Search

With the growing environmental awareness, renewable energy sources that can replace crude oil are being indepth studied. One of these is the bio-oil, a renewable energy source that can be obtained from biomass pyrolysis. It is characterised by the fact that its components include ketones, furans, and phenols. Among the ketones, cyclopentanone, 2-butanone, and 2,3-butanedione are the most significant, as they are useful for producing fine chemicals. The first objective of the present study is the design of a suitable separation process for the mixture composed of cyclopentanone, 2-butanone, and 2,3-butanedione, considering the presence of an azeotrope between the 2-butanone and 2,3-butanedione. For this purpose, the enhanced distillation method of pressure-swing distillation is used. To the best of our knowledge, this technique has not been applied before for this particular separation, as existing studies consider the mixture as ideal and do not take into account the presence of the azeotrope. Therefore, the separation process becomes simpler. The second objective is to optimise the aforesaid process. Given the combination of real and integer variables, the high dimensionality of the problem and the constraints on the variables, it has been decided to apply a genetic algorithm as an optimisation method. The optimised variables are the number of stages and reflux ratios of the columns, the molar flow rate of the recirculation stream and the pressure of the high-pressure column. The genetic algorithm is implemented in MATLAB ® programming language, and rigorous simulations are performed using Aspen Plus ®. The optimised variables and compositions of all streams are determined; the results of the overall heating services are 12,788 kW, and cooling services are 12,512 kW for 100 kmol/h of the crude feed. By improving the process of compound separation from pyrolysis bio-oil, the present study contributes to the use of renewable resources such as biomass instead of crude oil to produce valuable chemical compounds. [ABSTRACT FROM AUTHOR]

The circular economy focuses on making the highest use of any molecule before being discarded. Compounds diluted in waste aqueous streams are usually eliminated instead of being recovered. When the separation process is not efficient enough, the energy consumed does not compensate the material recovered. The wastewater stream with diluted isopropanol and ethyl acetate from the pharmaceutical industry is an example of this situation, e.g., from the production of the antibiotic called ampicillin sodium. Pollution caused during ampicillin sodium production is due to the wastewater generated containing Ethyl Acetate (ETAC) and Isopropyl Alcohol (IPOH). In the literature, novel chemical processes have been proposed to recover these valuable compounds but require a third compound used as an extractive agent. Any third compound added to the mixture remains there and its presence in traces is unavoidable. The impurification of these solvents is a major issue for the pharmaceutical industry. In this study, a novel process is proposed that avoids the addition of an extractive agent. This type of wastewater has only 3 % of solvents and the ratio of isopropanol versus ethyl acetate in the feed is 5:1. Volatile solvents would be easily recovered from an ideal mixture; at least to reach a wastewater with 1 % solvents content. Unfortunately, there are four azeotropes present in the system studied and the separation is not straightforward. However, taking advantage of water / ethyl acetate immiscibility region and properly recycling and mixing process streams, then the mixture separation is possible employing only three distillation columns and a decanter. The process has been rigorously simulated and its feasibility proven. The environmental impact of the various alternatives proposed has been assessed usingWaste Reduction Algorithm Software V.1.0 (WAR). Ethyl acetate and isopropanol can be separated from water without extracting agents, possibility proven using residue curve maps. The study shows that diluted wastewater streams are a suitable source of chemicals. [ABSTRACT FROM AUTHOR]

The current work studies a novel and affordable methodology to estimate and quantify the photon flux absorbed and the amount of light that leaves from an illuminated photocatalytic system with TiO2 suspended in water. To achieve it, a new parameter B F S λ w a t $BF{S}_{\lambda }^{wat}$ is defined and presented. It indicates, for every wavelength, the fraction of the incoming radiation which is not absorbed by the system. B F S λ w a t $BF{S}_{\lambda }^{wat}$ was estimated by means of actinometric experiments in a jacketed reactor and a model based on Beer–Lambert law. For wavelengths below 388 nm and TiO2 concentrations between 0.05 and 2 g L−1, experimental values of B F S λ w a t $BF{S}_{\lambda }^{wat}$ were between 0.77 and 0.27. In the second part of the work, a simple kinetic model, which breaks down the effect of incident radiation and kinetic constant, is developed. For this, the photon flux absorbed by TiO2, previously determined, was included in the model. This new model was tested in the photocatalytic degradation of 2,4-dichlorophenol under different TiO2 concentrations. The kinetic model fits satisfactorily the experimental values and a new kinetic constant kʹap [mol·L−1 Einstein−1] was obtained, which is independent of the amount of catalyst loaded to the system. This achievement may be very useful for an easy initial comparison, design or scaling up of different photocatalytic reactors with similar geometry. [ABSTRACT FROM AUTHOR]

