The present invention relates to a method for removing wax from a pulp furnish and, more particularly, a method from removing wax from a pulp furnish containing waxed old corrugated containers.

Today many paper mills are utilizing recycled fiber as a portion of their papermaking furnish. Recycled fiber is a valuable raw material, though it is inherently weaker than virgin fiber and contains contaminants which effect system cleanliness and appearance. Many new chemistry technologies are emerging to improve the appearance and strength of recycled fiber containing furnishes, as well as improving system cleanliness. Raw materials of reduced cost and quality such as waxed old corrugated containers (wOCC), mixed office waste (MOW), and curbside mixed waste (CMW) may be utilized without loss in appearance and paper properties when chemical aids to pulp cleaning are incorporated. Replacement of 10% of the OCC with wax saturated OCC would represent a significant economic savings for the paper mill.

US-A-2 959 513 relates to a process for treating waste waxed material which comprises treatment of pulped waxed paper with agglomeration chemicals such as sodium metasilicate (Na₂SiO₃) at a temperature sufficiently high so as to melt the wax.

US-A-5 441 601 discloses a process for the recycling of xerographic waste which comprises adding an organic polymeric particulate and a substantially waster insoluble organic ester to a repulped aqueous slurry containing xerographic toner particles. The process may also comprise the use of a secondary agglomerating agent.

The present invention provides a method for removing wax from a pulp furnish. More specifically, a method for recycling waxed old corrugated containers (wOCC) is provided. In the method, a pulp furnish containing fibers and wax, such as waxed OCC, is first separated into fibers and wax, and then the wax is separated from the fibers. The separation of wax from the fibers is effected through the utilization of an agglomerization chemical comprising d-limonene and sodium metasilicate, with the pulp furnish being maintained at a temperature below the wax melting point. The method of the invention provides fibers from waxed OCC that preferably include less than about 0.5% by weight wax.

Through the method of the invention, waxed OCC can be recycled and used in a conventional pulping operation. A pulper furnish containing 10% wax saturated boxes has 95% yield through the operation. The wax content of pulp produced by the method meets the levels commonly accepted by the papermaking industry.

In the method, an agglomeration chemical comprising d-limonene and sodium metasilicate effectively increases the size of the wax particles removed from the fibers. The size increase facilitates their removal in the screening and cleaning stages in the mill. Chemicals that may further be included that provide wax removal and agglomeration include sodium sulfate, potassium sulfate, lauryl sulfate, propylene carbonate, and mixtures of these chemicals. In a preferred embodiment, the method further includes the addition of a caustic material such as sodium hydroxide at the pulping stage which enhances wax separation from the fiber.

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

• FIGURE 1 is a flow diagram illustrating a representative method of the invention;
• FIGURE 2 is a table summarizing the characteristics of pulp treated with various agglomeration chemicals, under the conditions according to the method of the invention;
• FIGURE 3 is a graph illustrating wax removal from a pulp furnish containing Waxed OCC according to methods carried out under the conditions of the method of the invention but with various agglomeration chemicals;
• FIGURE 4 is a table summarizing the basis weight and caliper of handsheets formed from pulp treated with various agglomeration chemicals under the conditions according to the method of the invention;
• FIGURE 5 is a table summarizing the density, SSC, SSC Index, moisture, Canadian Standard Freeness (CSF), and percent VFS rejects for handsheets formed from pulp treated with various agglomeration chemicals under the conditions according to the method of the invention;
• FIGURE 6 is a table summarizing the accepted wax extraction, percent total pulp wax extraction, wax lost, conductivity, pH before pulping, and surface tension before pulping for pulp furnishes treated with various agglomeration chemicals under the conditions according to the method of the invention;
• FIGURE 7 is a graph illustrating wax removal, percent rejects and wax, and SSC Index for handsheets formed from pulp furnishes treated according to methods carried out under the conditions of the method of the invention but with various agglomeration chemicals;
• FIGURE 8 is a graph illustrating wax removal and SSC Index for handsheets formed from pulp furnishes treated with sodium hydroxide and various agglomeration chemicals under the conditions according to the method of the invention;
• FIGURE 9 is a graph illustrating wax removal and SSC Index for handsheets formed from pulp furnishes treated with various agglomeration chemicals and not treated with sodium hydroxide under the conditions according to the method of the invention;
• FIGURE 10 illustrates the wax content profile for screen rejects during the course of wax removal for methods carried out under the conditions according to the method of the present invention but with various agglomeration chemicals;
• FIGURE 11 illustrates the wax content profile for thickener accepts and high density discharge during the course of wax removal according to the method of the present invention;
• FIGURE 12 illustrates the wax content profile for the clarifier outlet and cleaner rejects during the course of wax removal according to the method of the present invention;
• FIGURE 13 is a graph illustrating average wax content in thickener accepts and high density discharge with agglomeration chemicals according to the method of the invention;
• FIGURE 14 is a graph illustrating average stickies content in thickener accepts and high density discharge with agglomeration chemicals according to the method of the invention; and
• FIGURE 15 is a graph illustrating SSC Index for handsheets formed from pulp furnishes treated with agglomeration chemicals according to the method of the invention.

