PULPING PROCESS WITHOUT A RECOVERY FURNACE

PROCEDE DE PREPARATION DE PATE SANS FOUR DE RECUPERATION

English Abstract

A novel pulping process has been discovered whereby acid is added to the black
liquor mixture. The acid renders the lignin insoluble thus enabling it to be
separated from the black liquor. The invention obviates the need for a
recovery boiler which burns the sugars and the lignin. Additionally, sodium
salts are precipitated out of the process. Sodium carbonate from outside
sources is used in the novel process.

French Abstract

La présente invention concerne un procédé de préparation de pâte dans lequel un acide est ajouté à la liqueur noire. L'acide provoque l'insolubilité de la lignine, ce qui permet de la séparer de la liqueur noire. L'invention permet d'éviter le besoin d'une chaudière de récupération qui brûle les sucres et la lignine. En outre, dans ce procédé des sels de sodium sont précipités. Dans ce procédé, on utilise du carbonate de sodium provenant de sources extérieures.

Claims

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I claim:
1. A pulping process comprising the steps of:
(a) adding caustic solution to pulpable material;
(b) mixing said caustic solution and said pulpable material;
(c) separating cellulose components and liquor components from the caustic
solution and said pulpable material;
(d) treating said black liquor with an acid to render the lignin components
insoluble; and,
(e) separating inorganic and organic materials.
2. A black liquor separation process comprising the steps of
(a) adding acid to said black liquor to render the lignin insoluble; and,
(b) separating inorganic and organic materials from said black liquor.
3. A black liquor separation process as claimed in claim 2 wherein said
acid is an inorganic acid or an organic acid.
4. A black liquor separation process as claimed in claim 2 wherein said
acid is formed by adding carbon dioxide to said black liquor.
5. A black liquor separation process as claimed in claim 2 wherein said
acid is formed by adding sulphur dioxide to said black liquor.
6. A process as in claim 1 wherein sodium carbonates are added to said
caustic solution.
7. A process as claimed in claim 1 further comprising the steps of
removing organic materials; and,
replacing the energy content of said organic materials with natural gas.
8. A process as claim in claim 7 wherein an alternative fuel is used
instead of natural gas.
9. A black liquor separation process as claimed in claim 2 wherein
combinations of inorganic and organic acids are used to render said lignin
insoluble.
10. A process as claimed in claim 1 wherein said acid is acetic acid

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which produces sodium acetate.
11. A process as claimed in claim 1 wherein said acid is phosphoric
acid which produces a sodium phosphate.
12. A process as claimed in claim 1 wherein said acid is sulphuric acid
which produces sodium sulfate.
13. A process as claimed in claim 1 wherein said organic materials
include sugars and further comprising the steps of
converting said sugars into alcohol.
14. A process as claimed in claim 1 wherein said organic materials
include sugars and further comprising the steps of
converting said sugars into acetic acid.

