Note: Descriptions are shown in the official language in which they were submitted.
SEPARATING PHENOLS FROM ALKALINE PULPING
SPENT LIQUORS
This invention pertains to a process for separating phenols
from spent aqueous liquors derived from the alkaline pulping of
lignocellulose. It pertains particularly to a process for separa- y
ting phenols from the alkaline black liquors derived from pulping
, wood by the kraft and soda processes.
As used herein, the term "phenols" is used in its generic sense
and pertains not only to phenol itself, but also to phenolic-type
compounds generally, and in particular to phenol, ortho-cresol,
meta- and para-cresols, guaiacol, vanillin and acetovanillone.
10With the exception of the last named, all of the foregoing
phenols have known and important industrial uses. Phenol itself
~;~ is widely used in plastics, plasticizers, resins, adhesives, fibers,
; medicinals, herbicides and biocides. The cresols are used in making
herbicides, resins, plasticizers, disinfectants, anti-oxidants and
in ore flotation. Guaiacol is used in medicinals and for making
perfumes and flavoring materials. Vanillin is well known as a
flavoring agent and is used in making medicines.
It is well known that during the alkaline pulping of ligno-
cellulose, phenols of the class described above are produced in
substantial quantities by the breakdown of the lignin content of
the lignocellulose. For example, a typical sample of kraft black
liquor contains 0.S5% by weight on a solids basis of such materials.
-The spent aqueous liquors derived from the alkaline pulping
of lignocellulose thus represent a potential source of enormous
quantities of phenolic materials. A typical 1,000 tons a day kraft
pulp mill, for example, produces from 1550 to 1900 tons of black
;~ liquor solids per day. The phenolic con-tent of this quantity of
black liquor solids is of the order of from 21,500 to 37,500 pounds.
Up to the present time, there has been no successful attempt
to recover commercially the large quantities of phenolic compounds
present in this source. These materials presently remain in the
` 1 ~
'`
' '
4~3
.
black liquor and are burned in the mill recovery cycle.
The reason for this waste of important industrial chemicals
is that heretofore no practical, one-step method has been available
for isolating them in the small percentage quantities in which
they are present from the huge volumes of alkaline liquor in which
- they are contained.
U.S. patents 2,104,701, 2,489,200, 2,721,221 and 2,871,270
disclose procedures for producing vanillin from waste acid sulfite
pulping liquor. However, these procedures require first neutral-
izing the liquor, which is on the acid side, to produce an alkalineliquor; then oxygenating the alkaline liquor to convert part of its
lignosulfonic acid content to vanillin; and then separating the
vanillin from the oxygenated liquor.
U.S. patent 3,375,283 discloses a process for the preparation
of methoxyphenols from spent kraft pulping liquor, but by first
drying the liquor to a solid and then pyrolizing the resulting
solid at 300-600C. to generate the methoxyphenols which are sep-
;` arated from the pyrolysate by extraction with benzene.
Chernovsov et al Tr. Vies. Nauch.- Issled Iust. Tsellyul. -
Bum. Prom. 1972, No. 61, pp. 172-80 (Chemical Abstracts, Vol. 80,
p. 5089 x (1974) ) disclose a procedure for isolating from kraft
black liquor an extract one component of which is guaiacol. The
process consists of: (1) acidifying the alkaline liquor with con-
centrated hydrochloric acid; (2) heating the liquor to 70C.; (3)
filtering to remove lignin; (4) saturating with sodium chloride;
and (5) extracting with diethyl ether. However, the yield of gu-
aiacol is poor and the guaiacol product is heavily contaminated by
non-phenolic components from which it can only be extracted by a
time-consuming and difficult supplemental procedure.
