WO1993025584A2

WO1993025584A2 - Process for activation of cellulose

Info

Publication number: WO1993025584A2
Application number: PCT/US1993/005164
Authority: WO
Inventors: Melvin Glenn Mitchell; James Stafford Maginnis Jr
Original assignee: Eastman Kodak Co
Priority date: 1992-06-11
Filing date: 1993-06-01
Publication date: 1993-12-23
Also published as: WO1993025584A3; JPH08501326A; CA2136733A1; BR9306539A; EP0644901A1; KR950701649A

Abstract

Disclosed is a process comprising: A) introducing cellulose and water into an activation zone; B) introducing acetic acid and sulfuric acid into the activation zone; and C) subjecting the cellulose, water, acetic acid and a catalyst to an agitation in the range of 0.04 to 4.0 kilowatts per pound of the combined weight of the cellulose, water, acetic acid and sulfuric acid for a period of time of less than 10 seconds.

Description

PROCESS FOR ACTIVATION OF CELLULOSE
This invention relates to a process for activation of cellulose wherein the cellulose is subjected to high agitation for a short period of time.

In the manufacture of cellulose acetate beginning with wood pulp, the wood pulp is typically supplied to the manufacturer in the form of a relatively dense sheet which is either wound in compact rolls or is compressed into bales. The wood pulp does not readily disintegrate to form a composition capable of under going acetylation and therefore the sheets of wood pulp must be prepared for the acetylation step in a prior step typically referred to as "activation".

In accordance with methods well known in the art, the activation step can be conducted by mechanically subdividing the sheet of wood pulp and then contacting the units of subdivided wood pulp with acetic materials for a period of time.

Although the activation processes of the prior art are effective in producing a composition which can be satisfactorily acetylated, these processes require relatively long periods of time. For example, the activation processes of the prior art typically require times of several hours and often require times of more than 2 hours. Due to the time value of capital, it would be very desirable to reduce the time required to conduct the activation process.

We have now discovered a process for the activation of cellulose which can be conducted in an extremely short period of time compared to the processes of the prior art. We have accomplished the objective of conducting the activation process in a very short time by subjecting the activation composition to a very high rate of agitation.

In summary, our invention can be thought of as a process comprising
(A) introducing cellulose and water into an
activation zone,
(B) introducing acetic acid and a catalyst into
the activation zone,
(C) subjecting the cellulose, water, acetic acid
and catalyst to an agitation in the range of
0.04 to 4.0 kilowatts per pound of the
combined weight of the first and second
streams for a period of time of less than 10
seconds.

The wood pulp, often called cellulose, which is useful in our process can comprise any of the wood pulps typically sold in the trade. Specific examples of suitable cellulose include southern and Canadian hardwoods and softwoods.

The units of cellulose sheet must have a cross sectional diameter of less that 2 inches. This can be accomplished by mechanically subdividing the sheet of cellulose into units of this size by methods well known in the art, such as a hammer mill.

The amount of cellulose which is introduced into the activation zone is broadly in the range of 1 to 60 weight percent, preferably in the range of 30 to 55 weight percent, based on the combined weight of the cellulose, water, acetic acid and catalyst.

The cellulose can be introduced into the activation zone by conventional means such as allowing the cellulose units to fall under the influence of gravity from the means to subdivide the units into the activation zone. Preferably, the cellulose is sub divided in a hammer mill and the units of subdivided cellulose are allowed to fall from the exit of the hammer mill into the entry port of the apparatus used to perform the high agitation.

The amount of water in the which is introduced into the activation zone is broadly in the range of 0 to 99 weight percent, preferable in the range of 2 to 20 weight percent, based on the combined weight of the cellulose, water, acetic acid and catalyst.

The water is introduced into the activation zone using conventional means, preferably being pumped under pressure.

The first step of the process of this invention has been described as introducing a first stream of both cellulose and water into the activation zone. While the preferred embodiment is for both the cellulose and water to be combined into one stream it is fully within the scope of the invention for the cellulose and water to be introduced into the activation zone as separate streams.

The acetic acid useful in the second step of the process of this invention is the type typically used in the preparation of cellulose acetate and is well known in the art. Preferably glacial acetic acid is used.

The catalyst useful in the second step of the process of this invention can be methane sulfonic acid, methane disulfonic acid, sulfoacetic acid, sulfuryl chloride or sulfuric acid. Preferably the catalyst is sulfuric acid and more preferably is 98% sulfuric acid.

The acetic acid and catalyst are introduced into the activation zone using conventional means, preferably being pumped under pressure.

The second step of the process of this invention has been described as introducing a second stream of both acetic acid and catalyst into the activation zone.

While the preferred embodiment is for the acetic acid and catalyst to be combined into one stream it is fully within the scope of the invention for these materials to be introduced into the activation zone as separate streams.

The amount of acetic acid is broadly in the range of 1 to 99 weight percent, preferably in the range of 30 to 50 weight percent, based on the combined weight of the cellulose, water, acetic acid and catalyst.

The amount of catalyst is broadly in the range of 0.2 to 6 weight percent, preferably in the range of 1 to 3 weight percent, based on the combined weight of cellulose, water, acetic acid and catalyst.

The process of this invention can be operated either as a batch process or a continuous process.

