WO1998020199A1

WO1998020199A1 - Vanadyl catalyzed oxygen treatment of lignocellulosic materials

Info

Publication number: WO1998020199A1
Application number: PCT/CA1997/000813
Authority: WO
Inventors: Zheng Tan; Marco Solinas
Original assignee: Macmillan Bloedel Limited
Priority date: 1996-11-06
Filing date: 1997-10-30
Publication date: 1998-05-14

Abstract

A catalyst selected from vanadyl organic complexes and vanadyl sulfate is applied to lignocellulosic material together with oxygen to form a treated pulp and the treated pulp is then subjected to a caustic extraction to produce an improved pulp. The process may be applied to a chemical pulp or a mechanical pulp to obtain delignification or lignin modification. In the case of a chemical pulp, delignification improves the brightness of the pulp whereas in the case of a mechanical pulp, fiber conformability significantly improves.

Description

VANADYL CATALYZED OXYGENTREATMENT OF LIGNOCELLULOSIC MATERIALS

Field of Invention The present invention relates to a catalyzed oxygen treatment of lignocellulosic materials, more particularly, the present invention relates to a vanadyl catalyzed oxygen treatment of lignocellulosic materials. Background of the Invention

Treatment of lignocellulosic materials for both mechanical and chemical pulps to improve the characteristics or quality of the pulp for subsequent use in the manufacture of paper or the like, is an on-going challenge in the pulp and paper industry.

One of the main reasons why the coarse fibers such as Douglas fir fibers are difficult to form into high quality or high grade paper, is the lack of conformability of the thick walled fibers in that the fibers do not easily collapse in the paper making process and thereby form a strong bond in a relatively flat sheet.

With chemical pulps, it is important that the brightness of the pulp be increased or that lignin content be reduced without unduly reducing the strength characteristics of the pulp. A variety of vanadium containing compounds have been used to catalyze delignification reactions of lignocellulosic materials using a variety of different reactants.

U.S. patent 4,039,374 issued August 2, 1977 to Deutsch et al. describes a process for bleaching cellulose fibers with chlorine dioxide in the presence of vanadium compounds containing vanadium in the +4, +5 in an oxidation stage under acid conditions. The brightness reversion of the so brightened pulp is inhibited.

Canadian patent 1,043,514 issued December 5, 1978 to Phillips describes a system for oxygen bleaching using a divalent transition metal as a catalyst under alkaline pH conditions. The process increases the rate of delignification while protecting the cellulose against excessive viscosity (strength) loses. Canadian patent 1,110,018 issued October 6, 1981 to Kempf describes another process for delignification and bleaching lignocellulose pulp using vanadium compound. This patent teaches the use of vanadium (and other metal additives) during peroxide bleaching. U.S. patent 4,596,630 issued June 24, 1986 to Hull et al. describes a reductive bleaching treatment of lignin containing pulps using a polydentate lignin complex of dipositive vanadium, chromium and titanium and wherein the complexes may be regenerated electrochemically.

U.S. patent 4,702,807 issued October 27, 1987 to Bhattacharjee et al. describes an electrochemical process using metallic chlorates and vanadium catalysts to provide a pulp of improved brightness with minimal viscosity loss.

An article by Perng et al., "The Effect of Metal Complexes in the Electrochemically Mediated Oxygen Bleaching of Wood Pulp", TAPPI Journal, Vol. 76, No. 10, October 1993 describes another electrochemical system using oxygen in the presence of metals including vanadium. In these tests, none of the vanadium complexes tested showed an effect on Kappa number or viscosity and thus, vanadium was deemed to be ineffective.

PCT patent publications WO94/05849 published March 17, 1994 and

WO95/26438 published October 5, 1995, both by Weinstock et al. disclose methods for delignifying wood pulps using vanadium substituted polyoxometalates for delignifying or oxidative bleaching of the wood pulp. In these cases, polyoxometalates were used as stoichiometric reactants (rather than catalysts) in the delignification of pulp materials.

It will be apparent that the vanadium compounds have been applied in the pulp and paper industry, in particular, for catalyzed bleaching, and have been used or tested in relation to the use with oxygen, peroxide and some chlorine compounds with varying success, both at high or alkaline pH's and under acid conditions. Brief Description of the Present Invention

It is an object of the present invention to provide a catalyzed oxygen system for treating lignocellulosic fibers. It is a further object of the present invention to provide a system for improving the conformability of thick walled mechanical fibers, of different species such as Douglas fir.