The present invention provides a method for removing wax from a pulp furnish that includes waxed old corrugated containers (wOCC). In the method, wax is separated from wax saturated OCC and then agglomerated and removed from the pulp furnish. The method provides a pulp furnish having an acceptably low wax content, preferably less than about 0.5% by weight based on the total weight of fibers.

In the method, an agglomeration chemical comprising d-limonene and sodium metasilicate is added to a pulp furnish that includes waxed OCC. In one embodiment, the agglomeration chemical is added to the furnish in the pulper. In another embodiment, the agglomeration chemical is added to the furnish after pulping and before transfer to the pulper dump chest. In a preferred embodiment, the pulper furnish further includes a caustic material. Suitable caustic materials include soda ash and hydroxides such as ammonium, potassium, and sodium hydroxides. Preferably, the caustic material is sodium hydroxide.

A representative method for removing wax from waxed OCC is illustrated by the flow diagram shown in FIGURE 1, Referring to FIGURE 1, waxed OCC and OCC bales are added to a pulper to provide a furnish having a consistency of about four percent by weight solids in water. Consistencies in the range from about 3 to about 8 percent by weight are suitable. The furnish is typically heated at a temperature of about 52°C (125°F). Suitable temperatures are generally in the range from about 49°C (120°F) to about 66°C (150°F). However, the temperature should not be so high as to melt the wax. For methods of the invention that utilize a caustic material to enhance wax removal, the caustic material is preferably added to the pulper prior to commencement of agitation. The agglomeration chemical can be added to the furnish in the pulper (addition point A) prior to pulping or downstream from the pulper (addition point B) after pulping and prior to the furnish reaching the pulper dump chest. The optimal addition point will depend on the particular agglomeration chemical utilized and the OCC plant configuration. After treatment with the agglomeration chemical, the pulp furnish is directed to screens and cleaners where the agglomerated wax particles are removed from the furnish.

The agglomeration chemical may further include additional chemical additives that effect wax removal and agglomeration from waxed OCC in a pulp furnish. Such chemicals include sulfates, such as sodium sulfate, potassium sulfate, and lauryl sulfate; silicates and metasilicates, such as sodium silicate; citrus oils; propylene carbonate; and mixtures of these chemicals. Preferred additional chemicals include sodium sulfate.

The method of the present invention provides for the effective removal of wax from a pulp furnish. The method is equally suited for the removal of stickies. The term "stickies" refers to materials including adhesives, glues, and waxes commonly used in conjunction with paper and which present a problem during their recycling.

The following examples are presented for the purpose of illustration, and not limitation, of the present invention.

In this example, the ability of agglomeration chemicals to remove wax from waxed OCC was determined. The pulp furnish included 10% by weight waxed OCC and 90% by weight OCC. The furnish was selected to simulate the estimated mill raw material mix. The estimate is based on grocery store projections.

General Procedure. Batches of OCC were pulped in a laboratory scale pulper. For methods including sodium hydroxide, it was added directly to the pulper before agitation began. The agglomeration chemicals were added either before or after pulping. The wax was then removed from the fibers by screening and washing the pulp. Handsheets were prepared from the resulting "cleaned" pulp and the handsheets were evaluated for wax content and strength properties.

The ability of the process to de-fiber the containers was evaluated with the Valley Flat Screen (VFS) Rejects test. In the test, the material which cannot pass through a 15/1000 cm (6/1000") slotted screen is considered "rejects". The weight percent of rejected material indicates the ability of the process to break down the containers into fiber and wax.

• 1. Place 30 g of waxed OCC pieces and 270 g of unwaxed OCC pieces (5cm x 5cm (2" x 2") maximum) in the small batch pulper.
• 2. Add 4700 ml of hot deionized water (DI) 52 °C (125 °F) to the pulper to obtain a 6% pulper consistency.
• 3. For the caustic sets, add 12 grams of 50% NaOH (2% NaOH by weight).
• 4. For sets with agglomeration chemicals added before pulping, add 0.75 gram of the as received chemical at an addition rate of 2.5 kg chemical/ton fiber (5 pounds chemical/ton fiber).
• 5. Run pulper for 30 seconds to obtain mixing. For each batch of pulp, run pulper for another 45 minutes. Insulate pulper to maintain pulp temperature.
• 6. Remove 50 grams of OD fiber (on an oven dry basis) from each batch for rejects test.
• 7. Dilute each batch to 1% consistency with hot water (52 °C).
• 8. Run Valley Flat Screen Rejects test with 15/1000cm (6/1000 inch) cut slots using hot water (about 50°C) for the rinse water.
• 9. Remove another 100 grams of OD fiber from each batch.
• 10. Repeat steps 7 and 8.
• 11. Dilute the accept pulp to 1.0 % consistency for sheet formation Adjust to pH 7.0. Prepare ten standard handsheets (basis weight 26 lb/MSF, i.e., 0.13 kg/m² (26 lb/1000ft²)) from the accepts with pressing at 345 kPa (50 psi.)
• 12. Prepare two handsheets from the unscreened pulp for wax testing.

