Catalyst, alumina zinc chloride

Gas Phase. The gas-phase methanol hydrochlorination process is used more in Europe and Japan than in the United States, though there is a considerable body of Hterature available. The process is typicaHy carried out as foHows vaporized methanol and hydrogen chloride, mixed in equimolar proportions, are preheated to 180—200°C. Reaction occurs on passage through a converter packed with 1.68—2.38 mm (8—12 mesh) alumina gel at ca 350°C. The product gas is cooled, water-scmbbed, and Hquefied. Conversions of over 95% of the methanol are commonly obtained. Garnma-alurnina has been used as a catalyst at 295—340°C to obtain 97.8% yields of methyl chloride (25). Other catalysts may be used, eg, cuprous or zinc chloride on active alumina, carbon, sHica, or pumice (26—30) sHica—aluminas (31,32) zeoHtes (33) attapulgus clay (34) or carbon (35,36). Space velocities of up to 300 h , with volumes of gas at STP per hour per volume catalyst space, are employed. 

Many catalysts are used to effect the reaction, such as zinc chloride on pumice, cuprous chloride, and ignited alumina gel. The reaction conditions are 350°C at nearly atmospheric pressure. The yield is approximately 95%. 

Dehydration Alcohols undergo dehydration (removal of a molecule of water) to form alkenes on treating with a pro tic acid e.g., concentrated H2SO4 or H3PO4, or catalysts such as anhydrous zinc chloride or alumina (Unit 13, Class XI). 

Thenaldehyde (thiophene-2-carbaldehyde) is readily available via the Vilsmeier-Haack reaction of DMF with thiophene catalyzed by phosphorus oxychloride. The Sommelet reaction with 2-chloromethylthiophene also gives reasonable yields (63AHC(l)l). Likewise, thiophene is readily acylated with acyl anhydrides or acid chlorides (equation 14), using mild Friedel-Crafts catalysts, such as tin(IV) chloride, zinc chloride, boron trifluoride, titanium tetrachloride, mercury(II) chloride, iodine and even silica-alumina gels or low-calcium-content montmorillonite clays (52HC(3)l). 

The redistribution reaction in lead compounds is straightforward and there are no appreciable side reactions. It is normally carried out commercially in the liquid phase at substantially room temperature. However, a catalyst is required to effect the reaction with lead compounds. A number of catalysts have been patented, but the exact procedure as practiced commercially has never been revealed. Among the effective catalysts are activated alumina and other activated metal oxides, triethyllead chloride, triethyllead iodide, phosphorus trichloride, arsenic trichloride, bismuth trichloride, iron(III)chloride, zirconium(IV)-chloride, tin(IV)chloride, zinc chloride, zinc fluoride, mercury(II)chloride, boron trifluoride, aluminum chloride, aluminum bromide, dimethyl-aluminum chloride, and platinum(IV)chloride 43,70-72,79,80,97,117, 131,31s) A separate catalyst compound is not required for the exchange between R.jPb and R3PbX compounds however, this type of uncatalyzed exchange is rather slow. Again, the products are practically a random mixture. 

For the preparation of small amounts of olefin, sulfuric acid, phosphoric acid, or zinc chloride may be used as catalysts. For larger amounts of olefins the alcohol is dehydrated by passing it over alumina heated at 200-300°. The use of sulfuric acid as a dehydrating agent involves the possibility of a number of side reactions, of which oxidation is the most important, and causes troublesome frothing. Phosphoric acid is preferred when it is desired to keep oxidation at a minimum. Ordinary (syrupy) phosphoric acid contains 15 per cent of water hence it must be first dehydrated by heating in an open vessel. 

Most of the HCI is recycled and utilized. The catalysts used are alumina gel, cuprous chloride, or zinc chloride. The reaction temperature is in the range of 490-530°C [30]. 

Metal chlorides can also be put on oxide supports. Zinc chloride was put on alumina in tetrahydrofuran, followed by dilution with methylene chloride, then boiling with a few drops of water and finally evaporation and drying. It was used as a catalyst to prepare a diketone (5.11).36... 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

In contrast to sulfur poisoning, ZnO gives no protection against chloride compounds. Zinc oxide reacts to form Zn chloride, which also has a low melting point and cause further poisoning and sintering problems. Chloride compounds in the feedstock can be reduced by guard beds of either alkalized alumina or extra, sacrificial catalyst. Today catalyst deactivation caused by poison (sulfur and chlorine) is rarely a problem in methanol synthesis, because poisonous compounds are effectively removed in the feedstock pretreatments. 

Originally Bergius felt that coal hydrogenation could not be catalyzed because the large quantities of sulfur present would poison the catalysts. He added luxmasse simply to absorb sulfur from the products although, coincidentally, the combination of iron oxide with titania and alumina was an excellent choice of catalyst. Since his first tests, however, the industrial use of the process has depended on catalysts that were developed more or less empirically. It was soon realized that the processes involved in hydrogenating coal were more complex than the simple reactions described by Sabatier and Ipatieff. Different catalysts such as iron oxide or iron snlfide, probably with traces of other metal oxides, were reqnired. These catalysts could be used in the presence of snUhr and were, in fact, even more active when sulfided. Several studies reported that iron, nickel, cobalt, tin, zinc, and copper chlorides were effective catalysts and claimed that aimnoninm molybdate was particularly active. 

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