We now have discovered, and it is the essence of this invention,
; that the phenolic content of spent a4ueous liquors derived from the
alkaline pulping of lignocellulose may be separ~ted from the li-
quors without acidification by the simple expedient of extracting
4~3
'
; them frQm the aIkaline liquor with a solvent comprising essentially
a lower aliphatic alcohDl having from 2-5 carkcin atoms inclusive,
~n particular ~ith a propyl alcohol. When this is done, the alcohol
solyent extracts the phenolic aompounds in the form of their sodium salts,
selectively and ~n high yield. m is is ac~,~lished without the necessity
of subLjecting the liquors to any chemical pretreatment prelimlnary to
the extxaction. In addition, it leaves the black liquor in a a~ndition
suitable for return to the rea~very system of the pulp mill.
Thus, in acaordance with the present teachings, a process is
proyided for n~nufacture of phenols which comprises pulping lignocellulose
hy an alkaline pulping process to produce a cellulosic pulp product
and an alkaline spent liquor oontaining a muxture of phenols as their
alkali metal salts, the said phenols comprising phenol, cresol,
- xylenol, guaiaaol, acetovanillone and vanillin and separating the spent
liquor ~rom the pulp. The spent liquor is concentrated to a solids
content o~ up to a60ut 50% by weight and the concentrated spent liquor
is extracted with a solvent comprising essentially a lower aliphatic
alcohol ~hich fias from 2 to 5 carbon atQms inclusive and at a temperature of
just a60ve the freezing temperature to about the koiling temFerature of
the solvent, thereky forming a solvent phase containing the aIkali
metal salts of the phenols and an aqueous phase. The solvent phase is
separated fr~" the aqueous phase and the solvent phase concentrated by
- the removal of solvent therefrom and acidifying with an acid selected
from sulphuric acid, phosphoric acid and acetic acid in order to
aonvert the alkali metal salts of the phenols aontained in the resulting
aonaentrated solvent phase to free phenols. m e acidified and
concentrated solvent phase is a solvent extracted with a substantially
water i~miscible selective solyent for free phenols, the resulting
- free phenols solvent extract is separated and the free phenols
solvent extract is fractionally distilled for the separation of the
phenols aontained therein.
:.
- B~
: ~1.14~8
~:"
DESCRlPTICN O;~ P~ EMBCDIME2~TS
OF THE lNVENTION
S~ent aqueous liquors suitakle for use in the presently described
prccess for separation of phenolic coLpoLnds broadly o~mprise those
deriyed from the alkaline pulping of lignocellulose, particularly those
derived frcm the aIkaline pulping of either hardwood or softwocd or muxtures
thereof SuitaEle liquors thus are those derived from the conventional
kxaft and soda processes as practiced throughout the world. Such liquors are
alkaline, having a pH of at least 10. The usual pH of oommercial kraft
or soda spent pulping liquor is from about pH 11 to about pH 13.
lQ In the kraft process, ~ood chips æ e cooked for from 2-4 hours at a
temperature of 160 to 175C. More specifically, they are cooked in a
typical instance at 170 to 173C. at a steam pressure of 100 to 110 psi.
The cooking liquor comprises oombined sodium hydroxide and sodium
sulfide used in amounts of 40 to 50 grams per liter, calculated as Na2O.
At the end of the ccok the pulp and black liquor are blown into
the blcw tank where they are diluted with weak black liquor resulting
frcm a prior run. The black liquor is separated from the pulp, the
latter then ~eing washed and applied to its intended use.
; The procedure followed in the soda process is similar except that
2Q s~dium sulide is used in a relatively m m ~r proportion, if
-3a-
448
at all. The principal cooking agent is sodium hydroxide. Cooking
temperatures range from 160 to 180 and cooking times from 4 to 6
hours. The sodium hydroxide cooking agent is used in an amount of
50 to 60 grams per liter, calculated as Na20.
Both of these alkaline pulping procedures attack the lignin
of the lignocellulose and convert it in part to phenol and its
derivatives. The black liquor resulting from a typical softwood
alkaline pulping procedure will contain about 0.85% by weight solids
basis, of phenolic compounds. Typically, these will be dist~ibuted
10 as follows:
Percent by Wei~ht
Phenol 1.44
Ortho-cresol 6.92
Meta- and para-cresols 10.97
Guaiacol 32.18
Vanillin 28.28
Acetovanillone 13.92
Other phenols 6.28
To render the waste liquors susceptible to the hereindescribed
- 20 procedure for separation of the phenols, it is only required, or.:~'`' at least desirable for practical reasons, to concentrate these
liquors to a solids content of up to about 50% by weight, preferably
; ~ from 25 to 45% by weight. This may be accomplished by the appli-
cation of multiple-effect evaporators or other suitable concentra-
ting equipment.
