Synthetic magnesia

Silica alumina Activated natural Silica magnesia Synthetic Natural ... 

The principal producers of synthetic normal magnesium carbonates and basic magnesium carbonates are J.T. Baker Inc., Philipshiirg, New Jersey GTE Corp., Sylvannia Chemicals Division, Towanda, Peimsylvania Mallinkrodt Specialty Chemicals, St. Louis, Missouri Marine Magnesia, San Erancisco, California Morton Specialty Chemicals, Manistee, Michigan and Ube Chemical Industries, Tokyo. 

Synthetic magnesia is most often produced from seawater, known as seawater magnesia. Seawater contains approximately 1294 ppm Mg. Synthetic magnesia can also be produced from brine wells or lakes which have much higher concentrations of magnesium. Regardless of the source of magnesium, the sea or brine water is treated with hydrated lime, Ca(OH)2, that precipitates Mg(OH)2 ... 

Florisil is a registered trademark of the Floridin Company, Warren, Pa., for a synthetic magnesia-silica gel. 

In the mid-1950s, alumina-silica catalysts, containing 25 percent alumina, came into use because of their higher stability. These synthetic catalysts were amorphous their structure consisted of a random array of silica and alumina, tetrahedrally connected. Some minor improvements in yields and selectivity were achieved by switching to catalysts such as magnesia-silica and alumina-zirconia-silica. 

A variety of material could be used as the basis for cracking catalyst, including synthetic silica-alumina, natural clay, or silica-magnesia. If these materials did not contain significant amounts of metals such as chromium or platinum that catalyzed the burning of carbon, the burning rate of the coke is independent of the base as shown in Fig. 7. 

Natural clay catalysts were replaced by amorphous synthetic silica-alumina catalysts5,11 prepared by coprecipitation of orthosilicic acid and aluminum hydroxide. After calcining, the final active catalyst contained 10-15% alumina and 85-90% silica. Alumina content was later increased to 25%. Active catalysts are obtained only from the partially dehydrated mixtures of the hydroxides. Silica-magnesia was applied in industry, too. 

Historical Development and Future Perspectives The Fischer-Tropsch process dates back to the early 1920s when Franz Fischer and Hans Tropsch demonstrated the conversion of synthesis gas into a mixture of higher hydrocarbons, with cobalt and iron as a catalyst [35, 36], Some 20 years earlier, Sabatier had already discovered the reaction from synthesis gas to methane catalyzed by nickel [37]. The FTS played an important role in the Second World War, as it supplied Germany and Japan with synthetic fuel. The plants used mainly cobalt catalysts supported on a silica support called kieselguhr and promoted by magnesia and thoria. 

Commercial production of synthetic silica-alumina catalysts for use in fluid cracking was initiated in 1942. The synthetic catalysts were first manufactured in ground form, but means were later developed for production in MS (micro-spheroidal) form. First shipments of the MS catalyst were made in 1946. The synthetic catalysts contain 10 to 25% alumina. Synthetic silica-magnesia catalyst has also been used commercially in fluid-catalyst units (19,100). Magnesia content is 25 to 35% as MgO (276). 

The crystal structures of synthetic silica-magnesia and Filtrol SR catalyst have not been published. However, it has been reported that silica-magnesia is converted to a crystalline nonporous magnesium silicate when heated to about 1400°F. (354). 

The ratio of CO2 to CO with Filtrol SR catalyst has been reported to be 1.2-1.3, closely resembling that obtained with synthetic silica-alumina (326). The ratio tends to increase with use for silica-alumina catalyst but not with silica-magnesia (355). The increase with silica-alumina is presumably due, at least in part, to accumulation of metal contaminants that promote complete combustion to CO2 total iron pick-up during commercial use was reported to be much less in the case of silica-magnesia than in a companion commercial run on silica-alumina (355). Intentional addition of a small amount of chromium to TCC bead catalyst is practiced commercially for the specific purpose of insuring complete combustion to CO2 and thereby avoiding afterburning (333). 

---