U.S. patent application number 11/420981 was filed with the patent office on 2007-02-15 for process for organosolv pulping and use of a gamma lactone in a solvent for organosolv pulping.
Invention is credited to Catharina Johanna Maria Petrus-Hoogenbosch, Leonardus PETRUS.
Application Number | 20070034345 11/420981 |
Document ID | / |
Family ID | 35501005 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070034345 |
Kind Code |
A1 |
PETRUS; Leonardus ; et
al. |
February 15, 2007 |
PROCESS FOR ORGANOSOLV PULPING AND USE OF A GAMMA LACTONE IN A
SOLVENT FOR ORGANOSOLV PULPING
Abstract
The invention provides a process for organosolv pulping, wherein
solid lignocellulosic feed material is heated at a temperature in
the range of from 50 to 210.degree. C. in a solvent to obtain a
solid cellulosic fraction comprising at least 50 wt % of the
cellulose present in the feed material and a liquid fraction,
wherein the solvent comprises at least 10 wt % of a compound
according to general molecular formula ##STR1## wherein R.sub.1 to
R.sub.6 each represent, independently, a hydrogen atom or an
organic group connected with a carbon atom to the lactone group.
The invention further provides the use of a compound according to
general molecular formula (1) in a solvent for organosolv
pulping.
Inventors: |
PETRUS; Leonardus;
(Amsterdam, NL) ; Petrus-Hoogenbosch; Catharina Johanna
Maria; (BB Heemskerk, NL) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Family ID: |
35501005 |
Appl. No.: |
11/420981 |
Filed: |
May 30, 2006 |
Current U.S.
Class: |
162/72 ;
162/24 |
Current CPC
Class: |
D21C 9/10 20130101; D21H
25/04 20130101; D21C 9/007 20130101 |
Class at
Publication: |
162/072 ;
162/024 |
International
Class: |
D21C 3/20 20060101
D21C003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2005 |
EP |
05105245.4 |
Claims
1. A process for organosolv pulping, wherein solid lignocellulosic
feed material is heated at a temperature in the range of from 50 to
210.degree. C. in a solvent to obtain a solid cellulosic fraction
comprising at least 50 wt % of the cellulose present in the feed
material and a liquid fraction, wherein the solvent comprises at
least 10 wt % of a compound according to general molecular formula
##STR5## wherein R.sub.1 to R.sub.6 each represent, independently,
a hydrogen atom or an organic group connected with a carbon atom to
the lactone group.
2. A process according to claim 1, wherein the solid cellulosic
fraction comprises at least 60 wt % of the cellulose present in the
feed material.
3. A process according to claim 1, wherein the cellulose in the
solid cellulosic fraction obtained has an average degree of
polymerisation of at least 300.
4. A process according to claim 1, wherein the feed material is
heated at a temperature in the range of from 100 to 200.degree.
C.
5. A process according to claim 1, wherein the solvent comprises at
least 20 wt % of the compound according to general molecular
formula (1).
6. A process according to claim 1, wherein the solvent comprises an
acid catalyst.
7. A process according to claim 6, wherein the acid catalyst is a
strong mineral acid having a pKa below 2.5.
8. A process according to claim 6, wherein the acid catalyst is a
strong organic acid having a pKa below 2.5.
9. A process according to claim 6, wherein the acid catalyst is
present in a concentration of at most 5% by weight of the
solvent.
10. A process according to claim 1, wherein the feed material is
heated at a temperature in the range of from 100 to 210.degree. C.
in a solvent that is free of mineral acid.
11. A process according to claim 1, wherein the feed material is
heated in the solvent at a pressure in the range of from 1 to 10
bar (absolute).
12. A process according to claim 1, wherein R.sub.1, R.sub.2,
R.sub.3 and R.sub.4 each are a hydrogen atom.
13. A process according to claim 12, wherein R.sub.5 is a methyl
group.
14. A process according to claim 13, wherein the compound according
to general molecular formula (1) is gamma valerolactone (R.sub.6 is
a hydrogen atom), 2-methyl-5-oxotetrahydrofuran-2-carboxylic acid
(R.sub.6 is a carboxyl group), a compound having a molecular
structure according to any one of molecular formulas (2) to (5):
##STR6## or an ester of a compound having a molecular structure
according to molecular formula (2) or (3).