-- For separation of their content of phenolic compounds, the
spent aqueous liquors are extracted with a selective solvent for
such compounds. Such a solvent must meet the following criteria:
It must be a good solvent for phenolates, since the phenols
: 30 are in the form of their alkali metal (sodium) salts.
It must not be substantially soluble in the waste liquor, so
that a two-phase system may be established.
It should not react with the black liquor or with sodium
-4-
.~
~114~8
. ..
phenolates.
It should remove the phenolates selectively from the spent
liquors, a matter difficult of accomplishment in view of the highly
diverse composition of the same.
- It should not be too high boiling and should be readily remov-
able from the extracted phenolates in a condition suitable for re-
cycling and without introducing impurities into the phenolates.
It should be economically practical, i.e. available in large
quantities at low cost.
It must be recoverable.
Its density should be such as to establish as high a density
differential as possible between the solvent and black liquor phases.
It must establish as large an interfacial tension as possible
~ between the solvent and black liquor phases.
; Finally, the distribution coefficient for the sodium phenolates
between the black liquor and solvent must be as high as possible.
Of all the commercially available organic solvents, we have
found that one group of solvents meets the foregoing criteria best
- and is most suitable for the large scale commercial separation of
20 phenolic compounds from spent aqueous pulping liquors. The solvents
comprising this group are the low molecular weight aliphatic alco-
hols, including ethanol, n-propanol, i-propanol, n-butanol, second-
ary butanol, isobutanol, tertiary butanol, and all of the pentanols.
- For the purposes of the present invention these alcoholic solvents
may be used singiy or in admixture with each other.
The extraction of the spent pulping liquor with the alcohol
solvent is carried out using a suitable ratio of solvent to liquor,
as determined by the source and composition of the liquor and the
other operating conditions. In general, a ratio of 0.5-3 to 1,
30 solvent to liquor, is suitable.
The extraction with solvent is carried out in any appropriate
type of extraction equipment, operated in any desired number of
stages, depending upon the distribution coefficient of the particu-
4~
lar solvent mixture employed.
The temperature of extraction varies from just above the fre-
ezing temperature to about the boiling temperature of the solvent.
Atmospheric pressure may be employed. Where atmospheric pressure
is used, since the black liquor normally is processed hot from the
mill, the temperature of extraction will vary between about 20 and
about the boiling temperature of the solvent.
The extraction results in the formation of a solvent phase
containing the phenols, and a raffinate, or residual black liquor
phase. These are separated in conventional manner. The solvent
phase then is treated for separation of its content of phenolic
materials.
In one mode of operation the solvent phase is distilled to
remove solvent and concentrate the extract. The concentrated ex-
tract is acidified with a slight excess of an acid such as sulphuric
acid or phosphoric acid. This converts the sodium phenolates to
the free phenols. The medium containing the free phenols is ex-
tracted with a suitable solvent such as toluene, after which the
solvent is removed by evaporation. This leaves a residue of mixed
phenols which may be separated by fractional distillation.
The black liquor from which the phenolic materials have been
removed is steam stripped to remove any residual solvent and then
returned to the spent liquor recovery system and processed in the
usual way. The solvent removed by the steam stripping is combined
with the solvent recovered by distillation from the solvent phase
and recycled to the extractor for treatment of a further quantity
of spent liquor.
The process of the invention is further illustrated by the
following examples.
EXAMPLE 1
This example illustrates the application of the process of the
invention to the extraction of phenols from kraft black liquor
using isopropanol as a solvent.
48
Black liquor, 0.35 liter, resulting from the commercial kraft
pulping of softwood chips was employed as a starting material. It
had a solids content of 35.50% and a pH after soap skimming of 13.20.
