Cellulose continuous methods

The two procedures primarily used for continuous nitration are the semicontinuous method developed by Bofors-Nobel Chematur of Sweden and the continuous method of Hercules Powder Co. in the United States. The latter process, which uses a multiple cascade system for nitration and a continuous wringing operation, increases safety, reduces the personnel involved, provides a substantial reduction in pollutants, and increases the uniformity of the product. The cellulose is automatically and continuously fed into the first of a series of pots at a controlled rate. It falls into the slurry of acid and nitrocellulose and is submerged immediately by a turbine-type agitator. The acid is deflvered to the pots from tanks at a rate controlled by appropriate instmmentation based on the desired acid to cellulose ratio. The slurry flows successively by gravity from the first to the last of the nitration vessels through under- and overflow weirs to ensure adequate retention time during nitration. The overflow from the last pot is fully nitrated cellulose. 

Most cotton is bleached with peroxide, by far the greater proportion by continuous methods. Synthetic fibres seldom require bleaching, but where it is necessary either peroxide or chlorite bleaches are recommended. Most regenerated cellulosic fabrics are only bleached... 

The continuous method of nitration is particularly useful when the rate of nitration is rapid (such as in case of manufg NG, NGc, or PETN) and an overheating and expln might take place with the batch process. Nitration of cellulose, on the other hand, does not proceed very rapidly (unless mixed acid contains phosphoric or glacial... 

Continuous methods have also been developed for manuf of expls other than NG. As examples may be cited nitration plants for benzene (Refs 5 6a) aromatic hydrocarbons other than benz (Refs 7, 13 16) PE (Refs 17, 19, 21, 21b 22) DEG (Refs 21, 22 28) various org compds (Ref 36) cellulose, starch, sugar, etc (Ref 21) methyl nitrate (Ref 23a), etc. A continuous method for manufg propellants is described in Ref 46. A continuous method for manuf of TNT by the method of Bofors was installed in 1955 at the Fabrica Naval de Explosivos, Azul, Argentina (Ref 34a) Description of Some Continuous Methods for Manufacturing Explosives. 

Kramer, A. and Schneider-Mergener, J. (1998) Synthesis and application of peptide libraries bound to continuous cellulose membranes. Methods Mol. Biol. 87, 25-39. 

The mato feature of a contiguous process is that the final expl product does not remain in the app for a prolonged period of rime and the quantity accumulated at any period of time is much smaller than that in the batch process. The large quantity of expl material accumulated in a batch process, especially at the end of exothermic nitration,presents a serious safety hazard which is more or less absent in current continuous processes The continuous method of nitration is particularly useful when the rate of nitration is rapid (such as in case of manufg NG, NGc, or PETN) and an overheating and expln might take place with the batch process. Nitration of cellulose, on the other hand, does not proceed very rapidly (unless mixed acid contains phosphoric or glacial... 

Finishing wood cellulose Other sources of cellulose Drying cellulose before nitration Industrial nitration of cellulose Mixed acids Nitration m pots Centrifugal nitration Thomsons method Nitration with mechanical stirring German method Continuous methods of nitration Literature... 

Nevertheless wood cellulose has a lower molecular weiglit than cotton cellulose. which explains the lower molecular weight of nitrocellulose from wood. Some attempts have been made to produce a higher quality nitrocellulose from wood by carrying out the nitration in two stages, for example [9) but this technique did not seem to find a wider application although the semi-continuous method of nitration of Bofors-Nobel-Chematur (see p. 346, Fig. 48) includes the nitration in two stages ... 

As pointed out in Vol. 11, p. 391 numerous attempts have been made introduce continuous methods of cellulose nitration. In addition to those me tioned in Vol. II. the following continuous methods were reported by Iliatl ar Rebel [2] Plunkett [22, Plunkett and McMillan [23], Reinhardt 24, Kai sey (25) described a continuous method with nitric-phosphoric acid mixture and Bergman [26] - nitration of powdered cellulose. Diels and Orth (27) us. spent acid for the first step of nitration followed by the second with fresh mix-acid. 

Diagram of Continuous Method of Hercules Powder Co. Ind. 32). A continuous fully automatic nitrating method is show n in Fig. 50. Dried cellulose and mixed nitrating add are introduced continuously to a nitration. A suspension of nitrocellulose in the acid enters a centrifuge. Tlic centrifuge is the essential part of the system. It is divided into zones and nitrocellulose is advanced from one zone to another. In the first zone most of the original acid from the nitration is removed. In each of the succeeding zones the acid in nitro-... 

Blends of nylon and cellulosic fibres may be bleached with either H O, or NaClOj, using batchwise or continuous method [145, 146]. 

Methods for increasing the accessibility and, hence, the reactivity of cellulose continue to receive attention. These methods are based on the fact that swelling agents can bring about some decrystallization of the structure and this, in turn, increases the extent by which it can be penetrated by chemical reagents. 

Recent Developments. A considerable amount of cellulose acetate is manufactured by the batch process, as described previously. In order to reduce production costs, efforts have been made to develop a continuous process that includes continuous activation, acetylation, hydrolysis, and precipitation. In this process, the reaction mixture, ie, cellulose, anhydride, catalyst, and solvent, pass continuously through a number of successive reaction zones, each of which is agitated (92,93). In a similar process, the reaction mass is passed through tubular zones in which the mixture is forced through screens of successively small openings to homogenize the mixture effectively (94). Other similar methods for continuous acetylation of cellulose have been described (95,96). 

To develop a continuous process, the immobilisation of aminoacylase of Aspergillus oryzae by a variety of methods was studied, for example ionic binding to DEAE-Sephadex, covalent binding to iodo-acetyl cellulose and entrapment in polyacrylamide gel. Ionic binding to DEAE-Sephadex was chosen because the method of preparation was easy, activity was high and stable, and regeneration was possible. 

Figure 2. CM-cellulose chromatography of pectolytic enzymes. The activity peaks of the flow-through of a DEAE-cellulose chromatography was applied to a CM-cellulose column. The column was eluted with a NaCl (0-0.5M) continuous gradient at a flow rate of 34 ml/h. 10 ml fractions were collected and assayed for pectolytic activities Symbols (0) pectate lyase ( ) polygalacturonase (reducing sugar-releasing activity) (x) protein. Other details in Methods.

The vat dyes section of the Colour Index incorporates a subgroup called solubilised vat dyes. These are sodium salts of sulphuric acid esters of the parent leuco vat dyes, such as Cl Solubilised Vat Blue 6 (1.50). In contrast to the leuco compounds, the vat leuco esters dissolve readily in water at neutral pH. They have relatively low substantivity for cellulose and thus have been used mainly in continuous dyeing and printing. In the presence of an oxidant in mineral acid solution (sodium nitrite and sulphuric acid, for example) the leuco ester is rapidly decomposed and the insoluble vat dye regenerated. Thus application of a vat leuco ester represents a simpler (but more costly and less versatile) alternative to conventional dyeing methods via the alkaline leuco compound. 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

The acid-oxidant method is based on the idea that the hydrolysis of cellulose might be continuously determined from the rate of carbon dioxide evolution. Since, under controlled conditions, the rate of evolution of carbon dioxide is proportional to glucose concentration, it should be possible to follow the course of cellulose hydrolysis by means of the rate of carbon dioxide evolution provided that the sole final product of hydrolysis of cellulose is glucose. The latter assumption appears to be justified where the sample is reasonably pure. 

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