Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1997-08-20
1998-10-13
Nutter, Nathan M.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
536 69, 536 70, 536 71, 536 76, C08H 504, C08B 306, B27K 500
Patent
active
058213597
DESCRIPTION:
BRIEF SUMMARY
This application is filed under 35USC371 as a continuation of PCT/SE95/01531 filed Dec. 18, 1995.
The present invention relates to a process for the production of acetylated lignocellulosic fibres (LF) wherein the lignocellulosic 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 characteristics 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 immersion technique is that they are 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 lignocellulosic 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 acetylating agent in a single stage, if necessary, in a continuous 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.degree.-140.degree. 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.degree.-220.degree. C. and a pressure of 100-150 kPa. Afterwards the LFs may optionally be purified by hydrolysis.
The known process produces, under correct operating conditions, a good product but the process is complicated and time consuming 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 acetylation 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.degree. 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 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.degree. C., suitably from 140.degree.-220.degree. C., preferably from 160.degree.-195.degree. 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 th
REFERENCES:
patent: 3403145 (1968-09-01), Edge et al.
patent: 5525721 (1996-06-01), Ohshima et al.
patent: 5608051 (1997-03-01), Nelson et al.
Nelson Helen Louise
Richards David Ian
A-Cell Acetyl Cellulosics AB
Nutter Nathan M.
LandOfFree
Acetylation of lignocellulosic fibres does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Acetylation of lignocellulosic fibres, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Acetylation of lignocellulosic fibres will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-314258