Activated alumina/carbon

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. 

In GSC, separation occurs based on differences in the adsorption of the various components in the sample onto the solid adsorbent. While GSC may not offer as much flexibility in stationary phase functionality as GLC, it has its own advantages. For separation applications, advantages include higher available operating temperatures, higher column efficiencies, and no stationary phase leakage. Typical solid phases for GSC include zeolites, silica gel, activated alumina, carbon, carbon molecular sieves, diatomites, and porous polymers. 

See Adsorption, LIQUID separation Aluminum compounds, aluminum oxide (alumina) Carbon, activated carbon Ion exchange Molecular sieves Silicon... 

Amorphous Adsorbents. The amorphous adsorbents (siUca gel, activated alumina, and activated carbon) typically have specific areas in the 200—1000-m /g range, but for some activated carbons much higher values have been achieved (- 1500 /g). The difficulty is that these very high area... 

Amorphous siHca gel, activated alumina, activated carbon, and molecular sieve carbons. 

Traditional adsorbents such as sihca [7631 -86-9] Si02 activated alumina [1318-23-6] AI2O2 and activated carbon [7440-44-0], C, exhibit large surface areas and micropore volumes. The surface chemical properties of these adsorbents make them potentially useful for separations by molecular class. However, the micropore size distribution is fairly broad for these materials (45). This characteristic makes them unsuitable for use in separations in which steric hindrance can potentially be exploited (see Aluminum compounds, aluminum oxide (ALUMINA) Silicon compounds, synthetic inorganic silicates). 

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. 

High Surface Sodium. Liquid sodium readily wets many soHd surfaces. This property may be used to provide a highly reactive form of sodium without contamination by hydrocarbons. Powdered soHds having a high surface area per unit volume, eg, completely dehydrated activated alumina powder, provide a suitable base for high surface sodium. Other powders, eg, sodium chloride, hydride, monoxide, or carbonate, can also be used. 

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. 

At temperatures of 300—600°C in the presence of an activated alumina catalyst, carbon dioxide and hydrogen sulfide are formed in almost quantitative yields (29) ... 

Carbon disulfide reacts with alkanols or diaLkyl ethers at 250—500°C over activated alumina catalyst to give diaLkyl sulfides. For example, methanol yields dimethyl sulfide [75-18-3]. 

The properties of 1,1-dichloroethane are Hsted ia Table 1. 1,1-Dichloroethane decomposes at 356—453°C by a homogeneous first-order dehydrochlofination, giving vinyl chloride and hydrogen chloride (1,2). Dehydrochlofination can also occur on activated alumina (3,4), magnesium sulfate, or potassium carbonate (5). Dehydrochlofination ia the presence of anhydrous aluminum chloride (6) proceeds readily. The 48-h accelerated oxidation test with 1,1-dichloroethane at reflux temperatures gives a 0.025% yield of hydrogen chloride as compared to 0.4% HCl for trichloroethylene and 0.6% HCl for tetrachloroethylene. Reaction with an amine gives low yields of chloride ion and the dimer 2,3-dichlorobutane, CH CHCICHCICH. 2-Methyl-l,3-dioxaindan [14046-39-0] can be prepared by a reaction of catechol [120-80-9] with 1,1-dichloroethane (7). 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

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%. 

Adsorbents are natural or synthetic materials of amorphous or microcrystalhne structure. Those used on a large scale, in order of sales volume, are activated carbon, molecular sieves, silica gel, and activated alumina [Keller et al., gen. refs.]. 

Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

Methane reacts with sulfur (an active nonmetal element of group 6A) at high temperatures to produce carbon disulfide. The reaction is endothermic, and an activation energy of approximately 160 KJ is required. Activated alumina or clay is used as the catalyst at approximately 675°C and 2 atmospheres. The process starts by vaporizing pure sulfur, mixing it with methane, and passing the mixture over the alumina catalyst. The reaction could be represented as ... 

Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized hed using activated carhon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. 

Therefore, in this study, activated carbon, activated alumina, molecular sieve 5A, and molecular sieve 13X were used as dry sorbents to control carbon dioxide in a fluidized bed. In addition, the attrition and percentage loss of adsorption capacity of the dry sorbents were investigated. 

Fig. 1 shows that minimum fluidization velocities of activated carbon, activated alumina, molecular sieve 5A and molecular sieve 13X are 8.0 cm/s, 8.5 cm/s, 6.2 cm/s and 6.5 cm/s, respectively. Also, theoretical calculation values of minimum fluidization velocity and terminal velocity of each dry sorbent were summarized in Table 1. 

Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others.

The purpose of this paper Is 1) to describe the electrochemistry of ferrl-/ferro-cyanlde and the oxidation of ascorbic at an activated glassy carbon electrode which Is prepared by polishing the surface with alumina and followed only by thorough sonlcatlon 2) to describe experimental criteria used to bench-mark the presence of an activated electrode surface and 3) to present a preliminary description of the mechanism of the activation. The latter results from a synergistic Interpretation of the chemical, electrochemical and surface spectroscopic probes of the activated surface. Although the porous layer may be Important, Its role will be considered elsewhere. 

There are several potential treatment technologies that may be applicable, but are more expensive than the methods currently used. These potential treatments include sulfide precipitation, ultrafiltration, reverse osmosis, deep-well disposal, activated carbon adsorption or activated alumina adsorption, solidification, or ion exchange.19-21... 

Activated carbon has high specific surface area with respect to its volume, and thus has high adsorption capacity. Activated carbon adsorption is considered to be one of the most versatile treatment technologies and can remove classical pollutants such as COD, TOC, BOD, and nitrogen, as well as toxic pollutants such as phenol, refractory organic compounds, VOCs, and soluble heavy metals.38 Activated alumina and peat have also demonstrated similar abilities. 

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