47 Vapor Phase Hydration of Ethylene Catalyzed by Solid Acids* by Kozo Tanabe** and Masahiro Nitta** Summary: The hydration of ethyleneover various solid acids such as metal sulfates, phos- phates, oxides, solid phosphoricacid and cation exchangedzeolites was investigatedin a closed circulation system at 160～300℃. Ferric and aluminum sulfates and zeolites Y showed high catalytic activity in comparison with solid phosphoricacid, SiO2-Al2O3,zeolites A and all other catalysts. The selectivityfor ethanolformation was extremelyhigh in metal sulfates and zeolites A, but low in SiO2-Al2O3 and zeolites Y. The order of activities of metal sulfates was Fe2(SO4)3>Al2(SO4)3>Ni- SO4> Cr2(SO4)3>CuSO4>MnSO4>CaSO4. The catalysts those acid strength in their dried state was as strong as -8.2<Ho≦-3 were found to be active and selective for ethanol for- mation. The activitiesof cation exchangedzeolites A which varied in order of Mg-A>Cd-A> Zn-A>Ca-A>Ag-A>Sr-A>La-A～Ce-A were shown to correlate with the electronegativities of exchangedcations and the adsorptionheats of ethylene. The rate of ethanolformation increasedas the mole ratio of H2O/C2H4 decreased. The experimenton the reaction of ethylenewith heavy water showed that deuterium did not transfer into ethyleneat all. It was concludedby analyzing the kinetic data that theformation of an ad- sorbedethyl carbonium ion from an adsorbedethylene and a proton on acid sites was the rate-deter- miningstep of the hydration. 1 Introduction 2 Experimental The direct synthesis of alcohol from ethylene 2.1 Catalysts and Materials and water is important in petroleum chemistry Hydrates of metal sulfates of Ni, Cu, Mn, and has been extensively studied over various Ca, Fe, Cr and Al (guaranteed or extra pure solid acid catalysts such as silicotungustic reagents), ZnO (guaranteed reagent), NiO acids1)～5), silicophosphoric acids6), solid phos- prepared from NiSO4, Al2O3 (Wako Junyaku phoric acids5)～7), and metal oxides1)8),9) Co., Activated Alumina), SiO2-Al2O3 (Nikki However, no study has been made on the cor- Kagaku Co., N 631 L), SiO2-MgO and solid relation between the acidic properties of the phosphoric acid (both supplied by Mitsui Toatsu catalysts (amount, strength and type of acid Chemicals Co.) were calcined in air at various sites) and their activities or selectivities. temperatures for 3hrs. Samples of 10～20 In the present work, the correlation has been mesh were used as catalysts. Aluminum and studied by using new catalysts such as metal boron phosphates were prepared from H3PO4 sulfates, phosphates and zeolites together with and AlCl3・6H2O10)and from H3PO4 and H3BO311) some of the well-known catalysts. In the case respectively. of cation exchanged zeolites, the correlation of Cation exchanged zeolites A and Y were the electronegativities of cations or the adsorp- prepared by repeatedly immersing 4A pellets tion heats of ethylene with the activities or selec- and SK-40 powders of the Linde Co. in 1N tivities was also examined. The mechanism aqueous solutions of various metal chlorides, of the hydration reaction was discussed on the nitrate or acetates at 85℃ and then drying at basis of a kinetic study on the effect of the mole 120℃ after washing with deionized water. The ratio of H2O/C2H4 on the rate of ethanol forma- degree of ion exchange was calculated from the tion and on the deuterium exchange reaction amount of unexchanged sodium ion, which was between ethylene and heavy water. determined by flame spectrometry. The change in crystal structure of zeolite before and after ion exchange, evacuation and hydration reac- * Received December 8, 1971. ** Department of Chemistry tion was examined by X-ray diffraction , Facutly of Science, . Hokkaido University (Sapporo, ,Japan) The ethylene used was C. P. grade reagent of Volume 14, No. 1, May 1972 48 Tanabe and Nitta: Vapor Phase Hydration 99.99% purity. Water was deionized water reaction system (volume: 255ml) consisting of a which was degassed by boiling. Heavy water reaction tube R containing 5～10ml of catalyst, a was Merck's reagent of 99.75% purity. water carburetor W and a circulation pump P 2.2 Measurements of Acidic Property and was evacuated. After R attained the desired Heat of Ethylene Adsorption temperature, cocks C1, C2 and C3 were closed Acid amounts of catalysts at various acid and ethylene was introduced. Then, 3ml of strengths were measured by titrating with 0.1N water was put into W through sampling rubber n-butylamine in benzene, using various in- S and the vapor pressure of water was kept con- dicators12). The measurement was made on stant by working P. The reaction was started dried samples at room temperature, with special by opening C3 to pass the mixture of ethylene attention being paid to minimize the effect of and water through R. The