FI112795B - Manufacture of cellulose carbamate used as alkaline solution in, e.g. manufacture of fibers and films, by reacting cellulose and urea in mixture containing cellulose, liquid, auxiliary agent and urea, and having specified liquid content - Google Patents

Abstract

Cellulose carbamate is manufactured by absorbing auxiliary agent and urea into cellulose, and reacting cellulose and urea in a mixture containing cellulose, liquid, the auxiliary agent and urea. The mixture has a liquid content of less than 40, preferably less than 22%.

Description

112795

METHOD FOR THE PREPARATION OF CELLULOSE CARBAMATE

Technical field

The invention relates to a process for the production of cellulose carbamate (CCA) which comprises reacting the cellulose with an alkalizing agent and urea.

Carbamate cellulose can further be used as an alkaline solution, such as viscose cellulose, for example for the manufacture of fibers and films and for the consolidation of paper products, by regenerating the solution back into the pulp fibers as is done in the viscose process. Another possibility is to use it directly as carbamate fibers or films.

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Technology background

The manufacture of fibers and films from cellulose by the viscose process has been known for over a hundred years. Even today, almost 20 all cellulose-based fibers are made by the viscose process. It is a known method by which various end product properties are achieved by changing material and process parameters. Viscous-*. however, there are significant drawbacks to the process: the preparation of spinning liquor involves laborious steps, the sulfur-25 carbon used to dissolve is toxic, highly flammable and flammable and difficult to recover. In addition, some of the sulfur carbon decomposes to hydrogen sulfide, which is likewise; ['· Toxic and explosive. In addition, the viscous solution is an unstable product, so it cannot be stored as an intermediate, but all production steps must be carried out immediately from start to finish, keeping the pulp temperature at ma-30 Tal.

There are several attempts to replace the viscose process with a more environmentally friendly one. Most promising has been the conversion of cellulose to cellulose carbamate by urea (see, e.g., D. Klemm et al.,; 35 Comprehensive Cellulose Chemistry, Wila-VCH 1998). However, despite its obvious advantages and several known attempts, this method has remained at the laboratory scale. This has been due to problems in product homogeneity, recovery and residues of used organic media (e.g. hydrocarbon) or / and solvents (usually ammonia), to unsatisfactory properties of the final products (mainly fibers) and to the cost of using the developed methods.

Known attempts to process carbamate pulp have been based on the soaking of cellulose sheets in an alkaline solution (mercerization) to which in some cases ammonia and / or other solvents or accelerators have been added. After the mercerisation, the partially dried pulp is treated with a solution of urea, to which alkali may be added, usually also ammonia and possible solvents or salts. Finally, the reaction between urea and pulp is carried out in a furnace at a temperature of about 130 ° C. The methods have required the best viscose pulp with a DP level lowered, for example, by long-term maturation in mercerization solution or by prior irradiation. Examples of the above processes are disclosed in F1 61033, EP 0 402 606 and WO 00/08060.

One of the first attempts to make cellulose carbamate is disclosed in U.S. Patent 2,134,825. It employs an aqueous solution of urea and sodium hydroxide in which the pulp is first impregnated. After impregnation, standing and pressing, the pulp is dried and heated in an oven to achieve a reaction between cellulose and urea. The patent discloses a number of chemicals which are intended to improve absorption and to reduce the gel tendency of the solution. However, according to the patent, the pulps have only been partially soluble, leaving a large amount of unreacted fiber in the solution which clogs the spinning nozzle. The reason for this is probably the unevenness of the substitution.

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Cellulose carbamate is alkaline soluble at a degree of substitution of 0.2 to 0.3. Cellulose carbamate formation begins when the mixture of cellulose and urea is heated above the latter melting point (133 ° C). Upon heating, urea decomposes to isocyanic acid and ammonia according to the following reaction formula: NH2 - CO - NH2 HN = C = 0 + NH3 3 112795

Isocyanic acid is highly reactive and forms carbamates with the hydroxyl groups of cellulose as follows: Cell - OH + H - N = C = 0 Cell - O - CO - NH 2

The side reaction may be the reaction of urea and isocyanic acid into the biuret, or the formation of cyanuric acid and other isocyanic acid polymerization products.

