Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B1/00—Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/05—Derivatives containing elements other than carbon, hydrogen, oxygen, halogens or sulfur
  • C08B15/06—Derivatives containing elements other than carbon, hydrogen, oxygen, halogens or sulfur containing nitrogen, e.g. carbamates

Definitions

• the invention relates to a process for the production of cellulose carbamate and a process for the activation of a mixture containing cellulose and urea, which is intended for the production of carbamate. It also relates to an activated cellulose / urea mixture obtained hereafter.
• urea When urea is heated to its melting point or higher temperature, it begins to decompose to form isocyanic acid and ammonia. Isocyanic acid is not a particularly stable compound and tends to trimerize to isocyanuric acid. In addition, isocyanic acid tends to react with urea to form biuret. Isocyanic acid reacts with cellulose, producing an alkali-soluble cellulose compound, so-called cellulose carbamate. The reaction can be represented as follows:
• cellulose carbamate After washing, cellulose carbamate can be dried and stored for a long time, or it can be immediately dissolved in an alkali solution. From this solution e.g. Cellulose carbamate fibers can be produced by spinning, similar to viscose production.
• a newer process according to DE 42 42 437 AI converts cellulose with excess urea in an inert liquid organic reaction medium at a temperature of 130 to 160 ° C.
• the reaction carrier is then washed out of the reaction mixture and the latter with water.
• this is how that a) the cellulose is mixed with aqueous urea solution, b) the water content of the mixture is replaced by the organic reaction carrier, c) the reaction is carried out with the formation or supply of an inert vaporous or gaseous medium which is removed from the reaction zone.
• the inert vaporous or gaseous medium contains ammonia formed during the reaction.
• the organic reaction carrier in the reaction mixture is then exchanged for an aqueous urea solution.
• the cellulose carbamate formed is separated from the urea solution and washed. It is preferred that the cellulose have a degree of polymerization DP of 200 to 500, preferably 300 to 400.
• the cellulose is preferably mixed with a urea solution having a concentration of 20 to 60% by weight.
• Inert liquid organic reaction carriers used are aliphatic or aromatic hydrocarbons, preferably alkylaromatic hydrocarbons or a mixture of such hydrocarbons with boiling points in the range from 100 to 185 ° C., mono-, di- or trialkylbenzene or mixtures thereof being very particularly preferably used.
• the inert vaporous medium referred to is the reaction carrier vapor formed by boiling the reaction carrier.
• the reaction is preferably carried out in the range from about 135 to 150 ° C.
• the medium of the remaining inert organic reaction medium must be converted to an aqueous medium, which is done by adding water, in particular aqueous urea solution, and distilling off the inert organic reaction medium azeotropically. Due to the poor penetration of the cellulose in the initial phase with the aqueous urea solution, a largely inhomogeneous process product ultimately arises, with the result that difficulties arise in the subsequent dissolution in aqueous sodium hydroxide solution before spinning into an acidic precipitation medium.
• the cellulose is preferably treated with a liquid ammonia-urea solution at a temperature below -33 ° C. However, a higher temperature can also be selected if the cellulose with the liquid ammonia-urea solution under pressure at a temperature higher than the boiling point of the ammonia is treated. Ammonia is preferably removed by means of evaporation. According to EP 0 057 105, the reaction temperature should preferably be between about 110 and 150 ° C. The alkali-soluble cellulose carbamate product obtained is preferably finally washed with liquid ammonia at a temperature of about -40 ° C. to + 30 ° C.
• EP 0 057 105 A particular advantage is pointed out in EP 0 057 105 that, unlike the above process according to DE 42 42 437 A1, the urea is largely distributed in the crystalline structures of the cellulose starting material by the ammonia treatment shown. As a preferred framework, it is emphasized in EP 0 057 105 that the loading of the cellulose with the urea-containing liquid ammonia should be between about -40 to about + 10 ° C. Although, as can be seen, considerable advantages can be achieved with this method according to EP 0 057 105 with regard to activation and distribution of the urea, this method is nevertheless unsatisfactory from various points of view.
• the invention has for its object to develop the known methods so that the disadvantages of the prior art are largely eliminated.
• a highly reactive mixture of cellulose and urea should be proposed in an economical manner, in particular with regard to the expenditure of energy and materials.
• An energy-intensive solvent exchange should not be necessary.
• this object is achieved by a method in which
• the invention further relates to a process for activating a mixture containing cellulose and urea, which is intended for the production of carbamate, in which the cellulose with the liquid ammonia at an initial pressure which is higher than atmospheric pressure and at a temperature of at least about 25 ° C. in the presence of the urea is brought into contact, the amount of liquid ammonia being sufficient at least for wetting the surface of the cellulose and the volume available to the cellulose / urea / liquid ammonia system being explosively increased by lowering the pressure by at least 5 bar, the activated Cellulose / urea mixture is obtained.