It is yet another object of the invention to provide a system for reducing the energy required to refine mechanical pulps.

It is a further object of the present invention to provide an improved system for oxygen bleaching of chemical pulps such as kraft pulps.

Broadly, the present invention relates to a method of treating lignocellulosic material by applying an effective amount of catalyst selected from a group consisting of vanadyl organic complexes and vanadyl sulfate and subjecting the pulp to oxygenation conditions in an O-stage at a temperature of between 60° and 200°C for up to 6 hours and an oxygen over pressure of at least one atmosphere, said pulp being in a consistency of less than 40% and having a pH of between 1.5 and 7 at the completion of the O-stage to produce a pretreated pulp and then subjecting said pretreated pulp to a caustic extraction step (E-stage) to provide a treated pulp.

Preferably, said vanadyl organic complex is selected from a group consisting of vanadyl acetylacetonate and vanadyl porphyrins.

Preferably, said catalyst is selected from a group consisting of vanadyl sulfate and vanadyl acetylacetonate. Preferably said catalyst is applied to said pulp in said O-stage

Preferably, said applying of said catalyst and said subjecting to oxygen conditions occur in sequence with pulp first being treated with the catalyst in a Catalyst stage to provide a catalysed pulp and then subjecting said catalysed pulp to said oxygenation in said O-stage. Preferably, said catalyst can be present in the amount of 0.01% to 2% by weight of the pulp.

Preferably, said extraction stage (E-stage) will apply between 0.5% and 4% caustic as NaOH to said pretreated pulp.

Preferably, said pulp will be at a consistency of less than 15%. Brief Description of the Drawings

Further features, objects and advantages will be evident from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings in which; Figure 1 is a schematic illustration of the preferred process of the present invention.

Figure 2 is a modified version of the process described in Figure 1.

Figure 3 shows the graph comparing the density at different degrees of second stage wet pressing for an untreated sample and controls at different pH's with pulp produced using the vanadyl oxygenation, extracted process of the present invention.

Figure 4 is a plot of density versus second stage wet pressing for hemlock CTMP pressed according to the present invention.

Figure 5 is a plot similar to Figure 4 showing the effect of varying the dosage of vanadyl acetylacetonate. Figure 6 is a plot similar to Figure 5 showing the effect of vanadyl porphyrin.

Figure 7 is a plot similar to Figure 6 showing the effect of vanadyl sulfate.

Figure 8 is a plot of applied energy versus freeness showing the effect of the present invention on refining energy required. Description of the Preferred Embodiments The pulp to be treated in the present invention may either be a chemical pulp or a mechanical pulp. Chemical pulp may be any suitable chemical pulp such as a kraft brown stock and the mechanical pulp may be suitable CTMP, TMP or the like type pulp. The process of the invention particularly suitable to produce mechanical pulps from thick walled fibers such as west coast Douglas fir and should be applicable to southern pine to improve the conformability of such mechamcal pulps, by softening the cell walls so that the fibers tend to collapse more easily.

The pulp may be made from any suitable raw materials including pulps treated by an impressifiner or coarsely refined wood fibers wood chips or bundles as well as non-woody plant materials or chemical pulps. The catalysts used with the present invention are selected from the group consisting of vanadyl organic complexes (vanadyl acetylacetonate and vanadyl porphyrin) or vanadyl sulfate. Most preferred catalyst are vanadyl acetylacetonate and vanadyl sulfate.

In Figure 1 of the embodiment, the cataylst 10 is applied in a catalyzed stage as indicated at 12 to the pulp which is introduced at 14, and the catalyst is preferably uniformly distributed over the pulp. The catalyst will be applied in an effective amount which generally will be less than about 5% based on the dry weight of the pulp, and preferably will be in the range of about 0.01% and 1%. The catalyst applied pulp is then transferred as indicated by the arrow 16 to an oxygen stage (O- stage) 18 wherein oxygen is introduced as indicated at 20 and uniformly applied to the catalyst applied pulp.