The following agglomeration chemicals were utilized in the above described procedure as indicated. Identifier Chemical SAF42-1 Control SAF42-2 2% NaOH The following examples included 2% NaOH added before pulping. SAF42-3 Potassium sulfate before pulping SAF42-4 Potassium sulfate after pulping SAF42-5 Cytec 3523 before pulping SAF42-6 Lauryl sulfate before pulping SAF42-7 2-propanol after pulping SAF42-8 Lauryl sulfate before pulping and 2-propanol after pulping SAF42-9 Potassium sulfate before and citric acid after pulping SAF42-10 Citric acid after pulping SAF42-11 MLTRPHY'S OIL SOAP and Cytec 3523 both before pulping SAF42-12 Lauryl sulfate before and potassium sulfate after pulping SAF42-13 Sodium metasilicate before pulping SAF42-14 SIMPLE GREEN before pulping SAF42-15 Sodium metasilicate before and potassium sulfate after pulping SAF42-16 Potassium sulfate before and 2-propanol after pulping SAF42-17 Sodium sulfate before pulping SAF42-18 d-Limonene before pulping SAF42-19 Sodium metasilicate, 2.5 kg/ton (5lbs/ton) and Darasperse 2372, 0.5 kg/ton (1lb/ton) both added before pulping. SAF42-20 Sodium lignosulfonate before pulping SAF42-21 Terpineol before pulping SAF42-26 PAC (polyaluminum chloride)

The following examples did not include sodium hydroxide. SAF42-22 Potassium sulfate before pulping SAF42-23 Potassium sulfate after pulping SAF42-24 Sodium metasilicate SAF42-25 SIMPLE GREEN SAF42-27 NaOH to pH 8-8.5 SAF42-28 NaOH to pH 8-8.5 and potassium sulfate

In addition to the agglomeration chemicals identified above, other agglomeration chemicals (i.e., SAF41-15 through SAF41-42) evaluated in the procedure include those in FIGURE 2. The visual appearance, VFS rejects, reject ranking, accepted wax extraction percentage, and total wax extraction for these chemicals are summarized in FIGURE 2. In the FIGURES, the agglomeration chemicals are referred without their SAF41 or SAF42 prefix.

Initial Results. With the selected furnish ratio of 10:90 by weight waxed:unwaxed OCC, the raw material for this experiment contained 3% by weight wax. Several of the chemical processes were able to reduce the wax to 1.5% or less and have defiber-to-rejects of 10% or less. The results of the wax and rejects evaluation for the above-noted agglomeration chemical additions are presented graphically in FIGURE 3. In FIGURE 3, wax removal is illustrated by plotting percent accepted wax versus percent rejects.

Referring to FIGURE 3, many of the chemistry formulations were able to de-fiber the raw material as evidenced by reject rates less than 10%. None of the chemistries were able to reach the wax content target of 0.5%. The results indicate that more effective agglomeration chemicals and conditions include 2% NaOH with Cytec's polyacrylamide 3523 (23), 2% NaOH with lauryl sulfate (36), 2% NaOH with sodium metasilicate (40), 2% NaOH with SIMPLE GREEN (42), 2% NaOH with potassium sulfate (19), 2% NaOH with MURPHY'S OIL SOAP (38), 2% NaOH with 1-octanol (26), 2% NaOH with citric acid (35), and 2% NaOH with 2-propanol (27).

In addition to the agglomeration chemicals noted above, inert materials were also evaluated for their ability to agglomerate wax. The materials included calcium carbonate, clay, talc, ammonium zirconium carbonate, diatomaceous earth (silicate remains of plankton), and sodium borate. These materials were ineffective at reducing the wax content in the cleaned pulp and, in some cases, created more rejects.

In this example, the sheet strength of handsheets formed from pulp furnishes treated by the method of the invention was determined. In addition to evaluating the ability of agglomeration chemicals to remove wax from a pulp furnish containing waxed, the short span compression strength (SSC) was determined. The short span compression strength (SSC) was determined using TAPPI Method T826. The SSC Index is calculated as the SSC in lb/inch divided by the basis weight in lb/MSF and thus is normalized for basis weight. The pulp furnish included 10% by weight waxed OCC and 90% by weight OCC. As described below, the method of the invention provides handsheets having high sheet strength with low rejects and low wax content.