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General description of the invention

The purpose of the invention is to depart from the premise of said U.S. Patent 2,134,825, but to eliminate the problems related to the quality of the product with the new processing technique and to provide a number of parameters for controlling the properties of the final product. It is also an object of the invention to provide a process by which high quality solutions and finished end products can also be made starting from conventional and inexpensive wood pulp having a significantly higher DP level than soluble pulp. To accomplish these 20 purposes, the invention is characterized in what is claimed in claim 1. In the process of the invention, absorption of the alkalizing agent and urea up to the core of the cellulosic fiber is promoted and / or the cellulose-urea reaction is at least partially performed by mechanical shaping. less than 40%, preferably less than 30%, most preferably less than 25%, and most preferably less than 22%. The cellulose is allowed to react with the alkalizing agent and urea in a high solids content and without organic solvent or other auxiliaries. In the method, the penetration of chemicals into the fiber, the homogenization of the pulp, the reduction of the crystallinity of the pulp, the DP control of the product and, in part, the reaction are caused by mechanical modification. The reaction is completed in an oven. The process of the invention is a dry process wherein the amount of water is | remarkably low. Unlike known methods, dewatering as a separate step need not be carried out at all. Efficiency: 35 is very high, which means that the recycling and recovery of chemicals: is very low, in contrast to the known methods. When using the process of the invention, the homogeneity of the reaction and the purity of the 4112795 solution are so good that no additional auxiliaries are needed, but the solution is sufficiently stable as such. The invention also provides advantages in terms of overall process time. In the prior art, different pre-maturation and / or post-maturation requires multiple emotions. When using the method of the invention, chemical dosing and shaping can be done in immediate successive steps, where time is determined solely by technical device solutions - the minimum delay from dosing to the furnace (for a single material particle) can be only a few minutes. The reaction time may be indirectly affected by the new process 10 by eliminating the need for separate dewatering.

Other claims disclose some preferred embodiments of the invention.

In the process of the invention, the penetration of the alkalizing agent and the urea into the cellulose is promoted in a forming device. During processing, the fiber bundles are broken down, the pores of the fiber open and the liquid penetrates into the fiber. The alkalizing agent acts as a fiber activator and aids in urea penetration. Mechanical shaping also serves as a homogenizer for a 20 mass-chemical mixture. In particular, the forming device is a screen press, a roll mixer or an extruder. The reaction is carried out in a mixture with a small amount of liquid, as described above. Nes- :. for example, more than 50%, preferably more than 70%, most preferably more than 90% of tea, and most of all, substantially all is water. As cellulose, for example, wood pulp, soluble pulp or liner can be used. Starting material Γ. the cellulose is preferably finely ground cellulose (e.g., particle size less than 0.7 mm).

The forming device is a mechanical forming device in which the mixture is pressed, rubbed and stretched several times. In particular, the forming device may be a screen press, a continuous roll mixer or an extruder. Due to the external heat generated during processing and / or introduced into the system, the temperature of the mixture can be raised to such an extent that the actual reaction can also be initiated and carried out at least partially in the forming apparatus.

5, 112795

In particular, the alkalizing agent may be an alkali metal hydroxide, such as sodium hydroxide. The alkalizing agent may be added to the reaction mixture, for example as an aqueous solution and / or dry. The alkalizing agent may be added before the urea, or partially or completely simultaneously with the urea. The urea may be added as a dry and / or aqueous solution. In order to correct the amount of urea in the reaction mixture and the water content of the reaction mixture, it is preferable to add part of the urea as an aqueous solution and part as a solid. Dispensing of liquid substances can be made in a foggy form in a premixing apparatus, for example a fluidized bed mixer, followed by reaction in a forming apparatus.

According to one aspect of the invention, the forming device is a screen press or roll mixer that is reliable and does not clog as easily as extruders.

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In a sieve press, the pulp is pressed through channels. Rotary rollers are usually used for pressing. Compression efficiency depends on the diameter and length of the channels, the number of channels per area, and the pressure exerted on the mass over the channel matrix. There are different types of such equipment. The channel matrix may be rotatable disposed below a press roll located on a fixed shaft. There may be several rollers. The press rolls may also be located inside a cylindrical rotary matrix. The matrix or rolls may, if desired, be heated or cooled.

'25> ·, The track mixer has two counter-rotating rollers. Mixed; the mass is fed into a nip formed by the rolls, where the mass adheres to a '' mat on the surface of another roll and is pressed into the nip several times. In a continuous weaving roller mixer, the mass is fed to one end of the nip, V 30, and the carpet passes to the opposite end of the nip. To facilitate migration, the rolls may have shallow screw grooves or brushes, the rolls may be:. inclined towards the outlet end, or there is a speed difference between the rollers. The surface material of the rolls is selected so that the mass adheres to a desired roll on a uniform mat. One or both rolls may be heated or cooled as necessary.

6, 112795

According to one aspect of the invention, the pulp is passed through the forming device several times, for example 2-10, such as 4-6 times. This may involve replacing the screening plate for a screen press after a single press or using two different presses in succession.

