Note: Descriptions are shown in the official language in which they were submitted.
~ 5~n ~ .
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1 SPECIFICATION
3This invention relates to the utilization of
4 cellulosic and lignocellulosic material to produce certain
S chemicals such as ethanol and methane and to produce thermal
6 I energy which can be used within and/or outside the system.
7 I
3 ¦ The material which is subjected to the process of
9 ¦ the present invention includes all manner of cellulosic and
10 1 lignocellulosic materials such as, for example, softwoods,
11¦ hardwoods, agricultural residues such as straw and cotton
12¦ stalks, orchard trimmings and various other crops.
131
14¦ For convenience, such materials will be referred
15¦ herein from time to time as biQmass.
- 161 .
17 It is known that biomass may be converted by
18 ¦ hydrolysis and/or oxidation followed by fer~entation, etc.
19 ~ to useful products such as ethanol, acetic acid, methane, etc.
20 I Certain of such processes are described in a paper by
21~ Schaleger and Brink in TAPPI 61, No. 4, pages 65 to 68 (1978)
23 and in the literature cited in that paper.
24
261
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1 It is an object of the present invention to provide
2 ¦ an integrated process whereby biomass material constituting
31 the raw feed material is subjected to a series of operations
4 I which result in hydrolysis of the cellulose and the hemi-
S I celluloses and oxidation of the lignin and conversion of the
6 I hydrolytie products (monosaccharides) and oxidation products, to
7 useful chemicals such as ethanol, acetic acid and methane,
such process optimizinc; the production of such end products
',' and resulting in thermal energy which can ~e used within
and/or outside the process.
11 . .
12 ¦ The above and other objects of the invention will
131 be apparent from the ensuing description and the appended
14l claims.
151
16¦ Representative examples of biomass materials
17l susceptihle to the process of the present invention include
18 1 all manner of forest products including particularly material
19 which is otherwise waste such as saw mill residues, cull logs,
products of thinning forests, sawdust, bark, etc.; it includes,
21 ll among forest products, softwoods, e.g. firs, pines, junipers,
221 cedar, Douglas firs and hemlock, hardwoods such as oak,
23 cottonwood and poplars, mountain mahogany, myrtles and
2~1 sac~ebrl1sh; aqricultural crop residues such as the straw
residues o~ cereal grcl~Lns and the residues o~ other crops
26 I ,uch ~n ~:otLon orchnL~I trimmin~ls, oL~
31
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Certain embodiments of the invention are illustrated,
21 particularly for softwoods, by way of example in Figures l
3l and 2, Figure l being a simplified flow diagram and Figure 2
41 being a more detailed flow diagram. Figure 3 represents
Sl preferred modification of Figure 2.
6I Referring no~ to Figure l, biomass material enters
7I the system at lO. By way of example this could be green wood
8j containins approximately equal quantities of lignocellulosic
ql ~material (oven dry wood) and naturally occurring moisture.
10l This material in suitably comminuted form is introduced into
' a Eirst hydrolyzer or zone indicated by the reference numeral .
12 ll in which stage I hydrolysis is carried out. In this
13 hydrolysis unit the biomass materiai is subjected to an
. Ii
l4,i elevated temperature, for example, 140 to 220~C., preferably
15l about 160 to 180C. The pressure in the hydrolyzer is
16" autogenic being, for example, 75 psi gauge at 160C. (All
17,l temperatures are centigrade.) A recycle line 12 serves an
181'~ important Eunction in recycling sugars (hexoses) produced in
;~ 19 1l second stage hydrolysis. The obiect is to increase the
20 li concentration of sugars (hexoses) in an aqueous solution
21!, ~hich is routed to another part Oc the system. ~It is desirabl~
22, to ~eep the residence time in hydrolysis zonc Il as short as
231' possible consistent with ~ccompli.shinc; the desired hydxolysis.
2~l By way o~ e~ample in processing white fir at about 160C. the
25~ residence time in zone ll that qives a ma:~im~lm reduc;.ng SU~Jar
26 ! yield ~las 30 minutes and i.5 a lun~tiorl oE sever~l variables
27l including pli, paxticle size, mi~in~ eEficiency and species
2al . .
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1 of plant material. Yn Table I below there is given
2 representative ranges of hemicelluloses, cellulose and
3 ligneous compositions of softwoods and hardwoods. It is
4 the hemicelluloses (galactoglucomannans and glucurono~ylans)
sl and the rea~ily accessible amorphous l-egions of the c~llulosc
61 that are hydrolyzed in the first hydrolysis unit to simple
7 , sugars (hexoses and pentoses) which in turn are converted to
81 useful products such as ethanol, methane, methanol, acetic
91 acid and furfural.
T~BLE I .
~ 121
13 GymnospermsAngiosperms
~41 (Softwoods?( _ dwoods and Grasses)
15¦ Cellulose 42 + 3%43 + 3%
16¦ Galactoglucomannans 20 + 5~ 4 1- 2%
1 17 ¦ Glucurono~ylans12 ~ 3~ 27 + 7%
13 I Lignins30 -~ 53 25 + 5
19 I
20 ¦ The effluent product from hydrolyzer ll, which is
21 I in the form of a slurry, is introduced thlough line 13 into
22 ¦ a separator l~ whicll may be any of several well ~no~7n types
23 ¦ such as centrifucJes or filters that are preferably continuously
2~ ¦ opera~ cJ types and ~re capab.l.e of sep~rati.ng soli~s from
25 ¦ liqllids. (P~eEerellce i.s made ~hroucJhout to "lines" and to
flow of m.ll:erial throu(;h "lines". In the preEerred practice
2~
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1 of the invention there are in fact conduits through which
21 materials flow, preferably in a continuous manner. However,
31 the effluent from a given piece of equipment may be stored
4l and introduced into the next piecc of equipment as needed.)
