Furfural purification

Figure 41. Furfural Purification Plant for a Feed Rate of 3200 kg/h.

It was not until the twentieth century that furfural became important commercially. The Quaker Oats Company, in the process of looking for new and better uses for oat hulls found that acid hydrolysis resulted in the formation of furfural, and was able to develop an economical process for isolation and purification. In 1922 Quaker announced the availability of several tons per month. The first large-scale appHcation was as a solvent for the purification of wood rosin. Since then, a number of furfural plants have been built world-wide for the production of furfural and downstream products. Some plants produce as Httie as a few metric tons per year, the larger ones manufacture in excess of 20,000 metric tons. 

The rotating-disk contactor (RDC), developed in the Netherlands (158) in 1951, uses the shearing action of a rapidly rotating disk to interdisperse the phases (Eig. 15b). These contactors have been used widely throughout the world, particularly in the petrochemical industry for furfural [98-01-1] and SO2 extraction, propane deasphalting, sulfolane [126-33-0] extraction for separation of aromatics, and caprolactam (qv) [105-60-2] purification. Columns up to 4.27 m in diameter are in service. An extensive study (159) has provided an excellent theoretical framework for scale-up. A design manual has also been compiled (160). Detailed descriptions and design criteria for the RDC may also be found (161). 

These precursors are prepared by reaction of fuming nitric acid in excess acetic anhydride at low temperatures with 2-furancarboxaldehyde [98-01-1] (furfural) or its diacetate (16) followed by treatment of an intermediate 2-acetoxy-2,5-dihydrofuran [63848-92-0] with pyridine (17). This process has been improved by the use of concentrated nitric acid (18,19), as well as catalytic amounts of phosphoms pentoxide, trichloride, and oxychloride (20), and sulfuric acid (21). Orthophosphoric acid, -toluenesulfonic acid, arsenic acid, boric acid, and stibonic acid, among others are useful additives for the nitration of furfural with acetyl nitrate. Hydrolysis of 5-nitro-2-furancarboxyaldehyde diacetate [92-55-7] with aqueous mineral acids provides the aldehyde which is suitable for use without additional purification. 

The largest use of NMP is in extraction of aromatics from lube oils. In this appHcation, it has been replacing phenol and, to some extent, furfural. Other petrochemical uses involve separation and recovery of aromatics from mixed feedstocks recovery and purification of acetylenes, olefins, and diolefins removal of sulfur compounds from natural and refinery gases and dehydration of natural gas. 

Separation and Purification. Separation and purification of butadiene from other components is dominated commercially by the extractive distillation process. The most commonly used solvents are acetonitrile and dimethylformarnide. Dimethylacetamide, furfural, and... 

Furfural is a colourless liquid which darkens in air and has a boiling point of 161.7°C at atmospheric pressure. Its principal uses are as a selective solvent used in such operations as the purification of wood resin and in the extraction of butadiene from other refinery gases. It is also used in the manufacture of phenol-furfural resins and as a raw material for the nylons. The material will resinify in the presence of acids but the product has little commercial value. 

Pure xylan is not employed in industry. but crude xylan or pentosans are of industrial importance. Xylan has been proposed as a textile size but is not employed as yet for this purpose.130 Perhaps the largest use of pentosans is in their conversion to furfural, which has many applications and serves as the source of other furan derivatives. At the present time, large quantities of furfural are used in the extractive purification of petroleum products, and recently a large plant has been constructed to convert furfural by a series of reactions to adipic acid and hexamethylene-diamine, basic ingredients in the synthesis of nylon. In commercial furfural manufacture, rough ground corn cobs are subjected to steam distillation in the presence of hydrochloric acid. As mentioned above, direct preferential hydrolysis of the pentosan in cobs or other pentosan-bearing products could be used for the commercial manufacture of D-xylose. 

This work also suggests other research and development directions needed to bring the price of ethanol down to an automotive fuel level. We need a lower capital cost hydrolysis process which can produce a concentrated sugar solution. We also need a fermentation process adaptable to concentrated sugar solutions to lower alcohol purification costs. Finally we need to recover and include by-product values - lignin, furfural, acids, methanol, etc. -in our income. 

