperature ranges where loss of mass was observed. The first region between ambient to 400°C was distillation. The second region between 400 and 600°C was visbreaking and thermal cracking. Arrhenius-type kinetic model is used to determine the kinetic parameters of crude oils studied. It was observed that as crude oils gets heavier (°API decreases) cracking activation energy increases. Activation energy of cracking also show a general trend with asphaltene content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Characterization of Boron Incorporated Polyester Polyol from Linseed Oil: A Sustainable Material

Polyols obtained from seed oils have established themselves as excellent building blocks of polymers, viz. polyurethanes. In this work, a novel attempt has been made to incorporate boron in the backbone of polyol [LPO] derived from linseed oil. Furthermore, LPO was treated with phthalic anhydride [PA] and boric acid [BA] (in different molar ratios) to obtain boron incorporated linseed polyester polyols [BPPEs] through solvent less synthesis process. BPPEs were characterized by spectroscopic techniques (IR, ¹H NMR and ¹³C NMR) to confirm the incorporation of boron and also to elucidate their structures. Physico-chemical characterization and antibacterial behavior of BPPEs was also investigated. It is speculated that these resins may serve as excellent raw materials for adhesives, coatings and as antibacterial agents.     

Calorimetric and Scattering Studies on Micellization of Pluronics in Aqueous Solutions: Effect of the Size of Hydrophilic PEO End Blocks,Temperature, and Added Salt

Micellar behavior of five ethylene oxide–propylene oxide (EO–PO) triblock copolymers, called Pluronics, with similar molecular weights of middle block PPO (～2250 g/mol) and varied percentages of poly(ethylene oxide) (10%, 40%, 50%, 70%, and 80%, referred to as L81, P84, P85, F87, and F88, respectively) was examined by thermal (isothermal titration calorimetry and high-sensitivity differential scanning calorimetry), spectral (UV–vis), and dynamic light scattering (DLS) techniques. Micellization was decreased with increasing hydrophilicity of copolymer but induced in the presence of salt. Critical micelle temperatures (CMTs) of copolymers at different concentrations, with and without sodium chloride, are reported. Viscosity and DLS results reveal that highly hydrophilic copolymers (F87 and F88) did not show significant change in micelle size even at temperatures close to cloud point, whereas micelle growth and sphere-to-rod transition occurred for P84 and P85. Surface tension of solutions in water and salt also show enhanced surface activity and salt-induced micellization. The CMTs for different systems using different methods are compared.     

Thermal characterization of tetrafluoroethylene-perfluoroalkylvinylether copolymers: Melting behavior and low-temperature transitions

Differential scanning calorimetry has been used to study the melting and the low-temperature transitions of tetrafluoroethylene-perfluoroalkylvinylether copolymers (PFA). Melting is similar to that of PTFE in that it is subject to superheating, moreover the melt-crystallized samples show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal-crystal transitions are observed for copolymers containing 2 mol % of perfluoromethyl-, perfluoroethyl-, and perfluoro-n-propylvinylether. In the case of perfluoromethylvinylether as a comonomer, low-temperature transitions are present only up to a content of 4 mol %. The effect on melting and low-temperature transitions of both the comonomer content and of the type of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonomer concentration and have been found to be independent on the chemical nature of the side group. © 1994 John Wiley & Sons, Inc.     

Assessment of Staling Aldehydes in Lager Beer under Maritime Transport and Storage Conditions

Beer flavor stability is greatly influenced by external temperature, vibrations, and longer delivery times. The present study assessed the impact of transport and storage conditions on staling aldehyde evolution in lager beers across five sample groups (fresh, transport, and storage simulation, and their controls), which differed in their bottle opening system (either crown cap or ring pull cap). Maritime transport conditions (45 days of travel, vibrations of 1.7 Hz, and warm temperatures (21–30 °C)) were simulated, together with storage time in a distributor’s warehouse (up to 75 days). The results revealed that the concentration of Strecker aldehydes increased more quickly after transport and storage simulation in beer bottles with the ring pull cap opening system, and the contents of 2-methylpropanal and 3-methylbutanal, in particular, were up to three times higher. Benzaldehyde content also increased significantly, by 33% on average, in these samples. Hexanal was only found in beers with a ring pull cap that underwent transport simulation. Further storage after transport simulation significantly reduced the content of 2-methylpropanal, 3-methylbutanal, and hexanal, by 73%, 57%, and 43%, respectively, suggesting the formation of a bound state. 5-hydroxymethylfurfural was continuously increased by 78.5% and 40.5% after the Transport and Transport & Storage simulations, respectively. Transport conditions lead to a slight increase, of 0.6 EBC units, in beer color.