In this work, a procedure based on the use of boundary and temperature diagrams for selecting safe and productive operating conditions of homogeneous semibatch reactors is presented and the influence ...of the reaction kinetics on the shape and extension of such diagrams is discussed. It has been found that using correlations developed for (1,1) reaction order kinetics can lead to both unsafe or not necessary low production operating conditions, especially with reference to the reaction order of the dosed coreactant. Moreover, the dependence of the shape and extension of such diagrams on the chemical kinetics has been found to be completely different when homogeneous or heterogeneous reacting systems are considered. A number of ready-to-use boundary and temperature diagrams is presented, together with some rules of thumb for their use, allowing for the easy selection of safe and productive operating conditions for homogeneous semibatch reactors.
In this work a procedure for easily selecting safe and productive operating conditions of homogeneous semibatch reactors in which exothermic autocatalytic reactions are performed is developed and ...presented. Such a procedure is based on the boundary and temperature diagram method previously proposed in the literature for nonautocatalytic reactions. In the autocatalytic case an additional parameter appears in the mathematical model of the reactor as well as in the safety criterion, that is, the initial catalyst amount which is directly related to the coreactant accumulation in the system. A number of diagrams for identifying inherently safe operating conditions is provided, together with some rules of thumb for their use, allowing for easily selecting safe and productive operating conditions of homogeneous semibatch reactors in which exothermic reactions with autocatalytic behavior occur.
Redo surgical aortic valve replacement has been the gold standard for the treatment of degenerated bioprostheses; however it carries an inherent risk associated with a reoperative open heart surgery. ...Valve-in-Valve transcatheter aortic valve implantation (ViV-TAVI) has emerged as an alternative approach. Few articles in literature review transcatheter aortic valve replacement’s failure rates, complications (i.e., valve dislocation, paravalvular leaks) and their surgical management. The rate of reoperations after a percutaneous approach is expected to increase, with the currently rising number of transcatheter procedures worldwide even in patients with a longer life expectancy. Valve dislocation is a rare but serious complication that can severely impact on the outcome of patients. Paravalvular leaks and structural valve degeneration are the most common causes of surgical re-intervention. We present the case of a complex patient with previous surgical aortic valve and ascending aorta replacement who underwent a transfemoral valve-in-valve TAVI for bioprosthesis degeneration, complicated by valve dislocation requiring surgical reoperation. (
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Cardiac surgery is associated with perioperative bleeding and carries high risk of allogeneic blood transfusion. Recently new scores for prediction of severe bleeding have been developed. This study ...aims to compare the WILL-BLEED, CRUSADE, PAPWORTH, TRUST, TRACK and ACTION scores in predicting major bleeding after CABG in patients with low estimated operative risk.
A multicenter observational study included 1391 patients who underwent isolated CABG from July 2015 to January 2018. We tested the hypothesis that the WILL-BLEED score, specifically designed for CABG, would perform at least as well as the CRUSADE, PAPWORTH, TRUST, TRACK and ACTION scores in predicting postoperative major bleeding in low operative risk patients. The primary endpoint was the performance of known bleeding risk scores after CABG. The secondary endpoint was the evaluation of in-hospital mortality.
Mean age was 68.2±9.4 years and median Euroscore II value was 1.69% (IQR 1.15-2.81%). Mean blood losses in the first 12 postoperative hours was 339.75 mL. Seventy-three (5.2%) subjects underwent administration of blood products. The rate of severe-massive bleeding according to UDPB grades 3-4 was 1.5%. WILL-BLEED, TRUST, TRACK and ACTION scores were significantly associated with severe postoperative bleeding. WILL-BLEED presented the best c-index (AUC: 0.658; 95% CI: 0.600,0.716). Reclassification analysis showed a worsening in sensitivity and significant negative reclassification of CRUSADE, PAPWORTH, TRACK and ACTION scores when compared with WILL-BEED. The combination of WILL-BLEED and TRUST scores improved the prediction ability (AUC: 0.673; 95% CI: 0.615-0.732). Overall in-hospital mortality was 1.65%. Early mortality in patients with severe versus no-severe bleeding was found to be 11.8% vs. 1.0% Severe bleeding (OR: 13.26; P value<0.001) was found to be significantly associated with early mortality.
Severe bleeding after CABG is a harmful event associated with adverse outcomes. WILL-BLEED Score has the better performance in predicting severe-massive bleeding after CABG. The TRUST Score, although suboptimal, represents a valuable alternative in this setting.
When strongly exothermic chemical processes are dealt with, safe and productive operating conditions may be difficult to identify; particularly if the reaction scheme is complex and the desired ...product is an intermediate. In this work, a new procedure for building boundary and temperature diagrams is developed to account for arbitrary kinetic expressions and multiple reactions. Such a procedure has been validated by comparison with literature experimental data involving autocatalytic consecutive reactions.