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In one aspect of the invention, the total processing time is less than 30 min, preferably less than 20 min, most preferably less than 15 min, most preferably less than 10 min. For example, the pre-mix time is less than 30 min, preferably less than 15 min, and most preferably less than 10 min. The drying and reaction times depend on the 10 temperatures used so that at higher temperatures the time can be shortened.

For example, ammonia, organic solvents or other auxiliaries are not required in the process of the invention. Thus, the invention is well suited to the ammonia-free process wherein ammonia is not introduced from outside into the mixture to enhance the process. The water required as a medium is provided with chemicals added to the system. Due to the high solids content, the mixture can be transferred directly to the reaction stage after furnishing or the like without intermediate drying.

BRIEF DESCRIPTION OF THE DRAWINGS: ·: Some embodiments of the invention will be described in detail below. 25 per item. The accompanying drawings are part of the description. In the drawings 1 · * Fig. 1 shows in three cross-sections a screen press in which the reaction according to the invention can be carried out and> 30: Fig. 2 shows a top and side view of a continuous roll mixer,. wherein the reaction of the invention can be carried out.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION: 35: The screen press 1 of FIG. 1 has a drive shaft 3 disposed in a stationary vessel 2 with a horizontal roller shaft attached thereto and rolls 4 mounted on its ends 7112795. when the drive shaft is rotated. The screen plate matrix is interchangeable. The side walls of the vessel and the matrix form a sheath through which heat transfer medium can be passed. The rollers can also be equipped with 5 heat transfer devices. The rotating rollers press the mass fed into the container through the holes in the screen plate matrix, thereby compacting the mass into pellets. The compression efficiency depends on the diameter and length of the ducts, the number of ducts per surface area, and the compression pressure exerted by the rolls on the pulp over the matrix.

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The roll mixer 6 of Fig. 2 has two rolls rotating in opposite directions: a roller roller 7 and a roller roll 8. The rollers have a screw groove 15 for conveying the material to one end of the nip. The rollers are equipped with heat transfer devices.

In the following examples, various recipes are used and the screening method is used as a editing method. Common to all is batch chemical delivery in a fluidized bed mixer. Depending on the chemicals used, pulp may be required during and after dosing:. Also the processing equipment is cooled or heated-, ·; VIA. The screen plate press can be used to complete the reaction by running the pulp several times through the press. This will be optimized proportionately ··. 25 tea to the target quality (DP, viscosity, filter residue).

Examples 1-7.

In the examples, three different types of pulp and different amounts of NaOH were used: V 30 and urea. The mechanical shaping was performed on a screen plate press with multiple throughput times.

* ·

The quality of the process was evaluated by analyzing alkali-dissolved carbamate cellulose solution by various methods. Here, case by case, 35 some or all of the following methods are used: 8 112795 1) Degree of Polymerization (DP), which predicts the mechanical and physical properties of the final product (fibers and films) and acts as a measure of quality control in the process. The higher the DP level, the thinner its solutions have to be used for a given flow requirement. The ideal would be a high pulp fiber content and a sufficiently low viscosity. It would be advantageous if DP could be adjusted on a case-by-case basis (to optimize product and runnability). The method for determining DP here is that of SCAN-CM 15:99. The method determines a viscosity ratio of 10 d on the basis of which an empirical evaluation of DP is made (see, e.g., J. Gullichsen, H. Paulapuro, Papermaking Science and Technology, Fapet 2000).

2) The blockage number Kw (filtration residue) represents the proportion of insoluble matter in the solution. This is a measure of the quality of the solution in general and a measure of the tendency of the fiber nozzle to clog. This analysis is performed according to H. Sihtola, Paper and Wood 44 (1962): 5, pp.295-300.

3) The nitrogen content of the solution represents the degree of substitution. The degree of substitution refers to the average number of substituents attached to one glucose unit. A method according to SFS 5505 (Determination of inorganic and organic nitrogen in wastewater. Modified Kjeldahl method, 1988.1 p) is used.

25 S · 4) Carbamate pulp is analyzed for purity by washing and measuring:. / racket residue percentage.

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(i) * 5) The viscosity of the solution is measured by the conventional ball method (cf.

! \: 30 Sihtola article mentioned) and / or Brookfield viscometer. The viscosity

t * I

adjustment is essential for machining (nozzle flows and mass transfer in general) as already mentioned for PD analysis.

6) The fiber residue of the solution is also evaluated microscopically using a subjective scale of 1-5 such as 1: a clear, completely fibrous lye and 5: a cloudy solution containing very high levels of whole fibers.

9 112795

The chemicals are dispensed in a fluidized bed mixer such that the pulp moves continuously during dispensing and the chemicals are added in a mist to achieve maximum homogeneity. Both chemicals (urea and alkalizing agent) are dosed sequentially. The urea is dosed both as a solid flour and as a 50% aqueous solution so that the total humidity remains as indicated in the table. NaOH is administered as a 40% aqueous solution. Cellulose is a finely ground wood pulp.

