Recovery of methanol

Feed Composition. Feed composition has a substantial effect on the economics of a distillation. Distillations tend to become uneconomical as the feed becomes dilute. There are two types of dilute feed cases, one in which the valuable recovered component is a low boiler and the second when it is a high boiler. When the recovered component is the low boiler, the absolute distillate rate is low but the reflux ratio and the number of plates is high. An example is the recovery of methanol from a dilute solution in water. When the valuable recovered component is a high boiler, the distillate rate, the reflux relative to the high boiler, and the number of plates all are high. An example for this case is the recovery of acetic acid from a dilute solution in water. For the general case of dilute feeds, alternative recovery methods are usually more economical than distillation. 

P. Stepnowski, K.-H. Blotevogel and B. Jastorff, Applied water-free recovery of methanol. A sustainable solution for chromatography laboratories. Environ. Sci. Poll. Res. 9 (2002) 34—38. 

If the small proportion of acetone present in synthetic methanol is objectionable it may be removed when present in quantities up to 1 per cent by the following procedure (Morton and Mark, 1934). A mixture of 500 ml of methanol, 25 ml of furfural and 60 ml of 10 per cent sodium hydroxide solution is refluxed in a 2-litre round-bottomed flask, fitted with a double surface condenser, for 6-12 hours. A resin is formed which carries down all the acetone present. The alcohol is then fractionated through an efficient column, the first 5 ml which may contain a trace of formaldehyde being rejected. The recovery of methanol is about 95 per cent. 

Figure 9.21 Methods of integrating pervaporation membranes in the recovery of methanol from the MTBE production process [15]. Courtesy of Air Products and Chemicals, Inc., Allentown, PA...

One of the most active areas of research involves the use of pervaporation for or-ganic/organic separations. The industrial interest is extremely high and several authors have reported the use of pervaporation for separation of aromatic/ahphatic hydrocarbon mixtures at high temperature (Matsui and Paul, 2003), as well as the separation of binary organic mixtures involving methyl tert-butyl ether (MTBE) and methanol (Yoshida and Cohen, 2003). As an example, Sulzerchemtech has already reported the possibility for industrial recovery of methanol and ethanol from organic mixtures. 

Water/hydrocarbon mixture Condensation, separation of the liquid water/ben-zine. The waste gas is ignited and the wastewater is fed to a treatment plant, e) Recovery of methanol and toluene [115]. During the production of a textile chemical a solution (mother liquor) is produced containing methanol and an aromatic solvent (toluene or xylene). An azeotrope containing methanol and toluene is produced by discontinuous ditillation. The toluene-containing phase separates out on addition of water. Methanol is recovered from the methanol-containing phase by continuous... 

By carrying out the transesterification reaction in several stages, the process can be carried out with a lesser excess of methanol. This leads to an energy saving in the methanol recovery and methanol purification processes. The use of a continuous process enables heat to be recovered during the recovery of methanol from the ester and glycerol. 

This column is designed by specifying a very small loss of methanol in the overhead vapor (0.01% of methanol fed to the column) and finding the minimum flow rate of extraction water that achieves this specification. Using more than 10 trays or using reflux did not affect the recovery of methanol. 

It was necessary to use the dimethyl ester because of the difficulties in purifying terephthalic acid caused by its poor solubility and high melting temperature. At present, terephthalic acid is being increasingly used in a direct esterification with ethylene glycol. This eliminates the expensive recovery of methanol in the transesterification. 

D9. A distillation column is separating a feed that is 20 mol% methanol, 50 mol% n-propanol, and 30 mol% n-butanol. Feed is 750 kmol/h. We want a 92 mol% recovery of methanol in the distillate and 95% recovery of n-propanol in the bottoms. Use L/D = 7. Feed is a saturated liquid. The column has a total condenser and a partial reboiler. As a guess, assume that n-butanol does not distribute (it all exits in the bottoms). Do not do iterations to inprove this guess. If we choose n-propanol as the reference, the relative volatilities are methanol = 3.58, n-propanol = 1.0, and n-butanol = 0.412. Assume relative volatilities are constant. Do not use Aspen Plus. This calculation is single enough that it can be done by hand or with a spreadsheet (with or without Visual Basic for Applications [VBA]) or with MATLAB. 

Sodium sulfite is used to destroy traces of peroxide in the methanol/water mixture before distillation and recovery of methanol. Because the presence of sulfite in MES may complicate formulation of finished consumer products, the possibility that sulfite from the recycled methanol may be present in the MES product has been investigated. Commercial MES made using the Chemithon MES process was analyzed for sodium sulfite. No detectable sodium sulfite was found. To verify that sulfite is not present, the commercial MES sample was also analyzed for residual hydrogen peroxide. Approximately 0.1% peroxide was detected, indicating that no sodium sulfite was present. 

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