• the methods according to the invention differ from the ammonia vaporization of the prior art.
• a pressure drop is usually brought about by opening a valve on an autoclave. This quickly vaporizes a small amount of the ammonia used, for example 20%, and the mass treated with liquid ammonia remains in the autoclave with the remaining ammonia.
• the remaining amount of liquid ammonia is continuously boiling, the evaporation of the ammonia takes a long time. If one speaks of "explosive" here, then this term is to be seen narrowly.
• the explosion-like increase in volume preferably takes place within a time of less than one second, in particular less than 0.5 seconds.
• the consideration is based on an incremental amount of cellulose / urea / liquid ammonia.
• the cellulose / urea mixture is preferably brought into contact with the liquid ammonia in a pressure device, and the cellulose / urea / liquid ammonia system is expanded by transferring it to an explosion chamber with a larger volume than the pressure device.
• the cellulose is brought into contact with the liquid ammonia and the urea dissolved therein in a pressure device, and the cellulose / urea / liquid ammonia system is expanded by transferring it into an explosion space with a larger volume than the pressure device.
• the outlet pressure is preferably between about 5 and 46 bar, in particular between about 25 and 30 bar.
• the minimum pressure drop of 5 bar is critical. If the value falls below this, the object of the invention is not achieved, ie the desirable properties of the process product are not achieved.
• the upper limit of about 46 bar does not lead to further advantages if it is exceeded. Its setting requires a relatively large expenditure on equipment, so that a further increase is not practical under practical considerations.
• the temperature correlates with the specified pressure frame from approximately 25 to 85 ° C or 55 to 65 ° C.
• the output pressure in the polysaccharide / liquid ammonia system is preferably explosively reduced by at least about 10 bar and in particular about 30 bar. The explosion preferably takes place in an explosion space which is kept under vacuum. The explosion space must be chosen large enough to allow the desired defibrillation or defibrillation into the large volume.
• a sufficient amount of ammonia must be injected into the printing device so that liquid ammonia is present under the pressure or temperature conditions required according to the invention and at least the surface of the cellulose is wetted.
• 1 part by mass of cellulose preferably accounts for at least about 0.25 part by mass Parts, in particular at least about 1 part by weight and particularly preferably about 5 to 10 parts by weight, of liquid ammonia. The action of the ammonia causes the cellulose to swell at least partially.
• 10 parts by weight of cellulose usually account for at least about 2 parts by weight, preferably at least about 4 parts by weight of urea, in particular about 6 to 12 parts by weight of urea.
• a particularly suitable cellulosic starting material for carrying out the process according to the invention are chemical pulps in rolls or bales with a density of about 0.6 to 0.8 g / cm 3 .
• the cellulose used according to the invention is preferably chemically pure. It preferably contains less than 18 mass%, in particular less than 9 mass, foreign substances.
• the degree of activation that can be achieved according to the invention depends on the water content of the cellulose. A too high water content leads to insufficient activation, which is probably due to the diluting effect of the water molecules on the ammonia.
• the water content of the starting cellulose is therefore preferably less than about 12% by mass, in particular less than about 9% by mass. In particularly preferred embodiments, the water content is less than about 0.5% by mass. Since cellulose is to a certain extent hygroscopic and absorbs water during storage at ambient conditions, it may be necessary to subject the cellulose to suitable drying steps in order to maintain a low water or moisture content.
• the process according to the invention can be carried out batchwise or continuously.
• the apparatus essentially has a pressure container which can be filled with the material to be treated and a collecting or expansion container connected to it via a valve.
• the valve has a large clear opening in the open state, so that the explosion process S
• the expansion tank has a multiple volume compared to the pressure tank, for example the volume of the pressure tank is 1 1 and the volume of the expansion tank 30 1.
• the pressure tank is connected to a supply line for ammonia, optionally with the interposition of a pressure-increasing device.
• a supply line for inert gases e.g. Nitrogen.
• the process could be carried out continuously using a tubular or cylindrical, pressure-tight reactor in which cellulose, urea and liquid ammonia are brought into contact in the cylinder of the reactor and the impregnated material is transported as a plug through the reactor using a screw conveyor and is discharged intermittently through a valve or a suitable system of pressure locks into a collecting room.
• Suitable components which the person skilled in the art can readily adapt to carry out the method according to the invention are described in EP-A-329 173 and US Pat. No. 4,211,163.
• the contact time between the liquid ammonia and the other starting materials within the pressure vessel is not critical. It is usually about 20 minutes. A reasonable time frame can be set between 10 minutes and 60 minutes. A treatment of longer than about 60 minutes usually has no further technical advantage.