The basis weight and caliper for handsheets prepared from pulp furnishes treated using agglomeration chemicals and conditions as described above in Example 1 are summarized in FIGURE 4. The density, SSC, SSC Index, moisture, Canadian Standard Freeness (CSF), and percent VFS rejects for these handsheets are summarized in FIGURE 5. FIGURE 6 summarizes the accepted wax extraction, percent total pulp wax extraction, wax lost, conductivity, pH before pulping, and surface tension before pulping for the identified pulp furnishes. FIGURE 7 shows the impact of the chemical additions on the rejects, wax, and short span compression strength (SSC).

Referring to FIGURE 7, sets 2 through 21 and 26 all contained 2% sodium hydroxide in the pulping stage. Sets 27 and 28 included only enough sodium hydroxide to elevate the pH to 8.5 (about 0.5% sodium hydroxide is required to obtain pH 8.5). Sets 1 and 22 to 25 did not contain any sodium hydroxide. As illustrated in FIGURE 7, the addition of sodium hydroxide is required to reduce the rejects to an acceptable level in the process.

Agglomeration chemistries that do not achieve a short span compression strength index of 0.5 or greater are not preferred. All of the chemistries evaluated provided reject rates below typical industry reject rates of 8 to 10%. Preferred chemistries provide handsheets having a final sheet wax content of less than 1% by weight.

Regarding certain of the agglomeration chemicals, the Daraclean product is comprised of 85% d-limonene and other organic components. The major component of SIMPLE GREEN is oil of bitter orange which contains d-limonene, citral, terpineol and pinene. A major component of both is d-limonene

Some agglomeration chemicals and their wax removal characteristics are illustrated in FIGURE 8. Agglomeration chemicals with suitable characteristics include potassium sulfate (K₂SO₄), sodium sulfate (Na₂SO₄), lauryl sulfate (sodium dodecyl sulfate or SDS), d-limonene, and sodium metasilicate (Na₂O₃Si).

Some mills are not equipped to run sodium hydroxide in the pulping operation. However, mills that are not equipped to utilize sodium hydroxide benefit from the addition of agglomeration chemicals to the pulper. The results for removing wax from a pulp furnish without using sodium hydroxide according to the method of the present invention is illustrated in FIGURE 9.

None of the chemicals shown in FIGURE 9 achieve a reject level as advantageous as the sodium hydroxide-containing chemistry schemes, however, all are below the industry target of 8% rejects.

Most of the chemistries depicted in FIGURE 9 provide handsheets that contain as much wax as the control. The addition of SIMPLE GREEN (conunercial household cleaner) to the pulper does reduce the wax to less than 1%. Because the major component of SIMPLE GREEN is d-limonene, the addition of d-limonene to the pulper in a mill not set up for sodium hydroxide provides an alternative for that mill for reducing wax content. Furthermore, as illustrated in FIGURE 9, the addition of SIMPLE GREEN increased the strength of the handsheet.

In this example, the ability of the combination of d-limonene and sodium metasilicate to remove wax from waxed OCC was determined. The pulp furnish included 10% by weight waxed OCC and 90% by weight OCC.

The fine screens were able to concentrate the wax by removing it with the rejects. The wax content of the fine screen rejects increased with the addition of caustic (i.e., sodium hydroxide) as shown in FIGURE 10. The addition of d-limonene and sodium metasilicate also increased the removal of wax in the fine screen rejects. The high variability in the wax content appears to be partially due to variability of the wax in the pulper accepts. The wax variability also appears in the thickener accepts and the high density storage discharge as seen in FIGURE 11.

There were concerns that the wax removed in the cleaners would be returned to the system via the clarifier. As illustrated in FIGURE 12, the clarifier is capable of removing the wax from the cleaner rejects. The cleaner rejects wax content was higher when the d-limonene and metasilicate were added.

FIGURE 13 shows the average wax content of the thickener and the high density storage discharges during the trial. All of the pulps contained caustic, except for the baseline pulp. The wax content of the high density storage did decrease with the addition of caustic. The lowest wax content occurred with the addition of 0.5 kg/ton (1 lb/ton) of d-limonene and caustic.

The stickies count of the pulp samples are shown in FIGURE 14. The addition of caustic reduced the stickies count slightly. The addition of d-limonene and sodium metasilicate was successful in reducing the stickies of the high density discharge pulp. A preferred combination for producing low stickies counts is caustic (e.g., sodium hydroxide) with d-limonene ((1 kg/ton) 2 lb/ton) and sodium metasilicate ((2.5 kg/ton) 5 lb/ton).

The addition of d-limonene and sodium metasilicate lowers the strength of handsheets formed from the pulp as shown in FIGURE 15.