51l The liquid leaves by way of line 15 and the solids by way of
61 line 16 A recycle line 17 is sho~n ~hich is primarily for
7I water as needed in the separator 14.
8 I .
9 I The slurry of solids separated in separator 14 is
10 , then introduced into a sensitizer unit 18. There are also
introduced into the sensitizer unit ~ or air and acid
121 as needed through lines 19 and 20. The slurry of solids
13jl separated in separator 14,then passes through a refiner 16a
14 I which serves to refine the solids so as to make them quite
l~ ¦ fine, incxease their surface area and make them more amenable
l6~ in the ~e,ct step which is carried out in sensitizer 18. Air
17 I or oxygen and acid are introduced into sensitizer 18 as
18 I needed through lines 19 and 20, respectively. In the
19 , sensitizer 18 important variables are temperature, residence
201 time, pH, rate of oxygen introduction, degree of dispersion
21 of the oxy~en and the particle size of the lignocellulosic
22 ; material. These variables are interacting and are optimiæed
231 to ma:cimize production of reduciny sugars. A temperature,,in
24j the ran~3e oi 1~10 to 220C~, preferably 160 to ~00C., is
2511 m.lirlt~-lined in the sensi.ti~er unit 18 and the input of air is
26~ ~dml~ed ~t a pr~ssuro oE 50 ~o 400 p~i tb-ve n~togolic
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1 ¦ pressure of the system in a manner to give fine dispersion and
2 ¦ in an amount o~ 0.2 to 4.0 grams of oxygen per minute per
kilogxam of biomass on an oven dried ~O.D.) basis. The acid
4¦ used m~y be ~ mineral acid or it may be an organic acid or
acids produced in the process itself ~hich, being one or more
61 of the end products of the system, does not require removal
7 as a waste material but rather is a marketable end product.
8I F u r th e r, nitric acid may be an acid of preferance since
~' 91 it has the advantage that nitrogen compounds derived from the
10¦ nitric acid provide a nutrient for the fermentation step. By 3
11 way of example white fir ~ood of particle size minus -2 * 4,
12¦ after treatment in hydrolysis zone ll, was sensitized by
13¦ heating a slurry at pH 2.l and 170C. for 60 minutes while
41 sparging with air at a rate of l~0 gram of oxygen per minute ,
15¦ per kilogram o~ o.D. pre-hydrolyzed wood. The sensitized G'
16l solids and accompanying li~uid are transferred through line 25
I7¦ to a stage II hydrolysls unit i6 in which a temperature in~
1 18¦ the range of~160~to 240C., preferably app7-oximately 180
19 ¦ to 220~C. i5 maintalned. Spent gas is removed through line 27~, ,r
20 ¦ such being rlitrogen, unconsumed oxygen, other constituents
. I ~ . i,:
21 ¦ o~ the air and any gas, such as carbon dioxide and carbon~
22 ¦ monoxide, produced in the sensitizer.
23
24
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1 Heat necessary for the hydrolysis stages including
2 I sensitization may be supplied from a source external to the
3 ' system but preferably steam generated in the system itself is
` 4 ¦1 used as described hereinafter with reference to Figure 2. i~
S¦l Also the flow of materials is designed to optimize the use of
61' heat exchange in ord~r to minimize the steam requirements of
7 , the system. ~ ~;
8 ¦ ~;
9 The product of the stage II hydrolysis, which is in
101l the form of a slurry, proceeds by way of line 28 to a
separator 29 which may~be similar to the separator l4. Water
1211 as needed for dlsplacement or other types of washing solids, i ;
1311 and for slurrying of solids in the operation of the separator
i ~ 14 ¦¦ is provided through recycle line 30. The liquid effluent
lSI~ (an aqueous solution of sugar~, ~oth hexoses and pentoses,
~ 16 ha~ing a concentration ty~pically of about l to 10% ol reducLng
.'~1 17 1 sugars) leaves by way of line 12 as recycle material to go to
18 the stage I hydrolysis un1t. The separated solids ~in the ,
19 form of a slurry) proceed~by way of line 31 to a wet oxidation
step described hereina~ter.
21 ~
22~ An il~portant reature of the invention is the recycle
;' 23 o~ liquld material erom the separator 29 by way o~ line 12 to
24 the first hydrolysls unlt 11. The ~irst hydrolysis uni~
functions primarily to hydrolyze hemicelluloses, which are
'~ 26¦ more readily hyclrolyzed than cellulose. Tlle hydrolyisis
;i 27
28
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31 .
32 ;
~ 1 7 5 ~ 2 ~)
1 products are hexoses and pentoses. Cellulose is hydrolyzed
2 I in unit 26 (aided by the pretreatment in sensitization unit 13),
3I the hydrolysis product being predominantly glucose. By reason
41 of the recycle throug}l line 12, the concentration of mono- ¦
51~ saccharides routed to other parts of the system through line 15
61, is considerably increased.
7,,
8~ As a preferred alternative, the recycle hydrolysis
9l may pass from line 12 to line 12a, through hydrolyzer 11
10' countercurrently to the biomass feed material passing through
this hydrolyzer an~ our through line 12b to line 15.
