Note: Descriptions are shown in the official language in which they were submitted.
2144302
This invention relates to a ~h~mi~l hydrolysis
processing of renewable lignocellulosic biomass in order
to produce a single solution of sugars and a solid lignin-
residue.
Heretofore, a plug-flow-reactor has been proposed to
try to gain higher hydrolysis-conversion of cellulose to
glucose, by using extremely-high hydrolysis-rates,
achieved by high-temperatures of reaction, as provided by
direct-injection of high-pressure steam into high-solids
density slurries.
~ ven-so, hemicellulose hydrolysate sugars are all
degraded, by such a single-stage high-temperature poly-
saccharide hydrolysis reaction process. The hydrolysate-
~ugars high-dilution by steam condensation causes the
resulting single-solution of glucose to have a low-
concentration and large-volume with a high-cost acid-
neutralization and inefficient fermentation.
U.S. Patent No. 4,201,596 issued to Church ~1980)
shows a continuous process for effecting the acid-
hydrolysis of cellulosic waste materials in high-solids
density slurries. By control of high temperature, through
direct steam injection, the high density slurry solids may
be converted to yields of about fifty percent of the
potential glucose in cellulose in seconds. This chemical
processing method, for converting polysaccharides into
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pentose and/or hexose ~ugar~, is by a known use of a
tubular-type plug-flow-reactor (PFR) for dilute-acid
cellulose hydroly~is. Unfortunately, relatively low
conversions, negative byproduct formations, high energy
requirements and impractical high-density slurry-pumping
to pressure over 500 psi have limited the commercial use
of that cellulo~e-conver~ion by PFR method to Research
Development investigations.
Researchers, at Dartmouth College, in 1978-79, were
investigating the acid-hydrolysis of municipal refuse and
other material~, using a plug-flow-reactor. The Dartmouth
research work involved a 1.3 cm. ~0.5 inch) diameter
plug-flow-reactor (PFR) for dilute-acid, ligno-cellulosic
hydrolysis, at solids concentrations up to 13.5 wt%. The
system was a continuous-flow electrically-heated tubular
reactor.
The Dartmouth research hydrolysis was flashed through
an orifice to stop the reaction at residence detention
time~ of 5-30 B., and then cooled. Glucose yields from
20hard-wood flour ranged as high as 55% in 1983. This work
showed that high yields were obtainable on a small scale.
Several operational problems were encountered that
were difficult to ~olve on a small bench-scale system.
Problems included tar build-up and rapid plugging of the
small-diameter reactor prevented 5 long runs from being
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conducted to obtain extensive operating experience.
The Dartmouth Process iB known to have the following
characteristics~ relatively high-density slurries
are very difficult to be pumped at high-rates to high-
pressures and through the PFR, 2.) very high reaction-
temperatures/ on the order of 260 degrees Celcius/500
degrees Farenheit, require up to 600 psi steam and 3.) very
~hort hydrolysis reaction-times, of fractions of one-
minute, for flow through the PFR, generally.
U.S. Patent No. 4,615,742 issued to Wright ~1986)
shows a processing batch percolation-type hydrolysis
reactor. In this counter-current hydrolysis, a flow of
dilute-acid solution contacts a body of particulate wood
which is moving in a direction opposite to the flow of the
dilute-acid solution. The counter-current flow of the
dilute-acid solution and the particulate wood results in:
a much higher yield of sugars from the wood, a minimal
degradation and a relatively high concentration of
glucose, but the process conditions result in a low xylose
in the dilute-acid hydrolysate solution.
The primary disadvantage of this particular approach,
for counter-current hydrolysis, i~ the extreme mechanical
complexity and expense of moving by conveying the solids
and pumping the liquids in the opposite directions.
~.S. Patent No. 4,612,286 issued to Sherman ~1986)
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show~ a method conceived in an attempt to ~olve the above
problems and provide an approximate counter-current flow
processing, without the necessity for actual movement of
the wood particles. In general, a plurality of Kamyr
percolation hydrolysis reactors are piped together, in
series. This method utilizes a counter-current diffusional
treatment structure. Cellulose hydrolysis is practiced in
upright diffu~ion vessel with counter-current flow.
