Hydrogenation reactive distillation

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

EfiBdent hydrogen supply iiom decalin was only accomplished by the si terheated liquid-film-type catalysis under reactive distillation conditions at modaate heating tempaatures of 210-240°C. Caibcm-supported nano-size platinum-based catalysts in the si ietheated liquid-film states accelerated product desorption fixjm file catalyst surface due to its temperature gradient under boiling conditions, so that both hi reaction rates and conversions were obtained simultaneously. 

The dehydrogenation of decalin to naphthalene has been investigated on Pt/C, Pt/A1(0H)0 and Pt/Al203 catalysts. The maximum conversion of decalin on 3.9% Pt/C, which did not repel decalin, was observed at 483 K under the conditions of 0.3 g of the catalyst and 1ml of decalin, which was corresponded to the liquid film state under reactive distillation conditions. However such a maximum was not observed on Pt/Al(OH)0 and Pt/Al203, which repelled decalin. Furthermore it was found that the reaction temperature, at which the maximum hydrogen evolution was observed on Pt/C, was shifted from the boiling point of decalin to that of naphthalene with increasing the amormt of naphthalene in the reaction solution. 

Removal of thermodynamic restriction through reactive distillation and enhancement of hydrogen generation reactivity due to this concept made it possible to utilize organic chemical hydrides in the field of hydrogen storage from a novel standpoint. 

The HI decomposition section flow sheets for both CEA and GA are heavily focused on efficient heat recovery. The basic principle for decomposition is the same for each. Reactive distillation of the HIX feed results in the production of hydrogen. The operating pressures in the distillation columns typically... 

The third reaction takes place in a reactive distillation tower where the iodhiric acid is concentrated and decomposed simultaneously, to produce hydrogen at a temperature range from 200 to 310°C and pressure up to 22 bar (Brown, 2003). This section requires analysis of iodhidric acid leak and hydrogen explosions, though these sections are not covered in this paper as they will be the subject of future developments. 

Benfree A process for removing benzene from gasoline by reactive distillation. The benzene is hydrogenated in a distillation column. Developed by the Institut Franqais du Petrol and announced in 1998. Three units had been licensed in 2006. 

This section receives HI from Section I for decomposition and produces H2. Hydrogen iodide (HI) within the HI feed stream is distilled and decomposed into H2 and I2, and there are two alternatives to carry out this process extractive distillation or reactive distillation. The reaction conditions and chemicals used in these two processes are different, and their flow sheet will be addressed separately. 

For the hydriodic acid decomposition section III, a first step is tire iodine separation, due to contact with phosphoric acid in a counter current contactor. Tlren a reaction with catalyst in a reactive distillation column separates the Hydrogen from Iodine. This reaction is veiy slow and a residence time of some 3s is estimated in the column. The mixture that contains Iodine is adjusted and recycled to the main reactor of the Bunsen section, while the unreacted hydriodic acid is re-circulated. 

Other industrial processes that have taken advantage of the process intensification deriving from the introduction of reactive (catalytic) distillation are (i) production of high purity isobutene, for aromatic alkylation (ii) production of isopropyl alcohol by hydration of propylene (iii) selective production of ethylene glycol, which involves a great number of competitive reactions and (iv) selective desulfurization of fluid catalytic cracker gasoline fractions as well as various selective hydrogenations. Extraction distillation is also used for the production of anhydrous ethanol. 

Phases gas-liquid, gas-liquid catalytic solid, gas-liquid plus catalytic solid minimizes catalyst poisoning, lower pressure than fixed bed. Used for hydrogenation reactions and MTBE and acrylamide production. For example, 90% conversion via reactive distillation contrasted with 70% conversion in fixed-bed option. Liquid with homogeneous catalyst etherification, esterification. Liquid-liquid HIGEE for fast, very fast, and highly exothermic liquid-liquid reactions such as nitrations, sulfonations, and polymerizations. Equilibrium conversion <90%. Use a separate prereactor when the reaction rate at 80% conversion is >0.5 initial rate. The products should boil in a convenient temperature range. The pressure and temperature for distillation and reaction should be compatible. 

Due to slow kinetics, the conventional heterogeneous catalysis of the dehydrogenation of decalin in the solid-gas phase is performed at temperatures of more than 400 °C, which might result in the formation of by-products or carbonaceous deposit on the catalyst in addition to thermal energy loss. In a recent study, an attempt was made to apply the so-called liquid-film concept to hydrogen evolution from decalin with carbon-supported platinum-based catalysts under reactive distillation conditions in order to obtain high electric power suflficient for PEMFC vehicle operations in the temperature range 200-300°C [236]. 

A comparison of the processes shown in Figs. 11.5-1 and 11.5-2 demonstrates the high potential of reactive distillation for process simplification. This type of processes is generally applieable to systems with reversible chemical reactions, e.g., to esterification and etherification of alcohols, to alkylations, to dimerization of olefins, and to hydrogenation of aromatics (Sundmacher and Kienle 2003). 

There is no constant of integration due to the boundary condition that both AG/T and A(l/7 ) are zero at equilibrium. However, AH will be temperature-dependent most of the time. For example, in producing ammonia from hydrogen and nitrogen, the goal is to maximize the output of ammonia at the exit. An approximately constant AT between the optimal path and the equilibrium temperature provides the optimal temperature profile, which reduces the exergy loss by approximately 60% in the reactor. The equipartition of forces principle for multiple, independent rate-controlled reactions and multiphase and coupled phenomena, such as reactive distillations, may lead to the improved use of energy and reduced costs (Sauar et al., 1997). 

In subsequent developments, Eastman has reported two new alternative manufacturing routes to vinyl acetate (38). The first uses the carbonylation of dimethyl ether to acetic anhydride, followed by the reaction between acetic anhydride and acetaldehyde in a reactive distillation column to 3ueld vinyl acetate, whereas the second involves the intermediacy of ketene. Here ketene is hydrogenated to acetaldehyde, and the acetaldehyde is reacted with a second equivalent of ketene to produce vinyl acetate. Both of these routes are claimed to avoid the problematic and expensive acetic acid recycle. 

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