PROCESS FOR ACETYLATION OF CELLULOSE

Abstract: Disclosed is a process for acetylation of cellulose comprising: a) introducing cellulose, water, acetic acid, a catalyst and acetic anhydride into an acetylation zone; b) subjecting the materials within the acetylation zone to an activation which is in the range of 0.01 to 2.0 kilowatts per pound of the materials per minute for a period of time of less than 10 seconds.

Description: PROCESS FOR ACETYLATION OF CELLULOSE This invention relates to a process for acetylation of cellulose wherein the cellulose is subjected to high agitation for a short period of time. Typically cellulose acetate is prepared by a process wherein wood pulp is acetylated to cellulose triacetate and the cellulose triacetate is then hydrolyzed to cellulose diacetate, which is often simply called cellulose acetate. The cellulose acetate is then recovered and used to prepare fibers or molded objects. In accordance with processes well known in the art, the acetylation step can be conducted by taking mechanically sub—divided units of a sheet of wood pulp which have been contacted with acetic materials in a prior activation step and contacting the activated wood pulp with acetic acid, acetic anhydride and sulfuric acid for a sufficient period of time for the wood pulp to fully esterify to cellulose triacetate. • Although the acetylation processes of the prior art are effective in producing a properly acetylated cellulose, these processes require relatively long periods of time. For example, the acetylation processes of the prior art typically require times of thirty minutes and often require times of more that one hour. Due to the time value of capital, it would be very desirable to reduce the time required to conduct the acetylation process. We have now discovered a process for the acetylation 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 acetylation process in a very short time by subjecting the acetylation composition to a high agitation. In summary, our invention can be thought of as a process comprising (A) introducing cellulose, water, acetic acid, a catalyst and acetic anhydride into an acetylation zone, (B) subjecting the materials within the acetylation zone to an activation which is in the range of 0.01 to 2.0 kilowatts per pound of the materials for a period of time of less than 10 seconds. As described above, the first step of the process of this invention broadly comprises introducing cellulose, water, acetic acid, a catalyst and acetic anhydride into an acetylation zone in one stream. In a preferred embodiment, these materials are introduced into the acetylation zone in two steams. In this embodiment, the first two steps of the process can be described as (A) introducing into an acetylation zone a first stream comprising cellulose, water, a portion of the total acetic acid and a catalyst, and (B) introducing into the acetylation zone a second stream comprising the remaining portion of the acetic acid and acetic anhydride. The wood pulp, often called cellulose, which is useful as the starting material for the activation process which is conducted prior to the acetylation process of this invention can comprise any of the wood pulps typically sold in the trade. Specific examples of suitable cellulose include southern and Canadian hardwood? and softwoods. The cellulose can be activated using any of the many methods well known in the art. The activated cellulose can be introduced into the acetylation zone according to methods well known in the art for handling activated cellulose. Typically the water is not added as a separate stream but is included in the activation composition. The acetic acid and acetic anhydride useful in the process of this invention are the type typically used in the preparation of cellulose acetate and are well known in the art. Preferably the acetic acid is glacial acetic acid. The catalyst useful in 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 can be entirely in the form of a liquid but due to the exothermic nature of the acetylation reaction the use of portion of the acetic acid as frozen acetic acid, sometimes called "ice", simplifies the need to remove heat from the reaction and therefore is preferred. Preferably, 70 weight percent of the total acetic acid is added as ice. The acetic acid, acetic anhydride and catalyst are introduced into the acetylation zone using conventional means, preferably being pumped under pressure. When a portion of the acetic acid is in the form if ice, it is introduced into the acetylation zone using conventional means, such as a conveyor. Preferably, the activation composition is mixed with the ice and the combined stream is introduced into the acetylation zone. In this embodiment, the activation mixture is introduced into the