~.S. Patent 4,070,232 i~sued to Funk ~1978) has found
that yield and operability are improved by conducting a
ligno-cellulose pre-hydrolysis first and then a hydrolysis
of the residue. By pre-hydroly~is of the fre~h feed~tock,
at below 150 Degree~ Celcius, the hemi-cellulose can be
hydrolyzed at temperature~ where pentose-sugar degradation
is relatively insignificant. This allows high yields and
recovery, by ~epration of sugars from hemi-cellulose
hydrolysis. It also open~ up the structure of the wood
particles to provide infusion of acid and diffusion of
cellulose hydrolysate-ffugars are enhanced, minimum fouling
in the pipes by tars and limited degradation products.
The present invention'~ moderate solids-density
slurrie~ and moderate hydrolysis-reaction temperatures and
the improvement for recycle of a fraction of unhydrolyzed
alpha cellulose residue, in ~tage-two, provides
approximately 65~ cellulose to glucose conversion
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compared to approximately 50% for known processes. In
addition, other process improvements in the present
invention results in over two times higher hydrolysate-
sugar concentrations in the two-hydrolysates single-
solution final product than that of known single solutionprocesses.
It is a primary object of this invention to provide
an improved two-stage hydrolygis process for the
continuous dilute-acid saccharification of ligno-
cellulosics biomass, or of other cellulosic materials, to
produce hydrolysate sugars in a single-solution, of
moderate concentration, and a solid lignin-residue, and
including four ligno-cellulose hydrolysis process
improvements.
In stage one, the fresh cellulosic feedstock is
admixed with hot, pressurized dilute-acid water-solution.
The resulting heated a~ueous feedstock slurry ii further
heated by additional surplus flashed-steam process-heat.
Both of the~e surplus process-heat supplies are from gtage
two.
That heated fresh cellulosic feedstock slurry,
containing lOwt% to 20wt% solids, is therefore ready for
immediate hemicellulose hydrolysis reaction processing in
stage one. All of stage one's process heat is supplied by
reverse, inter-stage, transfer-flow, from stage two, of:
1) flash-steam and 2~ hot, pressurized alpha-cellulose-
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hydrolysate and dilute-acid solution.
That transferred surplus process-heat completely
provides for hemicellulose hydrolysis processing, at
reaction-temperature of 135 degrees to 195 degrees
celcius, saturated-pressure of 45 to 200 psia and
hydrolysis reaction time of 1 to 20 min. The resulting
hemicellulose hydrolysis reaction slurry is flashed to a
reduced-pressure to terminate degradation of ~ugars and to
generate the stage one surplus flash-steam process-heat
~upply.
The flashed, reduced temperature, hemicellulose
hydrolysate and unhydrolyzed residue slurry is separated
into: 1) a single solution, including the combined
hemicellulo~e hydrolysate pentose- and hexose- sugars and
the alpha cellulose hydrolysate glucose-sugar, and 2) an
unhydrolyzed cellulosic solids residue, which is passed on
to stage two as part makeup for the alpha cellulose
hydrolysis feedstock. That single solution, from stage
one slurry separation, is the final liquid product of the
improved process of this invention.
In stage two, the unhydrolyzed cellulosic residue
from stage one is admixed with the recycled fraction of
unhydrolyzed alpha cellulose residue, within stage two.
Together they are admixed with fresh dilute acid water
solution into the alpha cellulose hydrolysis reaction
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2144302
feedstock Ylurry, with lOwt% to 20wt% sollds. The fresh
dilute-acid solution preheated by stage one surplus flash
steam process heat.
In stage two, fresh high temperature process heat is
supplied for alpha cellulose hydrolysis reaction
processing at temperatures of 165 degrees to 260 degrees
Celcius, saturated pressure of 100 to 200 p~ia and
hydrolysis reaction time of 0.5 to 20 minutes, to produce
alpha cellulose hydrolysate glucose sugar, dissolved in
the dilute acid water solution of stage two.
Subsequently, stage two reaction process slurry is
flashed to ter~inate glucose sugar degradation. The alpha
cellulose hydrolysis slurry is then separated in order to
recover surplus process heat as: 1) flashed steam, 2) at
high saturated pressure, alpha cellulose hydrolysate and
dilute acid water solution and 3~ unhydrolyzed alpha
cellulose with lignin, residue solids.