The liquor was extracted with azeotropic isopropanol containing
12.20% water at room temperature continuously ~or ten cycles, using
3500 ml. of azeotropic isopropanol (350 ml/cycle).
The isopropanol solvent in the light phase was removed by dis-
tillation at 79-~2C. The resulting concentrated extract was dilu-
ted with 120 ml. of water to give a solution having a pH of 12.65.
10 The solution was acidified with 29.00% sulphuric acid until its
- pH was 6.50.
:
. The resulting black, heavy precipitate was removed by filtra-
tion and the filtrate was extracted three times with 50 ml. diethyl
ether at room temperature. The combined ether extracts were evapo-
rated in a rotary evaporator at 15-25C. to a minimum volume of
- about 5.0 ml.
The concentrate was then examined by gas chromatography for
phenolic compounds, using Hewlett Packard Model 700 gas chromato-
graphy, 12 feet 10% SE 30' 1/8" stainless steel column at 140C.
20 with 20 ml. per minute helium.
The results of the analysis are given in Table I below:
. Table I -
COMPOUNDS PHENOLS CONTENT BASED ON 40%
BLACK LIQUOR (grams/gallon)
(Converted from 35.50% values
for purposes of comparison)
Phenol 0.169
o-Cresol 0.391
m-, p-Cresols 1.508
Guaiacol 4.132
30 Xylenols 0.938
Vanillin 6.470
Acetovanillone 4.855
Other Phenols 0.556
49~8
.' :
EXAMPLE 2
This example illustrates the application of the process of the
invention to the extraction of phenolic compounds from soda black
liquor using isopropanol as the solvent.
The procedure of Example 1 was followed, but using 35.0% solids
soda liquor as the starting material. The results of the analysis
; are shown in Table II below.
Table II
COMPOUNDS GRAMS/GALLON OF 40% BLACK
~; LIQUOR
Phenol 0.131
10 o-Cresol 0.483
.
m-, p-Cresols 1.590
~- Guaiacol 4.971
;; Xylenols 0.583
Other Phenols 1.011
: .
Vanillin 6.257
Acetovanillone 4.591
- EXAMPLE 3
..
f'X' This example illustrates the application of the process of the
invention to the extraction of phenolic compounds from kraft cook-
ing waste liquor using n-propanol as the extracting solvent.
; Six hundred milliliters of commercial softwood kraft black
liquor having a pH of about 12.5 and containing 37.50% solids was
extracted continuously in a 1.5 inch by 4.0 foot glass column with
; azeotropic n-propanol containing 28.2% water. The extraction temp-
- erature was 60C. 6.50 Cycles of extraction were employed using
- 600 ml. azeotropic n-propanol.
The organic phase resulting from the extraction was separated
and evaporated to a thick syrup followed by acidification with
10.00 ml. glacial acetic acid to a pH of 7.00.
The neutralized extract containing the free phenols was ex-
tracted with three 50 ml. portions of diethyl ether. The combined
ether extracts were concentrated to about 20 ml. under vacuum at
B
room temperature.
The resulting ether concentrate was examined by gas chromato-
graphy. The results are shown in the following table.
Table III
GRAMS/GALLON OF 40% BLACK
C~MPOUNDS LIQUOR
Phenol 0.181
o-Cresol 0.462
:
m-, p-Cresols 1.592
Guaiacol 5.270
10 Xylenols 0.761
Other Phenols 1.010
Vanillin 6.939
` Acetovanillone 4.224
EXAMPLE 4
-
This example illustrates the application of the process of the
: invention to the extraction of phenolic compounds from black li~uor
using n-butanol as the solvent.
4.00 Liters of commercial softwood kraft black liquor having
a solids content of 32.33% and a pH of 13.15 was extracted contin-
uously for 48 hours in a 125 cm. by 8.20 cm. glass column with
; azeotropic n-butanol containing 20.1% water. At the end of the
extraction the organic solvent phase was separated and distilled
until most of the butanol had been removed.
