Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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I' I [;:LD 0~` Tl{E INVENTIO'`l
This invention is directed to a method to recover
valuable lignin and other extractable components Erom
kraft black liquor using supercritical 1uids and to
covert said recovered lignin into chemical products and to
apparatuses to carry out reactions of supercritical
fluids. By supercritical fluids is meant a gas or a
liquid at a temperature above its critical temperature and
a pressure above its critical pressure.
PRIOR ART
An extens-ive literature search conducted by the
inventor has revealed that no one has published any
in~ormation which may have bearing on ap~licant's
invention:
The search has revealed that no one has thought of
extracting lignin and other components from black liquor
using supercritical gases, nor of reacting lignin
dissolved in supercritical gaseous product in a fluidized
bed catalytic reactor.
The following is a brief review of the current
black liquor recovery process in which the polymeric
lignin is combusted to CO2 for its fuel value: It is
recognized that the Kraft process for pulp production wili
be used by the industry for many years to come. The
pulping chemicals NaOF~ and ~a2S extract lignin ,rom the
wood to produce a pulp and a weak black liquor. The weak
; black liquor contains water, organic lignin derivatives,
hydroxy acids and inorganic compounds derived ~rom the
sodium. ~n essential criterion for the economic viahility
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~of the ~Craft p~ocess is the recovery o~ inor(3anic
cnemicals Eor récycle to ~ulping and tle production of
process steam. T`ne original Tomlinson recovery Eurnace
was developed in the 1930's. Since that time, several
modiEications and design improvements have been carried
out, however the ori-~inal concept is still retained and
universally practiced throughout the industry. ~eak black
liquor is concentrated to about 65~ total solids in
multiple effect evaporators and burnt in the recovery
furnace at about 9~0C. The organic constituents in the
black liquor provide the fuel for combustion. The
resultant inorganic Na2CO3 and ~la2SO4 form a smelt (at
these high tem~eratures) at the bottom of the furnace and
pass throuqh a char bed where the ~a2SO4 is reduced to
Na2S. Subsequently, the Na2CO3 is causticized with CaO to
regenerate the NaOH required for pulping. The recovery
furnace contains boiler tubes in which steam is raised for
process purposes.
The two major shortcomings oE this conventional
process are the smelt/water explosions and the high
capital and operating costs. Periodically, the steam
tubes inside the furnace burst causing water to flow on
the smelt and explode. These explosions are dangerous and
have sometimes caused death. They are extremely costly
and the insurance premiums are high. The maintenance
costs are also high because of the above.
This new method ofEers many technical and
economic advantages over the conventional black liquor
recovery furnace technology in which the lignin
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derivatives are simply burnt for their fuel value.
BROAD DESCRIPTION OF THE INV~NTION
In the proposed supercritical fluid extraction process,
the lignin is recovered and converted, in applicant's
invented apparatuses, to higher value added products and the
inorganic values are recycled to pulping.
The novel process offers the opportunity to recover the
valllable lignin (natural high molecular weight polymer) and
convert it to useful chemical products of a very high value-
added, instead of burning it for its fuel value and thus to
C2 which eventually goes up the stack. In addition, the
energy savings in evaporation and chemical recovery make
this process very attractivs to the industry.
Broadly stated this invention is directed to a method
to extract lignin from black liquor using supercritical
fluids. In another embodiment in accordance with the
invention, while maintaining said lignin dissolved in the
supercritical state, the same is fed in a fluidized bed
catalytic reactor to convert said lignin to high value added
chemical products and to special apparatuses for carrying
out said method. Preferably this method is conducted using
supercritical CO2 and the supercritical gas contalning
lignon is reacted in a fluidized bed catalytic cracker to
produce lower molecular weight higher value added products:
25 - There are many special advantages of supercritical
fluid extraction of lignin and subsequent conversion to
higher value added chemical products.
For example, with supercritical fluid extraction:
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(i) its mutual solubility with water is small and it
ean therefore be used as a solvent to extraet
organies from aqueous blaek liquor.