conveyor transporting the ice and the combined stream is introduced into the acetylation zone. In the broadest embodiment of the invention wherein all the materials are introduced into the acetylation zone as one stream the amount of cellulose is in the range of 5 to 17 weight percent, water is in the range of 0 to 2 weight percent, acetic acid is in the range of 10 to 62 weight percent, the catalyst is in the range of 0.1 to 1.2 weight percent and acetic anhydride is in the range of 27 to 41 weight percent, based on the weight of the stream. Preferably, the amount of cellulose is in the range of 10 to 14 weight percent, water is in the range of 0.5 to 1.5 weight percent, acetic acid is in the range of 42 to 62 weight percent, the catalyst acid is in the range of 0.2 to 0.8 weight percent and acetic anhydride is in the range of 27 to 41 weight percent, based on the weight of the stream. In the preferred embodiment wherein the materials are introduced into the acetylation zone as two streams, in the first stream the amount of cellulose is in the range of 5 to 17 weight percent, water is in the range of 0 to 2 weight percent, acetic acid is in the range of 10 to 62 weight percent and the catalyst is in the range of 0.1 to 1.2 weight percent, based on the combined weight of the first and second streams. In the second stream the amount of acetic acid is in the range of 0 to 52 weight percent and the amount of acetic anhydride is in the range of 27 to 41 weight percent, based on the combined weight of the first and second streams. Preferably, in the first stream the amount of cellulose is in the range of 10 to 14 weight percent, water is in the range of 0.5 to 1.5 weight percent, acetic acid is in the range of 42 to 62 weight percent and the catalyst is in the range of 0.2 to 0.8 weight percent, based on the combined weight of the first and second streams. Preferably, in the second stream the amount of acetic acid is in the range of 0 to 10 weight percent and acetic anhydride is in the range of 31 to 37 weight percent, based on the combined weight of the first and second streams. Regardless whether the materials are introduced into the acetylation zone as one or two streams, it is a critical aspect of this invention to subject the materials to a high agitation for a short period of time. In this invention, the agitation is expressed in terms of the requirement for electrical energy to mechanically perform the agitation and is broadly in the range of 0.01 to 2.0 kilowatts per pound, preferably 0.05 to 0.5 kilowatts per pound, of the combined weight of cellulose, water, acetic acid, acetic anhydride 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. Examples of suitable apparatus include are a Single Disk Refiner made by Sprout Waldron, a Single Disk Refiner made by Beloit and a Model 48 Micar High Consistency Mixer sold by Black Clawson, Shartle Division. Preferably the Model 48 Micar High Consistence Mixer is used. Other apparatus suitable for use in this invention are disclosed in U.S. 4,016,353. When the Model 48 Micar High Consistency mixer sold is used in the broadest embodiment wherein only one stream is introduced into the mixer the stream is introduced into the agitation zone of the* mixer. In the preferred embodiment wherein two streams are introduced into the mixer the first stream is introduced into the hopper of the mixer and the second stream is introduced into the highly agitated mixing barrel. The period of time the acetylation composition is subjected to the high rate of agitation is an extremely important feature of this invention. Regardless whether the materials are introduced into the acetylation zone as one or two streams, the period of time the acetylation composition is subjected to the high rate of agitation is broadly less than 10 seconds, preferably less than 4 seconds. The acetylation 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 can be operated either as a batch process or a continuous process. Preferably, the process in operated as a continuous process. The process of this invention has been described as an "acetylation process". By the term "acetylation process" we mean that the composition which exits from the mixer can, in some instances, be fully acetylated and therefore can be immediately introduced into the next step of hydrolysis 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 acetylated and must be aged prior to introduction of the composition into the hydrolysis 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 1 to 60 minutes, preferably 5 to 35 minutes. In a particularly preferred embodiment, the composition is aged for 20 minutes. As has been discussed earlier, an advantage of this invention is that the time for the acetylation 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 