The O-stage 18 will normally have an oxygen pressure of at least one atmosphere and preferably between four (4) and ten (10) atmospheres gauge pressure and will extend for a period of at least one quarter A) of an hour up to about six (6) hours, preferably less than about four (4) hours. The temperature in the O-stage 18 will be between 60°C and 200°C, preferably in the range of 80°C to 125°C. Obviously, the higher the temperature, the less time required and similarly, the higher the pressure, the less time required at a given temperature.

In the oxygenation stage, O-stage 18, the consistency will preferably be in the range of 10% to 15%. However, consistencies between 1% and 40% may also be processed.

It is important that the end pH, i.e. pH at its completion of the oxygenation stage (O-stage 18) be between about 1 and 7, preferably between about 2 and 6 and that the starting pH not exceed about 8. Generally, it has been found that the drop in pH during the O-stage will be in the order of about 1 to 3 points in pH. In most operations, the medium surrounding the fibers in the O-stage 18 will be water or water with some surfactants such as sodium dodecyl sulfate or water containing organic solvents compatible with the catalyst being used such as amides, alcohols and acetonitrile.

It is also possible to add small amounts of hydrogen peroxide or organic peroxide in addition to the pressurized oxygen gas in O-stage 18. A pretreated pulp leaves the O-stage 18 and may be washed as indicated at 22 or the pretreated pulp may simply pass directly without washing into the caustic extraction stage (E-stage) 24 which is another important step in the process of the present invention. The caustic E-stage 24 generally will apply similar conditions to those commonly practised in caustic E-stage 24 in pulp bleaching. Generally, the caustic charge will be about 0.5% to 4% calculated as NaOH based on the dry weight of the pulp (preferably between 0.5% and 2% temperature) as is normally the case would be essentially the same as using the oxygenation stage, may be slightly lower depending on the actual temperature used during oxygenation. Temperature should not be too high and thus, the temperature generally will be between 60 and 125°, preferably, between 60° and 80°C. Time for the E-stage will normally be between a quarter (%) and four (4) hours, preferably, between a half (^lA) and two (2) hours. The consistency is not important during the caustic E-stage but will generally be essentially the same as that used in the O-stage 18 and thus may vary between 1% and 40% but preferably will be somewhere between about 5% and 25%.

The caustic E-stage need not apply solely caustic; it may also apply oxygen or peroxide, for example, in an alkaline oxygen extraction or alkaline peroxide extraction, i.e. the E-stage may be an E₀ stage or an E_0P stage, etc.

In the modified system shown in Figure 2, steps 12 and 18 have been combined into a single unified catalyst application and oxygenation stage 26 wherein the catalyst is applied at 10 and the oxygen at 20 to a pulp introduced as indicated at 14, and all are uniformly mixed and treated in stage 26 using oxygenation conditions described above for the O-stage 18. It is important that in all cases, the catalyst be uniformly distributed throughout the pulp and similarly that the oxygen be uniformly distributed through the pulp regardless of whether they are both applied simultaneously (Figure 2) or in sequence (Figure 1).

As with the embodiment shown in Figure 1 , the pretreated pulp leaving stage 26 may then be washed as indicated at 22 and is subjected as indicated at 24, to a caustic extraction in the same manner as described hereinabove. Examples

Douglas fir TMP was prepared in a pilot refiner and screened through a 6 cut screen plate and retained at 150 mesh screen box and used in some of the tests. Mill produced hemlock CTMP secondary screen rejects were collected and used for other tests and mill produced kraft pulp fibers were used for others of the tests.

The vanadyl catalysts tested were vanadyl acetylacetonate, vanadyl sulfate and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine vanadium (IV) oxide (vanadyl porphyrin). These catalysts were purchased from Aldrich Chemical Company.

The pulp fibers and catalyst(s) were mixed at 10% consistency and then reacted at 100°C at about seven (7) atmospheres (100 psig) for two hours, the so treated fibers were then washed with water and then subjected to a caustic extraction using 1.5%

NaOH based on dry pulp, at 10% consistency and 80°C for one hour. Thereafter, the pulp was again washed with water. The treated pulp was then classified using a Bauer

McNett Pulp Classifier to isolate the R28 fiber fractions according to TAPPI method T233 and the R28 sheet was pressed and density measurements were performed by forming handsheets of the R28 fiber following the TAPPI T205 procedure and the density was measured based on TAPPI T220 method except that first pressing was always done at 50 psi and the second pressing respectively at 50 psi (standard), 100 psi and 715 psi to determine fiber conformability using the basic principle of Steadman and Luner's Wood Fiber Flexibility method as described by Steadman and Luner in "The

Effect of Wet Fiber Flexibility of Sheet Apparent Density", Papermaking Raw

Materials, 8th Fundamental Research Symposium, Oxford, vol. 1, 311-337 (1985).