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Screening plate shaping is done with a continuous screening plate apparatus, where the feed is made with a twin screw feeder. The feed rate is selected so that the material does not begin to accumulate in front of, on, or on the wheels, but all feed material is squeezed through the hole in the matrix. On the outflow side of the matrix, the material is cut into granules by a cutter. The jacket can be cooled by external water circulation.

Process and Run Parameters for Screening Press: _

Diameter of holes and length D / H mm_ 3/40

Number of holes: 120

Hole spacing inner / outer diameter d / D mm__160 / 190: Number of press rolls and diameter D1 mm__2 / 150: Roll speed rpm_ 10-20 *: ·: Shell cooling setpoint T ° C__- 5 ... + 100 Number of passes _ 1-20 . ··! 20 The following table shows the pulp types (starting pulp DP), dosing volumes (chemicals in relation to the dry weight of pulp), ... calculated total water content and number of passes through screening plate: 112795 __10 ___

Test pulp type NaOH Urea% Water% Modification number% pulp total rounds __pulp__pulp 1 Birch pulp, DP 950__7__62__21,2__14_ 2 __Bully pulp. DP 950__7__22__22,2__J3_ 3 Birch Cellulose, DP 950 7__70__20,4__14 4 __Eucalyptus Liquid Cell, DP 600 7 42__18,1__4_ 5 __Eucalyptus Liquid Cell, DP 600 11 50__20,7__7_6 __Eucalyptus Liquid Cell, DP 600__uu 5u 5uupu 5u 6u

After working up, the reaction is completed in an oven at T = 140 ° C and holding time t = 4 h and then milled on a disk refiner. After grinding, the powder is dissolved in aqueous NaOH so that the final concentration of the solution becomes 9.6 wt% NaOH. The carbamate pulps thus obtained have the following properties:

Experience Polyme- Clog- Ball Solution- Nitrogen Purity- Solution

No. degree of degree Maluku viscosity N% degree quality DP Kw (cP) s / CCA% ____ / concentration% lightness____; . · '1 220 ___ 2740/6 52/6 1.96 63.2 2: V 2 600____ 0.15 76.9 5 * 3 100 ___ 596 / 5.5__ 2.52 61.2 3 \ J 4 250 37500 5500/6 36/9 1.13 76.4 4: \ j 5 69 934 265/6 102/10 3.16 67.5 1 O 6 240 2177 ___ 60/7 ___ 73.0 1 l 7 l 315 | 1945 l 38/5 Γ 73.0 1 1 I *

Claims (13)

A process for the preparation of a cellulose carbamate comprising impregnating the cellulose with an alkalizing agent and urea and carrying out a reaction between cellulose and urea in a mixture of cellulose, liquid, alkalizing agent and urea, characterized in that the urea reaction is at least partially performed by subjecting the mixture to mechanical shaping and that the amount of liquid in the mixture is less than 40%, preferably less than 30%, most preferably less than 25% and most preferably less than 22%. Method according to Claim 1, characterized in that the mixture is subjected to molding between two surfaces moving relative to one another. Method according to Claim 2, characterized in that, during shaping, the mixture is extruded through openings in one of the surfaces, e.g., by forming in a sieve press (1). 20 Method according to Claim 2, characterized in that the shaping is carried out by passing the mixture through the 'nip' formed by two rolls (7,8). A method according to claim 4, characterized in that * ·: at least one of the rolls is grooved on the surface. ;, J A method according to any one of claims 2 to 5, characterized in that the same mixture is recycled several times; 30 den with respect to each other between the moving surface. A process according to any one of the preceding claims, characterized in that more than 50%, preferably more than 70%, most preferably more than 90% of the liquid, and most preferably substantially all is water. *: 35 112795 Process according to any one of the preceding claims, characterized in that the alkalizing agent and the aqueous urea solution and the dry powdered urea are premixed in the cellulose by adding the liquid substances 5 as a mist. Method according to claim 8, characterized in that the premixing is carried out in a fluidized bed mixer. A method according to any one of the preceding claims, characterized in that the processing time is less than 30 min, preferably less than 20 min, most preferably less than 15 min and most preferably less than 10 min. A process according to any one of the preceding claims, characterized in that the cellulose is wood pulp or soluble cellulose or liner. Process according to any one of the preceding claims, characterized in that the cellulose is finely ground to a grain size of <2 mm, preferably to less than 1 mm, and most preferably to less than 0.7 mm. A method according to any one of the preceding claims, characterized in that during the shaping the temperature of the mixture is controlled by the circulation of an external heating or cooling medium. / 25 * v · 1 »112795