Furfural polymers

All reactors have a diameter of 1.5 m and a height of 8 m. Rather oddly, they are made of mild steel and have an enormous wall thickness of 50 mm to sustain the corrosion. There is no lining, but the inside wall gets covered, and somewhat protected, by furfural polymers naturally formed in the process. The raw material usually consists of ground corncobs from which the fines were removed by sifting. The particle size is between 20 and 30 mm, and the initial moisture content of the raw material is in the order of 15 percent. 

In 1992, a rather unusual furfural plant was built. With a front end according to the AGRIFURANE process described in chapter 10.2, the back end was designed as shown in Figure 112. The filtered reactor condensate containing 5 % furfural, 1.7 % acetic acid, 0.17 % formic acid, and various low boilers was introduced into an extraction tower 1 fed with chloroform at the top. On the way downwards, the heavy chloroform (density 1.498 g/cc at room temperature) picked up the furfural, and in view of the poor solubility of chloroform in water, it formed a chloroform/furfural extract at the bottom. This extract entered a distillation column 2 removing the chloroform as the head fraction. From a buffer tank 3, this chloroform was recycled to the extraction tower 1. The sump fraction of the distillation column 2 consisted of furfural, polymers, waxes, and some low boilers. This fraction was introduced into a distillation column 4, which yielded a head fraction of low boilers, a side stream of furfural, and a sump fraction of polymers and waxes. 

If formaldehyde is replaced by furfural, the furfural - phenol polymer (U.S.A. Durite) results. The above polymers are largely used for moulding purposes. 

Tetrahydrofuran (3) is produced commercially from furfural by decarbonylation followed by hydrogenation it is also produced by several different methods from other raw materials. A complete discussion of tetrahydrofuran is found under Ethers. Polymers of tetrahydrofuran are covered under the general topic. Polyethers. Several other compounds containing the tetrahydrofuran ring, which are most readily produced from furfural, are discussed here. 

Furfural can be classified as a reactive solvent. It resiniftes in the presence of strong acid the reaction is accelerated by heat. Furfural is an excellent solvent for many organic materials, especially resins and polymers. On catalyzation and curing of such a solution, a hard rigid matrix results, which does not soften on heating and is not affected by most solvents and corrosive chemicals. 

Furfural is a resin former under the influence of strong acid. It will self-resinify as well as form copolymer resins with furfuryl alcohol, phenoHc compounds, or convertible resins of these. Conditions of polymerization, whether aqueous or anhydrous, inert or oxygen atmosphere, all affect the composition of the polymer. Numerous patents have issued relating to polymerization and to appHcations. Although the resins exhibit a degree of britdeness, they have many outstanding properties a number of appHcations are discussed under "Uses."... 

Several early interpretations of the polymerization mechanism have been proposed (1,17,29—31). Because of the complexity of this polymerization and insoluble character of the products, key intermediates have not ordinarily been isolated, nor have the products been characterized. Later work, however, on the resinification of furfural (32,33) has provided a new insight on the polymerization mechanism, particularly with respect to thermal reaction at 100—250°C in the absence of air. Based on the isolation and characterization of two intermediate products (9) and (10), stmcture (11) was proposed for the final resin. This work also explains the color produced during resinification, which always is a characteristic of the final polymer (33). The resinification chemistry is discussed in a recent review (5). 

The flash point of furfural is 143°F by Tag Closed Cup. Because of its chemical reactivity, furfural should be kept away from strong acids, alkaHes or strong oxidi2ing chemicals. When furfural is stored for long periods in contact with air, there is a gradual darkening of color, increase in acidity, and formation of a soluble polymer. 

Furfural reacts with ketones to form strong, crosslinked resins of technical interest in the former Soviet Union the U.S. Air Force has also shown some interest (42,43). The so-called furfurylidene acetone monomer, a mixture of 2-furfurylidene methyl ketone [623-15-4] (1 )> bis-(2-furfurylidene) ketone [886-77-1] (14), mesityl oxide, and other oligomers, is obtained by condensation of furfural and acetone under basic conditions (44,45). Treatment of the "monomer" with an acidic catalyst leads initially to polymer of low molecular weight and ultimately to cross-linked, black, insoluble, heat-resistant resin (46). 

Furfural—acetone resins have been used to form resin-aggregate mixtures referred to as organic concretes. Despite the reportedly excellent properties, there has been virtually no commercial use of such resins outside the former Soviet Union. The stmctures and polymerization mechanisms of these furfural—aldehyde—ketone polymers are discussed in a review (6). 

