Chromium oxide applications

Metallocenes give polyethylene producers a long list of opportunities to work on. They have already created polyethylene copolymers that compete well in applications that have been formerly the exclusive domain of the more costly, so-called high value plastics. Further, they are augmenting the chromium oxide and Ziegler-Natta catalysts systems that have been used for HDPE and LLDPE with metallocene catalysts. That creates even further... 

There have been several initial applications of the NMR method to the study of solids of catalytic interest. Selwood and co-workers (14) have measured proton relaxation times (Ti) of water-soaked 7-aluminas containing iron oxide, copper oxide, and chromium oxide. 

Natural, minable deposits of chromium oxide are not known. In addition to pigment grade, chromium oxide producers usually also offer a technical grade for applications based on properties other than coloration. These include ... 

Chromium(III) oxide crystallizes in the rhombohedral structure of the corundum type space group D3d-R3c, Q 5.2 g/cm3. Because of its high hardness (ca. 9 on the Mohs scale) the abrasive properties of the pigment must be taken into account in certain applications [3.44], It melts at 2435 °C but starts to evaporate at 2000 °C. Depending on the manufacturing conditions, the particle sizes of chromium oxide pigments are in the range 0.1-3 pm with mean values of 0.3-0.6 pm. Most of the particles are isometric. Coarser chromium oxides are produced for special applications, e.g., for applications in the refractory area. 

Chromium oxides with a minimal sulfur content are preferred for metallurgical applications. These are obtained by reacting sodium dichromate with ammonium chloride or sulfate in a deficiency of 10 mol% [3.51]. Chromium (III) oxides with a low sulfur content can also be obtained by thermal aftertreatment [3.52], Thermal decomposition of chromic acid anhydride (Cr03) yields high-purity chromium(III) oxide [3.53],... 

Chromium oxide is equally important as a colorant and in its other industrial applications. As a pigment, it is used predominantly in the paint and coatings industry for high quality green paints with special requirements, especially for steel constructions (coil coating), facade coatings (emulsion paints), and automotive coatings. 

Another important application is in the refining of steels when the oxygen content must be controlled at the parts per million level and monitored continuously on line and many oxygen sensors are currently used in the steel industry for this purpose. The principle of operation is as described for the lambda sensor and one form is shown schematically in Fig. 4.39. In this case the reference activity is established by a chromium metal/chromium oxide mix rather than being defined by air. 

Membrane reactor models of various configurations, complexity, and ranges of applicability have been previously reported [Sun and Khang, 1988 Itoh and Govind, 1989 Liu et al., 1990], Several previous investigators have presented water-gas shift membrane reactor models. A model of the iron-chromium oxide catalyzed water-gas shift reaction at 673 K in a cylindrical, palladium membrane reactor was developed to demonstrate... 

Regulated Colorants That Are FDA Approved. It often seems a contradiction that many of the colorants that are suitable for use in food contact applications must also appear on an MSDS as a reportable or hazardous material. Examples include zinc oxide and zinc sulfide, both zinc compounds chromium oxide green (pigment green 17), a chromium compound carbon black and cobalt aluminate blue (pigment blue 28), which is not only reportable because of its cobalt content but is also a suspected carcinogen. 

Relevant to this issue is dehydrogenation of ethylbenzene for the manufacture of styrene which uses alumina supported iron oxide as the preferred catalyst in most cases. Therefore, when an alumina membrane is used in conjunction with stainless steel piping or vessels as the membrane reactor, caution should be exercised. An estimate of the effects of their exposure to the reaction mixuire at the application temperature of 600 to 640 C is desirable. Wu et al. [1990b] estimated that the alumina membrane contributes to less than 5% conversion of ethylbenzene and the stainless steel tubing or piping could account for as much as 20% conversion. The high activity of the stainless steel is attributed to iron and chromium oxide layers that may form on the wetted surface. 

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