Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1996-07-25
1998-07-07
Kight, John
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
536 58, 536 63, 536115, 536124, 536128, C08B 300, C07H 100
Patent
active
057771014
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB95/00371, filed Feb. 23, 1995.
The present invention relates to a process for the production of acetylated lignocellulosic materials wherein the lignocellulosic material is treated with acetic anhydride.
By the expression "lignocellulosic materials" is meant here and throughout the specification a material in any shape or form such as eg shreds, fibres, splinters and shives, and which are derivable from a source comprising wood, sisal, jute, coconut and/or other plant material and which have optionally been subjected to a pretreatment with a non-acetylating chemical such as eg sodium acetate in order to improve subsequent acetylation thereof will hereafter be referred to as "LM" for convenience.
It is well known in the art to improve the physical characteristics of LMs by treatment with acetic acid and/or acetic anhydride. 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 LM 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 LM in two stages, if necessary, in a continuous process.
Accordingly, the present invention is a process for the acetylation of lignocellulosic materials (LM) comprising comprising acetic anhydride as the major component at a temperature from 80.degree.-140.degree. C. and inert under the reaction conditions in a stripper at a temperature above 140.degree. C. and reducing the acetic acid or acetic anhydride content of the acetylated LM produced in step (a) to below 10% by weight by stripping.
In the process, the acetylating agent used in step (a) suitably comprises at least 50% w/w of acetic anhydride, preferably at least 60% w/w and most preferably at least 70% w/w and typically contains 90% acetic anhydride and 10% acetic acid. This agent may be in the form of a liquid, a vapour or a mixture of the two. Thus the weight ratio of liquid to vapour in the acetylating agent present in the reactor used in step (a) may be anything within the range from 100% of one to 100% of the other, but is suitably from 1:5 to 5:1 and is preferably 1:2. The acetylating agent used in step (a) is pre-heated to a temperature in the region from 80.degree.-140.degree. C., preferably from 110.degree.-130.degree. C. using eg an oil jacket or a steam coil.
The LM is contacted with the acetylating agent in a first reactor. The acetylating reactor is suitably rendered gas tight eg by compaction using eg a plug screw feeder, at the point of entry into the reactor so as to minimise ingress of air into the acetylation reaction or egress of acetic anhydride out of this first reactor. This problem of egress of acetic anhydride can be minimized by operating the first reactor at a pressure which is slightly below atmospheric and is also a safety feature of the process. The compacted LM is then introduced into the first reactor which is suitably a screw-conveyor at the same time injecting into said reactor the hot acetylating agent. During this step, the compacted LM is dispersed (in order to loosen the LM strands and to spread it more thinly) using a dispersing device located at the entrance to this first reactor and thereby facilitates intimate contact between the LM and the acetylating agent. In this reactor, the rate of injection of the hot acetylating agent is suitably such that the ratio of the agent to the LM is suitably in the range from 1:1 to 10:1 by weight, preferably from 3:1 to 7:1, eg 5:1 by weight. During this acetylation reaction, which is exothermic, the reaction temperature is maintained substantially constant which may be achieved by several conventional means, eg by controlling the pressure in the reactor, or, by vapourization of the acetylating chemicals, or, by control of the rate of flow of the acetylating agent into t
REFERENCES:
patent: 3720661 (1973-03-01), Breton et al.
patent: 5608051 (1997-03-01), Nelson et al.
Nelson Helen Louise
Richards David Ian
A-Cell Acetyl Cellulosics AB
Kight John
White Everett
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