Patent Application
20090165969
This application relates to the reduction in the degree of polymerization (DP) of cellulose with enzymes to provide a pulp with acceptable metals levels suitable for lyocell manufacture.
In order to obtain a higher throughput in lyocell production (higher concentration of pulp in the solvent NMMO or higher throughput per hole per minute) it is necessary to use a lower DP pulp than currently used. Use of enzymes at various stages of the bleaching process can yield lower DP pulps which are suitable for lyocell.
Enzymes are used in the treatment of cellulosic pulp to improve the bleaching and to reduce the DP of the pulp. One use of enzymes is to control the viscosity of the pulp during the bleach treatment. A low uniform viscosity is needed for dissolving and non dissolving pulps useful for rayon or lyocell production. Enzymes may be used to control this viscosity.
Enzymes that are useful with cellulose include xylanases, cellulases, hemicellulases, peroxidases, mannases, laccases (oxidoreductases), lipases and combinations of these enzymes.
The cellulose pulp must be at the correct pH in order for the enzymes to work. The usual pH is 3 to 10. An acids such as sulfuric, nitric or hydrochloric acid, is usually used to adjust to the appropriate pH but there are problems associated with the use of these mineral acids. The mineral acids tend to harden the outside of the cellulose fibers and reduce the void volume within cellulose pulp fibers thus make it more difficult for the enzymes to interact with the cellulose pulp fibers. Mineral acids are applied as a liquid and the dispersion of the acid through the pulp can be non-uniform.
Carbon dioxide can be used to adjust the pH of the cellulose pulp fiber to the correct pH of 2 to 7.5 and does not create the problems that the use of mineral acids do. The carbon dioxide tends to maintain the openness of the cellulose pulp fiber or biomass and allow better interaction of the enzyme with both the outside and the inside of the cellulose pulp fiber or biomass. The carbon dioxide is applied as a gas and tends to disperse more uniformly throughout. Other organic acids such as acetic acid can also be used.
Various bleaching sequences can be used to make non dissolving pulp for lyocell. It is important that during the bleaching sequence that copper levels and total transition metals be kept low since this element adversely affects the NMMO which is used to dissolve the cellulose.
It has now been found that lyocell pulps with a low DP and suitable for lyocell production can be produced by the use of enzymes after oxygen delignification (before bleaching), intermediate in the bleaching sequence or alternatively at the end of the bleaching sequence. In one embodiment the bleaching sequence is OXDEpD where O is oxygen delignification stage, X is the enzyme treatment stage, D is the chlorine dioxide stage, Ep is the caustic extraction stage in the presence of peroxide and D is the bleaching stage with chlorine dioxide. In another embodiment the bleaching sequence is ODEpDX where O is oxygen delignification, D is bleaching with chlorine dioxide, Ep is caustic extraction in the presence of peroxide, D is chlorine dioxide bleaching and X is enzyme treatment. In yet another embodiment the bleaching sequence is OXDEpDX where O is oxygen delignification X is enzyme treatment, D is bleaching with chlorine dioxide, Ep is caustic extraction in the presence of peroxide, D is chlorine dioxide bleaching and X is enzyme treatment. Treatment of an unbleached kraft pulp with an IV of 6.2 and a Kappa of 28 to 30 using one of these bleach sequences, for example OXDEpD, can reduce the pulp to an acceptable D. P. range, and the pulp has an acceptable copper number and acceptable total transition metals levels.
Unbleached pulp with an IV (intrinsic viscosity) from 10 to 5 dl/g can be contacted in a bleaching sequence with at least one stage of an enzyme treatment and reduce the pulp by 8 to 2 units. The enzyme treatment can also occur after the bleach sequence or alternatively the enzyme treatment can be in the bleaching sequence and after the bleach sequence.
In one embodiment the pulp is reduced to 2 to 4 IV units; in another embodiment the pulp is reduced to 2.5 to 3.5 units.