15. A process according to claim 1, wherein the compound having a
gamma lactone group has a molecular structure according to
molecular formula (6) or (7): ##STR7## or is an ester of a compound
having a molecular structure according to molecular formula (6) or
(7).
16. Use of a compound according to general molecular formula (1) in
a solvent for organosolv pulping.
17. A process according to claim 1, wherein the solid cellulosic
fraction comprises at least 80 wt % of the cellulose present in the
feed material.
18. A process according to claim 2, wherein the cellulose in the
solid cellulosic fraction obtained has an average degree of
polymerisation of at least 300.
19. A process according to claim 2, wherein the feed material is
heated at a temperature in the range of from 100 to 200.degree.
C.
20. A process according to claim 3, wherein the feed material is
heated at a temperature in the range of from 100 to 200.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from European Patent
Application No. 05105245.4, filed Jun. 15, 2005, which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention provides a process for organosolv
pulping and the use of a gamma lactone in a solvent for organosolv
pulping.
BACKGROUND OF THE INVENTION
[0003] The most widely used pulp manufacturing process is the Kraft
process. An important drawback of the Kraft pulping process is,
however, that a large mineral waste stream comprising harmful
components is formed. In order to avoid the formation of mineral
waste material, organosolv pulping has been proposed and studied as
an alternative for Kraft pulping. In organosolv pulping,
lignocellulosic material is heated in a solvent comprising organic
compounds and optionally water, in order to dissolve the greater
part of the hemicellulose and lignin and to obtain a high-quality,
high-molecular weight cellulose that is suitable for paper
production. The solvent is separated from the dissolved
hemicellulose and lignin by simple distillation for recycling.
[0004] Well-known solvents for organosolv pulping comprise organic
compounds such as lower aliphatic alcohols, for example methanol or
ethanol, lower carboxylic acids, for example formic acid or acetic
acid, acetone, polyhydric alcohols, for example ethylene glycol or
glycerol, or mixtures thereof. Often water is part of the solvent,
typically in an amount up to 50 wt %. A small amount of strong
mineral acid, typically in the range of a few tenths to a few
percent, may be added as catalyst to the solvent. Oxidants such as
hydrogen peroxide or peroxy acids may be added to the solvent to
improve bleaching.
[0005] Organosolv pulping is typically carried out at a temperature
in the range of from 80 to 180.degree. C. The operating pressure
mainly depends on the volatility of the solvent. The pressure
should be such that the solvent is still in the liquid phase.
Typically, organolsolv pulping is performed just below the boiling
temperature of the liquor. A drawback of the use of relatively
volatile solvents is therefore that relatively high operating
pressures are needed.
[0006] An extensive overview of prior art organosolv processes is
given in E. Muurinen, "Organosolv Pulping--A review and
distillation study related to peroxyacid pulping", University of
Oulu, Finland, 2000, ISBN 951-42-5661-1.
SUMMARY OF THE INVENTION
[0007] It has now been found that compounds having a gamma lactone
group can very suitably be used as solvent or part of the solvent
for organosolv pulping.
[0008] Accordingly, the present invention provides a process for
organosolv pulping, wherein solid lignocellulosic feed material is
heated at a temperature in the range of from 50 to 210.degree. C.
in a solvent to obtain a solid cellulosic fraction comprising at
least 50 wt % of the cellulose present in the feed material and a
liquid fraction, wherein the solvent comprises at least 10 wt % of
a compound according to general molecular formula ##STR2## wherein
R.sub.1 to R.sub.6 each represent, independently, a hydrogen atom
or an organic group connected with a carbon atom to the lactone
group.
[0009] In a further aspect, the invention provides the use of a
compound according to general molecular formula (1) in a solvent
for organosolv pulping.
[0010] An important advantage of the use of a compound having a
gamma lactone group in a solvent for organosolv pulping is that it
has a relatively high boiling point and that the organosolv pulping
can thus be carried out at a relatively low pressure.
[0011] A further advantage of the process and the use according to
the invention is that the compound according to general molecular
formula (1) is both polar and relatively inert. As a consequence,
it is an effective organosolv solvent that does hardly form
reaction products with the lignocellulosic feed material or with
components formed during the organosolv process.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The process according to the invention is a process for
organosolv pulping wherein a solid lignocellulosic feed material is
heated in a solvent comprising at least 10 wt % of a compound
having a gamma lactone group to obtain a solid cellulosic fraction
and a liquid fraction. The liquid fraction contains the solvent and
dissolved hemicellulose and lignin degradation products. The aim of
organosolv pulping is to obtain a high-quality solid cellulose
fraction or cellulose pulp that is suitable for paper production.