• the gaseous ammonia is drawn off from it, preferably condensed to liquid ammonia and then recycled back into the process.
• a residual ammonia content of about 5 to 10% by mass in the activated cellulose / urea mixture is not disturbing for the further conversion to cellulose carbamate.
• the activated mixture for the production of cellulose carbamate is heated to a reaction temperature between approximately 110 and 150 ° C., in particular a temperature of greater than approximately 130 ° C.
• the necessary reaction time is usually one hour to several hours. The heating takes place in an inert liquid organic reaction carrier.
• the activated cellulose / urea mixture is taken up in an inert liquid organic reaction carrier and heated to a temperature of more than about 110 ° C., preferably of 110 to 150 ° C., in particular of more than about 130 ° C.
• Linear organic alkanes and / or alkyl aromatic hydrocarbons, each with a boiling point of 100 to 185 ° C. at atmospheric pressure and / or 1, 2,3,4-tetrahydronaphthalene or decahydronaphthalene with a boiling point of more than 185 ° C., are suitable as organic reaction carriers.
• Xylene is particularly suitable as an inert liquid reaction medium.
• the activated mixture is suspended in a water-miscible polar organic solvent with a boiling point of about 110 to 185 ° C., in particular more than about 130 ° C., and the mixture is converted to cellulose carbamate.
• a water-miscible polar organic solvent with a boiling point of about 110 to 185 ° C., in particular more than about 130 ° C.
• N-methylpyrrolidone and / or cellosolve are suitable as organic solvents.
• the heating and the reaction between cellulose and urea are preferably carried out by boiling the inert organic reaction carrier or by passing an inert gaseous medium through, preferably at a pressure below atmospheric pressure, the NH 3 formed, together with the NH 3 remaining from the activation step, being rapidly removed is withdrawn from the reactor.
• the inert organic reaction carrier and any unreacted urea are removed from the cellulose carbamate obtained.
• the inert organic reaction carrier is preferably removed by first separating it largely mechanically, mixing the residue with an aqueous medium and removing the remaining organic reaction carrier with part of the aqueous medium by azeotropic distillation. The the unconverted 40
• the aqueous solution containing urea is removed from the cellulose carbamate by filtering.
• the inert organic reaction carrier is removed by first separating it largely mechanically and the residue with a lower alcohol, e.g. a Ci-C. alcohol.
• the lower alcohol is preferably methanol, ethanol, n-propanol, isopropanol or a mixture thereof.
• Both the inert organic reaction carrier and any unreacted urea dissolve very well in the lower alcohol.
• the washing solution consisting of alcohol, inert organic reaction carrier and optionally urea is preferably worked up by distilling off the lower alcohol from the inert organic reaction carrier and recycling the inert organic reaction carrier.
• the urea which may be present is insoluble in the inert organic reaction carrier and precipitates. He can e.g. by filtration, easily removed.
• the distilled lower alcohol is preferably condensed and likewise recycled.
• the filtered urea can also be returned to the process.
• the process according to the invention is characterized by a circulation of ammonia, inert organic reaction carrier, lower alcohol and urea.
• the cellulose carbamate obtained can be dried and stored, or else it can be immediately dissolved in alkali.
• the invention relates to an activated cellulose / urea mixture containing exploded crystalline cellulose.
• the cellulose in the mixture according to the invention has an advantageous LODP value. This is preferably between approximately 50 and 200, in particular between approximately 100 and 160 and very particularly preferably between approximately 120 to 145.
• the mentioned range of LODP values is an indication of the largely homogeneous structure of the activated according to the invention Mixture.
• the LOPD value is determined by examining the course of the heterogeneous hydrolytic degradation.
• the heterogeneous hydrolytic attack by acid is more or less limited to the surface molecules of the elementary fibrils or their aggregations and the disordered segments of the cellulose macromolecules that connect the crystallites to form fibrillar strands. For this reason, the initial rapid molecular decomposition almost stops when the DP length of the crystallites is reached.
• LOPD value Leveling-off-Degree of Polymerization
• the mixture according to the invention is in the form of fluff and is notable for a previously low density of less than about 0.2 g / cm 3 . This advantage is increased if the density of the down is less than 0.1 lg / cm 3 .
• the density is a special measure here and provides information about the extent of the explosion treatment.
• the cellulose / urea mixture according to the invention can be converted into cellulose carbamate by heating to a reaction temperature between approximately 110 and 150 ° C., in particular a temperature greater than approximately 130 ° C.
• the heating can be done dry or alternatively in an inert liquid organic reaction carrier.