In one embodiment the enzyme is added at 0.045 to 4.5 kg/MT pulp. In another embodiment the enzyme is added at 0.136 g to 3.27 kg/MT pulp In yet another embodiment the enzyme is added at 0.227 g to 1.36 kg/MT pulp.
The term “degree of polymerization” (abbreviated as DP) refers to the number of D-glucose monomers in a cellulose molecule. Thus, the term “average degree of polymerization”, or “average DP”, refers to the average number of D-glucose molecules per cellulose polymer in a population of cellulose polymers. DP and IV were determined by ASTM 1795-96.
Pulp with a Kappa of 28 to 30 from the normal Kraft process underwent an oxygen stage delignification with H2O2 and sodium extraction at 121° C. (250° F.) to obtain unbleached pulp with an IV of 6.2 dl/g ( Falling Ball or FB of 86). This pulp was washed (POW, post oxygen washer) and the POW 3rd stage wash had an initial set point of 68° C. and stock exit pH of about 7 (CO2 adjusted), the pulp with the adjusted pH was treated with cellulase Biotouch C700 from Ashland Inc. (AB Enzymes) added at POW standpipe at a dosage of 0.45 kg/MT with a retention time of about three hours to lower viscosity the viscosity to an intrinsic viscosity (IV) of 5.5 (FB of 50) for DEpD bleaching. This bleached pulp (DEpD) had an intrinsic viscosity (IV) of 3.2 dl/g when taken from the couch trim (control sample in Table 1). This was the starting material for more treatment (Tables 1 to 5).
In one embodiment pulp with an IV of 6.2 dl/g is treated with an enzyme after the oxygen delignification stage followed by a chlorine dioxide (D), caustic extraction with peroxide (Ep), and then a chlorine dioxide stage. In another embodiment the pulp with an IV of 6.2 dl/g is treated with an enzyme after the oxygen delignification stage followed by a chlorine dioxide (D) stage, caustic extraction with peroxide (Ep), a chlorine dioxide stage and another enzyme stage, X, after bleaching.
The procedure for the preparation of the solution for the treatment is as follows. Table 1 gives the treatment conditions.
The same procedure as used in Table 1was used to treat the same never dried pulp with 0.23, 0.34, 0.45 and 2.27 kg/ton of C-700 to obtain samples 4, 5, 6 and 7, respectively.
This same procedure with 1 kg/MT of Biotouch C-700 was used to treat 600 gram (OD) pulp (never dried) to make “trial” pulp. The treated pulp and control pulp had the properties listed in Table 2.
The data indicates that cellulase treatment after bleaching can reduce viscosity; for example, at 0.9 kg/MT pulp the IV levels were reduced from 3.2 to 2.7 dl/g. High levels of enzyme have an adverse effect on copper number and increase it to unacceptable levels.
Cellulase treated Peach® had a low viscosity and still sugar content as starting control implying minimal yield loss The R10 and R18 are decreased.
R10 refers to the residual undissolved material that is left after attempting to dissolve the pulp in a 10% caustic solution. R18 refers to the residual amount of undissolved material left after attempting to dissolve the pulp in an 18% caustic solution. Generally, in a 10% caustic solution, hemicellulose and chemically degraded short chain cellulose are dissolved and removed in solution. In contrast, generally only hemicellulose is dissolved and removed in an 18% caustic solution.Thus, the difference between the R10 value and the R18 value represents the amount of chemically degraded short chained cellulose that is present in the pulp sample. Providing a pulp having a relatively broad molecular weight distribution of at least equal to or greater than about 2.8 is desirable from the standpoint of being able to provide customers with pulp which may not require blending with pulps of other molecular weight distribution to arrive at the desired composition. Sugar analysis was determined by the method described below.
The data indicate that Cellulase treated pulps still have acceptable transition metals (eg. copper, manganese and iron) and other metals content (metals such as calcium, sodium and magnesium) for lyocell manufacture. Metal levels were determined by EPA 3050 and EPA 200.8M.
