Activated alumina dehydration with

Comparing dehydration processes by activated alumina, molecular sieves, and methanol injection system, a methanol injection system is cheaper to build and operate than an activated alumina dehydration system when low water content natural gas is the feed. When natural gas with higher water... 

The second Hquefaction process is carried out at temperatures from 261 to 296 K, with Hquefaction pressures of about 1600—2400 kPa (16—24 atm). The compressed gas is precooled to 277 to 300 K, water and entrained oil are separated, and the gas is then dehydrated ia an activated alumina, bauxite, or siHca gel drier, and flows to a refrigerant-cooled condenser (see Drying agents). The Hquid is then distilled ia a stripper column to remove noncombustible impurities. Liquid carbon dioxide is stored and transported at ambient temperature ia cylinders containing up to 22.7 kg. Larger quantities are stored ia refrigerated iasulated tanks maintained at 255 K and 2070 kPa (20 atm), and transported ia iasulated tank tmcks and tank rail cars. 

Activated alumina and phosphoric acid on a suitable support have become the choices for an iadustrial process. Ziac oxide with alumina has also been claimed to be a good catalyst. The actual mechanism of dehydration is not known. In iadustrial production, the ethylene yield is 94 to 99% of the theoretical value depending on the processiag scheme. Traces of aldehyde, acids, higher hydrocarbons, and carbon oxides, as well as water, have to be removed. Fixed-bed processes developed at the beginning of this century have been commercialized in many countries, and small-scale industries are still in operation in Brazil and India. New fluid-bed processes have been developed to reduce the plant investment and operating costs (102,103). Commercially available processes include the Lummus processes (fixed and fluidized-bed processes), Halcon/Scientific Design process, NIKK/JGC process, and the Petrobras process. In all these processes, typical ethylene yield is between 94 and 99%. 

Cyclohexene can be prepared on a large scale still more rapidly and efficiently by the distillation of cyclohexanol over silica geP or, better, activated alumina. Using a 25-mm. tube packed with 8- to 14-mesh activated alumina (Aluminum Company of America) and heated to 380-450 over a 30-cm. length, 1683 g. of cyclohexanol was dehydrated in about four hours. After separating the water, drying with sodium sulfate, and fractionating with a simple column, 1222 g. (89 per cent yield) of cyclohexene, b.p. 82-84 , was obtained. 

The effects of post-synthesis alumination on purely siliceous MCM-41 material with A1(NC>3)3 on acidity have been studied by FTIR, NH3-TPD, and IPA decomposition reaction. The FTIR results of pyridine absorption show that both Lewis and Bronsted acid sites are increased by the post-modification. The amount of NH3 adsorbed on the alumina-modified MCM-41 samples increases with the loading of Al onto the surface of MCM-41. Due to the improved acidity, the alumina-modified MCM-41 materials show considerably higher catalytic activity for dehydration of isopropanol than purely siliceous MCM-41. In addition, XRD and N2 adsorption results show that all MCM-41 samples maintained their uniform hexagonal mesoporous structure well after they have been subjected to post-synthesis alumination with the loading of Al species on Si-MCM-41 varied from 0.1 wt. % up to 10 wt. % (calculated based on AI2O3). 

Post-synthesis alumination using A1(N03)3 as the precursor improves the acidity of siliceous MCM-41 materials significantly. FTIR results show that both Bronsted and Lewis acid sites are increased upon alumination. The number of acid sites increases with the Al content on MCM-41. NH3-TPD reveals the mild strength of these created acid sites. Due to the improved acidity, the catalytic activity for dehydration of isopropanol to propylene over these alumina-modified MCM-41 materials is considerably promoted by post-synthesis alumination. The results of XRD and N2 adsorption show that the enhancement of acidity for siliceous MCM-41 by postsynthesis alumination does not cause any serious structural deformation of the resulting material. 

To achieve a significant adsorptive capacity an adsorbent must have a high specific area, which implies a highly porous structure with very small micropores. Such microporous solids can be produced in several different ways. Adsorbents such as silica gel and activated alumina are made by precipitation of colloidal particles, followed by dehydration. Carbon adsorbents are prepared by controlled burn-out of carbonaceous materials such as coal, lignite, and coconut shells. The crystalline adsorbents (zeolite and zeolite analogues are different in that the dimensions of the micropores are determined by the crystal structure and there is therefore virtually no distribution of micropore size. Although structurally very different from the crystalline adsorbents, carbon molecular sieves also have a very narrow distribution of pore size. The adsorptive properties depend on the pore size and the pore size distribution as well as on the nature of the solid surface. 