vapor pressure of moisture on acidic property13). Indicators water was controlled by changing the tempera- used were phenylazonaphtylamine (pKα=4.0), ture with thermostat B. The condensation of p-dimethylaminoazobenzene (3.3), benzeneazodi- water vapor was prevented by wrapping the phenylamine (1.5), dicinnamalacetone (-3.0), entire reaction system with a tape heater. benzalacetophenone (-5.6) and anthraquinone Ethanol and acetaldehyde formed by the (-8.2). reaction dissolve in water in W. The aqueous The adsorption heats of ethylene on zeolites solution is taken up through S and analyzed at were calculated by applying the Clausius- appropriate time intervals by gas chromato- Clapeyron's equation to the adsorption isotherms graphy using a 100℃ column packed with poly- of ethylene. The isotherms were obtained by a ethylene glycol 6,000 and hydrogen as carrier constant volume method in the temperature gas (30ml/min). The initial rate of ethanol range of 70～280℃ and ethylene pressure of formation (V/%•min-1•g-1; volume% per unit 10～500mmHg. The zeolite samples were time and unit weight of catalyst) obtained from a evacuated at 400℃ and 10-4mmHg for 3hrs. curve of ethanol concentration vs. reaction time The ethylene used in this case was distilled twice. was taken as the catalytic activity. In the case 2.3 Apparatus and Procedure of the experiment on the effect of H2O/C2H4 on The hydration reaction was carried out at reaction rate, the rate was obtained from the 485～597mmHg of ethylene,23～132mmHg increase in ethanol concentration in W and of water vapor and 160～300℃ in a closed in the gaseous phase as described in 3.5. circulation apparatus as shown in Fig. 1. The The reaction of ethylene with heavy water was carried out over 1.1g of nickel sulfate at 220℃,580mmHg of ethylene and 23mmHg of heavy water vapor. The gas samples were collected in flask D at intervals of 2, 7 and 30 min after the start of reaction and ethylene in the sample was analyzed for deuterium content by a Hitachi RMU-6 mass spectrometer at 70V of electron accelerating voltage. 3 Results and Discussion 3.1 Correlation between Acidic Property and Catalytic Activity In the case of metal sulfate catalysts, only ethanol was formed, with byproducts such as acetaldehyde, diethyl ether or polymer not being detected. The acid amounts of nickel sulfates preheated at various temperatures and their catalytic activities are shown in Fig. 2. The activities correlate fairly well with the acid amounts at acid strength H0≦-3, but Fig. 1 Closed Circulation Type Reaction Apparatus not with those at -3<H0≦1.5. It was also Bulletin of The Japan Petroleum Institute of Ethylene Catalyzed by Solid Acids 49 mum of Bronsted acidity appeared when heat- treatment was at 250℃ and the maximum of Lewis acidity at 400℃14), while the sum of both acidities was maximum at 350℃15). Since the maximum activity of nickel sulfate for ethanol formation was observed at 350℃ and the activity curve correlated well with the Bronsted plus Lewis acidity curve as shown in Fig. 2, the ethanol formation is considered to be catalyzed by both Bronsted and Lewis acid. However, Lewis acid sites on dehydrated nickel sulfate may be converted to Bronsted acid sites when water vapor is present during reaction. The conver- sion takes place certainly by the addition of water at room temperature14), although it is not clear whether it does at high temperature. It is confirmed that water vapor does not affect Reaction temp.: 190℃, Mole ratio of H2O/C2H4: the acid strength of H0≦-3 on the surface of 0.04, Total pressure: 620mmHg dired catalyst, if temperature is higher than Fig. 2 Acidic Property and Catalytic Activity for 80℃16). Ethylene Hydration of Calcined NiSO4 3.2 Acidic Property and Selectivity The activity for ethanol formation of silica- alumina, which has a comparatively large acid amount at H0≦-3, was found to be much lower than that expected from the linear relation indicated in Fig. 3. Acetaldehyde was also formed in addition to ethanol and the formation of ethylene polymer is suggested from the large decrease in pressure. These are considered to be due to the existence of very strong acid sites of H0≦-8.2 on the catalyst. In fact, acetal- dehyde and ethylene polymer were also formed over the catalysts of alumina and aluminum phosphate which have strong acid sites of H0≦ -8 .2, but not over solid phosphoric acid and Fig. 3 Acid Amount at H0≦-3.0 and Catalytic Acti- boron phosphate which have no such strong vity for Ethylene Hydration of Various Solid Acids acid sites, as shown in Table 1. These results combined with those mentioned in 3.1 indicate found that there was no correlation between that the acid strength of active sites for ethanol the activities and the acid amounts at 1 .5<H0≦ formation is -8.2<H0≦-3.