Title of Invention

"A PROCESS FOR THE PRODUCTION OF ACETYLATED LIGNOCELLULOSIC FIBRES"

Abstract This invention relates to a process for acctylation of ligno-cellulosic fibres (LF) using an acetylating agent comprising acetic an-hydride at a temperature of above 140°C and a pressure-of 100-1,50 kPa wherein raw or substantially raw, LFs are treated with a super-heated acetylating agent comprising at least 20 % w/w acetic an-hydride for a duration of at least 1.5 minutes in an acctylation reactor (3), the treatment with superheated acetylating agent, also ensuring that the acetylated LFs are substantially free from occluded, adsorbed or absorbed acetylating agent, the amounts of which are less than 5 % w/w of the acetylated LFs recovered from the base of a circulation cyclone (5), so as to substantially acetylale the LFs to achieve a weight gain of at least 2 %. The LFs may optionally be pre-treated, prior to being treated with the superheated acetylating agent, with a liquid acetylating agent, preferably by spraying, for a very short period of time.
Full Text The present invention relates to a process for the production of acetylated lignocellulosic fibres (LF) wherein the lignoccllulosic fibre is treated with acetic anhydride.
By the expression "lignocellulosic fibre" is meant here and throughout the specification a material in any shape or form such as e.g. shreds, fibres, splinters and shives, and which is derivable from a source comprising wood, sisal, jute, coconut and/or other plant material and which has optionally been subjected to a pre-treatment with a non-acetylating chemical such as e.g. sodium acetate in order to improve subsequent acetylation thereof. The material will hereafter be referred to as "LF" for convenience.
It is well known in the art to improve the physical characteris-tics of LFs by treatment with acetic acid and/or acetic; anhydride. Processes by which LFs are treated in a single step by immersion of the LF in liquid acetic anhydride followed by heating and a drying step are known. One of the problems with systems which use the immer-sion technique is that they arc usually batch processes which need drainage facilities for the liquid in which the LF is immersed. A single step process of this type also does not ensure acetylation of the ligno-cellulosic material to the desired degree nor the removal of all of the unreacted chemicals in the treated product.
It has now been found that the above problems can be mitigated by treating the LF with a vaporous acctylating agent in a single stage, if necessary, in a contimious process.
From the process described in the British application number 9322187.7 it is known to use a two step process, wherein the first step comprises treating LFs with acetic acid/acetic anhydride at a temperature of 70-140°C and the second step comprises treating the reaction mixture from step 1 with a superheated chemical vapour of acetic acid and/or acetic anhydride at a temperature of 140-220°C and a pressure of 100-150 kPa. Afterwards the LFs may optionally be purified by hydrolysis.
The known process produces, under correct operating condi-tions, a good product bul the process is complicated and time con-suming because of the need for two main treatment steps prior to the optional hydrolysis.
One object of the present invention is therefore to provide an easier and quicker process for acetylation of LFs while maintaining the necessary degree of acetylation.
This object is obtained with the process according to claims 1-10.
Accordingly, the present invention is a process for the acetyla-tion of lignocellulosic fibres comprising bringing the LF into contact with a superheated acetylating agent comprising at least 20 % w/w acetic anhydride at a temperature above 140°C for a duration of at least 1.5 minutes so as to substantially acetylate the LF to achieve a weight gain of at least 2%.
The superheated acetylating agent used for this purpose has at least 20% w/w, preferably above 50% w/w of acetic anhydride. The superheated acctylating agent suitably comprises 50-100% by weight, preferably 70-95% by weight of acetic anhydride. The superheated acetylating agent is at a temperature above 140°C, suitably from 140-220°C, preferably from 160-195°C and the acetylation reactor is suitably operated at a pressure of 100-150 kPa.
Prior to commencement of acetylation, the acetylation reactor is suitably rendered gas-tight e.g. by using e.g. a plug screw or a rotary valve, at the point of entry into the reactor so as to minimise ingress of air into the acetylation reactor or egress of acetic anhydride out of this reactor. The superheated acetylating agent is used to start-up the process. As the concentration of acetic acid in the vapours emerging overhead from the reactor build up, such vapours can be admixed with the aliquots of acetic anhydride being superheated and can thereby restore the desired composition of the acetylating agent. The duration of this acetylation is relatively long and is usually of the order of at least 1.5 minutes, suitably at least 5 minutes, preferably up to about 10 minutes.
If desired, the LF to be acetylated may be optionally treated with a liquid acetylating agent, which may be hot or cold, for a very short period of e.g. less than a minute prior to being brought into contact
The known process produces, under correct operating conditions, a good product but the process is complicated and time consuming because of the need of two main treatment steps prior to the optional hydrolysis.
One object of the present invention is therefore to provide an easier and quicker process for acetylation of LFs while maintaining the necessary degree of acetylation.
This object is obtained with the process according to claims 1-7.
According to the present invention there is provided a process for the production of acetylated lignocellulosic fibres as herein described, using an acetylating agent comprising acetic anhydride, at a temperature of 140-220°C and a pressure of 100-150 kPa, said process comprising the steps:
a. optionally pre-treating raw lignocellulosic fibres with a liquid
acetylating agent for a less than a minute, preferably by spraying, and/or
with a catalyst, such as an acetate or alkaline salt of an alkali metal,
b. treating raw lignocellulosic fibres with a superheated
acetylating agent comprising from 20 to 100% w/w acetic anhydride and
from 80 to 0% w/w acetic acid, for a duration of from 1.5 minutes up to
about 10 minutes until the acetylated lignocellulosic fibres achieve a
weight gain of at least 2% and up to 30% by weight, in an acetylation
reactor (3), the treatment with superheated acetylating agent also
ensuring that the acetylated lignocellulosic fibres are substantially free
from occluded, adsorbed or absorbed acetylating agent, the amounts of
which are less than 5% w/w of the acetylated lignocellulosic fibers
recovered from the base of a circulation cyclone (5),
resulting in the production of acetylated lignocellulosic fibres, and optionally also
c. processing the acetylated lignocellulosic fibres emerging from
the reactor (3) in a hydrolysis chamber (7) by contact with superheated
steam, whereby any residual unreacted acetic anhydride remaining
adsorbed or occluded in the acetylated lignocellulosic fibres is hydrolysed
to acetic acid and removed overhead as a mixture of steam and acetic acid from the hydrolysis chamber so that the acetic acid in the acetylated lignocellulosic fibres is less than 0.5% w/w, resulting in the production of improved acetylated lignocellulosic fibres, the removed mixture optionally being recirculated to the superheated steam introduced into the hydrolysis chamber.
The superheated acetylating agent used for this purpose has at least 20%w/w, preferably above 50%w/w of acetic anhydride. The superheated acetylating agent suitably comprises 50-100% by weight, preferably 70-95% by weight of acetic anhydride. The superheated acetylating agent is at a temperature above 140°C, suitably from 140-220°C, preferably from 160-195°C and the acetylation reactor is suitably operated at a pressure of 100-150 kPa.
Prior to commencement of acetylation, the acetylation reactor is suitably rendered gas-tight e.g. by using e.g. a plug screw or a rotary valve, at the point of entry into the reactor so as to minimize ingress of air into the acetylation reactor or egress of acetic anhydride out of this reactor. The superheated acetylating agent is used to start-up the process. As the concentration of acetic acid in the vapours emerging overhead from the reactor build up, such vapours can be admixed with the aliquots of acetic anhydride being superheated and can thereby restore the desired composition of the acetylation agent. The duration of this acetylation is relatively long and is usually of the order of at least 1.5 minutes, suitably at least 5 minutes, preferably up to about 10 minutes.
If desired, the LF to be acetylated may be optionally treated with a liquid acetylating agent, which may be hot or cold, for a very short period of e.g. less than a minute prior to being brought into contract
the anhydride and thereby moistening it with acetic anhydride. This chamber (2) is maintained at a pressure slightly below atmospheric to prevent back flow of the acetic anhydride. The LF moistened with acetic anhydride and emergent from the chamber (2) is then fed to the acetylation reactor (3), also previously purged with nitrogen to exclude any air or oxygen therein, where it is brought into contact with super-heated vapour of an acetylating agent containing neat acetic an-hydride introduced at (4) or optionally containing some acetic acid from recycled streams at about 190°C. The pre-treated LP is entrained in the superheated vapour stream fed to the base of (3) and has a residence time in (3) of at least 1.5 minutes in order to achieve the degree of acetylation desired. Reactor (3) not only fulfils the function of acetylating the LF but is also a steam jacketed circulation stripper where the chemicals adsorbed or occluded in the acetylated LF are evaporated. The overheads from the reactor (3) entraining the acety-lated LF are fed into a circulation cyclone (5) where hot, acetylated LF is recovered from the base thereof and is fed through a rotary valve (not shown) into line (6). The overheads from the cyclone (5) is recircu-latcd back to reactor (3) except for a bleed (not shown) to processing and recovering of acetic acid formed as a by-product in the acetylation step, and admixed with acetic anhydride being superheated in order to restore the desired composition of the acetylation agent. In line (6) the acetylated LF is dispersed in and entrained by a mixture of super-heated steam and some acetic acid vapour (from partly recycled streams) and is then fed into a steam stripper (7). In (7), any residual, unreacted acetic anhydride in the acetylated LF is hydrolyscd to acetic acid and the acetic acid is stripped out. The overheads from the steam stripper (7), which are at a temperature of about 150°C, are fed into a steam stripper cyclone (8) where the acetylated LF is separated from the vapours and recovered from the base thereof whereas the acidic vapours are recovered overhead therefrom to be processed and re-cycled. The acetylated LF substantially free of all free acids and an-hydrides (and hence the odours of these components) recovered from the base of (8) can either be sent to an adjacent board manufacturing facility (not shown) directly or can be humidified and cooled for the purposes or bagging and storage (not shown).
The process of the present invention is further illustrated with reference to the following Example:
EXAMPLE:
A mixture of fibres of pine and spruce was brought into contact with superheated acetic anhydride (containing 5% w/w acetic acid) at 190°C. The flow rate of the anhydride was approximately 19 g per gram of fibre per minute at atmospheric pressure. The results achieved are tabulated below:
(Table Removed)* Inclusive of naturally occurring aceLyls
** Occluded, adsorbed or absorbed acetylating agent and acetic acid
We claim:





We Claims
1. A process for acetylation of lignocellulosic fibres (LF)' using an
acetylating agent comprising acetic anhydride, at a temperature of
above 140°C and a pressure of 100-150 kPa, characterised in that
raw or substantially raw LFs are treated with a superheated acetylat-
ing agent comprising at least 20 % w/w acetic anhydride for a dura-
tion of at least 1.5 minutes in an acetylation reactor (3), the treatment
with superheated acetylating agent also ensuring that the acetylated
LFs are substantially free from occluded, adsorbed or absorbed acety-
lating agent, the amounts of which are less than 5 % w/w of the
acetylated LFs recovered from the base of a circulation cyclone (5).
2. A process according to claim 1, wherein the raw or substan-
tially raw LFs arc treated with the superheated acetylating agent until
the acetylated LFs achieve a weight gain of at least 2 %, preferably at
least 5 %, and more preferably between 5 and 30 % by weight.
3. A process according to claim 1 or 2, wherein the acetylating
agent comprises at least 50 % w/w acetic anhydride, preferably
70-95 % w/w.
4. A process according to any one of the preceding claims,
wherein the duration of the treatment is at least 5 minutes, preferably
at least 10 minutes.
5. A process according to any one of the preceding claims,
wherein the acetylation is performed at a temperature of 140 220°C,
preferably 160-195°C.
6. A process according to any one of the preceding claims,
wherein the treatment is performed in a gas-tight acetylation reactor
(3).
7. A process according to any one of the preceding claims,
wherein the raw or substantially raw LFs are pre-treated, preferably
by spraying, with a liquid acetylating agent for a short period of time
prior to being treated with the superheated acetylating agent.
8. A process accorrding to claim 7, wherein the pre-treatment is
performed in a closed system, preferably operated under slightly
reduced pressure in relation to atmospheric pressure.
9. A process according to any one of the preceding claims,
wherein the LFs are pre-trcated with a catalyst, such as an acetate or
alkaline salt of an alkali metal.
10. A process according to any one of the preceding claims,
wherein the acetylatcd LFs emerging from the reactor (3) arc further
processed in a hydrolysis chamber (7) by contact with superheated
steam, whereby any residual unreacted acelic anhydride remaining
adsorbed or occluded in the acetylated LFs is hydrolysed to acetic acid
and removed overhead as a mixture of sleam and acelic acid from the
hydrolysis chamber so that the acetic acid in the acetylated LFs is less
than 0.5 % w/w, the removed mixture optionally being recirculated to
the superheated steam introduced into the hydrolysis chamber.
11, A process for acetylation of lignocellulosic fibres (LF) substantially as herein described uith reference to the foregoing examples and the accompanying drawings.

Documents:

2346-del-1995-abstract.pdf

2346-del-1995-claims.pdf

2346-del-1995-correspondence-others.pdf

2346-del-1995-correspondence-po.pdf

2346-del-1995-description (complete).pdf

2346-del-1995-drawings.pdf

2346-del-1995-form-1.pdf

2346-del-1995-form-13.pdf

2346-del-1995-form-2.pdf

2346-del-1995-form-29.pdf

2346-del-1995-form-3.pdf

2346-del-1995-form-4.pdf

2346-del-1995-form-6.pdf

2346-del-1995-gpa.pdf

2346-del-1995-pct-210.pdf

2346-del-1995-petition-137.pdf

2346-DEL-2008-Petition-124.pdf


Patent Number 195275
Indian Patent Application Number 2346/DEL/1995
PG Journal Number 04/2008
Publication Date 25-Jan-2008
Grant Date 22-Dec-2006
Date of Filing 18-Dec-1995
Name of Patentee A-CELL ACETYL CELLULOSICS AB
Applicant Address SOTENASVAGEN 64, SE-433 64 PARTILLE, SWEDEN.
Inventors:
# Inventor's Name Inventor's Address
1 HELEN LOUISE NELSON 9 MANOR ROAD, BEVERLEY, HUMBERSIDE HU17 7AE, U.K.
2 DAVID LAN RICHARDS 7 COLLERIDGE GROVE, BEVERLEY, HUMBERSIDE HU17 7AR, U.K.
PCT International Classification Number D06M 1/14
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 9425765.6 1994-12-19 U.K.