- The resulting deep brown concentrate was dissolved in 200 ml.
or water and acidified to a pH of 6.50 with 50% sulfuric acid to
spring the phenols. The acidified mixture was extracted with three
100 ml. portions of diethyl ether. The combined ether extracts
were concentrated and the concentrate examined by gas chromatogra-
phy.
The analysis showed that the extract contained 4.0137 grams
of guaiacol and 0.1432 grams phenol per gallon of black liquor
starting material. The amounts of o-cresol, m- and p-cresols,
vanillin and acetovanillone were substantially the same as given
_g_
gt4~3
. . .
in Example 2 on the same black liquor concentration basis.
EXAMPLE 5
; This example illustrates the distribution coefficient of guaia-
col and vanillin in the solvent phase resulting from a single ex-
traction of phenolic compounds from kraft black liquor by the here-
in described process, using various organic solvents at two differ-
ent temperatures: 25C. and 65C.
Kraft blac~ uor, 100 ml., was vigorously shaken with 100 ml.
of an azeotropic organic solvent in a 250 ml. graduated cylinder.
The time required for maximum phase separation and its volume were
recorded.
;!:' '~
The organic solvent phase was worked up as in Example l; i.e.
; the organic solvent was distilled off, the phenolic compounds ex-
'~ tracted from the neutralized residue (pH - 6.50) with an equal
~`~ volume of diethyl ether three times. The concentrated ether ex-
~`~ tracts were then examined by the chromatograph. The yields of gu-
aiacol and vanillin from the single extraction and their distribu-
~ tion coefficients are shown in the following tables.
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49~8
EXAMPLE 6
This example illustrates the application of the invention to
the extraction of phenolic compounds from a hardwood black liquor.
Black liquor, 0.35 liter, resulting from the laboratory kraft
pulping of red alder chips (Alnus rubra) was employed as a starting
material. It had a solid content of 38.63% and a pH of 13.10. The
liquor was extracted with azeotropic isopropanol containing 12.20V/o
water at room temperature continuously for ten cycles using 3500
ml. of azeotropic isopropanol (350 ml/cycle).
The isopropanol solvent in the light phase was removed by
distillation at 79-~2C. The resulting concentrated extract was
diluted with 120 ml. of water and was acidified with 20% H2SO4
to pH 6.50. The resulting black, heavy precipitate was removed
by filtration and the filtrate was extracted with three portions
of 50 ml. diethyl ether. The combined ether extracts were evapo-
rated under rotary evaporators at room temperature to about 5.0 ml.
The phenolic content in the concentrated extract was examined
by gas chromatography as described in Example 1.
;~ The results of the analysis are given in Table V below.
Table V
- 20 COMPOUNDS PHENOLIC CONTENT BASED ON 40% BLACK
LIQUOR (G/GALLON)
Phenol 0.027
o-Cresol 0.054
: m-, p-Cresols 0.117
Guaiacol 0.470
Xylenols 0.116
Other Phenols 0.225
Vanillin 1.252
- Acetovanillone 0.973
Acetosyringone 0.437
EXAMPLE 7
- This example illustrates the application of the invention to
the extraction of phenolic compounds from black liquor using
-13-
: . .
.44~3
':.
: pentanol as a solvent.
- Black liquor, 0.35 liter, resulting from the commercial kraft
pulping of softwood chips was employed as a starting material. It
`- had a solid content of 35.50% and a pH of 13.20. The liquor was
; extracted with azeotropic 2-pentanol (67.80% by weight) at room
temperature for 16.00 hours.
The solvent, 2-pentanol, in the light phase was removed by
distillation and the concentrated extract was worked up as in
Example 1. The phenolic compounds in the extract were examined by
a gas chromatograph as it is described in Example 1.
The results of the analyses are given in Table VI.