The solid material is separated in separator 29 as
14l a washed slurry and passes by way of line 31 to a wet oxidizing
15 ¦1 unit 32 into ~hich air is delivered through line 33. The wet
16jl oxidation step carried out in the unit 32 may be, for example,
17l, that described in Brink U.S. Patent 3,562,319. The process
i8ll is exothernic and a steam coil (not shown) may be provided to
19 1l heat boiler feed water and generate steam. Gas leaves the
~ 201l wet oxidation unit through line 42, such being unconsumecl
1 21 jl oxygen, other eomponents of the air and carbon monoxide and
22 1l carbon dio.cide procluced in the wet oxidation unit. The product
2~ll of wet oxic1ation, whlch is in the form of a slurry, leaves
2~1j throug}l a line 43 and ;s introduced into a .;ep~ration unit
2511 or units ~4 in which by a process or succession of processes
2hll such ~s solvent cxtractioll, etc. useful end products such as
Ij . .
27 1 acetic acid, fonnic ac~d, furfural and rnethanol are scparated
28,1 arld may be further separated in fr~ctiona~ioll Ull.it or units 45.
29 ~
30~ . .
311 . ' ,
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1 ~he principal function of the irst hydrolysis
unit ll is to hydroly~e hemicelluloses to simple sugars
3 (he~oses such as glucose, mannose and c~alaetose and pentoses
4l such as xylose and arabinose) and to complete hydrolysis of
oligomers introduced into this unit with hydrolysate from
6~ the second hydrolysis unit througll line 12 or lines 12 and 12a.
7 1l The hemicelluloses are the ~nost easily hydrolyzed constituents
8jl of lignocellulose. The proportions of he~oses and pentoses
9,~ depends upon the plant (biomass) material used as raw material
lOj as indicated in Table I above. The function of the seeond
stage hydrolysis unit 2~ is to hydroly~e the eellulose to .
1211 glucose and for that purpose a higher temperature and higher
13j'i acidity, i.e. higher hydrogen ion concentration, are needec.
141j The f~nction of the sensitizer unit 18 is to pre-eondition
15¦j the cellulose with the result, as ~e have discovered, of
16 I increasing greatly the rate of hydrolysis and substantially
17 incr~asing the yield of glucose. The unction of the wet
18 , pxidation unit 32 is to brea]c down -the lignin to water soluble
19 organie fragments. In each of the units 11 (first stage
20l~ hydrolysis), 18 (sensitization), 26 (second stage hydrolysis)
21¦~ and 32 (wet oxidation) the purpose is to convert a fraction
~2 li o the blomass to products ~hich can in turn be eonverted by
23~ metllods such as fe~rlnerltatioll, extraction, fractionation and
~l met:llclllation t:o usc-flll encl prod-lcts sucll as ethano1, ~cetie
2~ acid, forlllic acicl, furEural, methanol and rnethane. It is an
26~j object of the invellltion to so carry out the process that the
27ll yield o thesc elld procluets is higll, the concentration of ~ugc1rs
281 introduced into the fennentatioll step is high, and the production
291 of o~idative products such as C02, CO alld degradation produets
30i of ].ittle value are minimi~ed. To thaf: end in each of the
31
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~¦ units 11 19, 26 and 32 the residence time and temper~ture are
21 balanced so that end products of little or no value are
I minimized. We have found that at the temperaturcs indicated
41I residence time of the biomass or partiallv conver~ed bion~ass
5 I should be as short as possibl~ generally not more that about
6 30 minutes and frequently much less.
7 I .
8 I The first stage hydrolysis the sensitization and
9 I the second stage hydrolysis are shown as being carried ou-t in
separate pieces of equipment. IIowever they may be caxried
ll I out in a continuous tube.
12 I
13 ¦ The circulation of solids out of wet o~idation unit 32
14 throug~ lines 43 76 and 79 is optimized to maximize production
15I of acetic acid and other organic products.
16~
17 Reverting now to the separation of a liquid phase
l8¦ ~a solution of sugars) from the hydrolysis sensitization part
lq of the system the liquid leaviny separator 14 through line 15
is routed to a liquid extraction unit 47 The extract is
21 routed by line 48 to the Liquid extraction unit 44 mentioned
22 above, ln whicIl acicls etc. are e~tracted and a~-e then
23 separated as described above. Solvellt: for these extractions
24 enters througll line 49. The raffirIate rrom unlt 47 passes by
way of line S0 to fermentation unit 5l into which necessary
2O~ acld;tives such ag yC!aSt~ nutrients and/or bases to neutralize
27I the aqueous medium to a desired pll for fermelltation are
28 I introduced through line 52. Solvent extraction in unlt ~7
29 ~ removes substances SUCII as furfural which ~ould interfere
31 ~ h fermentation in UIIit 510
32
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Excess yeas~ and o~her solids (if any) leave
fermentation uni~ 51 by line 53 and CO2 by line 54. The solids
may be used as cattle feed, for example. The clarified liquid
or beer leaves u~it 51 through line 55 to Eractionation unit 60.
Ethanol, e.g. 95% ethanol leaves the system through line 64 as
one of the end products. The still bottoms from rectification
unit 6Q pass by way of line 62 to methanation unit 63.