Both the control Peach(D and cellulose treated pulp (trial) were dissolved in lyocell solvent (NMMO (N-methylmolptioline N-oxide) in a lab kneading machine at different concentrations and the viscosity, Pas, at different shear rates (zero shear, 1 and 10 l/s were measured at different dissolution times (2, 4, and 6 hours) at different temperatures. The results are presented in Table 5.
The low DP pulp (trial) had lower viscosity at all shear rates compared with Peach® (control). This indicates that higher throughput (higher concentration at the same viscosity or higher throughput per hole per minute) for meltblowing is possible with lower DP pulp due to lower solution viscosity.
Cellulase treatment can lower pulp viscosity. The treated pulp has acceptable copper number and metal content for the lyocell process. Certain surfactants also help cellulase treatment. Treated pulp can have similar hemicellulose as a control (Peach®) pulp implying minimal yield loss. The lower DP pulp has lower solution viscosity in NMMO, thus it is possible to use lower DP pulp at higher throughput (higher concentration or higher thoughtput per hole per minute during lyocell production) to improve economics for lyocell production.
Weyerhaeuser Port Wentworth never dried pulp with bleaching sequence of DEDED with a intrinsic viscosity of 7.1 or FB viscosity of 140 was treated with 0.91 kg/MT or 0.9 lb/MT of Biotouch C-700 with the same condition listed in Table 1 and the treated pulp had intrinsic viscosity of 5.9 or FB of 72.
Kamloops never dried pulp with a bleaching sequence of DEDED with a intrinsic viscosity of 3.7 or FB viscosity of 22 was treated with 0.91 kg MT of Biotouch C-700 at the same condition as listed in Table 1 and the treated pulp had intrinsic viscosity (IV) of 3.4 dl/g or FB of 19 and a copper number of 0.9.
Weyerhaeuser Flint River Peach® (never dried) with an IV of 3.2 (OXDEpD) was treated with another Ep stage (2.0% NaOH, 3% H2O2, at 10% consistency, at 88° C. for 90 minutes). The treated sample has an IV viscosity of 2.6 and a copper number of 0.8. Part of the same sample from above treatment was dried and then treated with Biotouch C-700 again (same condition as sample 1 in Table 1) to obtain a sample with an IV of 2.5 and copper number of 0.8. Part of the same sample above from the Ep stage was not dried and then treated with C-700 (same condition as sample 1 in Table 1) again to obtain another samples having IV of 2.5 and copper number of 0.8.
Never dried pulp after DEpD bleaching with different DP levels were treated with 0.5% cellulase (Celluclast from Novozyme, on pulp) with or without surfactant (0.1% Tergitol on pulp);the conditions are shown in Table 6.
The analytical properties of the pulp are given in Table 7.
In a representative example, Peach®, a never dried bleached kraft southern pine pulp, available from Weyerhaeuser, Federal Way, Wash., was treated with cellulase (1% Ashland Biotouch 700) on air dry pulp weight with the same condition as sample 1 in Table 1) to yield a pulp having an average degree of polymerization of about 500 (IV of 2.63), a hemicellulose content of 12.0% by weight hemicellulose in pulp (6.8% and 5.3% by weight xylan and mannan, respectively) and an R10 and R18, of about 76.6 and 84.5, respectively. The pulp was dissolved in NMMO (N-methyl morpholine N-oxide)/water mixture as follows. A 250 mL three necked flask was charged with, for example, 66.4 g of 97% NMMO, 24.7 g of 50% NMMO, 10.4 g pulp, 0.1 g of propyl gallate. The flask was immersed in an oil bath at 105° C., a stirrer inserted and stirring continued for about 1 hr. A readily flowable dope resulted that was suitable for spinning. The cellulose concentration in the dope was about 12% by weight. The dope was extruded from a melt blowing die that had 3 nozzles having an orifice diameter of 457 microns at a rate of 1.0 gram/hole/minute. The orifices had a length/diameter ratio of 5. The nozzle was maintained at a temperature of 95° C. The dope was extruded into an air gap 30 cm long before coagulation in water and collected on a screen as either continuous or discontinuous filaments depending on dope rheology and meltblown conditions. Air, at a temperature of 95° C. and a pressure of about 10 psi, was supplied to the head. Air pressures of from 8 to 30 psi were used to achieve varying fibers diameters shown in Table 8.
