Rectification reactive

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. 

The pilot scale experiments were carried out in a CD column 23 ft (7 m) tall with a total packing height of 16 ft (4.9 m) and a 1 (2.54 cm) nominal I.D. The column is made of 316 SS and consists of 5 sections that are connected by flanges. Two 2 ft (0.6 m) sections located above a 9 ft (2.7 m) stripping section and below a 3 ft (0.9 m) rectification section, were used as the reaction zones, which contained the catalyst. The non-reactive sections were filled with i inch (0.64 cm) Intalox saddles. In the first experiment for which mesityl oxide was synthesized from acetone, the two sections were filled with 130 mL of Amberlyst-15, that had been swelled in 2-propanol for 24 hours, in wire mesh bundles. In the second experiment in which MIBK was synthesized from acetone, the top section and the top half of the bottom section contained 135.0 mL of Amberlyst-15 in wire mesh bundles that had been swelled in acetone for over 24 hours. The bottom half of the bottom section, immediately below the Amberlyst 15, was filled with 50.1 g of a commercial Pd/AlzOs catalyst (Aldrich 20,574-5). The hydrogenation catalyst was reduced ex situ in hydrogen at 350°C for 3 hours and was transferred to the CD column under a nitrogen blanket. 

After the chlorination, hydrogen chloride is removed from the reactive mixture by nitrogen flow the reactive mixture is sent to the rectification section (into tower tank 32). Carbon tetrachloride and intermediate distillate are the first to be distilled in the tower, at 120 °C in the tank and at 30 °C and 0.1 MPa on top. The vapours of carbon tetrachloride which escape the tower are condensed and collected in receptacle 34 the condensate is sent back to chlorinate. 

Methylchlorosilanes are difficult to separate due to the closeness of some of their boiling points. It is especially difficult to separate pure dimethyldichlorosilane (the boiling point is 70.2 °C) devoid of methyltrichlorosilane (the boiling point is 66.1 °C), because the difference of their boiling points is only 4.1 °C. It is known that the efficiency of separating reactive mixtures depends on the number of theoretical plates in the rectification towers moreover, in distillation there is a certain dependence between the number of theoretical plates and the difference in the boiling points of the components. For precise distillation and compete separation of methyltrichlorosilane from dimethyldichlorosilane, one needs a rectification tower with the efficiency of 60-80 theoretical plates. 

C (mainly benzene), which can be used to flush the equipment at subsequent rectification stages and to prepare reactive mixtures for the synthesis of various polyorganosiloxanes. 

The reaction is conducted in the presence of a catalyst, the solution of boric acid in methylphenyldichlorosilane with the mole ratio of parent reactants CH3SiHCl2 C6H6 of 1 3. The excess of benzene has a beneficial effect on the output of methylphenyldichlorosilane. It should be noted that in the synthesis conditions there is a disproportioning of methyldichlorosilane, which forms by-products, such as methyltrichlorosilane and di-methyldichlorosilane. These products can be separated in the process of the rectification of the condensate and added to the reactive mixture during the synthesis of methylphenyldichlorosilane to suppress the reaction of disproportioning. 

Raw stock methyldichlorosilane (not less than 98% of the main fraction, 61.3-62.5% of chlorine) benzene (d420 =0.876-0.879) technical boric acid. Methylphenyldichlorosilane production (Fig. 16) comprises three main stages the preparation of equipment and reactive mixture the synthesis of methylphenyldichlorosilane the rectification of methylphenyldichlorosilane. 

Agitator 5 is filled with methyldichlorosilane from batch box 1, with benzene from batch boxes 2 and 3 and with recirculating methylchlorosi-lanes (after rectification) from batch box 4. The reactive mixture is mixed in agitator 5 for 20-30 minutes after that one determines the chlorine content and density. The mixture prepared in this way is then sent into batch box 6 and from there to the synthesis. Then autoclave 8 is electrically heated (it can be heated by sending vapour into the jacket) and fed part of... 