TABLE VI
;` PHENOLIC COMPOUNDS PHENOLS GRAMS/GALLON 40% BLACK LIQUOR
~; Amount Extracted Amount Present
~: ,
Phenol 0.153 (0.169)
o-Cresol 0.283 (0.391)
m-, p-Cresols 0.908 (1.508)
Guaiacol 3.908 (4 132)
Xylenols 0.717 (0.938)
20 Other Phenols 0.347 (0.372)
Vanillin 4.054 (6.470)
.
Acetovanillone 2.067 (4.855)
Note: Parentheses denote the amounts of phenols in unextracted
- black liquor.
EXAMPLE 8
This example illustrates a manner of separation of vanillin
from other phenolic compounds of the phenolic extract produced by
the process of the invention.
A neutral ether soluble phenolic extract, 65 ml., obtained
from isopropanol exhaustive extraction of 3 liters of a 35.50%
` softwood black liquor was used as the starting material. The
solution contained 4.00 grams vanillin and 8.463 grams of other
phenolic compounds (see Table VII). The solution was mixed with
-14-
9t8
,-
4.105 grams NaHSO3 in 100 ml. water with continuous stirring for
three hours at room temperature at pH 2.50. The pH was controlled
by adding 5.50% sulphurous acid. After stirring, the oily light
phase was removed by extraction with three portions of 100 ml. di-
ethyl ether.
The light brown raffinate was concentrated to 50 ml. at 60C.
under vacuum to remove excess sulfur dioxide. The concentrate was
neutralized with dilute sodium hydroxide to pH 6.50 and was extract-
ed with three portions of 60 ml. diethyl ether. The combined ether
extracts were evaporated to dryness giving a dry weight of 3.876
- grams (96.90% recovered) of vanillin. The product had a melting
point of 78-~0C. and was not depressed by an authentic sample of
vanillin. The crude product showed only one peak (corresponding to
vanillin) in the gas chromatogram. Gas chromatographic examination
of the oily light phase after vanillin removal showed that the other
phenols had not been removed by the bisulfite treatment.
Table VII
COMPOUNDS BEFORE EXTRACTIONAFTER EXTRACTION
Phenol 0.104 0.101
20 o-Cresol 0.262 0.254
m-, p-Cresols 0.907 0.902
Guaiacol 3.476 3.453
Xylenols 0.582 0.573
Other Phenols 0.441 0.431
: Vanillin 4.000 0.170
Acetovanillone 2.753 2.749
EXAMPLE 9
Separation of phenols by fractional distillation using tall
oil as a heel oil.
A mixture of 54 grams of phenolic compounds and 100 ml. of
; tall oil in a 350 ml. round bottle flask was fractionally distilled
- using a 1.5 x 37 cm. glass column at atmospheric pressure. The
column was packed with 4.5 mm. (I.D.) glass helices and was insula-
:
-15-
.
48
;''
ted with 2" thick of glass wool. The mixture of phenolic compounds
consisted of: phenol, 3.00g; o-cresol, 6.50 g; m, p-cresols, 5.00
g; (1.0 to 1.0 ratio); guaiacol 32.50 g; and 3,5 xylenol 7.00 g.
Fractions of the distillate were collected based on the boil-
ing point ranges of each individual compound. The composition of
each fraction was determined by the gas chromatographic method as
it is described in Example 1. The results are given in Table VIII.
:
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EXAMPL,E lO
This example illustrates the unsuitability of various classes
of solvents other than the lower alcohols for the purposes of the
. . .
present invention.
~- The examples of commonly available solvents used are given
; below:
. Hydrocarbons - cyclohexane, toluene
Halogenated hydrocarbons - chloroform, 1, 1.1 - trichlorethane
Ethers - petroleum ether (B.P. 30-60C), diethyl ether,
~- tetrahydrofurane and dioxane (1,4 diethylene oxide).
Ketone - 4-methyl-2-pentanone
Black liquor, 0.35 liter, resulting from the commercial kraft
pulping of softwood chips was employed as the starting material.
The black liquor was extracted continuously with each individual
solvent fnr 16.00 hours at room temperature. The work ups followed
`; the procedure described in Example 1. The amounts of phenols ex-
tracted by each solvent are given in Table IX.
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