It is a ~pecific object of this invention that three
of the four cellulose hydrolysis process improvements are
the result of the reverse inter-stage transfer-flow, from
stage two to stage one, of: 1) dilute acid catalyst, 2)
surplus process heat, and 3) surplus ingredient and
solution water.
It is another specific object that the fourth
cellulose hydrolysis process improvement of this invention
is the recycle of up to 50wt% of the unhydrolyzed alpha
2144302
cellulose solids residue, after separation from the hot
pressurized alpha cellulose hydrolysate sugar and dilute
acid solution, all within stage two. That recycled
fraction is used identically with the regular alpha
cellulose hydrolysis feedstock, from stage one
hemicellulose hydrolysis processing. ~owever, the
remaining non-recycled fraction will be the final lignin
residue solids product of the improved ligno-cellulose
hydrolysis process of this invention.
It is another object of this invention that the best
method for operation of this improved ligno-cellulo~e
hydrolysis process invention will be with an apparatus
made up of two double tube heat exchanger plug-flow-
reactor systems, a~ two stages in series. Each such stage
will include: 1) slurry mixing and feeding means, 2)
slurry pumping and pressurizing means, 3) tubular reactor
as the inner tube of double tube heat exchanger plug-flow-
reactor sy~tem, 4) heat exchanger, provided by annulus
between the inner tube and outer tube, 5) ~lurry flash
means for pressure reduction, 6) reduced pressure slurry
~eparation means and 7) reduced pressure hydrolysate
solution proces~ ~torage means, and also includes a
reverse interstage transfer flow means for: 1) hot,
pressurized alpha cellulose hydrolysate and dilute acid
solution, 2) stage two flashed steam, to be the stage one
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21443~2
proce 8 heat ~upply, and 3) provisions to produce the
combined hemicellulose and alpha cellulose hydrolysates
sugars in a single solution, as the final liquid product.
It i8 a further object of this invention that the
critical hydrolysis reaction factoru required for each
stage hydrolysis processing, are pre-selected and added
only in stage two, and are: 1) concentration of fresh
dilute acid in water solution and 2) high temperature
process heat.
Another object of this invention is that the multi-
beneficial results from recycling of up to 50wt% of the
unhydrolyzed alpha cellulose solids residue, within stage
two includes: 1) increased net conversion of alpha
cellulose to glucose sugar, 2) reduction in the normally
required alpha cellulose hydrolysis reaction processing
time and 3) thereby reducing the exposure time of alpha
cellulose hydrolysate glucose sugars to hydrolysis
reaction degradation and 4) a resulting increase, by
approximately 15% in the effective and useful capacity of
the stage two alpha cellulose hydrolysis reactor.
It is a further object that the improvements in this
process provides approximately 36% reduction of catalyst
acid costs and 30% less alpha cellulose hydrolysis process
energy costs, and that the recycle of unhydrolyzed alpha
cellulose solids residue, within stage two, increases the
alpha cellulose feedstock's net conversion to glucose by
approximately 12%.
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21~3û2
A major object of the process improvement of this
invention is that it provides for the production of a
single solution which has a relatively high concentration
of the combination of the hemicellulose and alpha
cellulose hydroly~ates sugars in the single solution,
which is valuable when used by a variety of yeast
fermentation and chemical processing methods.
The hemicellulose ~8C~ fraction of pine wood can be
relatively easily hydrolyzed into pentose and hexose
sugars. The pine wood HC hydrolysis conversion is a
function of HC hydrolysis reaction time, ts = up to 14
minutes; at reaction temperature, T~ = 135~C/2750F and
with acid concentration, C_oll = up to 2.00%.
In pine wood feedstock, the HC hexan is a fraction of
about 0.72 and the HC xylan i8 a fraction of about 0.28.
At these relatively mild HC hexan hydrolysis conditions,
the resulting HC hydrolysate hexo~es continue to rise
through t~x = 14 minutes. The HC hydrolysate xylose
yield is a maximum of C~x = 0.225 at about t~x = 9
minute~. The HC hydrolysate xylose yield ~C~x) is 80%
of the pine wood feedstock xylan fraction ~C~O~ of 0.280.