• the particularly high activity in the production of cellulose carbamate is due above all to the fact that the spatial network structure of the cellulose is widened and the urea is evenly distributed therein. This leads to shorter reaction times and more homogeneous derivatization products.
• the cellulose / urea mixture activated according to the invention has an exploded crystalline cellulose content, the crystalline cellulose being a X-ray diffraction spectrum with peaks at the following diffraction angles 2 ⁇ and with the relative intensities:
• Parts of cellulose at least about 2 parts by weight, in particular about 4 parts
• the process of the present invention allows a very even distribution of the urea in the cellulose. This leads to a very homogeneous end product that is almost completely soluble in alkaline solution.
• the following processes presumably take place in the process according to the invention: At least partial swelling of the cellulose takes place under the action of the liquid ammonia. Intramolecular hydrogen bonds are released because the ammonia molecule competes with hydroxyl groups from neighboring molecules. At the same time, there is an even and finely distributed insertion of urea between the cellulose chains.
• the explosive increase in volume / decrease in pressure causes the ammonia located between the molecular chains to evaporate.
• the molecular chains, the intermolecular hydrogen bonds of which have previously been released, are torn apart. The even distribution of urea is retained. At the same time, hydrogen bonds can be formed at other points, but the crosslink density is lower than in the starting cellulose. The newly taken up room structure is fixed in this way.
• the process according to the invention for the production of cellulose carbamate is characterized in that no two-time azeotropic distillation is required to exchange the aqueous urea solution for the inert organic reaction carrier and back.
• the cellulose impregnated with urea is after Ammonia explosion, including the ammonia not removed during the explosion, is transferred directly to the inert organic reaction medium.
• the proposal according to EP 0 057 105 to remove ammonia by applying a vacuum and / or by heating means an additional expenditure of energy and a time-consuming process.
• the mixture obtained according to the invention is a favorable starting point for a further reaction under the action of heat due to the particularly high specific surface area, in that the exchange surfaces for transferring the thermal energy as a result of the high specific surface area after the explosion are several orders of magnitude greater than in the normal evaporation of ammonia carried out according to the prior art.
• This example illustrates the activation of a cellulose-urea mixture according to the invention in a batch process: 70 g more commercially available Chemical pulp with an alpha-cellulose content of about 96% in sheet form (water content about 8%) was cut into pieces measuring approximately 1.3 ⁇ 1.3 cm. 70 g of this were mixed with 100 g of urea. This mixture was placed in an autoclave with a volume of 1 l with a double wall for steam heating. Then 220 g of liquid ammonia were pressed into the autoclave via a valve. The temperature was raised to 66 ° C by the additional steam heating of the autoclave. This resulted in a pressure of approx. 20 bar within the autoclave. The system was held under these conditions for 20 minutes.
• the cellulose / urea mixture obtained according to Example 1 was treated as follows to produce a cellulose carbamate: It was heated in a glass vessel with a capacity of 200 ml to a temperature of 140 ° C. for 2.5 hours. The ammonia still present after the ammonia explosion escapes together with the ammonia formed during the reaction and the water still present in the mixture. X-ray analysis showed that this product is amorphous. A sample was washed once with methanol, three times with water, one more time with methanol and then dried. In this way, excess and unreacted urea was removed. The sample had a nitrogen content of 1.264% by weight, which corresponds to a degree of substitution DS of 0.15. -IS
• the urea washed out with methanol weighed 1.2 g, the urea consumed for the conversion to carbamate was 0.53 g.
• the urea contained in the reaction mixture was 1.9 g.
• the sample contained 12 g of xylene. It was then washed three times with a total of 300 ml of methanol. The carbamate no longer contained any xylene. 80% of the xylene was removed in the first wash.

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Citations (7)

• 1996
  • 1996-07-12 DE DE19628277A patent/DE19628277C2/de not_active Expired - Fee Related
• 1997
  • 1997-07-08 EP EP97930510A patent/EP0910585A1/de not_active Withdrawn
  • 1997-07-08 CA CA002260782A patent/CA2260782A1/en not_active Abandoned
  • 1997-07-08 CZ CZ9941A patent/CZ4199A3/cs unknown
  • 1997-07-08 TR TR1999/00025T patent/TR199900025T2/xx unknown
  • 1997-07-08 BR BR9710297A patent/BR9710297A/pt unknown
  • 1997-07-08 PL PL97331046A patent/PL331046A1/xx unknown
  • 1997-07-08 AU AU34434/97A patent/AU3443497A/en not_active Abandoned
  • 1997-07-08 JP JP10505577A patent/JP2000505135A/ja active Pending
  • 1997-07-08 WO PCT/EP1997/003593 patent/WO1998002464A1/de not_active Application Discontinuation

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