Therefore, the exact process conditions in terms of temperature,
pressure, heating time and the solvent used are chosen such that
the greater part of the cellulose remains intact, i.e. is not
depolymerised and dissolved in the liquid fraction. In the process
according to the invention at least 50 wt % of the cellulose
present in the feed material is recovered in the solid cellulosic
fraction, preferably at least 60 wt %, more preferably at least 80
wt %. The cellulose content of the feed material and of the solid
cellulose fraction obtained may for example be determined by
hydrolysing a sample of the material followed by identification and
quantification of sugars by means of gas chromatography according
to TAPPI method T 249 cm-00. After correction of the glucose value
by subtracting the glucose portion derived from the glucomannan
present in the sample, the cellulose content is calculated from the
corrected glucose value.
[0013] Preferably, the solid cellulosic fraction obtained has an
average degree of polymerisation of at least 300. Reference herein
to the average degree of polymerisation of the cellulose is to the
weight-average degree of polymerisation. The degree of
polymerisation may be determined by measuring the viscosity of a
solution of the cellulosic fraction of known concentration, for
example according to TAPPI method T 230 om-04.
[0014] Preferably, at least 50 wt % of the lignin in the
lignocellulosic feed material is removed from the feed material
during the organosolv process according to the invention, more
preferably at least 80 wt %.
[0015] The lignocellulosic feed material is heated in the solvent
at a temperature that is typical for organosolv processes, i.e. in
the range of from 50 to 210.degree. C., preferably of from 100 to
200.degree. C., more preferably of from 80 to 180.degree. C.
[0016] The solvent used in the process according to the invention
comprises at least 10 wt % of a compound having a gamma lactone
group, i.e. a compound according to general molecular formula (1).
Preferably, the solvent comprises at least 20 wt % of such
compound, more preferably at least 50 wt %, even more preferably at
least 80 wt %, based on the total weight of the solvent.
[0017] Reference herein to the solvent is to the total liquid phase
in which the solid feed material is heated. Apart from one or more
compounds according to general molecular formula (1), the solvent
may comprise further organic compounds that are known solvents for
organosolv pulping. Examples of such known compounds are lower
aliphatic alcohols such as methanol or ethanol, polyhydric
alcohols, in particular diols with the hydroxyl groups on adjacent
carbon atoms such as ethylene glycol, glycerol, 1,2-propanediol or
2,3-butanediol, lower carboxylic acids such as formic acid or
acetic acid, and acetone. The solvent may also comprise water,
preferably in an amount up to 50 wt %, more preferably up to 20 wt
%.
[0018] The solvent may comprise an acid catalyst. Any acid known to
be suitable as catalyst in organosolv pulping may be used. In
particular strong mineral acids such as phosphoric acid, sulphuric
acid, hydrochloric acid and nitric acid, are known to be very
effective catalysts for organosolv pulping. The catalyst preferably
is a strong mineral or organic acid with a pKa below 2.5. Preferred
strong mineral acids are phosphoric acid and sulphuric acid, more
preferably phosphoric acid. Preferred strong organic acids are
oxalic acid, 2-oxopropanoic acid, maleic acid, and
2,4,6-trihydroxibenzoic acid. Combinations of acids may also be
used.
[0019] It is preferred to keep the concentration of mineral
compounds in the solvent as low as possible in order to avoid
mineral waste streams. The acid catalyst, in particular in case of
a mineral catalyst, is therefore preferably present in a
concentration of below 5 wt % of the solvent, more preferably in a
concentration in the range of from 0.01 to 3.0 wt %, even more
preferably of from 0.05 to 1.0 wt %. For a heating temperature in
the range of from 100 to 210.degree. C., it is preferred to use a
solvent that is free of mineral acid. Therefore, in a preferred
embodiment of the process according to the invention, the feed
material is heated at a temperature in the range of from 100 to
210.degree. C., more preferably of from 120 to 180.degree. C., in a
solvent that is free of mineral acid. For lower heating
temperatures, i.e. below 100.degree. C., the presence of an acid
catalyst in the solvent is preferred.