The indicated sugar survival shows that hydrolyOate xylose
~ugars, plus in the unhydrolyzed HC xylan L~ ining at t~x
= 9 minutes is 0.866 of the initial HC xylan feedstock of
1.000.
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~ 2144~02
To hydrolyze the pine wood alpha-cellulose (AC~
glucan polysaccharideO into glucose and hexose sugars
requires more intense chemical hydrolysis reaction
processing conditions. The resulting unhydrolyzed AC
glucan feedstock and AC hydrolysate glucose sugar
fractional yields is a function of: 1) AC hydrolysis
reaction times, t~ = up to 14 minutes, reaction
temperature, T~ = 1800C/356~F, and acid catalyst
concentration, C_o~d = 2.0%.
10Glucose sugar yields are comparable without recycle
and with 50% recycle of unhydrolyzed AC feedstock.
Maximum glucose yield, without recycle is C_x = 0.584, at
t~ = 8.2 minutes. However, with a 50% unhydrolyzed AC
recycle, it is C~xx = 0.652, at t~ = 7.0 minutes. The
15ration of glucose yield to sugar survival is 0.79 with 50%
recycle, at t~XK = 7.0 minutes. However, that ratio is
0.75 without recycle, at t~ = 8.2 minutes. The recycle
of 50% unhydrolyzed AC residue, following AC hydrolysis,
directly results in a 12% increase in glucose yield with a
15% shorter reaction time required.
The invention will now be described reference being
had to the accompanying drawings in which:
Figure 1 is a block diagram depicting the continuous
process of this invention, showing the ligno-cellulosic
feedstock entering into the improved dilute acid
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hydrolysis process system, thereby producing a total
sugars-hydrolysate single solution final product and a
lignin residue solid final product.
~igure 2 is a schematic flow diagram of the
continuous process of this invention showing the best mode
and preferred embodiment for carrying out the improved
continuous saccharification of ligno cellulosics process
according to the invention.
Referencing specifically to the drawings, it will be
appreciated that as shown in ~igure 2, the preferred
embodiment of the improved process of the invention is a
two stage 3ystem, made up of two double tube heat
exchanger plug-flow-reactor and flash tank sub-systems, in
series.
Into stage on of the best mode, a ligno cellulosic
feedstock, that is dry and ground to pass 10 mesh, is
conveyed through conduit 2, and fed by a rotary-feeder to
slurry mixer 1, where it is admixed with a solution
supplied by conduit 3, which is a process improvement of
the invention. That solution in conduit 3 iB a hot and
pressurized dilute-acid and alpha-cellulose hydrolysate
solution, which is conveying, by reverse inter-stage
transfer flow from stage two to stage one, the following:
1) surplus process heat, 2) dilute acid catalyst and 3)
ingredient and solution water.
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2~ ~4302
The resulting preheated, fresh feedstock dilute acid
slurry, containing approximately 12wt~ ligno cellulosic
feedstock solids, passes to a progressive cavity slurry
pump 23. Thereby it is pumped into the inner tube of the
stage one double tube heat exchanger and plug-flow-
reactor 4, wherein, additional process heat is conveyed,
from stage two to stage one, by conduit 5 into the heat
e~changer 27, and thereby is indirectly added to the
slurry in order to immediately raise the feedstock
slurry's saturated temperature and pressure up to the
pre~elected and controlled hemi cellulose acid hydrolysis
reaction factors. That stage two surplus process heat is
added indirectly to the stage one reactor system 4. That
is another process improvement of the invention, because
it is supplied by the use of the reduced pressure and
temperature flash steam, conveyed in conduit 5, by
reverse, inter stage transfer flow, from the stage two
slurry flash tank 15, as a surplu~ process heat ~upply.
The flow rate of the slurry, in hemicellulose
hydrolysis reactor 4, is controlled by a pre~elected
pumping rate, to be compatible and provide the required
detention time in plug-flow-reactor 4. The result is
optimum hemicellulose hydrolysis of hemicellulose
hydrolysate sugars, dissolved in solution of the slurry.