Compensation effects have also been reported for the dehydration of alcohols on alumina (280) and on alumina modified with 10% potassium chloride (281). Values of A referred to unit area of active surface were not included in these reports, but for data in the latter article (281) we calculate e = 0.0836 and at = 0.0075. 

Corundum is aluminum oxide, q -A1203, which has a hexagonal crystalline structure that is analogous to hematite. However, water treatment systems most often use activated alumina, which is typically produced by thermally dehydrating aluminum (oxy)(hydr)oxides to form amorphous, cubic (y), and/or other polymorphs of corundum (Clifford and Ghurye, 2002, 220 Hlavay and Poly k, 2005 Mohan and Pittman, 2007). When compared with corundum, amorphous alumina tends to have higher surface areas, greater numbers of sorption sites, and better sorption properties. 

Other drying agents are activated alumina and bauxite, silica gel, sulfuric acid, and concentrated solutions of calcium chloride or sodium thiocyanate. Plants of this type usually require a packed tower for countercurrent treatment of the gas with the reagent, together with a regenerator for the dehydrating agent. 

The commercial alumina and silica gel sorbents are mesoporous, i.e., with pores mostly larger than 20 A (see Fig. 1). Activated alumina is produced by thermal dehydration or activation of aluminum trihydroxide, A1 (OH)3 (Yang, 1997), and is crystalline. Commercially, silica is prepared by mixing a sodium silicate solution with a mineral acid such as sulfuric or hydrochloric acid. The reaction produces a concentrated dispersion of finely divided particles of hydrated Si02, known as silica hydrosol or silicic acid ... 

Materials. Tetralin, purchased commercially, was passed over activated alumina and stored under argon before use. In order to correctly identify the isomer of methylindan found in the product mixtures, authentic 1- and 2-methylindans were prepared from the corresponding indanones by reaction with methyl-magnesium iodide, dehydration, and subsequent hydrogenation over Pd on asbestos. 

Styrenes are available by dehydration of either a-arylethyl or /S-aryl-ethyl alcohols. The procedures were reviewed in 1S>49. /S-Phenylethyl alcohol loses water at 140° over a roixture of molten sodium and potassium hydroxides to give styrene, C,H5CH=CH2, in 57% yield. The 2,4-dimethyI derivative has been prepared in a similar manner from the primary alcohol. " Many substituted styrenes have been made by dehydration of methylarylcarbinols with potassium hydrogen sulfate, phosphorus pentoxide, or activated alumina. 1,1-Diphenyl-ethylene and 2-phenyl-2-butene are easily obtained by boiling the corresponding tertiary alcohols with dilute sulfuric acid. 

Preparation of dienes is accomplished by dehydration of diols or ole-finic alcohols. Pinacol, (CHjljCOHCOHfCHjlj, is converted to 2,3-di-methyl-1,3-butadiene by heating with 48% hydrobromic acid or by passing the vapors over activated alumina at 420-470°, Yields of the diene are 60% and 86%, respectively. Aniline hydrobroniide is used as a catalyst in the dehydration of 3-methyl-2,4-pentanediol to 3 methyl-l,3-penta-diene (42%). An excellent laboratory preparation of isoprene from acetone in 65% over-all yield has been described. The last step involves catalytic dehydration of dimethylvinylcatbinol over aluminum oxide at 300° to give isoprene in 88% yield. ... 

Adsorption is the adhesion of molecules of a gas, liquid, or dissolved substance or of particles to the surface of a solid substance. Absorption is the assimilation of molecule into a solid or liquid subsunce, with the formation of a solution or a compound. Sometimes the word sorption is used to indude both of these phenomena. We say that a heated glass vessel adsorbs water vapor from the air on cooling, and becomes coated with a very thin layer pf water a dehydrating agent such as concentrated sulfuric add absorbs water, forming hydrates. Activated alumina sorbs water vapor, probably both by adsorption (the adhesion of a layer of water vapor to the surface of rhe particles.) and by absorptimi (the formation ipf aluimnunt hydroxMe). 

Trade Publication (F35-14481), Dehydrating Liquids With Alcoa Activated Aluminas, Alcoa, Pittsburgh, Pennsylvania, U.S.A., 15219. 

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