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Selectivity improvement in oxygen delignification and bleaching of lignocellulose pulp using singlet oxygen

a technology of lignocellulose and oxygen delignification, which is applied in the field of process for delignification and bleaching of lignocellulose pulp and improving selectivity, can solve the problems of peeling, reducing pulp strength, and reducing yield

Inactive Publication Date: 2009-04-09
ROSSI JOANNE MARY FOBARE
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

"The patent describes a new way to make chemical or mechanical pulps brighter or whiter. It involves using a chemical called singlet oxygen that is generated by a photochemical process and then transported to the pulp to remove the lignin that makes the pulp dark. This improves the bleaching of the pulp and makes it brighter. The process involves using visible light and a chemical to convert molecular oxygen into singlet oxygen, which is then applied to the pulp during the pulping procedure."

Problems solved by technology

These species interact with lignin in a complex fashion; however they can also degrade cellulose causing yield loss and decreased pulp strength.
However, when random chain cleavage is excessive, peeling can become a problem since two new chain ends are formed which have a reducing end group
Furthermore, as pointed out by Turner, the data in Table I in Liebergott indicate that activated oxygen [generated per Liebergott's process] was only marginally effective in delignifying and bleaching lignocellulosic pulps.
Furthermore, there is no assurance that residual H2O2 or NaClO may not carry out some bleaching.

Method used

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  • Selectivity improvement in oxygen delignification and bleaching of lignocellulose pulp using singlet oxygen
  • Selectivity improvement in oxygen delignification and bleaching of lignocellulose pulp using singlet oxygen
  • Selectivity improvement in oxygen delignification and bleaching of lignocellulose pulp using singlet oxygen

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0080]The equipment included a three-necked round bottom flask equipped with a mechanical stirrer, a condenser with gas bubbler, gas inlet with a U-tube (or reduced ends tube) filled with methylene blue prior to entering the round bottom flask, and a 500 W portable halogen worklight source (Stanley Tools, Manufacturer No. XG-1009) as shown in FIG. 1. The flask was charged with 110.82 g deionized water, 3.0 g sodium hydroxide (NaOH), 0.18 g magnesium sulfate (MgSO4) and 6.0 g softwood pulp with a starting Kappa number of 54.4. Softwood pulp was added after the sodium hydroxide and magnesium sulfate completely dissolved. The reaction flask was heated to reflux (100° C.) for four hours. Molecular oxygen flows from the oxygen tank and is treated in a separate stream in a chamber via a combination of visible light and a chemical agent, which is then applied to the pulp mixture. The flow rate of the molecular oxygen was between 110 to 140 mL / min and more typically 125 mL / min as measured b...

example 2

[0085]The Parr reactor was charged with 180 g deionized water, 19.31 g softwood pulp (18.0 g oven dried pulp), and 0.0072 g NaOH. Softwood pulp was added after the sodium hydroxide and magnesium sulfate completely dissolved. The reaction flask was heated to 100° C. at 275 kPa for 90 minutes. The one-piece pressure reactor manifold (Ace Glass, Vineland, N.J.) was packed with glass wool, Drierite® anhydrous calcium sulfate, and glass beads coated with the methylene blue photosensitizer. For the control molecular oxygen experiments, the methylene blue photosensitizer was covered with aluminum foil. The light from a halogen lamp (500 W) was applied during the singlet oxygen experiments. The pulp consistency was 10%.

[0086]After a specified time, the reacted pulp was isolated on a Buchner funnel with a Whatman #41 filter paper under aspirator vacuum. The pH of the filtrate was measured between 7.9 and 9.4. The pulp was rinsed by the addition of about 500 mL D.I. water to the funnel with a...

example 3

[0088]In this example, the Parr reactor was charged as described in Example 2. The pressure manifold was prepared as described in Example 2 except that the photosensitizer was rose bengal and compressed oxygen (or compressed air) was used as the gas. The amount of MgSO4 added for sample I.D. #3A, 3B, 3C, and 3D was 0.009 g.

TABLE 3EFFECT OF HIGH PRESSURE OF MOLECULAR OXYGEN VERSUS SINGLET OXYGEN ONSOFTWOOD USING ROSE BENGAL AS THE PHOTOSENSITIZER.IntrinsicMwSelectivitySelectivitySampleViscosityKappa(g / mol)SelectivitySelectivityImprovementImprovementTAPPII.D.Description[η], mL / gNumberSECfrom [η]from Mwfrom [η], %from Mw, %Brightness3AMolecular60724.9842,00024.433,800——26.8Oxygen3BSinglet71121.3930,00033.443,70036.929.426.9Oxygen3CAir -64627.8943,00023.233,900——24.6M.O.3DAir -66526.3892,00025.333,900 8.8 0.024.1S.O.M.O. = molecular oxygen andS.O. = singlet oxygen

[0089]The data set forth for unbleached kraft softwood pulp in Table 3 for rose bengal illustrates the selectivity improvemen...

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Abstract

A process to enhance delignification or bleaching in chemical or mechanical pulps comprising generation of singlet oxygen as a separate step and subsequent transport of singlet oxygen to pulp to effect bleaching or brightening of the pulp.

Description

FIELD OF INVENTION[0001]The present invention relates to a process for delignification and bleaching of lignocellulose pulp and improving selectivity by means of which a stream of molecular oxygen is treated with visible light and a chemical agent generating singlet oxygen and then applying the stream of singlet oxygen to pulp during the pulping procedure.BACKGROUND OF INVENTION[0002]Oxygen delignification is the use of molecular oxygen (i.e., ordinary oxygen) and alkali to remove a substantial fraction of lignin in unbleached chemical pulp before conventional bleaching. Oxygen bleaching is considered synonymous with oxygen delignification. The process is usually conducted with molecular oxygen under high pressure and at elevated temperatures. Molecular oxygen is usually applied to kraft unbleached pulps but can also be used for other chemical pulps. Oxygen delignification is now a commercial process, and a number of patents have been published. These patents describe the use of mol...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): D21C9/147
CPCD21C9/147D21C9/1015
Inventor HOLLOMON, MARTHA G.CHENG, HUAI N.
Owner ROSSI JOANNE MARY FOBARE
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