Pressure, operating, methanol

Methanol Crossover Catalyst Performance Catalyst Fabrication Carbon Support Membrane Performance MEA Fabrication Pressurized Operation Methanol Concentration Fluid Flow Heat Transfer... 

The German Lurgi Company and Linde A. G. developed the Rectisol process to use methanol to sweeten natural gas. Due to the high vapor pressure of methanol this process is usually operated at temperatures of -30 to -100°F. It has been applied to the purification of gas 1 plants and in coal gasification plants, but is not used commonlv natural gas streams. 

Since the air/methanol mixture is flammable in a methanol concentration range between 6 to 25 and 9 to 37 per cent volume according to temperature and pressure, operations can be carried out in two ways ... 

Another thing to consider with gradient elution is changes in the eluent viscosity. When gradient elution with a hydro-organic mobile phase is used (e.g., methanol-water), systematic variations in the flow rate are expected under conditions of constant-pressure operation, and systematic variations in the operating pressure will be found when a constant flow rate is used [1]. The compressibility of the solvent is species-specific. 

Figure 8 Carbamazepine polymorphs processed by SEDS at different operating temperatures and pressures using methanol as solution solvent and a flow rate of 0.5 mL/min. (From Ref. 7, Copyright 2001 Wiley-Liss Inc. and American Pharmaceutical Association.)...

As the synthesis reaction proceeds with a decreasing number of moles, low pressure operation meant lower methanol concentration in the effluent stream and therefore higher recycle rates. However, high operating pressures involve bulkier equipment and sturdier compressors, and a balance must be achieved between energy costs and capital costs. 

The absorption tower will be filled with 50-mm ceramic Pall rings. Design for a gas-pressure drop not to exceed 400 Pa/m of packed depth. Assume that cooling coils will allow isothermal operation at 300 K. The gas will enter the column at the rate of 1.0 m3/s at 300 K and 1 atm. The partial pressure of methanol in the inlet gas is 200 mmHg (ScG = 0.783). The partial pressure of methanol in the outlet gas should not exceed 15 mm Hg. Pure water enters the tower at the rate of 0.50 kg/s at 300 K. Neglecting evaporation of water, calculate the diameter and packed depth of the absorber. 

The bottoms product from the prerun colunrn is fed between tray 68 and 72 of the pressurized pure methanol column which contains a total of 80-85 trays. This column operates at a pressure of 7-8 bar corresponding to a bottoms temperature of 125 to 135°C, depending on the water content of the raw methanol. 

In view of the fact that the water content in the bottoms product of the pressurized column is twice that of the prerun column, the hydrocarbons transferred ftom the prerun column into the pressurized column will reliably be found in the bottoms product, i.e. they are transferred to the atmospheric distillation column. Thus, ethanol becomes the key component for the pressurized column. Since the bottom product of the pressurized column - unlike that of the atmospheric column - does nOt have to meet certain purity requirements, this column need not have a side outlet for ethanol, but the ethanol is quantitatively transferred to the atmospheric columit. The high methanol content in the bottom of the pressurized column facilitates ethanol separation. Nevertheless, for the same number of trays, the pressurized operation of this column leads to a higher reflux than in the atmospheric column. The bottoms product ftom the pressurized column is transferred to the atmospheric column at approximately 125-35°C. The overhead product is obtained at approximately 115-125°C, condensed in the reboiler of the atmospheric column, and fed to the reflux drum of the pressurized column. From there, some of the overhead product is withdrawn by way of an after-cooler as on-spec methanol while the rest is pumped back uncooled as reflux to the column head. 

The introduction of copper into methanol catalysts by ICI in the late 1960s, with other modifications to provide acceptable catalyst life, revolutionized this situation by permitting reaction temperatures of about 250°C. Thus pressures down to 50 atm. became usable, allowing the retention of centrifugal compressors, with smaller economic penalties, for modest scales of operation. Methanol yield also improved by 2-3%. Other process licensing companies... 

Four existing nonretrofitted processes solvent production from a primary oil, formalin production from methanol and air, oil refinery (atmospheric distillation), low-pressure Lurgi methanol production, are operating within one location and, therefore, the method... 

The higher pressure in the methanol column requires a higher reflux ratio and more heat input than the low-pressure operation because the higher pressure makes the separation more difficult. The reflux ratio increases from 1.61 to 2.91, and the reboiler heat input increases from 7.1 to 11.4 MW. 

In practice, the suitability of a reaction system is determined by the kinetics of the reaction, which depends on temperature, pressure of gases, electrode polarization, surface area of electrodes, and presence of a catalyst. A fuel cell that is thermodynamically and kinetically feasible must be considered from an econonuc viewpoint before it is accepted. Thus, since hydrogen, hydrazine, and methanol are too expensive for general application, their use in fuel cells has been limited to special cases. Hydrogen has been used for fuel cells in satellites and space vehicles, in which reliability and lightness are more important than cost. Hydrazine fuel cells have been used in portable-radio power supplies for the United States Army because of their truly silent operation. Methanol fuel cells have been used to power navigation buoys and remote alpine television repeater stations because such power systems are comparatively free from maintenance problems over periods of a year or more. The polarization at the electrodes of a fuel cell is the most important single factor that limits the usefulness of the cell. The various polarization characteristics for a typical fuel cell are plotted separately as a function of current density in Fig. 9.11. 

Entrained-flow gasifiers are attractive for synthesis gas derivatives, such as methanol, due to their high yield of synthesis gas with essentially no production of methane or other hydrocarbon products. In addition, the slurry feed Texaco process ensures reliable high-pressure operation and a relatively high Hj/CO ratio of synthesis gas. 

A typical PEM fuel cell uses hydrogen as the fuel and oxygen/air as the oxidant. Eor hydrogen, a separate reformer reactor is required. Some fuel cells use methanol as fuel. In this case there is no need of a reformer, and the fuel cell is called a DMEC. In effect, DMFC is a special iteration of PEMFC. Its low temperature and pressure operation coupled with the low cost of methanol are attributes that makes DMEC a promising energy source [7]. 

In 1968 a new methanol carbonylation process using rhodium promoted with iodide as catalyst was introduced by a modest letter (35). This catalyst possessed remarkable activity and selectivity for conversion to acetic acid. Nearly quantitative yields based on methanol were obtained at atmospheric pressure and a plant was built and operated in 1970 at Texas City, Tex. The effect on the world market has been exceptional (36). 

Low pressure methanol carbonylation transformed the market because of lower cost raw materials, gender, lower cost operating conditions, and higher yields. Reaction temperatures are 150—200°C and the reaction is conducted at 3.3—6.6 MPa (33—65 atm). The chief efficiency loss is conversion of carbon monoxide to CO2 and H2 through a water-gas shift as shown. 

The methanol carbonylation is performed ia the presence of a basic catalyst such as sodium methoxide and the product isolated by distillation. In one continuous commercial process (6) the methyl formate and dimethylamine react at 350 kPa (3.46 atm) and from 110 to 120°C to effect a conversion of about 90%. The reaction mixture is then fed to a reactor—stripper operating at about 275 kPa (2.7 atm), where the reaction is completed and DMF and methanol are separated from the lighter by-products. The cmde material is then purified ia a separate distillation column operating at atmospheric pressure. 

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