(ii) supereritieaL fluid diffuses as a gas (very high
dif~-usivity) yet has the solvent earrying
eapaeity of a liquid.
(iii) the reaetion rate of lignin dissolved in super-
eritieal fluid in a fluidized bed of eatalyst is
very high because the supereritieal fluid w-ill
have the density of a liquid and yet have the
diEfusivity eharaeteristies of a gas.
- (iv) the separation of lignin from the aqueous
solution of inoryanie eompounds is faeilitated
uith supercritieal flui~.
(v) the e~onomie benefit of this proeess is the
reeovery oE lignin and its eonversion to high
value added speeialty ehemicals.
This is even more so when CO2 is used, in that
ease Eor example:
(vi) supercritieal CO2 has a very hi~h volatility
compared with the or~anie extraeted, thus
Eacilitating its separation from extract
solutions for produet recovery and CO2 recycle.
(vii) The CO2 critical temperature (31.06C) and
pressllre (73.3 bar) are readily accessible with
well established proeess technology and
equii?ment.
Supercritical CO2 is non-toxic, non-flammable,
,`~ not orrosive and readily availat~le at relatively
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low cost.
BRIEF DESCRIPTIO~I OF THE DRAWINGS
Fur~her features, objects and advantages will be
evident follo~ing detailed description of the preferred
embodiments of the present invention taken in conjunction
with the accompanying drawings in which Figure 1 is a
process flow sheet illustrating one form of the present
invention. Figure 2 illustrates another form a pressur-
ized fluidized bed in accordance with the present
invention,
DESCRIPTION OF THE PRE~`ERRED EMBODI~IENTS
As .snoun in ~igure 1, the apparatus to conduct my
method consicts of a pressurized autoclave extractor 10
coopt~rating v~ith a pressurized fluidized bed 12.
A CO~ feed line source 14 conveniently at ambient
telnperatur2 is provided witn a flow control valve 16
~ollowed bv a heat exchanger 17 to raise the temperature
o~ the CO~ to above the supercritical temperature and a
compressor 18 ~or raising the pressure of the CO2 to above
the supercri~ical pressure. The compressor is itself
joined via lille 20 to the nigh pressure autoclave
extractor i0 which is generally thermally insulated and
p.ovided wi.h conventional heating means 27, and ini,Ying
means schelna~ically represented by ~1.
There .s also connectecl to said autoclave
eYtractor 10 via line ~2 a po.sitive displacelnent pump 24
to ~eeti ~la-,k liquor into the autoclave at the autoclave
pressure Erom line .26. The autoclave 1() is internally or
ext~rnally heated i~y the conventional means schematically
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shown by 27 when necessary. The black liquor source may
be fed directly from line ~6 or may be conveniently
contained in a reservoir or tank 28 and when needed fed
via line 26. The CO2 Source may also originate from a
storage tank 30 by maintaining the CO2 in liquid or
gaseous Eorm inside the tank at a suibable pressure.
The autoclave extractor is maintained at or above
the critical temperature and pressure of the solvent. In
the case of CO2 this is above 31.1C and above 73.8 bar.
Any black liquor resulting from the making of
pulp whether Erom kraft, sulfite or other methods may be
fed into the autoclave as long as in said liquor is
present the valuable lignin component or its derivatives
produced during pulping.
lS The high pressure autoclave extractor lO has
several functions: namely that of mixing or bringing
together the supercritical fluid with the black liquor,
maintaining the fluid in said supercritical fluid state,
transporting the lignin from the black liquor to the
supercritical fluid whereby the supercritical fluid
dissolves the lignin and immediately thereaEter bringing
said supercritical fluid containing said lignin to the
fluidized hed 1~ by means of a line 40 joining the upper
portion of the autoclave extractor to the lower p~rtion oE
the Eluidized bed 12, while removing the lignin de~leted
aqueous liquor outside said autoclave extractor 10. A
pressure regulating valve 41 in line 40 controls the
desired pressore in the ~luidized bed re~ctor.
