Note: Descriptions are shown in the official language in which they were submitted.
I
Method for rapid determination of -the contents of lignin,
monosaccharides and organic acids in tile process solutions
of sulfite pulping
The present invention is concerned with a
method for rapid determination of the contents of
lignin, monosaccharides and organic acids in the process
solutions of sulfite pulping.
The objective of the invention was to provide
a method for obtaining measurement information on the
contents of sulfonated dissolved lignin, monosaccharides
and organic acids at short time intervals for the purpose
of controlling sulfite cooking or other pulping or by-
product production processes and for the purpose of
characterizing the spent liquor.
The invention is characterized in that any
non-ionized compounds that disturb UV-absorption and
other measurements are separated from the lignin material
by fractioning by means of the ionwexclusion technique
and that the measurements of contents are performed out
of the liquid flow coming out from the separation column
by means of the UV-method at a wavelength of 280 no or
260 no, by means of the refractive-index method, and/or
by means of the polarimetric method.
In the paper by Skew ARC., "Determination of
sugars in waste sulfite liquor", Can Pulp Paper In.
10(1957):11, 49-50, it is suggested that the ion-exclusion
phenomenon should be used for the purification of the
sugars of sulfite spent liquor before the determination
of reducing sugars. Later, in certain studies, the
ion-exclusion technique has been used for lignosulfonate-
sugar separations in laboratory studies (see, e.g.,
Fullest OF Lung M., McCarthy JO spent sulfite
liquor VII. Sugar-lignin su]phonate separations using
ion exchange resins TAIPEI 42(1959):6, 496-502). The
method has been slow, the separations have taken from
an hour to several hours, and the purpose has been to
I ' ,
perform a group separation for further analyses in view
of properties and identification of the compounds in
sulfite spent liquor. Jon exclusion has not been
suggested in prior art for direct determinations of
contents, but it has rather been a step of preliminary
treatment before different methods of determinations of
contents, to be performed in the laboratory manually.
The most important feature of the method in accordance
with the present invention, i.e. the elimination of
compounds disturbing the UV-measurement of lignin by
means of ion exhalations also a new idea.
In prior art, attempts have been made to
obtain the information on contents provided by the
method in accordance with the present invention by
means of direct measurements out of the process solutions
In prior art, measurements of contents have been export-
minted with mainly out of kissing liquors.
Traditionally, the progress of sulfite cooks
has been observed visually by comparing the color of
the cooking liquor with a color standard. In the 1950's
- and 60's, calorimeters were introduced in the measurement
of the color, by means of which it is possible to
observe the transparency of the solution at a certain
wavelength of visible light (Mondale N., Lichtabsorptions-
messungen an Kochsauren, it Zusammenhanq mix dim Auf-
.. .. . .. . . . . . .. ..
schlussgrad undo don technologischen Anwendun~ in der_ulfitzellstoffhers-tellung. Doctor's thesis, Technische
Hochschule Grant, 1961). On the basis of calorimetric
measurement of the color of the cooking liquor, auto-
motion of sulfite cooking was suggested. (AT Potent).
In the 1950's, lignin measurement based on the
absorption of W-radiation was also suggested as a basis
for the cook control. In principle, UV-spectrophoto-
metric determination of lignin can be performed a-t the
extreme values of the UV-spectrum. Such values are
maximum values at 200 to 205 no and 280 no as well as
I
minimum at 260 no. The "shoulder at 230 no has also
been suggested. In the paper by Patterson OF
Keys JO Hart JO A Strap PI Lunger P., "The
spectrophotometric determination of lignin in sulfite
cooking liquor Pulp paper mug. Can. 52~1951~, 105-111,
Lenin measurement at 280 no has been suggested. It
was, however, noticed that during cooking, UV-absorbing
compounds not derived from lignin were produced which
cause errors in the measurement result, in particular
at the final stage of the cooking. In the paper by
Kleinert TON., Joyce CASEY "Short wavelength ultraviolet
absorption of lignin substances and its practical asp-
ligation in wood pulping." TAIPEI 40(1957):10, 813~821,
measurement at 205 no has been suggested by means of
very thin cuvettes together with a diluting device.
Later, it has been established (Skinning AGO., Johansson
G., "Roy ultraviolet absorption of sulfite waste cooking
liquor." Svensk papperstidn. 6211959), 646-648, and
Sjostrom E., Hag Lund P., "Spectrophotometric determi-
nation of the dissolution of lignin during sulfitecookiny". TAIPEI 47~1964):5, 286-291) that sulfur dioxide
interferes with the measurement at 205, and the measure-
mint does, consequently, not represent lignin alone.