Methanation may be carried out by any of several well known
processes resulting in CO2 and methane which leave by way of
line 64a and may be separated. Liquid containing some solids
lea~es methanation unit 63 through line 65 and is separated, in
separator 66, into commercially pure water (i.e. water which
can be used in the system~ and a dilute slurry of solids that
`~ have passed through the system without being solubilized and/or
have been produced-in the system as yeast or bacteria in the
biochemical processing steps. Part of the water is recycled
through lines 17 and 30 as described above and part is removed
from the syste~ through line 68. Make-up water is added as
~- needed at any convenient point in the system, preferably as wash
water to separator 29. The dilute slurry passes through line
75 and is recycled to wet oxidation unit 32. Raffinate from
liquid extraction unit 44 passes by way of line 76 to separator
77 where aqueous solution is separated and passed to methanation
unit 63 through line 78 and a dilute slurry is separated and
passed to wet oxidation unit 32 by way of line 79.
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1 ¦ Tlle procedure described above with reference to
2 ¦ Figure 1 is applicahle to both .softwoods and hardwoods.
l30wever, when the raw feed material is a hardwood, i.e.
4 , angiospenns having low proportion of hemicelluloses which
S contain hexoses, the hydrolysates from first and second stage
6 hydrolyses may be processed separately. For example, the
71 hydrolysate passing from separator 14 through line 15 ~which
81 is rich in pentoses) may be processed to recover furfural,
9 ~ hile the hydrolysate in line 12 (which is rich in glucose)
10~ may be subjected to fermentation. However, as explained
elsewhere in this specification, the hexose rich hydrolysate .
12 and the pentose rich hydrolysate may be combined (as they
13¦ are in Figure 1) and subjected to simultaneous fermentation
14 (after suitable processing to remove substances which
15¦ interfere with fe~nentation) to ethanol, employing a suitable
16 I mixture of micro-organisms, or the combined hydrolysa1:es may
17¦ be subjected to sequential fermentation of hexoses and
18 pentoses. Alternately, solids in the slurry of streams 75,
19 ¦ having nutritive value can be separated for appropriate
20 ¦ utili~ation with separated water used as described above.
`21
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¦~ l Referring llOW to Figure 2, biomass, for example,
2 green wood from trees or saw mill residues in suitably
3 comminuted form enters the system at 100 and is received in
4 a storage hopper 101. The comminuted wood then proceeds along
, the path 102 to a first hydrolyzer 103. This is the same
hydrolyzer as shown at 11 in Figure 1 and the temperature
`~i 7 and residence time are as described in connection with that
8 figure. Hydrolysate solution also enters the hydrolyzer 103
9 through the line 104 and recycle wash water tlirough the line 6
i 10 104a. The effluent leaves the hydrolyzer through line 105
ll and passes through a heat exchanger 106. Typically, in the
12 ¦ case of wood from trees, this effluent will consist of an
13¦ aqueous phase having dissolved therein approximately 30 to 35%
14¦ of the dry weight of the wood, the remaining 65 to 70~i being
151 solids. The~effluent slurry leaves the heat exchancJer 106
16j twhere it is cooled somewhat below the temperature prevailing
17 in hydroly~er 103) through line 107 and is introduced into
i 18 ¦ a separator 108~which serves to separate liquid phase from
19 solids. In this instance and in others like it, the separated
20 liquid, apart from traces of solids is entirely a liquid ;~
21 phase containing dissolved solids~ The separated "sollds" ~ ,
i~i 22 I are actually a slurry of undissolved solids and liquid, the
, ~ ~ .
23 ¦ liquid being the same as the separated liquid phase. As is
,!:' ' 24 ¦ well ~nown, the "solids" must contain a large proportion oP
1 25 ¦ liquid to be amen~ble to pumpiny through pipes and otherwise
~: 26 ¦ handling.
` 27
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29
30 I
31 ~
32 .
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I The liquid leaves by line 109 and the solids by
2 I line 110. The separator 108 may be of conventional variety
3 ' such as, for example, one or more centrifuges. The solids
4' leaving through line 110 will typically consist of about ~O
S to 85~ aqueous phase and 40 to 15% solids, and is introduced
6 into a separator-washer 111. Two strearns of water frorn a
7 recycle stream referred to hereinafter are introduced into
8 I the separator-washer 111 through lines 116 and 117. The
9 I separator-washer 111 may be of well known construction, e.g.
a washing centrifuge or drum filter. The portion of the water
introduced through line 116 serves to displace and remove, .
12l through line 118, a major proportion of the sugar content of
13j the aqueous phase introduced through line 110. This solution,
141 after passing through a heat exchanger 119, passes into line
lS 1 104a for recycling to the first hydrolyzer 103. Water intro-
16 duced in line 117 dilutes the washed solids in 111 to a
l7 ! transportable slurry carried in line 120. ~ slurry of solids
18 passes by way of line 120 through heat exchanger 106 to an
19 ~ agitator 121 and then into sensitizer 122 into which air or
20 I oxygen is introduced through line 123 from a source 123a. The
2l I function of the agitator~ is to provide an intimate
22 i dispersion of air, solids and liquid which then passes by
231 way of linc 12~ into sensitizer 122, ~Ihich corresponds to the
24 sensitizer 1t3 in Figure 1 and in wllich the conditions of
251 tempcrature a~ld tirnc of re~sidence are as described above in
26 I con!lectioll Wittl Figure 1. Acid as needed to control pEI in
27 I the sensltizer 122 and in the secolld stage hydrolyzer 135
28 (see belo~) enters throuyh line 130a directly lnto line 131
29 , and also by way of line 130b to a~3itat.or 121.