This method is applicable for the preparation and analysis of pulp and wood samples for the determination of the amounts of the following pulp sugars: fucose, arabinose, galactose, rhamnose, glucose, xylose and mannose using high performance anion exchange chromatography and pulsed amperometric detection (HPAEC/PAD).
Summary of Method
Polymers of pulp sugars are converted to monomers by hydrolysis using sulfuric acid. Samples are ground, weighed, hydrolyzed, diluted to 200-mL final volume, filtered, diluted again (1.0 mL+8.0 mL H2O) in preparation for analysis by HPAEC/PAD.
Sampling, Sample Handling and Preservation
Wet samples are air-dried or oven-dried at 25±5° C.
Equipment Required
Reagents Required
All references to H2O is Millipore H2O
72% Sulfuric Acid Solution (H2SO4)—Transfer 183 mL of water into a 2-L Erlenmeyer flask. Pack the flask in ice in a Rubbermaid tub in a hood and allow the flask to cool. Slowly and cautiously pour, with swirling, 470 mL of 96.6% H2SO4 into the flask. Allow solution to cool. Carefully transfer into the bottle holding 5-mL dispenser. Set dispenser for 1 mL.
J T Baker 50% sodium hydroxide solution, Cat. No. Baker 3727-01, [1310-73-2]Dionex sodium acetate, anhydrous (82.0±0.5 grams/1 L H20), Cat. No. 59326, [127-09-31.
Standards
Internal Standards
Fucose is used for the kraft and dissolving pulp samples. 2-Deoxy-D-glucose is used for the wood pulp samples.
Fucose, internal standard. 12.00±0.005 g of Fucose, Sigma Cat. No. F 2252, [2438-80-4], is dissolved in 200.0 mL H2O giving a concentration of 60.00±0.005 mg/mL. This standard is stored in the refrigerator.
2-Deoxy-D-glucose, internal standard. 12.00±0.005 g of 2-Deoxy-D-glucose, Fluka Cat. No. 32948 g [101-77-9] is dissolved in 200.0 mL H2O giving a concentration of 60.00±0.005 mg/mL. This standard is stored in the refrigerator.
Kraft Pulp Stock Standard Solution
Kraft Pulp Working Solution
Weigh each sugar separately to 4 significant digits and transfer to the same 200-mL volumetric flask. Dissolve sugars in a small amount of water. Take to volume with water, mix well, and transfer contents to two clean, 4-oz. amber bottles. Label and store in the refrigerator. Make working standards as in the following table.
Dissolving Pulp Stock Standard Solution
Dissolving Pulp Working Solution
Weigh each sugar separately to 4 significant digits and transfer to the same 200-mL volumetric flask. Dissolve sugars in a small amount of water. Take to volume with water, mix well, and transfer contents to two clean, 4-oz. amber bottles. Label and store in the refrigerator. Make working standards as in the following table.
Wood Pulp Stock Standard Solution
Dispense 1 mL of the fucose solution into a 200-mL flask and bring to final volume. Final concentration will be 0.3 mg/mL.
Wood Pulp Working Solution
Use the Kraft Pulp Stock solution and the fucose and rhamnose stock solutions. Make working standards as in the following table.