Sugar is destroyed by pH extremes, and inadequate pH control can cause significant sucrose losses in sugar mills. Sucrose is one of the most acid-labile disaccharides known (27), and its hydrolysis to invert is readily catalyzed by heat and low pH prolonged exposure converts the monosaccharides to hydroxymethyl furfural, which has appHcations for synthesis of glycols, ethers, polymers, and pharmaceuticals (16,30). The molecular mechanism that occurs during acid hydrolysis operates, albeit slowly, as high as pH 8.5 (18). 

Furfural — see Furan-2-oarbaldehyde, 532 Furfuryl acetate, o -(butoxycarbonyl)-anodic oxidation, 1, 424 Furfuryi acrylate polymerization, 1, 279 Furfuryl alcohol configuration, 4, 544 2-Furfuryl alcohol polyoondensation, 1, 278 reactions, 4, 70-71 Furfuryl alcohol, dihydro-pyran-4-one synthesis from, 3, 815 Furfuryl alcohol, tetrahydro-polymers, 1, 276 rearrangement, 3, 773 Furfuryl chloride reactions... 

Group of plastics composed of resins in which the furane ring is an integral portion of the polymer chain made from polymerization or polyconden-sation of furfural, furfural alcohol and other compounds containing furane rings also formed by reaction of furane compounds with an equal weight or less of other compounds. 

Euran Furan resins are thermosetting polymers derived from furfuryl alcohol and Furfural. The cure must be carefully controlled to avoid the formation of blisters and delaminations. To obtain optimum strength and corrosion resistance, furan composites must undergo a postcure schedule at carefully selected temperatures depending upon the laminate thickness. Equipment made with furan resins exhibits excellent resistance to solvents and combinations of acids and solvents. These resins are not for use in strong oxidizing environments. 

Tetra-n-butylammonium cyanide is a better catalyst for benzoin condensation reactions than is sodium cyanide, and >70% yields are obtained under mild conditions [63, 64] tetra-ethylammonium cyanide is less effective. Polymer-supported ammonium catalysts have also been used to promote the benzoin reaction and, although yields are only moderate (40-60%), the convenience of removal of the catalyst is an advantage. Use of chiral ammonium groups produces an enantiomeric excess of chiral products from the condensation of benzaldehyde, but furfural tends to produce a racemate [65]. 

A probable pathway for the degradation of hemicelluloses via free-radical intermediates has been proposed by Fengel and Wegener (1989) and is shown in Figure 5.1. Hemicellulose polymers are depolymerized to form oligosaccharides and monosaccharides, which are dehydrated to form furfural (pentoses) and hydroxymethyl furfural (hexoses). 

Recent work on the synthesis, structure and some properties of macromolecules bearing furan rings is discussed. Two basic sources of monomers are considered, viz. furfural for monomers apt to undergo chain polymerization and hydroxymethylfurfural for monomers suitable for step polymerization.Within the first context, free radical, catiomc and anionic systems are reviewed and the peculiarities arising from the presence of furan moieties in the monomer and/or the polymer examined in detail. As for the second context, the polymers considered are polyesters, polyethers, polyamides and polyurethanes. Finally, the chemical modification of aU these oligomers, polymers and copolymers is envisaged on the basis of the unique reactivity of the furan heterocycle. 

Uses. Solvent refining of lubricating oils, resins, and other organic materials as insecticide, fungicide, germicide an intermediate for tetrahydrofuran, furfural alcohol, phenolic and furan polymers... 

Hydroxymethyl furfural. 2,5-diformylfuran (DFF) is a furan derivative that has many uses, including use as a polymer building block. By utilizing a platinum catalyst supported on carbon, and running the reaction in water at high temperatures, DFF is produced as the major product in neutral solution. If low temperatures and high pH are employed, 2,5-furandicarboxylic acid results. 

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). 

The most import uni cyclic ethers arc (he furan compounds Furfural is manufactured by treating pentosan with sulfuric acid and steam stripping mil the furfural a n is formed The sources of pentosan arc such agricultural products uv comet tbs. oat hulls, and hagavtc Furfural is used to produce furan and tetrahydro furan fTHF) These products are used as organic intermediates, extraction solvent, polymer solvents, and in polyurethane applications... 

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