30 I "
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l I Spent gas (largely nitrogen, carbon dioxide and
2 other, minor components of air) is vented from the sensitizer
3¦ through line 130 to the atmosphere or if desired to any
4¦ desired ~crubber before ventillg to the atmosphere. A slurry
5 I of solids and aqueous liquid leave the sensitizer 122 through
6 line 131 ~nd a cellulose hydrolyzer agitator 132 to a heat
7 ! exchanger 133 where it is heated to the temperature of hydrolysis
` 8 i and then proceeds by way of line 134 to a second (cellulose)
1 9 j hydrolyser 135 corresponding to the second hydrolyzer 26 in
lOI Figure l and in WhiC}I temperature and time of residence are -
llll as described in connection with Figure 1. As explained above, .
12ll in this hydrolyzer the cellulose is substantially broken down
13l into glucose. To the extent that cellulose is hydrolyzed to
14 j oligomers, these are further hydrolyzed to glucose by virtue
lS of being recycled through line 104 to hydrolyzer 103. A
l6 slurry (an aqueous solution of glucose and solids, largely
17 lignin) passes by way of line 136 through a heat exchanger 137
18 into a separator 1380 A portion, typically about 70 to 903
19 of the aqueous phase ~a solution of glucose) passes by way of
~ 20 line 139 through heat exchanger 137 to line 104 for recycling.
:: 21 1l (As described about in connection with Figure 1, this
22 ll recycle hydrolysate may be passed through hydrolyzer 103
~3 ll counterc~uI rently to the hiomass ~eed material.) ~ slurry of
2~, sol.ids (largely lignill) and aqueous phase passes through
line 140 lnto 5eparator-washer 1.4]. into which two streams
2261 f water enter by way of lines 142 and 143. The wasll stream
28 '
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entering through line 142 carries wi-th it a major portion of
the aqueous phase which displaces the major part of the
hydrolysate remaining ~ith the insoluble ligneous residue.
The displaced solution then passes by way of line 144 to
line 104. The water entering through line 143 serves to dilute
the slurry of solids and contained liquid so that it can be
readily passed through line 145 to join another stream
(described hereinbelow) to a line 147, by means of junction 146,
then through heat exchanger 148 and line 149 into wet oxidation
~ 10 unit 150. Wet oxidati.on unit 150 is the same unit as shown at
: 32 in Figure 1 and the conditions prevailing therein as regards
temperature, time of residence, etc~ are as described in
connection with Figure 1~ The wet oxidation reactions which
occur in unit 150 are exothermic and generate steam in steam
coil 155 which passes in part through line 156 for use in the
system as described hereinafter. Depending upon the degree of
hydrolysis of polysaccharides effected, it would be possihle
to generate an excess of steam which would then be e~ported.
Spent gas from the wet oxidation unit 150 leaves through line
158 and joins the stream of spent gas leaving the system through
line. 130 for venting or scrubbing and venting as described above.
A liquid with. a controlled amount of solids contained in it
passes from unit 150 by way of line 159 through heat exchanger
148 to liquid extraction unit 160. Line 159a recycles liquor
to wet oxidation unit 150 to optimize oxidation of solids.
The extract from unit 160 passes through line 161 to e~llipment
generally designated as 162 and which may consist of several
pieces of equipment,
- 16
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1 I e.g~ for stearn stripping, for fractionation in a fractionating
21 colurnn, for precipitation, etc. to produce products such as
3l indicated. The raffinate from unit 160 leaves through line 163, ¦
4 then passes througll a heat exchanger 164 and by way of line 165
5¦ to separat:or 166 wherein the controlled amount of solids
6 remaining in the liquid (with a suitable quantity of liquid
7 to act as a carrier) passes through line 167 and join strearn
8 1 145. Boiler feed wat~r is shown entering the system through
9 I line 170 and heat exchanger 16-~ to steam coil 155 in wet
~ol oxidation unit lSOo
11 I . ~
12¦ Reverting no~ to the aqueous solution leaving
13¦ separator 108 through line 109, this solution enters liquid
14¦ extraction unit ~80 and passes countercurrently to solvent
15¦ entering throuqh line 181, the extract leaving through line
16 182 to liquid extraction unit 160 wilere it serves as the
17 extraction mediurn. The purpose of extraction in unit 180 is
18 to eliminate from the solution of fcrTnentable sugars those
19 solutes which would interfere with fermentation, e.g. furfural
20 ¦ and/or to remove organic acids. The purified aqueous solution
21 ~ of sugars passes through line 183 to fermenting unit 184,
22 ~hich is supplied throuc3h line 185 ~ith yeast or other suitabl~
23 I mic-ro-organism and any nutrient media and base to acl~u;t for
24 pll required for alcoholic ferlnentation. Gas (carbon dioxide)
leaves through line 196 and the fermented rnaterial ~beer)
26 throuqh line 187 ancl hezlt exchanqer 188 to rectifying colurnns
27 189. Steam is supplied to col-unn 1.89 through line 191 and
228 conclénsate leaves through line 192.
32
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lj The distillate, for e~ample, 190 proof ethanol leaves
through line 190 as an end product and the still bottoms leave
3 I through line 200 and pass through heat exchanger 188 to
4 methanation unit 201 whel-ein the pentoses are converted to
methane and CO2 which leave through line 202. The gaseous
6l, mixture may be used as fuel or the methane and carbon dioxide
71, may be separatedO Liquid, which for the most part is simply
8ll waste water but which may contain a certain amount of solids,
9! leaves methanation unit 201 through line 204 and passes to a
separator 205 which separates any remnant of solids. These -
11l solids leave through line 206 and are returned to wet .