Example 1

Douglas fir was treated with 1% vanadyl acetylacetonate in oxygenation and subsequently caustic extracted. During the O-stage, the pH drops by between 3.9 and

2.9 pH points during oxygenation. The controls were performed at both pH 3.9 and pH

2.9 to envelop the effect of the drop in pH. The treated pulps were then subjected to caustic extractions.

The results obtained using Douglas fir TMP, R28 fraction are given in Table I and shown in Figure 3. It will be apparent from Table I and Figure 3 that the vanadyl activated oxygenation extraction produces a pulp that compressed to a significantly higher density at a given pressure than both of the control and the untreated pulp. It is also apparent from Table I that if caustic extraction is not applied to the oxygenated pulp

(pretreated pulp), there is little gain and that the caustic extraction is an essential part of the present invention.

Table I

Douglas Fir TMP R28 Sheet Densities after Vanadyl Acetylacetonate Oxygenation and Caustic Extraction

Example 2

Vanadyl acetylacetonate oxygenation of hemlock CTMP was conducted both with and without pressurized oxygen followed by extraction. The results obtained are indicated in Table II and plotted in Figure 4. It is quite clear that the density curve for treatment without pressurized oxygen is much lower than that treated with pressurized oxygen. Thus, pressurized oxygen is required when using the vanadyl catalyst to produce a large increase in conformability. Hence, it is preferred to operate the present invention at elevated pressures (100 psig), i.e. six and seven atmospheres. Example 3

Hemlock CTMP secondary rejects were oxygenated in the presence of respectively 1%, 0.5% and 0.2% vanadyl acetylacetonate and subsequently caustic extracted. The results are listed in Table III and illustrated in Figure 5.

It will be apparent that the change in dosage of the catalyst vanadyl acetylacetonate, i.e. reduction from 1% down to 0.2% did not make any major differences in the sheet density tested after extracted and that the increase in sheet density in all cases was substantial.

Table II

Effect of Pressurized Oxygen in Vanadyl Oxygenation on Fiber Conformability of Hemlock CTMP

Table III

Effect of Various Doses of Vanadyl Acetylacetonate on Fiber Conformability of Hemlock CTMP

Example 4

Vanadyl porphyrin and vanadyl sulfate were also used with hemlock CTMP and the results obtained are listed in Tables IV and V respectively and shown in Figures 6 and 7. Example 5

The vanadyl acetylacetonate treated and extracted pulp was examined for mechanical properties compared with the same pulp but not treated. These tests were done based on secondary screen rejects which are essentially the long and coarse fiber fraction which is the reason the scattering coefficient and strength properties except tear are lower than pulps enriched with fines. Results obtained are shown in Table VI. This pulp was also tested for lipophilic wood extractives as it was expected that the oxygenation and caustic extraction would reduce these extractives which are mainly fatty and resin acids, etc. Table VII clearly shows that vanadyl acetylacetonate oxygenated and extracted hemlock CTMP secondary reject shows a very significant drop in extractives over that of the untreated pulp.

Table IV Effect of Vanadyl Porphyrin and Extraction on Hemlock CTMP

Table V Effect of Vanadyl Sulfate and Extraction on Hemlock CTMP

Table VI Some Mechanical Properties of Treated Fibers

Table VII

Concomitant Reduction of Extractives by Vanadyl Acetylacetonate Oxygenation and Extraction on Hemlock CTMP Secondary Rejects

Example 6

Both the untreated and vanadyl (vanadyl acetylacetonate) treated extracted hemlock CTMP secondary rejects wherein refined in a laboratory 12 inch Sprout- Waldron atmospheric refiner at 11% consistency for each sample, several refining passes were made, covering a range of Canadian Standard Freeness (CSF). Refining energy of each pass as well as the total energy were recorded on a computer system connected to the refiner. Starting freeness of the untreated pulp was 618 ml CSF.