~ ne way to remove said lignin depleted aqueous
liquor is to provide the bottom, or the lower portion, of
the autoclave where the liquid is present, with a line 42
and a pressure letdown valve 44. Then the aqueous liquor
substantially lignin free, may be disposed at 46 as is
well known in the art, and such as is disclosed herein-
above under the headiny prior art.
While in the supercritical state, the lignin is
catalytically reacted in the fluidized bed generally in
its lower portion and is allowed to react with the
catalyst pre~ent in said bed, to raise above said bed and
to escape at the upper portion.
The upper portion of the high pressure fluidized
bed ~catalytic reactor is connected to a heat exchanger 48
by means of prGduct lines 49 and 50. Line 50 is itself
provided witn a pressure letdown valve 52 connecting line
54 to a product separation tank 56. The product separa-
~ion tank wllich is at reduced pressure, has an upper
outlet 58 for delivering the gaseous fraction, and a lower
outlet 60 for delivering tne liquid and solid fraction of
tne lignin deci~tives. Preferably and generally outlet
58 is connected by line fi4 to line 14 and the reservoir 30
is used onl~ to supplement ~or the lost amount o~ super-
critical flu-d occuring durin~3 the Qrocess. The line 64
includes a Lil ter 66 to remove any liquid or soltd
?articles esc~ping outLet 58. ~ compression 70 is included
in line 64 after the filter 66 to boost the pressure of
the supercri~ic~1 fluid to the pressure in line 14.
The catalyst and other reaction conditions in the
high pressure fluid bed such as pressure, temperature,
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flowrate, depend upon the products one wishes to obtain.
The pressure is generally below that found in the auto-
clave extractor and can be as low as 2 bars, but always
above the supercritical pressure and the temperature may
range as hic3h as 50C and is always over and above the
supercritical temperature. Catalysts contemplated include
acid-treated natural aluminosiLicates, amorphous synthetic
silica~alumina combinations, crystalline synthetic
silica-alumina catalysts callecl zeolites or molecular
sieves, and crystalline mixtures of silica-alumina with a
small unifor~nly distributed amount of rare earths contain-
ed within the crystalline lattice.
Once the lignin is reacted to products they
escape via line 49 and by allowing the temperature to drop
lS by heat exchanger 48 as well as a drop in pressure, the
supercritica! fluid is allowed to disengage from the
lignin derivatives and to escape the tank 56 via the line
58. The solid and liquid particles are trapped by filter
o6, while the 3as is recycled via lines 64 and 14. The
lignin derivatives, which are generally liquid with
~ossibly some solids, are collected at 60. These
derivatives may be separated and purified by conventional
means such aS centrifu~ation, filtration, solvent
extraction, distillation and crystallization.
If desired, a promoter to enhance the extraction
process may be added for instance by means of a reservoir
7~ containing said promoter and joined by line 75 and pump
7 to line ~0.
~ more effi-cient way to remove the lignin
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depleted aqueous liquor is to insert in line 42 a heat
exchanger ~or raising the temperature of sai~ depleted
liquor, a pressure let down valve 44 to reduce the
pressure and to connect line 46 to a product separation
tank 82, where the solution is allowed to flash and where
steam is collected by line 8~ and a concentrated liquor
containing itlorganic salts is obtained at 86.
As sho.~n in Figure 2, a pressurized fluidized bed
reactor 112 is provided with insulation 114, inlet 116 and
0 partition or impervious 118 provided with outlet conduit
120 itself provided with a pressure reducing valve 122.
Within the lower portion of the fluidized reactor the
fluidizable catalytic bed 1.~ is able to react on a
compound dissolved in a supercritical fluid entering inlet
116 and raising through the bed 124 up to outlet conduit
120 to a disengaging zone 126 provided with heat exchanger
condenser 128. The disengaging zone 1~6 has a lower
portion defining a reservoir for liquid and solid
products, s~id reservoir being provided with outlet 128.
The 1isengaging ~one is also provided with 9clS outlet 130.
Examples
EXA~PLE 1
The Eoll~i~ing will serve only to illustrate
particular elnhodiments of the invention. Weak hlack
liquor containlng about 1~ solids is continuously fed to
the autoclave ln. Carbon dioxide fro~n the storage tank 3n
is mixed ~ith recycled CO2 and heated to 60C via heat
exchanger 17 and compressed to 150 bar via compressor 18.
