Improving Convergence Behavior of Nonlinear Equation Systems in Intensified Process Models by Decomposition Methods

The two decomposition methods Dulmage-Mendelsohn (DM) decomposition and bordered block transformation (BBTF) have been examined on their capabilities to eliminate convergence problems during the iteration of large, nonlinear equation systems as they occur frequently in process modeling. They both divide the overall system into lower dimensional subsystems, which can be solved separately in sequence. Exemplarily these methods were applied on the model of a reactive distillation column, where the decomposed systems show a higher robustness with respect to systematically selected initial points compared to the original system. Nevertheless, the improvement in DM seems small since a large subsystem with 576 of the 664 model equations remains. The convergence result from the iteration of the BBTF decomposed system depends a lot on the initial values for certain strongly coupled variables called tearing variables. In future, methods will be investigated and may also be developed to further reduce the dimension of the subsystems in DM and provide accurate initial values for the tearing variables in BBTF

Comparative study of conventional, reactive-distillation and pervaporation integrated hybrid process for ethyl tert-butyl ether production

Ethyl tert-butyl ether (ETBE) is widely used as an oxygenate additive to gasoline; however, a drawback in the conventional ETBE manufacture is the energy intensive product recovery process, making ETBE expensive. The purification process of ETBE involves the separation of ETBE, mixed C4 hydrocarbons and unreacted ethanol. The unreacted ethanol forms azeotropic mixtures with ETBE that are difficult to separate by distillation. In this work, a comparative study between the conventional process to produce ETBE and two alternative intensified processes is presented by means of process simulation in Aspen Plus. One of the alternative methods for improving the separation and purification section of ETBE is the use of a hybrid distillation-pervaporation process with alcohol-selective membranes, which allows to reach the target ETBE purity (95.2 wt%) with a lower energy consumption and at the same time the permeate stream, with a high ethanol content, is recycled back to the reaction section. Alternatively, the production of ETBE by means of reactive distillation is analyzed for the same basis of calculation. The results show that the reactive distillation allows a significant increase in the conversion of the reactants, but in contrast the energy consumption is higher than in the other processes evaluated.Financial support from the Spanish Ministry of Science under the projects CTM2013-44081-R (MINECO, Spain-FEDER 2014–2020), CTQ2015-66078-R and CTQ2016-75158-R is gratefully acknowledged. Adham Norkobilov also thanks the SILKROUTE Project for a PhD scholarship funded by the European Commission through the Erasmus Mundus Action 2 Programme

Kinetics of the Liquid-phase Synthesis and Hydrolysis of Butyl Lactate Catalyzed By Cation-exchange Resin

Esterification of lactic acid with butanol catalysed by cation-exchange resin was carried out in a batch reactor in dioxane and toluene. The reaction rate was found to be first order with respect to catalyst and acid concentrations. The inhibiting effect of water and butanol has been evaluated. The rate data were correlated with a kinetic model based on inhibition by water and butanol