1211 oxidation unit 150. The water leaving separator 205 passes
13!l through line 207 and is recycled to the system through lines
14 1 116 and 117 ~to separator ~ ) and lines 142 and 143 (to
16 separator ~t~.17 Make-up water (if needed) may be added to the
18¦ system at any convenient point, e.g. by introducing it into
19 ¦ line 117 and/or line 143. Water is removed from the system
through line 207a to prevent build-up of solutes.
221 .
, 231
2'11
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- 18 -
'
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1 Referring now to Figure 3, this is a flow diagram ,
2 of a modification of the flo~ diagram of Figure 2 centering
3 about the first stage hydrolysis unit (numbered 103 as in
4 Figure 2) and illustrating a different, and preferred method
of recycling the hydrolysate from the second stage hydrolysis~
6 Wherever in Figure 3 a line is interrup-ted (the interruption
7 being indicated by a zis-zag terminus), it is to be understood
8 I that such line connects to other equipment (not shown in
9 ¦ Figure 3) as in Figure 2.
10 I .
11¦ Lignocellulosic raw material suitably comminuted,
12¦ enters frorn hopper 101 and passes through a continuous feed
~31 device 220. This may be a screw type feed or a rotary feed.
14¦ The material passes into Eirst stage hydrolyzer 103 and passes
15¦ downwardly countercurrently to up-coming liquid described
16 hereinafter. (The arrangement need not be vertical; e.g.
17¦ it may be horizontal, but a vertical arrangement is convenient.)
13¦ The partially hydrolyzed material (solid and liquid) passes
l9¦ through line 221 and a refiner 222 to line 223, then throuyh
heat exchanger 119 to agitator 121 thence to sensitizer 122.
21¦ Hydrolysate solution from second stage hydrolysis unit 135
22¦ (see ~lgure 2) pass~s throu~h line 104 to a point near the
231 bottorn of hyclrolyxer unit 103 and, as inclicated hy curved
241 arrows it is distriblltec1 about the circumference o~ the
25 ¦ down~al-dly moving, partially hydrolyzed oass of solids and
27~ move, ~p~,rdly ~l~d oountor~rlontly to th~ solids. ~/ash
29
31
32
,~ . ' ' .
~ - 13a ~
': . ' ' '; ,,
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l water from line 207 (see Figure 2) is split into two streams 224
2 ¦ and 225 (which correspond to lines 117 and 116, respectively
3 j in Pigure 2). That portion of the wash water entering through
4 ¦ line 225 pass~s through heat exchanger 226, then th~ough
5 I line 227 into the bottom portion of hydrolyzer 103 below the
6 ¦ level where the hydrolysate enters through line 104. As in
; ' the case of the hydrolysate a distributor is employed and
ll 8 I the liquid moves upwardly, joining the hydrolysate, counter- ¦~
¦~ ¦. currently to the down-coming solids. Recycle ~ash water entering
10¦ through line 224 passes into the bottom of hydrolyzer 103 where
par, of it moves upwardly to join the other stre~-n counter-
12 currently to the down coming solids and part passes from the
13 I h~drolyzer 103 with -the solids through line 221. A connecting
`~ 14 line 228 connects line 227 with line 224. The portion of
wash water thus entering through line 228 is heated ~y steam
16 in heat exchanger 226. By proportioning the streams 224 and
17 228, the temperature of the liquid entering the bottom of the
1 hydrolyzer unit 103 can be adjusted. Steam enters heat
exchanger 119 from line 156, then passes through heat
; 20 exchanger 226 and connects to line 191. Steam as needed,
21¦ generated within the system or from outside the system, may
22¦ be introduced as neecled, e.g. into line 156 and/or heat
231 e~chan~er 119.
' ' 2,~1 . : .
251 . .
26~
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32
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1¦ Effluent liquid from the top oE hydrolyzer 103 passes
2 ¦ by way of line 229 and part is recycled by line 230 and feed
31 device 220 to l-ydrolyzer 103 and another part passes by way
4j of line 231 to liquid extraction unit 1800
.~ I
6 ~ By reason of the modification of Figure 3 certain
7 advantages are achievedO The down-coming partially hydrolyzed
8 solids in the biomass are washed and sugars are extracted;
9 the washing liquid [streams 104, 227 and 224 (in part)] are
10l cooled, giving up their heat to the solids; and the dissolved
~ sugars passing up with the combined streams are subjected .
12 j to high temperatures for a short time, which minimizes
18 ! degradation. i}eat in streams 104, 227 and 224 is adjusted .
~ to optimi7e t mper~ture for hydrolysis.
25~ ~
2~ . . .
31
32 . .
. - 18c -
'. . ' ' ' - . . . ~ ' ' . :
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~1 7582n
.
1 GENER~L DISC~SSlON OP THE SYSTEM
3 The system thus described and illustrated comprises
4 an hydrolysis-sensitization sub-system, a wet oxidation sub-
~ system and ~ Eermentation-methanation sub-system and certain
6 ¦ recovery stepsO In the hydrolysis-sensitization sub-system,
' primary hydrolytic operations are performed which break down
8 I high molecular weight polysaccharides (cellulose) and lower
molecular weight polysaccharides (hemicelluloses)` into
10 1 monosaccharides (hexoses and pentoses) by a process of
depolymerization. In the ~et oxidation sub-system a more .
