Apparatus for hydrogenation at atmospheric pressure

Fig. 1 Apparatus for hydrogenation at atmospheric pressure. Teflon is a trade name of E.l. Dupont De Nemours...

Flasks fitted with a magnetic stirrer and a manometer are available for hydrogenation at atmospheric pressure on a semimicro scale. Before hydrogenation is begun, the air is removed from the apparatus by repeated evacuation. Special apparatus can be obtained commercially for analytical microhydrogenation of a few miligrams of material. 

Atmospheric pressure apparatus. Isomerization experiments at atmospheric pressure were carried out in an all-glass system equipped with greaseless values, a flow meter, a U-shaped silica reactor, a double TCD system recording the pressure of reactant (provided by a saturator) before the reactor and the pressure of the products after the reactor, a system to extract the products for GC analysis and a needle valve to regulate gas flow. The catalyst was placed on a silica fritted disc and the reactor was operated as a fixed bed at constant pressure and temperature. Hydrocarbons were introduced at a set pressure and hydrogen was used as complement to the atmospheric pressure on the catalyst. 

Hydrogenation at atmospheric pressure standard procedure. This method for effecting hydrogenation at atmospheric pressure employs the apparatus shown semi-diagrammatically in Fig. 2.63(a) it is supported on a suitable metal rod framework. The essential features are a long-necked hydrogenation flask A fitted to the apparatus with sufficient flexible tube to allow shaking, a series of... 

In the laboratory small amounts of compound are usually hydrogenated in presence of a noble-metal or a Raney catalyst on a shaking machine. The nature of the vessel used is of minor importance. Rapid shaking is essential. The hydrogenation vessel is usually shaken horizontally, but sometimes vertically.197 The apparatus sketched in Figure 1 usually suffices for work at atmospheric pressure. 

The apparatus required is similar to that described for Diphenylmelhane (Section IV,4). Place a mixture of 200 g. (230 ml.) of dry benzene and 40 g. (26 ml.) of dry chloroform (1) in the flask, and add 35 g. of anhydrous aluminium chloride in portions of about 6 g. at intervals of 5 minutes with constant shaking. The reaction sets in upon the addition of the aluminium chloride and the liquid boils with the evolution of hydrogen chloride. Complete the reaction by refluxing for 30 minutes on a water bath. When cold, pour the contents of the flask very cautiously on to 250 g. of crushed ice and 10 ml. of concentrated hydrochloric acid. Separate the upper benzene layer, dry it with anhydrous calcium chloride or magnesium sulphate, and remove the benzene in a 100 ml. Claisen flask (see Fig. II, 13, 4) at atmospheric pressure. Distil the remaining oil under reduced pressure use the apparatus shown in Fig. 11,19, 1, and collect the fraction b.p. 190-215°/10 mm. separately. This is crude triphenylmethane and solidifies on cooling. Recrystallise it from about four times its weight of ethyl alcohol (2) the triphenylmethane separates in needles and melts at 92°. The yield is 30 g. 

DSC tests show a substantial reduction of the hydrogen desorption onset (red circles) (T J and peak (T ) temperatures due to the catalytic effects of n-Ni as compared to the hydrogen desorption from pure MgH also milled for 15 min. (Fig. 2.57). It is interesting to note that there is no measurable difference between spherical (Fig. 2.57a) and fdamentary (Fig. 2.57b) n-Ni, although there seems to be some effect of SSA. We also conducted desorption tests in a Sieverts apparatus for each SSA and obtained kinetic curves (Fig. 2.58), from which the rate constant, k, in the JMAK equation was calculated. The enhancement of desorption rate by n-Ni is clearly seen. At the temperature of 275°C, which is close to the equilibrium at atmospheric pressure (0.1 MPa), all samples desorb from 4 to 5.5 wt.% within 2,000 s. 

Hydrogenation catalyst. The catalyst is prepared from Ni(N03)2 - 6H, 0 slurried with A1203 and then dried at 120°. The catalyst is activated before use by heating at 400" for 30 minutes.1 The flow apparatus and general procedure for hydrogenation in the gas phase at atmospheric pressure have been described.2... 

After the reaction has been carried out, the apparatus is arranged for distillation as previously described (part A), and the reaction flask is heated at atmospheric pressure to facilitate removal of the dissolved hydrogen chloride, ethyl ether, and excess silicon tetrachloride. The vapor temperature is not allowed to rise above 55 to 60°. Vacuum is then applied, and the pressure in the system is lowered slowly to about 33 mm. The desired product distills at 66 to 68° under a pressure of 33 mm. Most of the distillate is obtained at 66°. The yield is about 130 ml., which is approximately 90% based on ethylene chlorohydrin. Anal Calcd. for ClC2H4OSiCl3 Cl, 66.3. Found Cl, 65.90, 66.15. 

B. Ethyl a-acetyl- - 2,3-dimethoxy phenyl) propionate. The product obtained in Part A is divided into two approximately equal portions, and to each are added 125 ml. of ethyl acetate and 5 g. of 5% palladium-on-carbon catalyst (Note 4). Each solution is shaken with hydrogen at pressures between 20 and 40 lb. in a low-pressure apparatus. About 45 minutes is usually needed for complete reduction. The two solutions are then combined, and the catalyst is removed by filtration and washed with 20 ml. of ethyl acetate. The ethyl acetate is distilled at atmospheric pressure, and distillation of the residue under reduced pressure yields 158-176 g. (56-63% over-all) of a colorless product collected at 175-177°/3 mm., 1.5042-1.5044 (Notes 3 and 5). 

The selective hydrogenation of C2 - C4 alkynes was studied at atmospheric pressure, using a fully computer-controlled flow apparatus. 0.5 g of catalyst was placed In a copper reactor tube (3/8" O.D.) between glass wool plugs. The catalyst was reduced prior to reaction In a stream of 50 % hydrogen in helium (40 ml/tnin) at 250 C for 4 hours. 

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