U.S. patent application number 09/974483 was filed with the patent office on 2002-05-23 for pulping process without a recovery furnace.
Invention is credited to Kurple, Kenneth R..
Application Number | 20020059994 09/974483 |
Document ID | / |
Family ID | 22285412 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020059994 |
Kind Code |
A1 |
Kurple, Kenneth R. |
May 23, 2002 |
Pulping process without a recovery furnace
Abstract
A novel process has been discovered whereby acid is added to the
lignocellulosic material (black liquor containing lignin). The acid
renders the lignin insoluble thus enabling it to be separated from
the lignocellulosic material. This allows the chemical value of
various components to be reclaimed. This process enables important
environmental and economic benefits to be achieved. 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. The supply of energy to the separation process is from a
source other than the recovery furnace.
Inventors: |
Kurple, Kenneth R.; (Casco,
MI) |
Correspondence
Address: |
Kenneth L. Mitchell
Woodling, Krost & Rust
9213 Chillicothe Rd.
Kirtland
OH
44094
US
|
Family ID: |
22285412 |
Appl. No.: |
09/974483 |
Filed: |
October 10, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09974483 |
Oct 10, 2001 |
|
|
|
09405207 |
Sep 24, 1999 |
|
|
|
60101583 |
Sep 24, 1998 |
|
|
|
Current U.S.
Class: |
162/29 ; 162/63;
162/76 |
Current CPC
Class: |
D21C 11/0042 20130101;
D21C 3/02 20130101; D21C 11/0007 20130101; D21C 11/0085
20130101 |
Class at
Publication: |
162/29 ; 162/63;
162/76 |
International
Class: |
D21C 011/00; D21C
001/04 |
Claims
I claim:
1. A pulping process without a lignin-fired recovery furnace, said
process includes recovering lignin and sugars from a lignin
containing solution, comprising the steps of: supplying energy to a
digester and blow tank for the generation of a lignin containing
solution and pulp, said energy being totally supplied from a source
other than a lignin-fired recovery furnace; separating said lignin
containing solution and said pulp; precipitating polymer-grade
lignin from the lignin containing solution by adding an acid
selected from the group consisting of sulfuric acid, acetic acid
and phosphoric acid or by adding a gas selected from the group
consisting of carbon dioxide and sulphur dioxide; removing said
precipitated lignin from said lignin containing solution leaving
inorganic ions to react with said selected acid forming inorganic
salts and leaving organic sugars in solution; and, separating said
inorganic salts and said organic sugars from said solution.
2. A process as claimed in claim 1 wherein said acid is acetic acid
which produces sodium acetate.
3. A process as claimed in claim 1 wherein said acid is phosphoric
acid which produces a sodium phosphate.
4. A separation process for separating lignin from a
lignocellulosic material without using lignin as a fuel, comprising
the steps of: supplying energy to said separation process, said
energy being totally supplied from a source other than said lignin:
separating lignin from said lignocellulosic material creating a
lignin containing solution; precipitating lignin from said lignin
containing solution by adding an acid selected from the group
consisting of sulfuric acid, acetic acid, and phosphoric acid or by
adding a gas selected from the group consisting of carbon dioxide
and sulfur dioxide; and, removing said precipitated lignin from
said lignin containing material leaving inorganic salts and leaving
organic sugars from said solution.
5. A separation process for separating lignin from a
lignocellulosic material without using lignin as a fuel, comprising
the steps of: supplying energy to the separation process, said
energy being totally supplied from a source other than said lignin:
separating lignin from said lignocellulosic material creating a
lignin containing solution; precipitating lignin from said lignin
containing solution by adding an acid selected from the group
consisting of sulfuric acid, acetic acid, and phosphoric acid or by
adding a gas selected from the group consisting of carbon dioxide
and sulfur dioxide; and, adding a compound having a sodium ion as
part thereof.
Description
[0001] This application claims the benefit of previously filed U.S.
Provisional Patent Application No. 60/101583 filed Sep. 24, 1998.
Further, this application claims the benefit of the filing date of
Sep. 24, 1999 of copending application Ser. No. 09/405,207. This
application is a continuation of Ser. No. 09/405,207.