Thus, the W -spectrophotometric measurements
are interfered with mainly by sulfur dioxide in the
initial part of the UV-spectrum and by the discharge
products of carbohydrates, furfural and 5-hydroxy-methyl-
furfural, at higher IJV-wavelengths, so that the measure-
mint is not reliable at the wavelength of any of
the extreme values in the UV-spectrum of lignln. Roy
calorimetric measurements also suffer from the same
deficiencies, i.e. compounds absorbing within the
visible wavelength range are also produced during the
cooking, depending on -the cooking conditions.
A rapid measurement has not been suggested in
prior art for the measurement of the carbohydrates,
mainly monosaccharides, produced under the conditions of
sulfite cooks. Polarimetric determination of carbon
hydrates, however, gives important information on the
progress of the cooking, in particular at the final
stages of the cooking. Direct measurement out of the
process solution would be mostly impossible, because
the lignosulfonates in the solution make the solution
non-transparent.
- For the measurement of the refractive index
directly out of the process solution, there are measure-
mint apparatuses, and they have been applied to pulping
processes for the determination of dry solids contents
The measurements have, however, been disturbed extensi-
very by the contamination of the measurement apparatus.
Measurement out of the process solution by means of a
differential refractometer after ion-exclusion separation
has not been suggested as a method of observation.
The greatest advantage ox the method in
accordance with the present invention is that the
lignin measurement can be performed undisturbed by an
other compounds. The lignin measurement is facilitated
additionally by the fact that, in the separation, the
sample is diluted considerably, whereat, for the measure-
mint, it is possible to use conventional apparatuses
provided with low through cuvettes. Direct measure-
mint out of the spent liquor always requires complicated steps of dilution.
Another advantage of the method in accordance
with the present invention is that it it possible to
determine the contents of monosaccharides and even of
organic acids. Such a measurement has not been
suggested in prior art as a source of information for
the controlling of processes, even though the observe
lion, e.g., of the content of monosaccharides at the
final stages of cooking taking place within the acid
fringe would be very useful.
Moreover, the new method offers an interesting
possibility for the recovery of pure fractions for
so
- pa -
further analyses, either on-line or manually.
The method of the invention will now be described
with reference to the accompanying drawings, in which:
Figure 1 is a graph showing measurements of a
typical spent-liquor separation;
Figure 2 is a graph showing the results of Example
l;
Figure 3 is a graph showing the results of Example
2;
Figure 4 is a graph showing the results of Example
3;
Figure 5 is a graph showing the results of Example
4; and
Figure 6 is a graph showing the results of Example
5.
~765~
According to the invention, the measurement
of lignin is carried out as based on absorption of
ultraviolet radiation or on changes in the refractive
index. The measurement of -carbohydrates is carried out
as based on polarimetry, i.e. extent of rotation of
polarized light, or on changes in the refractive index.
It is an essential feature of the invention that any
non-ionized compounds that interfere with the measure-
mints of lignin by means of US or by other means are separated before the measurement. At the same time,
the monosaccharides are separated, which can be de-
termined without interference by the intensive color
of lignin.
The separation takes place ion-exclusion-
chromatographlcally as based on the separation of
ionizable and non-ionizable compounds from each other
on the basis of their ionic nature. The separation is
induced by means of a simple column filled with a
cation-exchange material. When the cakion-exchange
material is in the cation form of the sample, the
ionizable compounds in the sample cannot be diffused
on the resin particles owing to electrical repulsion
forces and to the retaining of electro-neutrality. For
the non-ionizable compounds, there is no such restrict
lion, and under suitable conditions they may be
diffused on the resin, whereat their passage is
retarded as compared with the ionizable compounds when
the column is eluded with water In the case of
sulfite process solutions, the sulfonated ionizable
lignosulfonates are separated from monosaccharides,
furfural, weak acids, etch non-ionizable compounds.