12~, drastic oxidative attack (yet sufficiently mild to minimize
13 ! production of carbon dioxide, carbon monoxide and water) is
14 performed on the structure of lignin to break it down into
15 ¦ low molecular weight organic substances of commercial value
~ such as organic acids (typically acetic acid and formic acid),
17 furfural and methanol while minimizing production of CO2,
18 CO and 112O. The fermentation-methanation phase is described
19 I above with particular reEerence to fermentation of hexoses
20 ¦ to ethanol and the conversion of pentoses by methanation to
21 methane. However, by using a suitable mixture of micro-
22 ¦ orgallisms both hexoses and pentoses in admixture may be
23 fermented to ethanol or hexoses may be fermented to ethanol
24 ¦ with suitable micro-organisms and pentoses may then be
25 ¦ fermented to ethanol separately by other micro-oryanisms.
26 ~150, pentoses can be sub~ected to dehydration to produce
27 furEural. In the recovery steps, the desired end products
28 are recovered by recti.fication, solvent extraction, et~.
3 :
31 ~
32 ,'`
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. ,.,, , _ . .,,., !' .. .. - - - - .- -
.
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1 1 I In connection with these sub-systems and steps, the
2 , following observations will be helpful, reference being to
3 Figure 1.
4i
5l Stage I H~drolysis in Unit 11. The conditions
6l are not as severe as in the sensitization unit 18 and in
7I the second stage hydrolyzer Ullit 2~. For e~ample, a
8I temperature of 140 to 220r~C., preferably about 160 to 180C.,
9 is employed. A pH of 1.5 to 3.0 (preferably 2.0 to 3.0)
lOi; and autogenous pressure, such as 75 psi gauge at 160C. are
employecl. Residence time is sufficient to accomplish the
12j intended purpose of depolymerization of hemicelluloses to
~- 13l sugars yet to minimize degradation of these sugars. A
14 1l residence time preferahly not exceeding 40 minutes is
sufficient and would be decreased to a shorter time as
i 161, temperature is increased. Glucose solution, which includes
17 ¦ oligomers, produced in stelge II hydrolysis is recycled to
18 ¦ the first stage hydrolysis unit to maximize the concentration
19 j of monosaccharides leaving separator 14 by line 15.
20l Countercurrent flow is preferred as described above with
21ll reference to Figure 3. Representative concentrations of
22 1I recycle (line 12) and effluent (]ine 15) streams are optimized
231j in the rancJe of 2 to 12 perceni: monosaccharicles in line 15
24 !~ and 1 to 10 percent monosaccharides in line 12 -to maximize
25~1 yield of hexose sugars. Thi.s provides a high concentration
26~' of monosaccharide in the strearn going to ferment~tion
27 ¦ unit 51.
~8
29
3l .
32 ,
. ~' , '~ '' . , .
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11 Sensitization Skep in Unit 18. The conditions of
2l pH (1.0 to 3.0, preferably about 1.0 to 2.0~, temperature
3 ' (preferably about 160 to 200c.) and total pressure
41' (autogenous pressure plus pressure of air) are more severe
than in the hydrolysis unit 11. Limited and controlled
6l o~:idation is carried outO Suitable rates of introduction
7 1! are0.2 to 4.0 grams of o~ygen per minute per kilogram of O.D.
8l raw material and depend upon the variables and amount of
oxygen to be absorbed. The added acid may be a mineral acid
10l such as nitric, sulfuric or hydrochloric acid; an acid salt
such as ferric nitrate or ferric chloride or a mixture of
12 ll acid and acid salt or an organic acid such as acetic acid,
13 ll formic acid, oxalic acid generated in the process. The
14 ¦1 acid is added to adjust pl~. By using an organic acid
15ll generated in the process, recovery problems are simplified
16l since the added organic acid is separated along with end
17 ¦ products of the system. If nitric acid is employed, it
18¦ will provide the nitrogen required as a nutrient medium for
19 the fermentation step or steps. It is believed that in this
20 ~ sensitization step a mild attack occurs on the cellulose
21 structure which renders it more amenable to hydrolytic ¦~
22, cleavage in Stage II hydrolysis. In any event, it has been
23 I observed that the second stage hydrolysis in unit 26 proceeds
24 I at a considerably faster rate, that it can be accomplished
at a lowcr acidity (higher pll) and that a higher yield of
26 I reducing sugars results than would result in the absence of
27 . .
29 . . :
31 . .
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- 21 -
.
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, '
1 the sensitization step. In the hydrolysis of cellulose,
2 I acidity and an elevated temperature provide the desired
3 ~ hydrolysis ~nd also produce the compe~ing degradatioll of
monosaccharides. By enabling the second stage hydrolysis
Sj to be carried out under milder conditions (higher pH and
61 lower temperature) the sensi-tizing step promotes the production
7 I of sugar and minimizes the deyradation of sugars.
8 I
9 I Step II Hydrolvsis. This is carried out at a
10 , relatively high acidity (pll about l.0 to 3.0, preferably about
11' l.0 to 2.0) and at a higher temperature (about 160 to 2~0C.,
preferably about 180 to 220C.) and at corresponding autogenous
13 I pressure. These conditions are sufficiently severe to
14 I accomplish the desired hydrolysis of cellulose to glucose.
15 1 As pointed out, it is the object to maximize separation of
16 I hydrolysate from the ligneous residue by removal of as much
17 ¦ hydrolysate as possible and then use countercurrent washing
18 ¦ with the slurry wash being recycled to hydrolysis unit ll
19 I and the washed residue being slurried in a water stream which
goes to wet oxidation unit 32.
23~
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.
31 I '
32 ' ~' .
