Methanol purification

Figure 8.26 Colorimetric comparison of polycarbonate obtained (a) via acidified methanol purification (b) utilizing the Cr(PIBsalen)Cl/CH3CN/heptane system.

Methanol purification section. The crude methanol is fed to a two-column distillation system, which consists of a small topping column (11) and a refining column (12) to obtain high-purity Federal Grade AA methanol. 

After the condensed crude methanol is recovered in the high-pressure separator, it is sent to a methanol purification column. Typically, methanol purification requires two columns, one to remove the light ends (mainly by-products generated in the methanol synthesis reactor such as dimethyl ether and dissolved gases) and another to separate methanol and water and any other by-products with a lower volatility than methanol. Specification-grade methanol (greater than 99.85 wl% methanol) is recovered as the overhead product of the heavy ends column and sent to storage. 

Rapid purification Methanol purification is the same as for ethanol. 

Isocyanobutane (0.5 mL) is added to a stirred suspension of 0.25 g (0.50 mmole) dichlorobis(l,5-cyclooctadiene)dirhodium(I) in 15 mL methanol. The red-orange solution is filtered to remove any unreacted starting material. A solution of 0.41 g (1.2 mmole) sodium tetraphenylborate in 5 mL methanol is added to precipitate the product as yellow needles. The product is collected by filtration and washed with methanol. Purification of [Rh(n-C4H9NC)4] [BPh4] is achieved by recrystallization from dichloromethane/ethanol, mp 117-118°. The purple coloration of solutions of this yellow solid is caused by self-association of the planar monomer to form rhodium-rhodium-bonded dinuclear cations. 

Methanol Purification. To check methanol purity, 200 mL was diluted with an equal volume of contaminant-free dichloromethane and extracted twice with 200-mL portions of distilled water. After the resulting dichloromethane phase was concentrated to 1 mL, it was... 

Description Fatty acids are fed to the esterification section (1) where they are esterified to methyl esters in a reactive distillation column. Water released by this reaction is removed by excess methanol, which is treated in a methanol purification column. This column produces a clean water effluent and recycles methanol to the reactive distillation column. 

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. 

Impure methanol is fed into the methanol purification stage as a vapor, so that the energy consumption in methanol distillation is very low. 

The objective of methanol purification is to remove these impurities until a marketable product is obtained. Raw methanol produced over copper catalysts is today purified exclusively by way of distillation, except for a few cases in which traces of impurities (such as amines) have to be eliminated by ion exchange. 

Currently most mycotoxins are still assayed using TLC, which permits effective compound separation and characterization. When the compounds to be detected are fluorescent, a fluorodensitometry reads the plates quantitatively and objectively. However, the use of RPLC has expanded rapidly in recent years. The diversity of detection systems (DAD, fluorescence, and MS) permits identification and accurate assay of a great variety of these compounds. Recently, a database for 474 mycotoxins and fungal metabolites for dereplication by standardized LC-UV-MS has been reported. Sample preparation techniques include extraction of mycotoxins using mostly chloroform, acetone, or methanol, purification of the extract with cleanup methods, and concentration of the extract. 

The comparative ultraviolet absorbance test provides a quick and satisfactory quality check for methanol for general uses [6]. The method relies on the featureless response of methanol to UV and is sensitive to traces of aromatic and most other organic compounds. The ACS absorbance test [61] checks the measured sample absorbance as 0.001 from 280 to 400 nm, 0.04 at 260 nm, 0.10 at 240 nm, 0.20 at 230 nm, 0.40 at 220 nm, and 0.80 at 210 nm. The absorbance curve throughout the range 210400 nm should be smooth and without extraneous impurity peaks. A standard 1.00 cm cell is used, and pure water is used as the reference. Other ACS test methods can be found in Reference 61. Methods for methanol purification, especially the removal of water and... 

The residue, obtained from a chloroform extract of beer or upon boiling colupulone in aqueous buffer pH 5.4, is separated by chromatography on silica gel with ethyl acetate hexane 3 1 and ion exchange chromatography on Dowex 1X4 with 0.1% and 0.5% acetic acid, respectively, in aqueous 80% methanol. Purification is by... 

---