Methanol recovery

The oxidation reactor effluent and methanol ate sent to the esterification reactor, which operates at up to 250°C and a pressure sufficient to maintain the Hquid phase. This latter is about 2500 kPa (25 atm). The oxidation products are converted to methyl -toluate and dimethyl terephthalate without a catalyst. Excess methanol is suppHed, and steam and vaporized methanol ate removed and enter a methanol recovery column. The esterification products flow to a cmde ester column, which separates the toluate from the terephthalate. The overhead stream of methyl -toluate is returned to the oxidation reactor, and the bottoms stream of dimethyl terephthalate goes to a primary distillation. The distillate is dissolved in methanol, crystallized, and sohd dimethyl terephthalate is recovered. The dimethyl terephthalate can then be either recrystallized or distilled to yield the highly pure material needed for the polyesterification reaction. 

Generally, an alcohol or one of the glycols—usually methanol, ethylene glycol (EG), or diethylene glycol (DEG)—is injected as an inhibitor. All may be recovered and recirculated, but the economics of methanol recovery will not be favorable in most cases. 

Purge from the water recycle stream, to waste treatment, 10 per cent of the flow leaving the methanol recovery column. 

MRU [Methanol recovery unit] A process for removing methanol from the unreacted components from the synthesis of methyl /-butyl ether. It uses selective adsorption on multiple beds of a zeolite such as 4A. Developed by Union Carbide Corporation and now licensed by UOP as of 1992, eight units had been licensed. See also ORU. 

The most commonly used solvent for the extraction of both alkylphenols and APEO is methanol [15-19]. If sodium hydroxide (20%, w/w) is added to the methanol, recoveries may increase by 25% [16,20]. Nonylphenoxy carboxylates (NPECs) can also be extracted using Soxhlet with methanol, but recoveries are often below 50% [19]. Only one method similar to Soxhlet has been reported for the extraction of AEOs, in which a Soxtec system with methanol is used [18]. 

One of the major advantages of the metal oxide catalyst over that of the straight metal catalyst is the elimination of the need for a methanol recovery tower. The metal oxide catalysts result in not only high yields, but also very high conversion rates. Consequently, there is no need to recover the small amounts of methanol that remain unreacted. It becomes part of the aqueous formaldehyde solution and serves as a stabilizer for the system. By-products are CO, CO2, dimethyl ether, and formic acid. The process yields (the percent of the methanol that ends up in formaldehyde) are 95-98%. 

Continued methanol injection could be done at a cost of approximately 1.50-2.00 per gallon during the 1996-1997 winter. Since methanol recovery is problematic,... 

M.S.K. Chen, G.S. Markiewicz and K.G. Venugopal, Development of Membrane Pervaporation TRIM Process for Methanol Recovery from CH3OII/MTBE/C4 Mixtures, in Membrane Separations in Chemical Engineering, AIChE Symposium Series Number 272, A.E. Fouda, J.D. Hazlett, T. Matsuura and J. Johnson (eds), AIChE, New York, NY, p. 85 (1989). 

Pyrazines were eluted from the Sep-Pak with 2 x 1 ml. aliquots of methanol. Recoveries of wine spiked with methoxypyrazines in the ppb ranged from 10 to 63%. While recoveries appear low, they were reproducible and quite suitable to address the problem being investigated. 

The above solution makes sense from the economic viewpoint, because the methyl ester is by far the most demanded, while 2-ethyl-hexanol is a cheap alcohol, in general a waste. The flowsheet in Figure 8.2 is still valid, in which the heavy alcohol is fed on the top stage, as an entrainer. Figure 8.15 shows the liquid concentration, reaction rate and temperature profiles. It can be seen that 2-ethyl-hexanol indeed plays its double role. The concentration of methanol in the top can be maintained at the minimum, such that there is no need for additional columns for methanol recovery and recycle. Note also that the operation takes place at low pressure (1.5 bar), in contrast with 6-12 bar and vacuum with individual light and heavy alcohols. 

After pH adjustment the crude glycerol is submitted to methanol recovery by vacuum distillation. The bottom product is usually a glycerol-water solution of about 50%. Its concentration can be increased up to 85% by vacuum evaporation. The water is recycled to the washing step. Normally, the glycerol is shipped to a specialized refiner, where the purity can be increased further to 99.5 and 99.7% by ion-exchange techniques and vacuum distillation. 

In the DME column (4), DME is separated from the top and condensed. The DME is cooled in a chilling unit (5) and stored in a DME tank (6) as a product. Water and methanol are discharged from the bottom and fed to a methanol column (1) for methanol recovery. The purified methanol from this column is recycled to the reactor after mixing with feedstock methanol. 

MTBE is recovered as the bottoms product of the distillation unit. The methanol-rich C4 distillate is sent to the methanol-recovery section. Water is used to extract excess methanol and recycle it back to process. The isobutene-depleted C4 stream may be sent to a raffinate stripper or to a molsieve-based unit to remove other oxygenates such as DME, MTBE, methanol and tert-butanol. 

Methanol recovery (8) improves efficiency and extends catalyst life by allowing greater methanol slip exit from the converter. Addition of a methanol-recovery column to existing plants can help to increase production rates. 

DMA and TMA. Product ratios can be varied to maximize MMA, DMA, or TMA production. The correct selection of the N/C ratio and recycling of amines produces the desired product mix. Most of the exothermic reaction heat is recovered in feed preheating (3). The reactor products are sent to a separation system where firstly ammonia (4) is separated and recycled to the reaction system. Water from the dehydration column (6) is used in extractive distillation (5) to break the TMA azeotropes and produce pure anhydrous TMA. The product column (7) separates the water-free amines into pure anhydrous MMA and DMA. Methanol recovery (8) improves efficiency and extends catalyst life by allowing greater methanol slip exit from the converter. Addition of a methanol-recovery column to existing plants can help to increase production rates. 

In this instance distillation in a series of columns is necessary for methanol recovery [5]. 

Fig. 27 Methanol recovery by azeotrope breaking—example methanol/ethyl acetate. (View this art in color at www.

Figure 3.33 Flowsheet of the CDTech MTBE/ETBE/TAME process. (1) boiling point reactor, (2) CD column, (3) extraction column, (4) methanol recovery column. Source [61].

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