Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Reexamination Certificate
1997-09-19
2001-02-27
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
C008S116100, C201S008000, C201S037000, C201S039000, C203S046000, C568S492000, C585S242000
Reexamination Certificate
active
06193837
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of extracting the water soluble fraction of biomass pyrolysis oils from pyrolysis oils and using these extracts to maintain the brightness of bleached pulps and paper containing lignin. Maintaining brightness in the pulp and paper manufacturing industry is also known as retarding or reducing brightness reversion.
BACKROUND OF THE INVENTION
Pulp is the raw material used in the production of paper, paper board, fiber board and the like, and is obtained from plant fiber such as wood, straw, bamboo and sugar cane residues.
Wood is the source of 95% of the pulp fiber produced in the United States, and dry wood consists of 40 to 50% cellulose, 15 to 25% other polysaccharides known as hemicelluloses, 20-30% lignin (a biopolymer that acts as a matrix for the cellulose fibers), and about 5% of other substances such as mineral salts, sugars, fatty acids, resins and proteins.
Lignin is composed primary of methoxylated phenylpropane monomeric units interconnected by a variety of stable carbon—carbon and carbon-oxygen (ether) linkages. The color of paper produced from pulp arises essentially from the lignin.
Since paper or pulps containing lignin or lignocellulose are commonly dark, they must be bleached if a white paper is desired; however, a major disadvantage or draw back of bleached lignin-containing pulps is that they are easily and extensively darkened by light irradiation, and this darkening process limits use of these pulps in various grades of printing papers.
In making newsprint, the paper of pulp used in the process is generally not bleached. However, if it is bleached, it is relatively mildly bleached compared to a higher quality paper than newsprint. Such unbleached or mildly bleached pulps have a darker quality than bleached pulps. Since news print has a relatively high lignin content, it has a tendency to become even darker when exposed to light.
One means for determining whiteness of paper is estimated by brightness measurements which are based on the reflectance of light having an average wavelength of about 457 nm. And Elrepho Brightness Meter is one type of instrument used to measure paper brightness. In this measurement, a low brightness (40% Elrepho) indicates brown or dark paper, while 90% Elrepho is typically white paper. Lignin-rich pulps have brightness values in the range of about 50-70% Elrepho depending upon the wood species used and the pulping process. In the pulping process, these pulps can be bleached to 70-90% brightness using known brighteners such as hydrogen peroxide, sodium borohydride or sodium dithionite. When a brightness of more than 70% is required, hydrogen peroxide is normally used; however, a problem or drawback associated with bleached lignin-rich pulps is that they may darken by as much as 20 Elrepho points when exposed to natural sunlight during exposure over a period of only one day.
Another method of determining brightening imparted by a brightening agent is to observe the extent of lowering of the light absorption coefficient (LAC).
While several methods are known to decrease light-induced brightness reversion in pulps containing high levels of lignin, they accelerate the yellowing that occurs in routine storage in the dark (thermal reversion), and the disadvantage of these methods is that they add significantly to the cost of the paper manufacturing process.
The use hydroxyacetaldehyde (HAA), also known as glycolaldehyde dimer has been used per se to prevent brightness retardation in lignin-containing paper; however, various means of producing HAA, inclusive of the pyrolysis of carbohydrate containing feedstocks and distillation of pyrolysis products under reduced pressure to provide pure HAA at 2% yield (
1,2
) at a cost of about $18.00/gram, makes the use of HAA at these prices prohibitive in paper manufacturing.
1. Stradal, J. A. and Underwood, G. L.,
Process for Producing Hydroxyacetaldehyde by pyrolysis of carbohydrate
-
containing feed stocks and artifical tanning agent containing the product
, PCT Int. Appl. WO 91/14379 (Oct. 3, 1991).
2. Scott, D. S.,
Pyrolysis of Biomass to Produce Maximum Liquid Yields
, PCT Int. Appl. WO 88/00 935 (Feb. 3, 1988).
One known method is described in European patent No. 0 280 332 (Agnemo et al.) consists of several treatments to reduce the carbonyl groups (photosensitizers) contained in the pulp to alcohol groups. In addition, this process includes alkylation of the phenolic hydroxyl groups in the lignin, from which hydrogen atoms are abstracted, by the use of an alkaline propylene oxide. The addition of fluroescent compounds that absorb or reflect the ultraviolet light which would otherwise excite photosensitizer groups is also disclosed.
The bleaching of pulp in-situ to remove lignin from pulp to maintain the brightness is disclosed in U.S. Pat. No. 5,366,593. The patent also discloses the use of dioxirane.
U.S. Pat. No. 5,354,423 discloses the use of a gaseous bleaching agent such as ozone to impregnate pulp in the presence of dioxane. A bleaching action takes place which removes the lignin from the final pulp product without destroying the cellulose in the pulp.
A method for stabilizing the pulp or paper containing lignin, is disclosed in U.S. Pat. No. 5,368,689; however, while this process is like those mentioned in the two foregoing patents, the method in this patent is not a method for producing a brightness stabilization agent.
U.S. Pat. No. 5,080,754 discloses a methodology for stabilizing the brightness of lignin-containing pulps. In this process, formic acid and its derivatives either alone or in combination with copper sulfate or ascorbic acid are used to stabilize the brightness reversion reactions such as photoyellowing of the paper.
A method for reducing thermal and light-induced brightness reversion in lignin-containing pulps is disclosed in U.S. Pat. No. 5,360,515. This patent utilizes 2,5-dihydroxydioxane or glycoaldehyde dimer to reduce brightness reversion in bleached lignin-containing pulps or newsprint.
A method for preventing the discoloration of paper and paper treated to prevent discoloring is disclosed in U.S. Pat. No. 5,181,988, and this method is similar to those described in the foregoing patents in that it is independent of a chemical manufacturing process, and utilizes hypophosphorous acid to reduce brightness reversion in pulp and paper.
All pulps can be divided into two main classes, chemical and mechanical pulps. Chemical pulps are made by application of chemicals to wood chips to dissolve sufficient lignin from the middle lamella and subsequently defibrate the fibers without any mechanical action. The dominant chemical wood-pulping process is the Kraft or sulfate process.
Mechanical pulps are made by defibrating wood through mechanical action such as grindstone, refiner disks, or thermomechanical process. Mechanical pulping processes retain most of the lignin in the wood and therefore the yields are usually very high (93-95% based on wood). Mechanical pulp production in the USA was about 11% of the total pulp produced in 1992. On a world wide basis, mechanical pulp production consistituted about 22% of the total pulp production in 1992. The large differences in the production of these two pulps stem from quality issues. For example, the production of mechanical pulp has the following advantages compared to chemical pulps:
It is less capital intensive (50% of the cost of Kraft Mill); it consumes less wood (50% less than chemical pulp); it consumes less energy than chemical pulp production (33% of Kraft Mill); there is reduced emission of odorous compounds and sulfur dioxide which contributes to acid rain; the use of environmentally benign chemicals eliminates the concerns about dioxins, chlorinated furans, and other chlorinated organics; and there is zero liquid effluent discharges using modern technology.
However, a major quality problem with mechanical pulps is yellowing of the paper on exposure to light or thermal sources. This phenomenon known as brightness reversion confines mechanical pulps to low
Agblevor Foster A.
Besler-Guran Serpil
Alvo Steve
Midwest Research Institute
Richardson Ken
White Paul J.
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