[0002] After cellulose, lignin is the second most plentiful
biopolymer on earth. Wood and other vascular plants are comprised
of, by weight, approximately 25% lignin. As part of the processing
in the pulp and paper industry to recover cellulose to make paper,
lignin is treated as a by-product that is disposed of as part of
the waste stream. Based on the amount of wood that is processed by
a typical pulp mill, the removal of the lignin waste stream
represents a significant disposal problem to the pulp and paper
industry. The recovery furnace where the lignin is disposed of for
fuel value is often a bottle-neck in the pulping process.
Representing a tremendous capital investment to build, the recovery
furnace is expensive to maintain as its emissions require
additional machinery in order to reduce the environmental problem
of air pollution release to the surrounding communities.
[0003] The burden on the recovery furnace can be reduced by
removing the lignin from the waste stream. Reducing the load on the
recovery furnace allows the pulping process to operate more
efficiently and more profitably. Furthermore, the removal of lignin
from the recovery furnace will also greatly reduce the amount of
material being burned which will result in significant emissions
reduction of air pollutants and global warming gases such as carbon
dioxide.
[0004] U.S. Pat. No. 5,635,024 to Shall does not disclose a pulping
process which includes supplying energy to a digester for the
generation of a lignin containing solution and pulp, with the
energy being from a source other than a lignin-fired recovery
furnace. Plus the main goal of Shall is to use defoamers and
polymers to coagulate lignin while one of the objects of the
present invention is to produce a polymer grade lignin from the
pulping process instead of burning it as waste, while burning
conventional fuels to supply energy to the pulping process, and
while creating other valuable by products (salts) from the addition
of acid to the lignin containing solution (black liquor).
[0005] Shall as stated above does not include supplying energy
exclusively from a source other than a lignin fired recovery
boiler. U.S. Pat. No. 5,820,830 to McIlroy et. al does disclose
supplemental use of steam from a power boiler while using the
remainder of the steam to make electricity with the amount of steam
needed as a supplement to the pulp mill being a function of the
efficiency of the process. Shall and McIlroy are really not
amenable to combination because their respective teachings are
divergent. Shall is teaching how to coagulate the lignin for
burning and McIlroy is teaching make up power from conventional
sources and those teachings are seemingly divergent as Shall is
presumably trying to increase the efficiency of his process (lignin
recovery) and McIlroy is admitting failure of the energy
requirements of the lignin. Neither Shall nor U.S. Pat. No.
3,546,200 to Whalen et. al suggest a pulping process wherein the
energy is totally supplied from a source other than a lignin-fired
recovery furnace.
[0006] Lignin represents an abundant natural resource that, if
utilized, can provide more efficient pulping processes and reduce
environmental issues concerning its current method of disposal.
Based on the natural abundance of lignin and the disposal problem
it has historically posed for pulp mills, there are a number of
environmental and economic incentives to this process.
[0007] U.S. Pat. No. 5,034,094 to Kurple discloses lessening the
load on a recovery furnace used in a pulping process by recovering
lignin from the process. This permits more efficient use of the
plant and overall process efficiency while creating valuable
byproducts. It does not, however, teach the elimination of the
recovery furnace.
[0008] The present Kraft pulping system designed to maximize
pulping efficiency is more than one hundred years old. When the
Kraft pulping system was first put into use there was no polymer
industry of any significance. As a result, the pulping process
currently in use is based on the production of paper from the
optimum recovery of cellulose from pulpable material like trees.
However, today in the United States, over 70 billion pounds of
various polymers are produced with the majority derived from a
petrochemical feedstock. Worldwide production is over 270 billion
pounds annually. Markets have been developed for a commercial grade
of the lignin after the design of the pulping system. This demand
for polymers creates a market for commercial grade 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 naturally occurring
high molecular weight polymer (lignin) that is abundantly produced
in trees. The process of this invention provides a way of obtaining
both environmental and economic benefits from recovering this
valuable material from the current inefficient processes for
markets outside the pulp and paper industry.
[0009] 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.
[0010] 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.
[0011] 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 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
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. The recovery furnace greatly contributes to the cost of
operating a pulp mill and can significantly limit the efficiency of
the pulp mill based on excess accumulation of the waste stream. It
is the major advantage of this present invention that allows all of
this equipment to be eliminated from the pulp mill.