A typical sulfite spent liquor separation is seen in
the attached Figure 1. In this figure and in the other
figures, numeral 1 refers to ionizable compounds,
lignosulfonate, 2 refers to non-ionizable compounds,
mainly monosaccharides and other compounds interfering
~7~;5:~
with the Logan measurement, and 3 refers to organic
acids. The designation US means UV280-absorption as
measured by means of an ultraviolet detector, POD means
the extent of optical rotation as measured by means of
a polarime-ter detector, RI means the change in the
- refractive index as measured by means of a refractor
meter or RI detector, and ROD means the change in the
refractive index as measured by means of a polarimetric
detector
- When the UV-absorption, refractive index, and
extent of rotation of polarized light of the out coming
liquid flow are measured after the ion-exclusion
separation column, the contents of lignin and moo-
saccharides can be determined out of the areas or
heights of the concentration peaks. BY means of
integrators connected to the measurement detectors,
the concentration data are obtained directly in
electrical form. The separation and the subsequent
measurement technique make the method in accordance
with the invention entirely different as compared with
all prior-art measurement methods.
Unlike the other constituents of wood/
lignin absorbs ultraviolet radiation strongly, which
results from the aromatic nature of lignin. In this
way, lignin dissolved in the cooking liquor is also
UV-absorbing.
The determinations based on the UV-absorption
of lignin are usually carried out at the wavelengths of
202 to 205 no or 280 no, i.e. at the maximum values.
The other compounds present in sulfite cooking liquors,
however, interfere with the UV-measurement.
Table I shows the interfering components and
the maximum percentages of error caused by them at
ordinary measurement wavelengths.
I
Tab
Components interferirlg with UV-measurements of sulfite
cooking liquors and estimated maximum percentages of
error at different wavelengths
~onent of spent liquor Error in residual Lenin content,
per cent of Tut of pulp
202 no 205 No 280 no
Organic components
~ed~cLng sugars was muons) Oily oily Oily
Aldonic acids oily 0
Glucuronic acid kiwi oily O
Fhrfural Oilily ~,26-R,45
Acetic acid Quill 0
Formic acid oily oily O
Mbthylglyoxal Oily Oily Oily
Other substances oily oily O
Inorganic components
Solute ~0,001~0,001 0
Thiosulfate oilily 0
TbtrathionateSO,Ol-o,l9 Cole 0
Tuttle 0,l2-0,83 2~28-8,q7
S2 5 glue 0,66 0
1 glue 0,13 0
As is seen from Table I, pure measurement
of lignin is obtained at the wavelength of 280 no when
the non ionizable compounds have teen separated. A
measurement at 205 no is not equally good, because ion
exclusion also occurs with sulfur dioxide, which is
ionized in water solutions. Another advantage of 280 no
is that the absorptivity is lower, which facilitates
the requirement of dilution.
I
A novel feature of the method in accordance
with the present invention in respect of the wavelength
it 260 no, which it a minimum value A minimum value
is an equally good measurement point as a maximum value.
At 260 no, an even somewhat lower absorptivity would be
obtained, whereat the quantity of feed could be in-
creased and an even better margin of determination of
the monosaccharides be reached
optical activity, i.e. an ability to rotate
the plane of oscillation ox polarized light, is kirk-
touristic of compounds that possess so-called asymmetric
carbon atoms. In sulfite cooking liquors, such come
pounds are above all monosaccharides and, to a lower
extent, organic acids.
Polarimetric determination of monosaccharides
is highly usable, because -the phenomenon is completely
specific. Lignin or the other optically inactive come
pounds do not affect the measurement result if the
transmittance of the cuvette is only sufficient for the
equipment.
In prior art, no rapid measurement has been
suggested for the measurement of the carbohydrates
produced under conditions of sulfite cooking, mainly
of monosaccharides. Polarimetric determination of
carbohydrates, however, gives important information on
the progress of the cooking, in particular at the final
stages of the cooking. Direct measurement out of the
process solution would mostly be impossible, because
the lignosulfonates in the solution make the solution
non-transparent.
The measurement by the refractive index,
i.e. eke RI-measurement, is based on the measurement
of the difference in refractive index between two
different solutions. The refractive-index detector
or RI-detector is a general-purpose detector properly
speaking, because all compounds change the refractive
index of a solution on being dissolved. The refractive
65~
index is linearly dependent on the concentration. For
the measurement of the refractive index directly out
of the process liquor, there are measurement appear-
tusks, and they have also be applied to pulpfprocesses.
The measurements have, however, been disturbed extent
lively by contamination of the measurement apparatus-
Measurement out of the process liquor by means of a
differential-refractometer after ion exclusion has not
been suggested as an observation method.
In the method in accordance with the invention,
it is possible to determine the concentrations of both
lignin and monosaccharides by means of a RI-detector.
A drawback is that all compounds that are eluded at the
same time as the compounds to be studied are included
in the measurement. ivory, most of the dry solids in
the sulfite spent liquor consist of lignin, and in
acid cooks additionally of monosaccharides, so that
the concentrations and in particular their changes can
be established easily. The ion-exclusion separation is
also useful in this particular case.
