Paraformaldehyde, formaldehyde polymer Production

The most common grade of formaldehyde is known as formalin (37% formaldehyde). Polymer precipitation is usually inhibited by the addition of 7-15% methanol. The methanol does not interfere in resin production but is removed in the stripping operation. For economic reasons 44-50% uninhibited formaldehyde is used in commercial practice to save costs in stripping and to allow larger batch operations to be carried out. Occasionally paraformaldehyde is also used. The latter contains 91% formaldehyde and 9% water. 

Meth) i formate is also reported among the products obtained on heating formaldehyde polymers, such as paraformaldehyde, aloneand in the presence of sulfuric acid . 

Formaldehyde. Pure formaldehyde, CH2O, is a colorless, pungent smelling reactive gas (see Formaldehyde). The commercial product is handled either as soHd polymer, paraformaldehyde (13), or in aqueous or alcohoHc solutions. Marketed under the trade name Formcel, solutions in methanol, / -butanol, and isobutyl alcohol, made by Hoechst-Celanese, are widely used for making alcohol-modified urea and melamine resins for surface coatings and treating textiles. 

When catalyzed by acids, low molecular weight aldehydes add to each other to give cyclic acetals, the most common product being the trimer. The cyclic trimer of formaldehyde is called trioxane, and that of acetaldehyde is known as paraldehyde. Under certain conditions, it is possible to get tetramers or dimers. Aldehydes can also polymerize to linear polymers, but here a small amount of water is required to form hemiacetal groups at the ends of the chains. The linear polymer formed from formaldehyde is called paraformaldehyde. Since trimers and polymers of aldehydes are acetals, they are stable to bases but can be hydrolyzed by acids. Because formaldehyde and acetaldehyde have low boiling points, it is often convenient to use them in the form of their trimers or polymers. 

The formaldehyde process is an air oxidation of methanol, CH3OH, which has water as a by-product. Formaldehyde is a gas at room temperature, but is usually handled either as a water solution called formalin or as polymers called paraformaldehyde and trioxane. Both are readily converted back ro formaldehyde. Some uses of formaldehyde are the manufacture of polymer resins and as a germicide. 

Under the standard conditions formaldehyde is gaseous. However, its molecules can interact with each other by a mechanism similar to nucleophilic attack. The oxygen of the carbonyl group behaves as the nucleophilic atom (see the next scheme). The product of such a reaction is a polymer, the white powder called paraformaldehyde. Hence, formaldehyde can be provided either in the form of the water solution formol or as paraformaldehyde powder. Pure formaldehyde gas for use in chemical reactions can be prepared by heating paraformaldehyde under vacuum. Similarly, the molecules of acetaldehyde can condense into cyclic trimers giving the substance known as paraldehyde. 

Formaldehyde f6r- mal-d9- hld, fer- [ISV form- + aldehyde] (1872) (formic aldehyde, methanal, oxymethylene) n. HCHO. A colorless gas with a pungent, suffocating odor, obtained most commonly by the oxidation of methanol or low-boiling petroleum gases such as methane, ethane, etc. The gas is difficult to handle, so it is sold commercially in the form of aqueous solutions (formalin), solvent solutions, as its oligomer, paraformaldehyde, and as the cyclic trimer, 1,3,5-trioxane (a-trioxym-ethyl-ene). High-molecular-weight, commercial polymers of formaldehyde are called poly-oxymethylene or acetal resin. Formaldehyde is also used in the production of other resins such as phenolic resin (phenol-formaldehyde) and amino resin (urea formaldehyde). Syn methylene oxide, methanal. See formalin. 

In the preparation of high molecular weight polyformaldehyde the initial operation consists of the production of pure formaldehyde, free from low molecular weight polymers and other hydroxy compounds which cause chain transfer and termination. In a typical process [4, 5] potassium hydroxide-precipitated paraformaldehyde (degree of polymerization approximately 200) is carefully washed with water and dried for several hours in vacuo at 80°C. The dried polymer is then decomposed in nitrogen at 150—160°C the product is passed through several traps at —15°C to remove water, glycols, and other... 

As a preservative for industrial fluids, formaldehyde (formalin and paraformaldehyde) is preferably used in cosmetic products and in polymer dispersions (natural and synthetic latex) often in combination with other microbicides. Formaldehyde is listed in the EC list of preservatives allowed for the in-can protection of cosmetics (maximum authorized concentration 0.2%, except for products for oral hygiene 0.1%, prohibited in aerosol dispensers). Percentage of use in US cosmetic formulations 0.11% paraformaldehyde. Oil, fat and wax emulsions, starch and dextrine glues, adhesive dispersions, pigment and filler slurries, thickening solutions and other aqueous formulations containing no proteins can be preserved by the addition of formaldehyde, too in order to... 

Paraformaldehyde Manufacture. In general, commercial paraformalde-hj de is prepared from aqueous formaldehyde solutions by processes involving distillation and concentration to a point at which solidification or precipitation of polymer takes place. The process is so controlled that a product contaimng 95 per cent or more of formaldehyde is obtained. 

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