Chemistry: natural resins or derivatives; peptides or proteins; – Lignins or derivatives
Reexamination Certificate
2000-08-04
2002-07-16
Acquah, Samuel A. (Department: 1711)
Chemistry: natural resins or derivatives; peptides or proteins;
Lignins or derivatives
C530S205000, C530S208000, C527S400000, C527S604000, C524S073000, C210S634000, C210S767000, C210S194000
Reexamination Certificate
active
06420533
ABSTRACT:
BACKGROUND OF THE INVENTION
Pulping processes are employed to separate lignins from wood to produce a pulp. A solution containing sodium hydroxide is employed to dissolve lignins from the wood to yield a black liquor containing sodium hydroxide and depolymerized lignins. A recovery boiler is used to recover the sodium hydroxide and other compounds for reuse and release of the energy contained in the lignins to provide steam.
A state of the art Kraft pulping digestion process employs a solution containing sodium hydroxide and sodium sulfide to create a black liquor. After concentration of the black liquor, by means of a multiple-effect evaporator, the black liquor is sent to a recovery boiler to produce steam and a molten smelt containing sodium carbonate. The smelt of melted sodium compounds flows to a vat where it dissolves into green liquor The green liquor is slaked by calcium oxide to convert the sodium carbonate to furnish sodium hydroxide The calcium oxide, as a result, is converted to calcium carbonate which settles at the bottom of a white liquor clarifier tank. The resulting calcium carbonate, after separation of adhering white liquor, is transported to a lime kiln where the calcium carbonate is converted to calcium oxide. Thus the black liquor recovery cycle is completed.
Another pulping process employs a solution derived from sulfur burned to produce sulfur dioxide. The sulfur dioxide forms a bisulfite from a base, often magnesium, to form a solution. The solution containing bisulfites is used to depolymerize, disperse and dissolve lignins and create a “sulfite waste liquor.” In the process, soluble lignin sulfonic acid salts are formed from the solution. Recovery of the “sulfite waste liquor” is performed with a recovery boiler to produce sulfur dioxide and the inorganic base. Accordingly the recovery cycle has been completed
Thus, it is believed that only elaborate recovery methods have yet been developed.
This invention relates to a method of recycling a solution containing sodium hydroxide without using a recovery boiler, a lime kiln or a smelt.
Therefore, an object of this invention is to obviate many of the limitations and disadvantages of the prior art to depolymerize lignins from a solution containing sodium hydroxide.
Another object of this invention is to produce depolymerized lignins significantly free of sodium compounds.
Still another object of this invention is to produce depolymerized lignins significantly free of sodium compounds for use as a fuel.
An additional object of this invention is to provide recycling of a solution containing sodium hydroxide used to produce depolymerized lignins.
An significant object of this invention is to utilize a multiple-effect evaporator, previously required to concentrate black liquor, to remove water from the solution containing sodium hydroxide.
One more object of this invention is to separate black liquor from a soda pulping digestion process to produce depolymerized lignins and a solution containing sodium hydroxide
With the above and other objects in view, this invention relates to the novel features and alternatives and combinations presently described in the brief description of the invention.
PHRASEOLOGY APPLIED IN THE INVENTION
Lignins in the presence of a solution containing sodium hydroxide, at an elevated temperature, will depolymerize, disperse and dissolve lignins to form a black liquor. The term depolymerized lignins is often applied to lignins in a solution containing sodium hydroxide to depolymerize, disperse and dissolve lignins. Lignins are not well structured polymers. When a lignin polymer is fractured the term “depolymerized lignins” is often utilized even though no definite “lignin monomer” exists. The term “depolymerized lignin” is used interchangeably to designate lignins.
This invention relates to a black liquor or any mixture of sodium hydroxide containing depolymerized lignins, dispersed and dissolved in a solution containing sodium hydroxide. The mixture of sodium hydroxide containing depolymerized lignins dispersed and dissolved in a solution containing sodium hydroxide is generally separated by a membrane to provide depolymerized lignins and a solution: containing sodium hydroxide. The membrane, for example, can be a diffusion membrane or a nano filtration membrane. After separating, the depolymerized lignins are then counter flow extracted with water to produce depolymerized lignins substantially free of water soluble sodium compounds and an extractate containing water soluble sodium compounds. The previously extracted depolymerized lignins, substantially free of water soluble sodium compounds, necessitates an admixture of an acid to the depolymerized lignins to produce sodium salts from the depolymerized lignins containing sodium compounds. Depolymerized, lignins are prone to self condensation under acidic conditions. A solution of sodium salts is divided from the depolymerized lignins to produce depolymerized lignins free of sodium and a solution of sodium salts. The solution containing sodium hydroxide and the extractate are then combined and treated in a salt splitting procedure to remove salts and form sodium hydroxide and then the solution containing sodium hydroxide is evaporated to remove water to concentrate the solution. The concentrated solution regularly contains about 40% sodium hydroxide to about 10% sodium hydroxide. Either the solution containing sodium hydroxide or the concentrated solution must have salts removed by a salt splitter to prevent salt buildup in the concentrated solution. A salt splitting operation often utilizes either a bipolar membrane or an ion exchange resin to remove the anion from the salt. As a result sodium hydroxide is created from the salt. Salt splitting is dependent on a salt splitting action. Salt splitting is frequently accomplished with an aion ion exchange resin. The concentrated solution is then skimmed of tall oil containing sodium. Tall oil resembles a soap possessing sodium. The resulting tall oil, after separation from the concentrated solution, is then reacted with an acid to form a salt solution phase and a phase of crude tall oil.
The salt solution phase is combined with the solution of sodium salts, from the acidification of the depolymerized lignins containing sodium compounds, and then subjected to salt splitting, for example a bipolar membrane, to form a solution of sodium hydroxide and a solution of an acid and a solution of un-coverted sodium salts. The solution of un-coverted sodium salts, with water removed, is then recycled to the salt splitter. Purges are performed, as necessary, to prevent buildup of undesired impurities.
The multiple-effect evaporator, previously required to concentrate black liquor, is capable of being applied to remove water from the solution containing sodium hydroxide to produce “white liquor” for recycle. A multiple-effect evaporator is often employed in concentrating a solution, by removal of water. Means to separate the depolymerized lignins will depend on depolymerized lignins molecular properties including molecular size, density and diffusion rate. Membranes can be selected from the group of membranes including diffusion membranes and nano filtration membranes. Several other means of separation depend on depolymerized lignins molecular properties include cooling, adsorption, absorption, retardation, filtration and diffusion.
For supplementary particulars on lignin, for example, refer to
Pulp And Paper Technology
pages 33-36.
For information on tall oil, for example, refer to
KIRK
-
OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY FIFTH EDITION VOLUME
23, pages 615-622. Membranes, providing a means for separation, may employ a diffusion membrane, an ultra filtration membrane or a nano filtration membrane such as described, for example, in the bulletins supplied by membrane manufacturers Aqualytics and Desal membrane products, Inc. respectively.
Salt splitting, for example, is described in bulletins provided by several companies including Aqualytics and Dow Chemical Company.
BRIEF DESCRIPTION O
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