Abstract Multicomponent separation of synthetic petrochemical naphtha (hexane, cyclohexane, toluene and xylene) was carried out in a falling film distillation sequence with heat supply using a vapor chamber (thermosyphon). Tests were carried out by varying feed flow rate and temperatures of the feed and the vapor chamber in two ways of heat supply: isothermal and with a vapor chamber temperature profile. Regarding the distillation behavior of the multicomponent separation with the proposed falling film column, it was verified that the lower values of the studied variables and the profile temperature mode promoted the best results for hexane recuperation. With an indirect sequence of three columns, hexane mass fraction in the top column increases to the value of 0.82. Higher thermodynamic efficiency was found for two columns of the sequence in comparison with the conventional ones. This behavior is related to smaller energy consumption, showing a total energy reduction of 12% compared to the same separation performed in a conventional unit. Energy and exergetic efficiency values were higher than 95% and 85% in the three columns used. These analyses demonstrated that the falling film separation proposal is an energy efficient arrangement and could be considered for multicomponent separation.

ABSTRACT The present study addresses the novel application of the simulated annealing algorithm (SAA) to optimize the pressure-swing distillation (PSD) process for anhydrous ethanol purification. Three different softwares (Aspen Plus®, Excel® and Matlab®) were integrated to simultaneously optimize seven design and operational variables. The configuration with the best TAC represented a 40.2% saving per year in comparison to the non-optimized PSD. Such reduction was achieved by using the higher acceptance probability and the slower temperature decrement. This saving is mainly related to operational cost reductions, a fact that evidences the viability of using the herein described optimization methodology to improve the PSD design.

The choice of an appropriate background electrolyte (BGE) and its components for capillary electrophoresis analysis is the main step in capillary electrophoresis method development. The use of an inadequate co-ion component could lead to asymmetrical peaks and selecting an inappropriate counter-ion could affect the buffer capacity and the pH of the BGE, leading to unreliable analysis. In this paper, we describe a systematic procedure for the development of a capillary electrophoresis method, based on the effect of varying pH on the ion effective mobility, to optimize the BGE composition. The method was applied to the separation of L-ascorbic acid in different samples. The optimized background electrolyte composition was 40 mmol L-1 tris(hydroxymethyl)aminomethane and 20 mmol L-1 2-morpholinoethanesulfonic acid, at pH 8.1. Sorbic acid was used as the internal standard and separation was carried out in a fused-silica capillary (32 cm total length and 8.5 cm effective length, 50 µm inner diameter), with a short-end-injection configuration and direct ultraviolet (UV) detection at 266 nm. The separation was performed in 26 s. The method shows good linearity (R2 > 0.999), excellent values for inter-day and intra-day precision and good recovery (in the range of 94-107%). The values obtained for limit of detection (LOD) and limit of quantification (LOQ) were 0.14 and 41 mg L-1, respectively. The systematic procedure applied shows to be a very useful tool for the first step method development for capillary electrophoresis.

The substitution of volatile hydrocarbons by the use of water as blowing agent in the synthesis of expandable polystyrene particles has been studied in the last decades. In this work, an investigation was made of the influence of experimental parameters on the incorporation of water in the synthesis of water-expandable polystyrene. The synthesis procedure was based on a two-step polymerization, namely a water dispersion stage and a suspension polymerization stage. The use of a surfactant with a low HLB value resulted in a more stable water-in-oil system and smaller water droplets. The type of impeller used during the dispersion of the water in the monomer phase also influenced the formation of water droplets. In addition, the diameter of the droplets was strongly influenced by the duration of the water dispersion phase. Results suggested that these parameters can be used to control the characteristics of the water droplets formed inside the polystyrene particles.

O presente estudo utiliza um modelo matemático fenomenológico para simular um sistema de polimerização contínuo em dois estágios. Este sistema é composto por um reator contínuo tipo tanque agitado (CSTR), para pré-polimerização do monômero (primeiro estágio), associado em série a um reator tubular para conduzir a reação até elevados valores de conversão (segundo estágio). Um modelo detalhado, considerando variações axiais e radiais, assim como operação não-isotérmica, foi utilizado para simular o comportamento do reator tubular em diferentes situações. Um modelo de caracterização também foi desenvolvido para fornecer estimativas do peso molecular médio e do índice de polidispersão do polímero. Os resultados mostram que reações de polimerização conduzidas em sistemas contínuos de dois estágios fornecem um polímero com propriedades menos heterogêneas do que um polímero obtido em um sistema reacional composto por apenas um reator tubular. Além disso, quanto maior a viscosidade da mistura reacional alimentada ao reator tubular, mais homogêneo é o polímero obtido.

The present study uses a phenomenological model to simulate a continuous, two-stage polymerization process. This system is composed by a continuous stirred tank reactor (CSTR) for monomer pre-polymerization (first stage), connected to a tubular reactor (second stage) to carry out the reaction up to high conversion values. A comprehensive non-isothermal 2-D model (axial and radial variations) was used to predict the tubular reactor behavior. A polymer characterization model was also developed to provide estimates of the polymer average molecular weight and polydispersity. According to the results, polymerization reactions carried out in a continuous two-stage system provide a polymer with less heterogeneous properties than the one obtained in a single tubular reactor. Besides, it is possible to produce a more homogeneous polymer increasing the viscosity of the mixture fed in the tubular reactor.