Procedure
Sample Preparation
Grind 0.2±05 g sample with Wiley Mill 40 Mesh screen size. Transfer ˜200 mg of sample into 40-mL Teflon container and cap. Dry overnight in the vacuum oven at 50° C. Add 1.0 mL 72% H2SO4 to test tube with the Brinklman. dispenser. Stir and crush with the rounded end of a glass or Teflon stirring rod for one minute. Turn on heat for Gyrotory Water-Bath Shaker. The settings are as follows:
Place the test tube rack in gyrotory water-bath shaker. Stir each sample 3 times, once between 20-40 min, again between 40-60 min, and again between 60-80 min. Remove the sample after 90 min. Dispense 1.00 mL of internal standard (Fucose) into Kraft samples.
Tightly cover samples and standard flasks with aluminum foil to be sure that the foil does not come off in the autoclave.
Place a Comply SteriGage Steam Chemical Integrator on the rack in the autoclave. Autoclave for 60 minutes at a pressure of 14-16 psi (95-105 kPa) and temperature >260° F. (127° C.).
Remove the samples from the autoclave. Cool the samples. Transfer samples to the 200-mL volumetric flasks. Add 2-deoxy-D-glucose to wood samples. Bring the flask to final volume with water.
For Kraft and Dissolving pulp samples:
Filter an aliquot of the sample through GHP 0.45 μ filter into a 16-mL amber vial.
For Wood pulp samples:
Allow particulates to settle. Draw off approximately 10 mL of sample from the top, trying not to disturb particles and filter the aliquot of the sample through GHP 0.45 μ filter into a 16-mL amber vial. Transfer the label from the volumetric flask to the vial. Add 1.00 mL aliquot of the filtered sample with to 8.0 mL of water in the Dionex vial. Samples are run on the Dionex AS/500 system. See Chromatography procedure below.
Chromatography Procedure
Solvent Preparation
Solvent A is distilled and deionized water (18 meg-ohm), sparged with helium while stirring for a minimum of 20 minutes, before installing under a blanket of helium, which is to be maintained regardless of whether the system is on or off. Solvent B is 400 mM NaOH. Fill Solvent B bottle to mark with water and sparge with helium while stirring for 20 minutes. Add appropriate amount of 50% NaOH.
(50.0 g NaOH/100 g solution)*(1 mol NaOH/40.0 g NaOH)*(1.53 g solution/1 mL solution)*(1000 mL solution/1 L solution)=19.1 M NaOH in the container of 50/50 w/w NaOH.
Solvent D is 200 mM sodium acetate. Using 18 meg-ohm water, add approximately 450 mL deionized water to the Dionex sodium acetate container. Replace the top and shake until the contents are completely dissolved. Transfer the sodium acetate solution to a 1-L volumetric flask. Rinse the 500-mL sodium acetate container with approximately 100 mL water, transferring the rinse water into the volumetric flask. Repeat rinse twice. After the rinse, fill the contents of the volumetric flask to the 1-L mark with water. Thoroughly mix the eluent solution. Measure 360±10 mL into a 2-L graduated cylinder. Bring to 1800±10 mL. Filter this into a 2000-mL sidearm flask using the Millipore filtration apparatus with a 0.45 pm, Type HA membrane. Add this to the solvent D bottle and sparge with helium while stirring for 20 minutes.
The post column addition solvent is 300 mM NaOH. This is added postcolumn to enable the detection of sugars as anions at pH >12.3. Transfer 15±0.5 mL of 50% NaOH to a graduated cylinder and bring to 960±10 mL in water.
(50.0 g NaOH/100 g Solution)*(1 mol NaOH/40.0 g NaOH)*(1.53 g Solution/1 mL Solution) (1000 mL Solution/1 L solution)=19.1 M NaOH in the container of 50/50 w/w NaOH.
Calculations
Example for arabinose:
Example for arabinan:
Polymer Sugar Weight %=(0.043 wt %)*(0.88)=0.038 Weight Note: Xylose and arabinose amounts are corrected by 88% and fucose, galactose, rhamnose, glucose, and mannose are corrected by 90%. Report results as percent sugars on an oven-dried basis.