From reactor 4, the reactor slurry is continuously
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blown into the flash tank 6, for reduced pressure, flash
steam production, also temperature is dropped to interrupt
degradation of the hydrolysate sugars. The flash steam
from stage one flash tank 6 is conveyed by conduit 21 to
stage two, for continuous preheating of the fresh dilute
acid catalyst solution. The flashed slurry is conveyed
from flash tank 6 to the ~tage one separator 7, for
~eparation of unhydrolyzed ce1lulosic residue from the
solution of that slurry. That solution contains the
combined total sugars hydrolysates from the two atage
cellulosic hydrolysis proces~ing. It is conveyed out by
way of conduit 8, as the single solution, liquid final
product. That liquid final product is another process
improvement of the invention.
In addition, the recovered, unhydrolyzed, cellulosic
residue is conveyed from stage one ~eparator 7, by conduit
9, on into stage two. Therein, it is blended in with a
recycled fraction of the unhydrolyzed alpha cellulose
hydrolysis resldue which may be up to approximately 50wt%.
That fractionation is made by fractionator 27, following
the stage two separator 16, and conveyed by conduit 18
into a blending with the unhydrolyzed cellulosic residue,
conveyed in conduit 9. The ~~~ining fraction of that
unhydrolyzed alpha cellulose hydrolysis residue is
conveyed out by conduit 17, as the solid lignin re~idue
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final product, which i8 an improvement of the process of
the invention. The combination of the residues, from
conduit 9 and conduit 18, is conveyed by conduit 28, to
the stage two slurry mixer 10, along with the fresh
preheated dilute acid solution, conveyed by conduit 11,
for the admixing of the alpha cellulose hydrolysis
feedstock dilute acid slurry. Thereupon, the preheated
slurry is transferred at a flow rate controlled by slurry
pump 24, to the alpha cellulose hydrolysis plug-flow-
reactor 12.
Indirectly, to the stage two alpha cellulose
hydrolysis system, there is, incoming by conduit 14, which
indirectly, provides a supply of high temperature proces~
heat adequate for the overall two stage hemicellulose and
alpha cellulose hydrolysis processing operations. The
relatively high temperature process heat, transferred
indirectly to the alpha cellulose hydrolysis slurry
processing in plug-flow-reactor 12, provides for the pre-
~elected and controlled alpha cellulose hydrolysis
reaction saturated temperature and pressure levels, for
the preselected and controlled feedstock slurry flow rate,
and thereby the required reaction detention time. That
total overall process heat supply is initially conveyed,
for indirect heat transfer, by heat exchanger 26, into
reactor 12 in stage two, originally conveyed by conduit 14
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from the process heat producing source 13.
With a pre#elected and controlled slurry flow rate,
which provides the require cellulose hydrolysis reactor
detention time, the alpha cellulose hydrolysis slurry then
continuously flows from plug-flow-reactor 12 to stage two
flash tank 15, for immediate slurry flashing to a reduced
saturated pressure and reaction temperature. Thereby, the
large supply of moderate temperature flash steam is
continuously generated, along with the related needed
cooling of alpha cellulose hydrolysate solution, for
interrupting the degradation of it~ glucose sugar. That
flashed slurry then passes on by conduit 19, to the stage
two slurry separator 16, for separation of the reduced
pressure alpha cellulo~e hydrolysate and dilute acid
solution, from unhydrolyzed alpha cellulose lignin
residue, which passes, from the separator 16 on to the
fractionator 27, to be fractionated. Thereby i8 provided
a fraction of up to approximately 50wt% of that
unhydrolyzed alpha cellulose residue for recycle by way of
conduit 18, in order to be combined and blended with all
of the unhydrolyzed cellulosic feedstock residue, conveyed
in conduit 9 r from stage one separator 7. Thereby, that
combination becomes that most suitable feedstock for alpha
cellulose hydrolysis, which is an improvement of the
process of this invention. The remaining fraction of the
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unhydrolyzed alpha cellulose lignin residue, conveyed by
conduit 17 from stage two, beco~es the solid lignin
residue final product, which is a further improve~ent of
the process of thi~ invention.
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