The operation of an indirectly cooled semibatch reactor in which an exothermic reaction occurs is usually considered safe if the characteristic time of the coreactant dosing is much higher than the ...characteristic times of all the other phenomena involved (chemical reaction and mass transfer), so that the conversion rate is controlled by the coreactant supply itself. Such operating conditions imply a small accumulation of the coreactant in the system and are characterized by a temperature evolution which quickly approaches a target temperature and remains close to it throughout the dosing period, at the end of which the conversion is almost complete.
The so-called boundary diagrams are useful tools for identifying safe operating conditions without solving the mathematical model of the reactor. However, avoiding accumulation phenomena can be not sufficient for classifying a set of operating conditions as thermally safe when the maximum temperature reached by the system under normal operation exceeds a maximum allowable temperature (which can be related either to safety problems, when dangerous decomposition reactions can be triggered, or to productivity problems, when side reactions can significantly lower the product yield above a given threshold temperature).
In this work the boundary diagrams for the prevention of excessive accumulation conditions in liquid–liquid semibatch reactors are coupled with new diagrams, called temperature diagrams. These new diagrams, involving the same dimensionless parameters used for the representation of the boundary diagrams, allow determining—for a given set of operating conditions—the maximum temperature increase with respect to the initial reactor temperature which can be expected to occur during normal operation. This information can be compared with the maximum allowable temperature for the reacting mixture. Then the operating conditions can be verified through the boundary diagrams in order to reject conditions of excessive coreactant accumulation.
Several temperature diagrams are provided for various kinetically or diffusion controlled reactions with different reaction orders and their use together with a general procedure for calculating them is presented.
In this work, a simple and general procedure for optimally scaling-up exothermic semibatch processes has been applied to the analysis of a nitration reaction performed in the agrochemical industry ...for the production of an important class of herbicides. Such a reaction is performed in indirectly cooled semibatch reactors in which the species to be nitrated is added to a mixture of sulfuric and nitric acid, forming a heterogeneous (liquid−liquid) system. Adiabatic calorimetric experiments performed in an ARC equipment showed that the reaction in question belongs to the most critical class of exothermic reaction processes, for which maximum attainable temperature due to synthesis reaction (MTSR) is, at the same time, higher than system decomposition temperature and lower than boiling temperature of the reaction mass. It has been verified, through reaction calorimetry experiments (performed in an RC1 equipment), that the optimization−scale-up procedure previously developed allows, with minimum calculation and experimental effort, both for a selection, at laboratory scale, of operating conditions characterized by a rapid coreactant consumption and for their safe scale-up, maximizing industrial reactor productivity.
The thermally safe operation of an indirectly cooled semibatch reactor in which an exothermic reaction occurs corresponds to conditions of potentially very high effective reaction rate compared to ...the dosing rate of the coreactant, whose accumulation in the reaction system is consequently small. On this basis it is possible to build boundary diagrams in terms of suitable dimensionless parameters, which summarize all the possible thermal behaviors of the reactor and can be used for safe scaleup purposes.
In this work the influence of reaction kinetics on the shape and location of boundary diagrams for a single liquid–liquid reaction in the slow regime is discussed. First of all, the theory of boundary diagrams, originally developed for (1,1) reaction order, is extended to a generic
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rate of reaction expression. Then it is shown that in many practical systems, using boundary diagrams based on (1,1) reaction order can lead to both unsafe and unnecessary (from a safety point of view) low-production operating conditions. New boundary diagrams for a few
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reaction orders are presented. Some rules-of-thumb are also discussed to identify in which cases a boundary diagram developed for a given
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reaction order can be reasonably used to approximate the real kinetic behavior of the system of interest.
Moreover, since building a boundary diagram for the specific kinetics considered can be necessary, a simple and general procedure for building such diagrams that can be easily implemented in a computer code is also presented.
The thermally safe operation of an indirectly cooled semibatch reactor in which an exothermic liquid–liquid reaction occurs corresponds to conditions of potentially very high
macrokinetic conversion ...rates compared with the supply rate of the coreactant, which accumulation in the system remains consequently low. This leads to the definition of a target temperature that can be compared with the real temperature–time profile, in order to develop boundary diagrams which summarize all the possible thermal behaviors of the reactor and can be used for safe scale-up purposes. The variable parameters which appear in such diagrams are an exothermicity and a reactivity number derived from the expressions of the conversion rates in the kinetically or diffusion controlled regime, respectively.
In this work the influence of the
microkinetic rate of reaction on the shape and location of the boundary diagrams for single liquid–liquid diffusion controlled reaction systems is discussed, extending to this regime the results previously obtained for kinetically controlled reactions.
Also in the case of diffusion controlled reactions, it is shown that for many practical systems, using boundary diagrams based on
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reaction orders can lead to both unsafe or not necessary low production operating conditions. Consequently, a number of new boundary diagrams for arbitrary reaction orders is presented and some rules-of-thumb useful to their application are discussed.
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