[0020] The lignocellulosic feed material may be any lignocellulosic
material known to be a suitable feedstock for pulping processes.
Examples of such materials are hardwood, softwood, bagasse, wheat
straw, miscanthus, switch grass, reed, or flax. The feed material
may be in any form known to be suitable for organosolv pulping,
typically in the form of particles with dimensions in the order of
a few centimetres, for example wood chips or cutted stalks.
[0021] The organosolv process according to the invention may be
carried out in a batch, semi-batch or continuous operation. In a
batch operation, the ratio of solvent to solid feed material is
preferably in the range of from 2 to 50, more preferably of from 3
to 15. In a continuous operation, i.e. with continuous supply and
discharge of solvent, the liquid hourly velocity of the solvent is
preferably in the range of from 1 to 50 litre solvent per kg feed
material per hour, more preferably of from 2 to 25 litre/kg/h.
[0022] Reference herein to a compound having a gamma lactone group
is to a compound according to general molecular formula (1),
wherein R.sub.1 to R.sub.6 each represent, independently, a H atom
or an organic group connected with a carbon atom to the lactone
group. The total number of carbon atoms of the compound is
preferably at most 20, more preferably at most 15.
[0023] The compound according to general molecular formula (1)
preferably is a compound wherein R.sub.1, R.sub.2, R.sub.3 and
R.sub.4 are a hydrogen atom, more preferably a compound wherein
R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are a hydrogen atom and
R.sub.5 is a methyl group. Examples of such more preferred
compounds are gamma valerolactone (R.sub.6 is a hydrogen atom) also
known as 5-methyldihydrofuran-2(3H)-one,
2-methyl-5-oxotetrahydrofuran-2-carboxylic acid (R.sub.6 is a
carboxyl group), a compound having a molecular structure according
to any one of molecular formulas (2) to (5): ##STR3## or an ester
of a compound having a molecular structure according to molecular
formula (2) or (3).
[0024] The compounds according to formulas (2) to (5) are levulinic
acid dimers that may be obtained by contacting levulinic acid in
the presence of hydrogen with a strongly acidic catalyst having a
hydrogenating function, e.g. Pd/cation-exchange resin, at elevated
temperature and preferably at elevated pressure. Typical process
temperatures and pressures are in the range of from 60 to
170.degree. C. and of from 1 to 200 bar (absolute), respectively.
Such process for levulinic acid dimerisation is described in detail
in co-pending patent application EP 04106107.8. The catalyst and
process conditions of this process are similar to those applied in
the known single-step process for the production of methyl isobutyl
ketone from acetone.
[0025] Other compounds with a gamma lactone group suitable to be
used in the solvent of the organosolv process according to the
invention, which are obtainable by the above-mentioned levulinic
acid dimerisation process, are the compounds with a molecular
structure according to formula (6) or (7) or their esters:
##STR4##
[0026] If the compound with a gamma lactone group is an ester of an
acid according to molecular formula (2), (3), (6) or (7), then the
ester preferably is an alkyl ester with an alcohol fragment with at
most 10 carbon atoms, more preferably a linear alkyl ester with an
alcohol fragment with at most 5 carbon atoms, even more preferably
a methyl or an ethyl ester.
[0027] In the organosolv process according to the invention, the
feed material is preferably heated in the solvent at a pressure in
the range of from 1 to 10 bar (absolute), more preferably of from 1
to 5 bar (absolute). Since compounds according to general formula
(1) have a relatively low volatility as compared to conventional
organosolv solvents like lower aliphatic carboxylic acids or
alcohols, the organosolv process according to the invention can be
carried out at relatively low pressures.
[0028] Preferably, the compound(s) according to general molecular
formula (1) that are used in the solvent are recovered for
recycling. This may for example be done by applying the following
process steps, after the heating of the feed material in the
solvent as hereinabove described: [0029] (a) separating the solid
cellulose fraction from the liquid fraction; [0030] (b) adding
water to the separated liquid fraction and heating the separated
liquid fraction in the presence of an acid catalyst at a
temperature in the range of from 100 to 300.degree. C. to obtain a
hydrolysed liquid fraction; [0031] (c) distilling lower boiling
compounds in the hydrolysed liquid fraction from the compound
according to general molecular formula (1); and [0032] (d) using
the compound according to general molecular formula (1) obtained in
step (d) in the solvent wherein the feed material is heated.