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~'1 ':
l ¦ Wet Oxidation. This is an exothermic process which
2 may be used to generate steam for use as a source of heat in
3 the process (heat exchangers are shown in Figure 2). When
4 compressed air is used to supply oxygen, the hot gas leaving
unit 32 (or 150 in Figure 2) may be expanded through a gas
6 I turbine to produce power. The conditions of temperature,
7 pressure and o~ygen partial pressure are such as to result
8 in substantially complete breakdown of lignin into simple
9 products including commercially valuable products such as
10~ organic acids, methanol, etc. but such as to minimize
ll conversion to carbon dioxide, carbon monoxide and water,or ¦`
12¦ the products of breakdown of lignin may be converted to
13l methane. Generally speaking, the procedures described in
14 Brink U.S. Patent 3,582,369 may be used.
16 Among the advantages of this system the following
17 may be mentioned. The concentrations and yield of mono-
18 saccharides leaving the hydrolysis-oxidation through line lS
19 are maximized and the time required for overall hydrolysis
is reduced. Little or no solids leave the system to present
21 disposal problems. The production of ethanol, methane ancl
22 other useful organic compounds is accomplished. The wet
23 oxidation step i5 exothermic and the system as a ~hole can
2~ be made independent of an external energy source. The s.ystem
can be designed to prod~ce suf~icient thermal en~rgy to
2h operate the system with the possihility of providing surplus
27 energy for outside use.
28
2~ `
31
32
. .
- 23
",~
~ 2 (!
1 The manner in which the wet oxidation step is carried
2 I out can be adjusted to maximize the production of heat or to
3 maximize the production of useful organic materials such as
4 I methane, methanol, organic acids and Eurfural. By using more
51l o~.ygen, a greater amount of heat is generated and a lesser
6 ¦ amount of organic products of value is produced. Conversely
7 I by employing milder conditions, e.g. less oxygen, less heat
8 j and more useful OrgaQiC products result. The recycle of
9 ~ solids to the wet oxidation unit also influences heat
10 , production; the more solids recycled, the greater the
11 production of organic productsO By maximizing oxidation, .
12 a temperature of 2Z0C. or higher and greater heat production
13 result. By conducting wet oxidation to achieve temperatures
14 of 180 to 220Co r less heat and more useful organic compounds
15 I result.
16 I
17 ~ The following specific example, although based on
18 I laboratory work and lacking, therefore, the advantageous
19 ~ continuity of a commercial process will serve further to
20 ¦ illustrate the hydrolysis-sensitization sub-system of the
23~ proce~s.
224
26
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291 . . .
.
31 ;
32
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1~175~20
l Example
21!
3 ¦1 A. Stage I Hydrol~sis (Pre-~yd Iysis)~ White fir
4~ woocl comn~inuted to -2-~4 mesll ~as used. 4.0 Kilograrns
5; (O.D. basis) were used containing 0.5 kilogram water. The
6l wood was slurried in 35.5 kilograms of water and brought to
7i pH 3.0 with nitric acid. This slurry was stirred in a closed
8 1l reaction vessel and brought to 160Co in 10 minutes and held
9f~ at that ternperature ~or 30 minutes. I`his produced a solution
lOI containing 1.16% reducing sugars, pH = 2.54 with, of course;
llij undissolved solids. The slurry was cooled to room temperature .
121 and was separated by filtration and water washinc3 to give a
13 li ligrlocellulosic residue of 2.85 kg (O.D. basis) or 6.4 kg
14l (wet basis)~ (In commercial practice a separation would be
lSI made of hydrolysate (monosaccharide derived from hemicelluloses),
16 recycle hydrolysate ~ould be employed, and a combined
17l hydrolysate would be routed to Eermentation.)
181
l91 B. Sensitization. 4.0 Xilograms (O.D. basis) of
:, I _ . .
20 ¦ washed, pre-hydrolyzed residue such as produced in A and 3.2 kg
2ll of wash water are slurried with water to give 24.4 kcJ. which
22 1 is brought to p~ 2.45 by 72% nitric acic~ and is heated to
23~ :l70aC. in a closed vcsscl in about 10 niinutes and llelcl at
2~ such telnperature wi.th ayitation Eor 60 minutes with sparginy
25I¦ with air at the rate of 1.01 gram per miIlutc of oxygen per
26 kg oE O.D. wood. q'he total pres.surc was maintainecl at 17.58
27 kg/sq. cm, the auto(Jenous steam pr~ssure beiny calculated as
2~ 7.04 ky/sq. cm.
31
32
.. ' ' .
~ - 25 - I
~'11 .. ,
~ ' ~
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~ ~7~i3~)
l C. Stage II Hydrol~sis. Stirring of the slurry
resulting from B was continued, hydrolysis was initiated by
31 terminating the introduction of ai.r and increasing the
4~ temperature to 19~C. in three rninutes and releasing off gas
Sll to stabilize the pressure at about 24 kg/sqO cm. The
6 ll temperature was maintained at 195 - 205C. for 35 minutes at
7 ¦I which time a maximum sugar content was obtained in the
aqueous phase. The increased rate of hydrolysis in this
91 stage resulting from sensitization step B was calculated to
lO¦ be about four times the rate in the absence of step B.
111 .
12¦ It will therefore be apparent that a novel and
13¦ advantageous method and system have been provided for the
l~¦ conversion of lignocellulosic material to useEul products
lS¦ with a minimum of degradation to waste products, whether
16 ¦ gaseous, liquid or solid and with a minimum input or no
inp~t Oe the mal eDergy from an external source .
222 . '
23 .
~5 .
26
27 . .
2~ .
31
32 .
,,,. .
- 26 -- . .
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