acetylation steps of the prior art. The acetylation process of this invention can be illustrated by the following example wherein the preferred embodiment of the invention is practiced by introducing the materials into the acetylation zone in two streams. An activated composition is prepared in accordance with Serial Number 07/897,113 and comprises 188 lbs/min cellulose, 12 lbsmin water, 8 lbs/min of 98% sulfuric acid and 168 lbs/Tnin of liquid acetic acid. This composition is introduced into a conveyor transporting 608 lbs/min of frozen acetic acid. The combined stream exiting the conveyor is allowed to fall under the influence of gravity into the hopper of a Model 48 Micar High Consistency mixer sold by Black Clawson, Shartle Division. Two intermediate ports one third of the way down the mixer are adapted with piping to receive a stream of 87 lbs/min liquid acetic acid and a stream of 548 lbs/min acetic anhydride. The continuous acetylation process is then conducted wherein the activation composition and frozen acetic acid are continuously fed to the hopper of the mixer and the liquid acetic acid and acetic anhydride are continuously fed into the mixer. The rate of agitation of the mixsr is adjusted to 0.3 kilowatts per pound of the combined weight of all four components. This rate of agitation corresponds to the materials undergoing acetylation passing thorough the mixer at a rate of 1636 lbs min. Based on the physical configuration of the mixer, the time the activation composition is subjected to this rate of agitation was less than 10 seconds. The composition exiting from the mixer was aged for 20 minutes to become fully acetylated and fed to a conventional hydrolysis process and successfully hydrolyzed into cellulose diacetate which was further processed by conventional means into commercially acceptable cellulose acetate.

Claims: Claims 1. A process comprising (A) introducing into an acetylation zone a stream comprising cellulose in the range of 5 to 17 weight percent, water in the range of 0 to 2 weight percent, acetic acid in the range of 10 to 62 weight percent, 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 0.1 to 1.2 weight percent and acetic anhydride in the range of 27 to 41 weight percent, based on the weight of the stream, and (B) subjecting the stream to an agitation within the acetylation zone which is in the range of 0.01 to 2.0 kilowatts per pound of the stream for a period of time of less than 10 seconds. 2. A process comprising (A) introducing into an acetylation zone a stream comprising cellulose in the range of 10 to 14 weight percent, water in the range of 0.5 to 1.5 weight percent, acetic acid in the range of 42 to 62 weight percent, sulfuric acid in the range of 0.2 to 0.8 weight percent and acetic anhydride in the range of 27 to 41 weight percent, based on the weight of the stream, and (B) subjecting the stream to an agitation within the acetylation zone which is in the range of 0.05 to 0.5 kilowatts per pound of the stream for a period of time of less than 4 seconds. 3. A process comprising (A) introducing into an acetylation zone a first stream comprising cellulose in the range of 5 to 17 weight percent, water in the range of 0 to 2 weight percent, acetic acid in the range of 10 to 62 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 0.1 to 1.2 weight percent, based on the combined weight of the first and second streams, (B) introducing into the acetylation zone a second stream comprising acetic acid in the range of 0 to 52 weight percent and acetic anhydride in the range of 27 to 41 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 0.01 to 2.0 kilowatts per pound of the combination of the first and second streams minute for a period of time of less than 10 seconds. 4. A process comprising (A) introducing into an acetylation zone a first stream comprising cellulose in the range of 10 to 14 weight percent, water in the range of 0.5 to 1.5 weight percent, acetic acid in the range of 42 to 62 weight percent and sulfuric acid in the range of 0.2 to 0.8 weight percent, based on the combined weight of the first and second streams, (B) introducing into the acetylation zone a second stream comprising acetic acid in the range of 0 to 10 weight percent and acetic anhydride in the range of 31 to 37 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 0.05 to 0.5 kilowatts per pound of the combination of the first and second streams for a period of time of less than 10 seconds.

Inventors: GERMROTH TED CALVIN, JOHNSON GRIFFIN IVAN, MITCHELL MELVIN GLENN, SPAUGH ARTHUR THALER JR, GERMROTH, TED, CALVIN, JOHNSON, GRIFFIN, IVAN, MITCHELL, MELVIN, GLENN, SPAUGH, ARTHUR, THALER, JR.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1993
Main classification: C08B3
IPC codes: C08B3