Practical grade furfural from Fluka Chemical Corporation or Aldrich Chemical Company, Inc. was used without any purification. Very dark furfural can be used, but It foams at the beginning of the reaction and leads to lower yields. 

Recovery experiments were conducted with the following standards, which were used as received without further purification 5-chlorouracil (Calbiochem), furfural (Aldrich), crotonaldehyde (Aldrich), caffeine (Aldrich), isophorone (Aldrich), 2,4-dichlorophenol (Aldrich), anthraquinone (Aldrich), biphenyl (Ultra Scientific), 2,4 -dichlorobiphenyl (Ultra Scientific), 2,6-bis(l,l-dimethylethyl)-4-methylphenol (Aldrich), 2,2, 5,5 -tetrachlorobiphenyl (Ultra Scientific), benzo[e]pyrene (Aldrich), bis(2-ethylhexyl) phthalate (Scientific Polymer Products), 4-methyl-2-pentanone (Aldrich), quinoline (Kodak), 1-chloro-dodecane (Eastman), stearic acid (Kodak), quinaldic acid (Aldrich), trimesic acid (Aldrich), glucose (Aldrich), glycine (Aldrich), and chloroform (Burdick and Jackson). 

Furan-2-carbaldehyde (furfural) is widely used in the vegetable oil, plastics, rubber and petroleum industries as well as being a versatile starting material for furan syntheses. It is the major source of commercial furans. It is used to extract unsaturated hydrocarbons from hydrocarbon mixtures, a process important in the purification of petroleum and vegetable oils. The chemistry of furfural has been extensively studied because of its industrial importance and availability. 

Reactive extraction uses liquid ion exchangers that promote a selective reaction or separation. The solutes are very often ionic species (metal ions or organic/inorganic acids) or intermediates (furfural phenols, etc.), and the extraction chemistry is discussed elsewhere (11-13). Reactive extraction can be used for separation/ purification or enrichment or conversion of salts (14). A 2001 review on reactive phase equilibria, kinetics, and mass transfer and apparative techniques is given in Ref. 8. Reactive extraction equipment is discussed in detail in Ref. 15, and recent advances are given in Ref. 16. 

The second distillation column has 30 trays, with the feed on tray 15. It delivers 26 730kg/h distillate where the concentration of ethanol is 92.5% (weight). The reflux ratio is 2. The distillate is free of furfural, the ethanol recovery being 99.5%. The bottoms are mixed with the bottoms of the first column and sent to water purification. 

The recovery and purification of furfural from aqueous effluents by high-pressure extraction is of technical interest. Alternative extraction tests with supercritical carbon dioxide were carried out [1,2]. Further research [3-5] led to the conclusion that carbon dioxide is a good alternative to organic solvents with comparable and even better extraction results. For all these experiments the system furfural - water without acetic acid was used. 

Phillips was the first to practise extractive distillation on the industrial scale around 1940, using furfural as the solvent A number of improvements were made in the 1960s, The process has a single extraction regeneration step and a purification step. 

To minimize polymerization losses, the purification of furfural must be carried out at greatly reduced pressure, as in the case of dehydrating FU. The separation process is shown schematically in Figure 41. The raw FU is fed into the sump of a rectification column 1 energized by a reboiler 2. The head vapor stream of this column is liquefied in a condenser 3, a portion of the condensate being used as reflux while the remainder is collected in a buffer... 

In this context, it must be noted that it would be unreasonable to use purified FU to make furfuryl alcohol as essentially all of the furfuryl alcohol is used to make foundry resins, where any 5-methyl furfural, hydrogenated to 5-methyl furfuryl alcohol, does not matter at all, and may in fact be beneficial. Thus, only FU used as FU, for instance in extraction processes, is a candidate for the given purification process. For most FU manufacturers, this is only 35 percent of their production. 

Method of purification Extractive distillation in the presence of furfural, absorption in aqueous cuprous ammonium acetate, or use of acetonitrile. 

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