[0012] The economic impact of a more effective pulping process will
be significant for a number of different aspects in the pulp and
paper industry. In the pulp and paper industry which generates
approximately 500 billion pounds of lignin containing waste
annually, disposal costs are at a premium. Further, the control
measures and maintenance costs involved in protecting the
environment from the release of emissions from the burning of
byproducts of the pulping process adds to the operating and
maintenance cost of mill operations. Based on the fact the pulp and
paper industry is the fourth largest industrial consumer of energy,
improving the efficiency of the pulping process can also be a
source of significant cost savings. The pulp and paper industry is
coming under increasing pressure from the recent environmental
regulations which cover the air and water discharges. Control
technology to limit Volatile Organic Compounds and Hazardous Air
Pollution (HAP) emission is an increasing cost to pulp mills.
[0013] Another major advantage of this invention is that by
removing the lignin from the black liquor it now becomes possible
and economical to produce a variety of other products such as
sodium acetate, sodium sulfate, wood sugars, acetic acid, and
lignin.
[0014] It is this equipment (recovery furnace) that contributes to
the high cost of operating a pulping mill and significantly affects
the profitability 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.
[0015] 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 may be used
which produces a sodium phosphate salt. These salts, sodium acetate
and sodium phosphate, are considerably more valuable as compared to
sodium carbonate which is much cheaper than the salts produced. 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 sodium carbonates to
make this process economical. The reasons include the equipment
cost savings by not having a recovery furnace, the value of the
recovered lignin which can be further processed into polymer grade
lignin (i.e., low sodium lignin), and recovery of sugars.
[0016] In the prior art process, the smelt from the recovery
furnace includes the sodium ion which is later used to form sodium
hydroxide for use in the digester and blow tank. Smelt is generated
by burning the lignin which contains the sodium ion. The carbon in
the lignin is burned in the recovery furnace leaving the sodium ion
behind in the salt. In the present invention, sodium carbonate
which is inexpensive is added to the return water. The sodium ion
from the sodium carbonate is used to form sodium hydroxide which is
used in the digester and blow tank.
[0017] In the digester and blow tank, lignin is separated from a
lignocellulosic material, for example from trees, as black liquor.
The black liquor and pulp are then washed in a washer and pulp is
extracted therefrom for the processing of paper and other well
known products. Lignin, sugars and sodium salts are then separated
out of said black liquor as is disclosed herein.
[0018] FIG. 1 is a schematic representation of a pulping process
without a recovery furnace.
[0019] FIG. 2 is a schematic of a known pulping process with a
recovery furnace.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] A separation process whereby lignin is separated from a
lignin containing material is disclosed and claimed. The lignin is
precipitated from the lignin containing material by the addition of
an acid such as sulfuric acid, acetic acid, or phosphoric acid. A
simplified chemical equation is, for example:
C.sub.6H.sub.12O.sub.6+2Na-L+H.sub.2SO.sub.4.rarw..fwdarw.2H-L+2Na+SO.sub.-
4+C.sub.6H.sub.12O.sub.6
[0024] Where L represents lignin, Na represents the sodium ion, SO4
represents the sulfate ion, and C6 H12O6 represents the sugar.
[0025] The lignin can them be removed by various filtration means
such as filter press, vacuum filter belt or various other filtering
or extraction methods. The extraction of the lignin from the
solution leaves behind a solution containing inorganic ions (such
as sodium Na) initially present in the lignin containing material,
the anion from the acid (such as the sulfate ion SO4), as well as
the sugars initially present in the lignin containing material.
[0026] Once the lignin is removed the difficulty in separating and
extracting the remaining salts and sugars is greatly reduced. The
salt is formed from the cation, sodium, already present in the
lignin containing material with the anion from the acid that is
added initially to the beginning solution. In this case, sodium
from the lignin containing material and the anion from the acid,
sulfate, combine to form sodium sulfate.
[0027] The remaining salt, sodium sulfate, an inorganic material,
can be removed by filtering the salt crystal from the remaining
solution which will contain primarily sugars (organic
material).
[0028] 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.
* * * * *