From batch boxes 1 and 2 the original reactants in given quantities are sent into agitator 3, where they are mixed with nitrogen, which is fed from container 6, for 10-15 min. Before the installation is launched, reactor 8 is loaded to 2/3 of its volume with reactive mixture and electrically heated. The temperature is raised to 250-260 °C and after it is held for 5 hours, the reactive mixture from apparatus 3 is continuously fed through run-down box 4. The products formed are separated from the lower part of the reactor at 2-2.1 MPa. The products are sent through cooler 10 are sent into separator 11 and collector 72 from there they are sent to rectification. 

The process comprises the following stages (Fig. 45) the preparation of the reactive mixture hydrolytic condensation the neutralisation and drying of the cocondensation products catalytic regrouping and filtering rectification. 

Ammonia chloride is destroyed in reactor 5 immediately after the ammonolysis is finished. For this purpose, a 15% solution of NaOH is prepared in reactor 6. The agitator is switched on and the contents of reactor 6 are agitated until sodium hydroxide dissolves completely. The alkali solution prepared in this way is sent through batch box 4 into reactor 5, and the contents are mixed for 5-10 minutes. The reactive mixture is held for about an hour and sampled to determine the ammonia chloride destruction shown by the absence of NH4C1 in the aqueous layer. The lower layer, the aqueous NaCl solution, is poured into settling box 9, the top layer, the hexame-thyldisiloxane solution of hexamethyldisilazane, is poured through a rundown box into collector 10 and then in druck filter 11, which operates below 0.07 MPa. The filtrate is collected into collector 12, from where it is sent into tank 13 for rectification. The tank is heated with vapour (up to 1 MPa). 

The process is carried out periodically, in the presence of OP-7 catalyst. The supplementaiy reactions are the flushing of the reactive mixture, the separation of the target product from the flush waters, the diying of the moist product and the rectification and absolution of ethyl alcohol. 

The feasibility of the above setup can be evaluated by simulation with Aspen Plus [19]. The RD column is built-up as a reboiled stripper followed by a condenser and a three-phase flash, with organic phase refluxed to column. The result is that only 3 to 5 reactive equilibrium stages are necessary to achieve over 99% conversion. The stripping zone may be limited at 2-3 stages, while the rectification zone has 1-2 stages. 

The catalytic distillation process of Smith [15], by providing for the fixing of the catalyst in a reactive section of a column between nonreactive stripping and rectification sections, and thereby for the continuous removal of MTBE from the reactants, boosts the conversion of isobutene to well in excess of 99%. The concept is still more economically attractive when OCFS are employed to secure the catalyst in the reactive section— DeGarmo et al. [16]—due to their significantly higher mass transfer efficiency. 

In reactive rectification a rectification process is coupled with a chemical reaction. A simple example is the combination of a stirred tank in which an esterification takes place with a column for separation of the water of reaction [Stichlmair 1998, Frey 1998a],... 

Reactive rectifications without a separate reactor, in which the reaction takes place in the distillation column, are increasingly being used in industry. Typical classes of reactions are esterification, transesterification, acetal formation and cleavage, etherification, oxidation, and hydrogenation. With regard to the design of such processes, three cases can be distinguished ... 

While process synthesis gives good qualitative reference points, for industrial implementation we need quantitative results, which are as exact as possible. The development of a program called Designer to simulate reactive rectification was therefore a further major focus of the first EU project. 

In recent years reactive (or catalytic) distillation (or rectification) has gained some importance in the process industry. Reactive rectification denotes the simultaneous performance of chemical reaction and physical separation within a countercur-rently operated column. The integration of these two unit operations in one column offers advantages for reversible liquid-phase reactions where the reaction products hinder the progress of the reaction (e.g., Sundmacher and Kienle 2003 Frey et al. 2003 Frey and Stichlmair 1998). 

The principles of reactive rectification are explained for the following liquid-phase reaction ... 

Reusch D., A. Beckmann, F. Nierlich, and A. Tuchlenski, Method for producing terf-butanol by means of reactive rectification, U.S. Patent 7,115,787 (2006). 

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