The essential feature of the method of the
present invention is ion-exclusion separation. In order
to accomplish this separation, it is required, in the
first place, that the filler in the separation column,
i.e. the cation-exchange material, is appropriate.
Thereat, the porosity of the cation-exchange material
must be sufficient in order to diffuse pentoses and
hexoses into the inner volume of the material. An
excessively low porosity excludes diffusion starkly.
In the styrene~divinylbenzene resins used in accordance
with the invention, the porosity is determined by the
degree of cross linking, i.e. by the quantity of
divinylbenzene. The quantity of divinylbenzene also
determines the mechanical strength of the resin, which
just be addicts as to endure the strong flow. Thus,
rapid separation requires a resin of an entirely
particular type. The particle size of the resin is
~2~7~5~
1 0
also essential; a smaller particle size improves the
separation, but the counter-pressure to pumping is
then also increased. It is also essential that the
counter-pressure it suitable for a simple pump solution.
Another factor affecting the ion-exclusion separation
in accordance with the present invention is the length
of the column, which affects the separation time directly
and whose suitable value is 10 to 40 cm. The flow rate
in the column also affects the separation time directly
in the way that the higher the flow rate, the faster
goes the separation; high flow rate, however, dotter-
rates the separating ability, it the resolution. An
increased temperature increases the rate of diffusion,
i.e. improves the separation. On the contrary, the
ion-exclusion separation is rather indifferent in
respect of changes in the quantity of feed, and the
collapsing point of the separation is very high, owing
to the nature of group separation. The quantity of feed
must, however, be such that the separation is success-
fur and all the detectors operate within an acceptable
range. Variation of the size of analytical feeds
(< 2 % of the column volume) does not affect the
separation.
i Example 1
Into an ion-exclusion column; whose diameter
was 10 mm and length 30 cm and in which the ion-exchange
material was "DOWER WOW x I" 100-200 mesh cation-e~change
resin in the Cay form and which was eluded with pure
gas-free water (means that distilled or ion-exchanged
water has been evacuated and boiled) at OWE ml/min 1,
whereat the linear flow rate was 2.55 cumin 1, at a
temperature of 50C, was fed 50 Al of calcium sulfite
cooking liquor from the end of the cooking. The swooper-
lion time was 10 mint the lignin could be determined
in 6 minutes.
In the ultraviolet-spectrophotometric deter-
munition of lignin, as a detector was used the Knauer
* Trade Mark
~2~7~5~
UV-filterphotometer and a 0.4 mm flow-through cuvette,
and the measurement was carried out at a wavelength of
280 no. In the polarimetric determination of moo-
saccharides, a Perkin-Elmer Polarimeter 241 and a 10 cm
flow-through cuvette were used, and the measurement was
carried out at a wavelength of 365 no. In the refractor
metric determination both of lignin and of monosaccha-
rides, the Knauer Differential Refractometer was used.
l The result curves of the measurements are
shown in Fig. 2.
Example 2
The procedure was the same as in Example 1,
except that the solution to be analyzed was magnesium-
sulfite cooking-liquor and the ion-exchange material
15 was "DOWER WOW x 4" 100 200 mesh cation-exchange resin
in the Mg2~ form. The result curves of the measurements
are shown in Fig. 3.
Example 3
The procedure was the same as in Example 1,
except that the solution to be analyzed consisted of
cooking liquors from a multi step sodium-sulfite cook:
A) from the end of the soda step,
B) from the end of the acid step,
and the ion-exchange material was cation-exchange resin
25 "DOWER WOW x A" 100~200 mesh in the No form, and the
polarimeter was not in use The result curves of the
` measurements are shown in Fig. 4.
Example 4
The procedure was the same as in Example 3,
except that the solution to be analyzed was sodium-
neutral-sulfite-anthraquinone cooking liquor. The
result curves of the measurements are shown in Fig. 5.
Example 5
The procedure was the same as in Example 1,
except that the quantity of feed was 73 Al, the
rate of elusion 6.9 ml/min 1, i.e. 8.8 cumin 1, the
:~2~'7~
12
particle size of the ion-exchange resin was 200-400
mesh, and the length of the column was 20 cm for the
achievement of a very rapid separation, and the Polaris
meter was not used. The separation time was 2.5 mint and
the lignin could be determined in 1.5 minutes. The
`, result curves ox the measurements are shown in Fig. 6.