The autociave 10 is therrnally insulated and heated by
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conventional means to maintain the temperature of the
contents at 60C. The supercritical CO2 containing the
liquor derived organic compounds leaves the autoclave via
line 40 and the pressure is reduced by the pressure
regulating valve 41 to the desired operating pressure of
the fluidized bed which in this example i5 5 bar. In this
example, the reaction produces carbon (coke) which remains
on the catalyst particle and rapidly lowers its activity.
To maintain the catalyst activ;ty, the catalyst is
reyenerated by burning orf this carbon using air~
Regeneration may also be carried out by having
two similar fluidized beds in parallel and operated in a
cyclic fashion such that while one bed is in the reaction
mode, the other bed is in the regeneration mode. Another
regeneration method is to have a separate regeneration bed
and to move the catalyst from the reactor bed to the
regeneration bed.
Since the cracking reaction is endothermic and
the regeneration reaction is exothermic, the fluidized bed
system may be kept in thermal halance at the desired
reaction temperature of 500~. The catalyst is a highly
reactive zeolite crac~ing catalyst and under tilese
conditions produces a product containing benzene,
toluene,zylene, phenols and longer chaill aromatic hydro-
carbons. The ~roduct is collected in the separating vessel
56 and removed via 60. The product is separated into
separate products via conventional technology using for
e:~ample disti]iation.
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EX~MPLE 2
Although the above example l illustrates
catalytic cracking in the fluidi2ed bed reactor, in
E~ample 2, tne reactions carried out were hydrocraclcing
that is catalytic cracking with hydrogenation super-
imposed. The hydrocracking catalyst consists of a
crystalline mixture of silica-alwnina wi~h a small
uniformly di~tributed amount o~ rare earths contained
within the crystalline lattice. The silica alumina
promotes cracking while the rare earth metals encourage
hydrogenation. One typical example was a cobalt/
molybdenum mi:sture on activa~ed alumina. The hydro-
cracking reac~ions were generally carried out at average
catalyst temperacures between 250C and 450C and at
lS reactor pressures between 70 bar and 200 bar with a
separate ~eed of hydrogen supplied to the fluidized bed in
order to carry out the reac~ions. In a preferred emhodi-
ment the unreacted hydrogen was separated fromtl1e ~roduct
stream leavin~ the fiuidi~ed bed and recycled to the inlet
for economic~l purposes. Since the cracking reactions are
endot!1ermic and nydrogenation is exothermic, the systeln
may be operate.1 in thermal balance with little or no
auxil-ary el1ergy required.
Pro~ucts produced were more fully saturated
aromatic co~ ounds such as cyclohexanes, cyclopentanes,
cyclooctanes anJ their olefinic and aliphatic derivatives,
~nenols and l~en~ene. Further crac]cing produced straight
chain m,olecules. In or~er to remove more efficiently the
lignin dep~eted aclueous liquor, the system as shown on
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Fig. 1 was used including a heat exchanger 80 and a
product separation tank. The pressurized autoclave
extraction 10 operating in the order of 60C. The lignin
depleted liquor in line 42 was raised to a temperature of
the order of 120C to 300C. During this operation/ it
became clear that steam could be obtained at ~4 and a
concentrated liquor at 86 which included the sodium
carbonate and other sodium salts.
EXAMPLE 3
In another example carried out as in Example 1 to
the supercritical CO2 fed in line 14, was added a promoter
(dimethyl ether) for enhancing the extraction process in
au~oclave ln.
EXAMPLE 4
Other supercritical fluids suitable for
e :t traction of Lignin were used. For instance acetone,
tetrahydrofuran, dioxane and toluene. However, these
supercritical fluids are generally less practical and
therefor less preferred, from an indu~trial viewpoint than
~2 Al~hough they may be preferred if one wished to
react the sa~e with the lignin derivatives in some cases.
Modi'ications may be made without departing froln
'.he spirit o~ the invention as defined in the appended
claims .