Table VIII indicates the pass number, total energy in freeness data for both the treated and untreated pulps. These results are plotted in Figure 8. It will be noted that six (6) passes in a total energy consumption of 1890 kWhr/ton for the untreated pulp was required to reach a CSF of 94 ml while the treated pulp required only two (2) passes in a total specific energy of 810 kWhr/ton to reach essentially the same freeness (95 ml CSF) indicating in this example, a clear saving of 50% of the refining energy which is very substantial. This is also supported by the excellent development of mechanical properties in the refining of the treated pulp. Not only is the energy required to refine reduced, but also properties of the treated pulp are developed very well by refining as evident from Table VIII.

It is expected that the vanadyl oxygenation treatment followed by extraction could be applied to pulps after primary refining or even applied to fibrous material after impressifiner and then the pulp further refined to obtain the advantages of energy reduction. Example 7

Kraft pulp at a Kappa no. of 29 ml, brightness 25.6% ISO was delignified by application of vanadyl catalyst in an O-stage followed by caustic extraction. The catalyst used were vanadyl acetylacetonate and vanadyl sulfate, both applied in the amount of 0.5% based on the oven dried weight. In each case, the oxygenation runs were carried out at a pH of 5. The results obtained are described in Table IX.

It is apparent that both vanadyl acetylacetonate and vanadyl sulfate oxygenation followed by caustic, resulted in a significant degree of delignification, with the vanadyl sulfate accounting for about 27.9% and the vanadyl acetylaceetonate 24.8%, while the control only generated a delignification of 12.8%.

Table VIII Laboratory Refining of Hemlock CTMP Secondary Rejects

Table IX

Delignification of Kraft Pulp by Vanadyl Catalysts Oxygenation and Caustic Extraction

Example 8

In a companion experiment on the kraft pulp, 1 % vanadyl acetylacetonate was used and in another, 2% sodium dodecyl sulfate. These experiments starting pH at 7.6 and an end pH of 4.1 were followed by caustic extraction. Delignifications of 30% were obtained.

It will be apparent that the use of vanadyl catalyst described herein in an oxygenation stage followed by a caustic extraction stage which may take any suitable form including traditional alkaline oxygen delignification stage produce very substantial improvements in refinability of the mechanical pulps tested and substantial increases in delignification for chemical pulps.

Having described the invention, modifications will be evident to those skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMSWe claim:

1. A method of treating lignocellulosic material by applying an effective amount of catalyst selected from a group consisting of vanadyl organic complexes and vanadyl sulfate and subjecting the pulp to oxygenation conditions in an O-stage at a temperature of between 60° and 200°C for up to 6 hours and an oxygen over pressure of at least one atmosphere, said pulp being in a consistency of less than 40% and having a pH of between 1.5 and 7 at the completion of the O-stage to produce a pretreated pulp and then subjecting said pretreated pulp to a caustic extraction step (E-stage) to provide a treated pulp.

2. A method of treating lignocellulosic material as defined in claim 1 wherein said vanadyl organic complex is selected from a group consisting of vanadyl acetylacetonate and vanadyl porphyrin.

3. A method of treating lignocellulosic material as defined in claim 1 wherein said catalyst is selected from a group consisting of vanadyl sulfate and vanadyl acetylacetonate.

4. A method of treating lignocellulosic material as defined in claim 1, 2 or 3 wherein said catalyst is applied to said pulp in said O-stage

5. A method of treating lignocellulosic material as defined in claim 1, 2 or 3 wherein said applying of said catalyst and said subjecting to oxygen conditions occur in sequence with pulp first being treated with the catalyst stage to provide a catalyst applied pulp and then subjecting said catalyst applied pulp to said oxygenation in said O-stage.

6. A method of treating lignocellulosic material as defined in claim 1, 2 or 3 wherein said catalyst can be present in the amount of 0.01% to 2% by weight of the pulp.

7. A method of treating lignocellulosic material as defined in claim 1, 2 or 3 wherein said extraction stage (E-stage) will apply between 0.5% and 4% caustic as NaOH to said pretreated pulp.

8. A method of treating lignocellulosic material as defined in claim 7 wherein said extraction stage (E-stage) will apply between 0.5% and 4% caustic as NaOH to said pretreated pulp.

9. A method of treating lignocellulosic material as defined in claim 1, 2 or 3 wherein said pulp will be at a consistency of less than 15% in said O-stage.