Preferably, the process in operated as a continuous process.

This invention has been described in terms of first introducing the stream of cellulose and water into the activation zone and then introducing the stream of acetic acid and catalyst into the activation zone.

Preferably, the process is operated continuously and both of these streams are introduced into the activation zone simultaneously. If the process is practiced on a batch basis, the streams can be introduced in any order or can be introduced simultaneously.

Agitation of the activation composition is a critical feature of this invention. In this invention, the activation composition is agitated within a particular range. The range is expressed in terms of the requirement for electrical energy to mechanically perform the agitation and is broadly in the range of 0.04 to 4.0 kilowatts per pound, preferably 0.1 to 1 kilowatts per pound, of the combined weight of cellulose, water, acetic acid and catalyst.

Mechanical apparatus required to achieve this rate of agitation is well known in the art and is commercially available. Since a mixing function is inevitably associated with the high rate of agitation, this apparatus is often referred to as a "mixer".

Specifically, the apparatus is often called a high consistency mixer by those skilled in the art.

Preferably the apparatus is a Model 48 Micar High
Consistency mixer sold by Black Clawson, Shartle
Division. Other apparatus suitable for use in this invention are disclosed in U.S. 4,016,353.

In the preferred embodiment where the apparatus is a Model 48 Micar High Consistency mixer the first stream is introduced into the hopper of the apparatus and the second stream is introduced into the highly agitated mixing barrel.

The period of time the activation composition is subjected to the high rate of agitation is an extremely important feature of this invention. The period of time the activation mixture is subjected to the high rate of agitation is broadly less than 10 seconds, preferably less than 5 seconds.

The activation composition is subjected to the high rate of agitation for the specific period of time by operating the mixer continuously and adjusting the rotor/stator configuration.

The process of this invention has been described as an "activation process". By the term "activation process" we mean that the composition which exits from the mixer can, in some instances, be fully activated and therefore can be immediately introduced into the acetylation step without the necessity to age the composition for a period of time. By this term we also mean that the composition which exits from the mixer is not fully activated and must be aged prior to introduction of the composition into the acetylation step. Whether any additional aging is required, or how much additional aging is required, varies widely depending on numerous factors understood by those skilled in the art, such as the temperature of the composition, the type of catalyst and the amount of catalyst.

Typically, the composition is aged for a period of time in the range of 10 minutes to 3 hours, preferably 20 minutes to 40 minutes.

As has been discussed earlier, an advantage of this invention is that the time for the activation step is significantly decreased over the prior art. Thus, even when aging is required the combination of the time required for agitation and the time required for aging is still significantly less than the time for the activation steps of the prior art.

The practice of this invention can be illustrated by the following example.

A hammer mill is positioned such that the output of subdivided cellulose units will fall into the hopper of a Model 48 Micar High Consistency mixer sold by Black
Clawson, Shartle Division. The highly agitated mixing barrel entry port of the mixer is adapted with piping to receive the a stream of acetic acid and sulfuric acid.

A continuous activation process is then conducted wherein a roll of hardwood cellulose containing water is fed into the hammer mill at ambient conditions and subdivided into units having a cross sectional diameter of less than 2 inches which fall into the hopper of the continuously operating mixer. The composition of this stream is 96 lbsomin cellulose and 4 lbsomin water. 84 lbsomin acetic acid and 4 lbsomin sulfuric acid are continuously pumped into the mixer through the highly agitated mixing barrel entry port. The rate of agitation is adjusted to 1.5 to 2.5 kilowatts per pound of the combined weight of all four components. Based on the physical configuration of the mixer, the time the activation composition is subjected to this rate of agitation for 1 to 3 seconds.

The composition exiting from the mixer was aged 20 to 40 minutes to become fully activated and fed to a conventional acetylation process and successfully acetylated into a product which was further processed by conventional means into commercially acceptable cellulose acetate.

Claims

1. A process comprising (A) introducing into an activation zone a first stream comprising cellulose which has a cross sectional diameter of less than 2 inches and is in the range of 1 to 60 weight percent and water in the range of 0 to 99 weight percent, based on the combined weight of the first and second streams, (B) introducing into the activation zone a second stream comprising acetic acid in the range of 1 to 99 weight percent and a catalyst selected from the group consisting of methane sulfonic acid, methane disulfonic acid, sulfoacetic acid, sulfuryl chloride and sulfuric acid in the range of 0.2 to 6 weight percent, based on the combined weight of the first and second streams,

and (C) subjecting the first and second streams to an agitation in the range of 0.04 to 4.0 kilowatts per pound of the combined weight of the first and second streams for a period of time of less than 10 seconds.

2. A process comprising (A) introducing into an activation zone a first stream comprising cellulose which has a cross sectional diameter of less than 2 inches and is in the range of 30 to 55 weight percent and water in the range of 2 to 20 weight percent, based on the combined weight of the first and second streams, (B) introducing into the activation zone a second stream comprising acetic acid in the range of 30 to 50 weight percent and sulfuric acid in the range of 1 to 3 weight percent, based on the combined weight of the first and second streams, and (C) subjecting the first and second streams to an agitation in the range of 0.1 to 1 kilowatts per pound of the combined weight of the first and second streams for a period of time of less than 5 seconds.