[0033] In step (a), the solid and liquid fraction obtained in the
organosolv process according to the invention are separated from
each other by conventional means, e.g. filtration. The
thus-obtained liquid fraction comprises solvent and dissolved feed
material degradation products, mainly depolymerised hemicellulose
and lignin. In step (b), the liquid fraction is further hydrolysed
after addition of water in order to convert the dissolved feed
material degradation products into compounds that boil at a lower
temperature than the compound according to general molecular
formula (1). Hydrolysis step (b) is carried out in the presence of
an acid catalyst. In case the liquid fraction already contained an
acid catalyst, i.e. the acid catalyst used in the organosolv step,
no additional catalyst needs to be added. In case the organosolv
step has been carried out without an acid catalyst, an homogeneous
or heterogeneous acid catalyst, preferably a heterogeneous acid
catalyst, has to be added to the liquid fraction obtained in step
(a).
[0034] In step (c), the hydrolysed dissolved feed material
degradation products are distilled from the compound(s) according
to general molecular formula (1). If lower boiling conventional
solvent compounds were present in the solvent, for example
methanol, ethanol, formic acid or acetic acid, they will also be
distilled from the compound(s) according to general molecular
formula (1). If, however, high boiling conventional compounds for
organosolv solvents are present in the solvent, i.e. compounds with
a comparable or higher boiling point than the compound according to
formula (1), they will be retained in the bottom fraction, together
with the compound according to general molecular formula (1).
[0035] In step (d), the compound according to general molecular
formula (1) is recycled to the organosolv step to be used in the
solvent.
[0036] It is an advantage of the process according to the invention
that the solvent boils at a relatively high temperature and, thus,
the solvent may be recycled by distilling the hydrolysed dissolved
feedstock degradation products from the solvent. In conventional
organosolv processes, the solvent boils at a lower temperature and,
thus, the solvent needs to be distilled from the feed degradation
products, which requires a larger distillation capacity.
EXAMPLES
[0037] The process according to the invention will be further
illustrated by means of the following non-limiting examples.
Examples 1 to 5
[0038] Approximately 4 grams of dried birchwood (Betula ssp.)
sawdust having a cellulose content of 49 wt % was weighted into the
reactor tube of a plug flow reactor. Solvent was continuously
supplied to and discharged from the reactor tube at a liquid hourly
velocity of 8 litre per kg wood per hour. The reactor pressure was
kept at 4 bar (absolute). During the first hour, the solvent was
heated from room temperature to the reaction temperature, then the
temperature was maintained for one hour at the reaction temperature
and then the solvent was cooled from reaction temperature to room
temperature. After cooling, the solvent supply was stopped and
acetone was supplied to the reactor to remove remaining liquid from
the solid residue. The acetone-washed residue was dried by purging
it overnight with nitrogen, removed from the reactor, and
weighed.
[0039] During all experiments, a dark liquid fraction was
discharged from the reactor tube and the acetone-washed residue
obtained, i.e. the solid cellulosic fraction, had a considerably
lighter colour than the feed material.
[0040] In the Table, the composition of the solvent, the reaction
temperature, the amount of residue as percentage of the weight of
the feed material and the cellulose content of the residue are
shown for EXAMPLES 1 to 5. The cellulose content was determined by
hydrolysing all polysaccharides followed by identification and
quantification of sugars by means of gas chromatography according
to TAPPI method T 249 cm-00. TABLE-US-00001 TABLE EXAMPLES 1 to 5
cellulose T residue content EXAMPLE Solvent (.degree. C.) (wt %)
residue 1 10.0 wt % gVL* 100 47 n.d.** 90.0 wt % formic acid 2 90
wt % gVL 150 43 n.d.** 10 wt % oxalic acid 3 97.1 wt % gVL 175 34
80 2.5 wt % phosphoric acid 0.4 wt % water 4 89.2 wt % gVL 175 65
63 10.8 wt % formic acid 5 78.6 wt % gVL 175 57 72 20.7 wt %
ethylene glycol 0.6 wt % phosphoric acid 0.1 wt % water *gVL: gamma
valerolactone **n.d.: not determined
* * * * *