In the acetic acid esterification, ethanol (EtOH) in excess is used to produce ethyl acetate (EtAc), which is commonly used as an organic solvent in biochemical and food industries. On the other hand, EtOH is useful considering the growing production of bioethanol for the fuel market. The resulting mixture of EtAc with unreacted EtOH forms an azeotrope which is difficult to separate by conventional distillation. Literature data shows that the azeotropic binary mixture EtOH – EtAc is separated mostly through extractive distillation. Unfortunately, this procedure has some drawbacks, such as high energy cost and environmental concerns (quite related to the extracting agent recovery). However, taking advantage of the azeotrope sensitivity on pressure, the extracting agent use can be avoided. This paper presents an optimal design for the separation of the abovementioned mixture, using pressure-swing distillation (PSD) as separation process. In order to achieve a fully optimised system in terms of energy and capital, the method followed consists in simulating the process with Aspen Plus® and making use of genetic algorithms (GAs) to optimise the process variables, including, among others, the pressure of the high-pressure column. This process variable is of great importance, and from our point of view, this factor has not been properly studied nor discussed in literature so far. The starting population consists of points that group a set of values for all the design variables. These sets are a mixture of random and calculated values, obtained by application of heuristics, so that the initial population contains some potentially good initial individuals. The optimisation code is written in Visual Basic language and the link between Aspen Plus® and Visual Basic is also programmed so that a continuous connection can assure information flow from the optimisation program to Aspen Plus® and vice-versa. [ABSTRACT FROM AUTHOR]

A method for generating atomistic models of dense amorphous plymers is presented. The generated models can be used as starting structures of Monte Carlo and molecular dynamics simulations, but also are suitable for the direct evaluation physical properties. The method is organized in a two-step procedure. First, structures are generated using an algorithm that minimizes the torsional strain. After this, an iterative algorithm is applied to relax the nonbonding interactions. In order to check the performance of the method we examined structure-dependent properties for three polymeric systems: polyethyelene (ρ = 0.85 g/cm[SUP3]), poly(L,D-lactic) acid (ρ = 1.25 g/cm[SUP3]), and polyglycolic acid (ρ = 1.50 g/cm[SUP3]). The method successfully generated representative packings for such dense systems using minimum computational resources. [ABSTRACT FROM AUTHOR]

A computational strategy to model flexible molecules tethered to a rigid inert surface is presented. The strategy is able to provide uncorrelated relaxed microstructures at the atomistic level. It combines an algorithm to generate molecules tethered to the surface without atomic overlaps, a method to insert solvent molecules and ions in the simulation box, and a powerful relaxation procedure. The reliability of the strategy has been investigated by simulating two different systems: (i) mixed monolayers consisting of binary mixtures of long-chain alkyl thiols of different lengths adsorbed on a rigid inert surface and (ii) CREKA (Cys-Arg-Glu-Lys-Ala), a short linear pentapeptide that recognizes clotted plasma proteins and selectively homes to tumors, covalently tethered to a rigid inert surface in aqueous solution. In the first, we examined the segregation of the two species in the monolayers using different long-chain:short-chain ratios, whereas in the second, we explored the conformational space of CREKA and ions distribution considering densities of peptides per nm ranging from 0.03 to 1.67. Results indicate a spontaneous segregation in alkyl thiol monolayers, which enhances when the concentration of longest chains increases. However, the whole conformational profile of CREKA depends on the number of molecules tethered to the surface pointing out the large influence of molecular density on the intermolecular interactions, even though the bioactive conformation was found as the most stable in all cases. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]