Description

CA 02345394 2001-03-23
WO 00/17444
PCT/US99/22271
PULPING PROCESS WITHOUT A RECOVERY FURNACE
This application claims the benefit of previously filed United States
Provisional Patent Application No. 60/101583 filed September 24, 1998.
The present Kraft pulping system is more than one hundred years old.
S When the Kraft pulping system was first put into use there was no polymer
industry of any significance. However, today in the United States alone the
polymer industry produces over 70 billion pounds of various polymer products
with the majority derived from petrochemical feedstock. Worldwide
production is over 270 billion pounds annually. This demand for polymers
creates a market for polymers from lignin which is part of this process. In
the
current kraft pulping process the lignin is burned as a fuel and its only
value is
its BTU value. This is an inefficient use of the lignin.
Current technology has demonstrated that lignin can be used in the
foundry industry, urethane foam industry and also the plastics industry.
Lignin has more value when it is used in lignin based products in the polymer
industry as compared to lignin used as a fuel. Once the lignin is removed
from the black liquor it is possible to easily separate the sugars that are
present
and convert them into ethanol that can be added to gasoline. Obviously, the
use of ethanol as a fuel supplement to gasoline was not popular or even
known at the time of the Kraft pulping process.
Natural gas is readily available as a fuel and is environmentally clean.
Natural gas boilers can provide the necessary steam requirements for a pulp
mill at a fraction of the cost of a recovery boiler. Recovery boilers which
burn lignin are difficult to control and maintain in compliance with
environmental laws. Natural gas boilers are environmentally friendly and
clean.
At the present time in the kraft pulping process, the kraft soda pulping
process and the semi-chemical pulping process it is necessary to have the
black liquor concentrated and burned in a recovery furnace in order to have
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the sodium compounds converted into sodium carbonate. Then the sodium
carbonate is reacted with calcium hydroxide to produce sodium hydroxide
which is the desired pulping chemical. However the capital costs for such
processing steps as oxidation of the black liquor, using a multiple effect
S evaporator and then further evaporation of the black liquor with a direct
contact evaporator are very expensive. The most expensive piece of
equipment is the recovery furnace and also the most dangerous to operate.
Additionally, recovery furnaces fired by black liquor are not environmentally
clean to operate. This novel process produces valuable byproducts from the
black liquor and enables alternate, cheaper fuels such as natural gas, to be
used in the process without a recovery boiler. Boilers fired by natural gas
and
other fuels are used in the process to produce the required steam.
Another major advantage of this invention is that by removing the
lignin from the black liquor it now becomes possible and economical to
1 S produce a variety of other products such as sodium acetate, sodium
sulfate,
wood sugars, acetic acid, and lignin.
It is this equipment (recovery furnace) that contributes to the high cost
of operating a pulping mill and signif cantly affects the prof tability of a
pulp
mill. It is the major advantage of this present invention that allows all of
this
equipment to be eliminated from a pulp mill.
By acidifying the black liquor with an acid, it is possible to precipitate
the lignin and produce a sodium salt which has a commercial value in the
marketplace. Organic acids and inorganic acids may be used. As an example
one such acid is acetic acid whereby sodium acetate is produced or phosphoric
acid could be used which produces a sodium phosphate salt. By producing
sodium salts which are more valuable than sodium carbonate, it is more
economical and more profitable than using the present recovery furnace to
produce sodium carbonate by using the present recovery furnace and its
auxiliary equipment. Also, sodium salts do not have to be more valuable than
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sodium carbonates to make this process economical.
PCT/US99/22271
Fig. 1 is a schematic representation of a pulping process without a
recovery furnace.
Fig. 2 is a schematic of a known pulping process with a recovery
furnace.
As an example, addition of acetic acid to the black liquor until the
lignin is insoluble, will render the lignin insoluble and will be filtered
from the
liquor by various means. A filter press, vacuum filter belt or ordinary
filters
are some of those means.
As an additional example, 10% solution of sulfuric acid may be added
to the black liquor until the lignin is insoluble enabling the lignin to be
filtered
from the liquor by various means. Most of the lignin is insoluble at pH of
approximately 2-3. After the lignin is removed, the solution is concentrated
by
evaporation or other means forming crystals of sodium sulfate. Then the
sodium sulfate crystals are filtered from the solution thereby producing a
sugar solution which can be used to produce alcohols or other products. A
filter press, vacuum filter belt or ordinary filter may be used to filter the
sodium sulfate crystals.
Optionally, carbon dioxide and sulphur dioxide may be added to the
black liquor. These gases become acids when added to the black liquor as
they react with water.
Those skilled in the art will recognize that many changes may be made
to the invention heretofore described without departing from the spirit and
the
scope of the appended claims. Commercially valuable sodium salts are also
produced by the addition of the acid to the black liquor. This process enables
the pulping process to occur without a recovery furnace.
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Representative Drawing