PROCESS FOR DEODORIZING TRIACETIN PRODUCED FROM NATURAL GLYCERIN

Abstract: Process for deodorizing triacetin produced by the esterification of natural glycerin includes subjecting the triacetin to elevated temperature in the range of about 80° to about 130°C (preferably 90° to 100°C) while continuously sparging the triacetin with air or oxygen for between about 10 to about 36 hours (preferably 20 to about 24 hours).The process sufficiently removes odoriferous compounds from the triacetin, thereby producing an acceptable triacetin product of deodorized quality which is at least comparable to the deodorized quality of triacetin produced from synthetic glycerin and thus is suitable for use as a plasticizer in the production of cigarette filters from filamentary tow.

Description: FIELD OF INVENTION The present invention relates generally to a process whereby triacetin (i.e., glycerol triacetate) of acceptable odor quality can be produced from natural glycerin feedstock. More particularly, the present invention relates to the novel discovery that the combined action of elevated temperature and air sparging for a sufficient time period deodorizes to acceptable levels triacetin formed from the esterification of a natural glycerin feedstock. As used herein and in the accompanying claims, the term "natural glycerin" is meant to refer to glycerin having as its origin the fats and oils of animals or vegetables. Thus, "natural glycerin" is to be understood as referring to that by-product formed as a result of the direct splitting of animal or vegetable fats and oils in the production of fatty acids of the general formula CH₃(CH₂) n COOH or when such fats and oils are saponified in the process of manufacturing soap. "Natural glycerin" as used herein is therefore to be understood as being distinguishable from "synthetic glycerin" as the latter is intended to refer to glycerin synthesized from petroleum-based feedstocks, for example, the synthesis of glycerin from a propylene feedstock via an allyl chloride intermediate or like synthesis processes. Additionally, it should be understood that the term "glycerin" refers to purified commercial products containing greater than about 95% glycerol (i.e., 1,2,3-propanetriol) with the balance being water. BACKGROUND OF THE INVENTION Triacetin is widely recognized as a useful plasticizer for filamentary crimped tow, particularly cellulose acetate tow, in producing cigarette filters The procedure for producing such filters generally involves providing a tow (or untwisted bundle of several thousand filaments), crimping the tow, opening the tow to deregister adjacent crimps, fluffing the tow to permit subsequent uniform application of a plasticizer, pulling the tow through an appropriate plasticizer applicator, and thereafter treating the plasticized tow to reduce its cross-sectional size until it is approximately equal to the cross-sectional size of a tobacco column which, together with the filter, comprise a filtered cigarette. The plasticizer causes bonding of the filaments in the filter to thereby assist in forming a coherent filter rod or plug having the desired pressure drop, compressibility and like properties. The triacetin can either itself be used as the principal active ingredient in plasticizer liquids (i.e., in concentrations of about 99% by weight or more) or can be blended with other suitable plasticizers such as, for example, triethyl citrate, dimethylethyl phthalate, or the dimethyl ether of triethylene or tetraethylene glycol, in dependence upon the type of filamentary tow being utilized and/or the resulting properties which are desired for the cigarette filter. The production of triacetin from glycerin is very well known in this art and is practiced by the reaction of glycerin under triacetin-forming conditions with an acetic acid source (e.g. acetic anhydride). The glycerin is thus esterified to form triacetin as a reaction product. Residual acetic acid and/or acetic acid source which may be present in the reaction product stream is then subsequently removed, preferably by means of distillation. A finished triacetin product suitable for use as a plasticizer in the production of cigarette filters from crimped filamentary tow will typically be substantially free of residual acetic acid; that is, will contain less than about 0.005%, and preferably less than about 0.002% acetic acid. Additionally, the triacetin product will be substantially colorless, and will not exhibit unpleasant odors. However, not all glycerin which is commercially available is suitable for producing triacetin of a quality demanded by filtered cigarette manufacturers. For example, glycerin which contains detectable odoriferous compounds will not be used as a feedstock for the production of triacetin since such odoriferous compounds will carry over into the resulting triacetin product which, if applied as a plasticizer during the production of cigarette filters from crimped filamentary tow, will evidence themselves in the form of an objectionable taste when the cigarette is smoked. For this reason, triacetin manufacturers have conventionally exclusively used synthetic glycerin (i.e., glycerin having its origin in and synthesized from petroleum-based compounds, for example, propylene) as their feedstock owing principally to its odor purity; that is to say its highly desirable deodorized quality. Commercial sources of synthetic glycerin however are not plentiful, thereby creating significant problems for the triacetin producer should the commercially available supply sources of synthetic glycerin be reduced or eliminated. The available supply of natural glycerin on the other hand is relatively plentiful from numerous commercial sources and thus represents an attractive alternative to the triacetin producers' conventional use of synthetic glycerin feedstock. Notwithstanding the alternate source (and possibly lower cost) incentive to producers of triacetin, natural glycerin has, until this invention, presented significant problems mitigating against its substitution for synthetic glycerin as a feedstock for the production of triacetin. Foremost is the problem associated with the odor quality of natural glycerin. Because of its origin in the fats and oils of animals or vegetables, odoriferous compounds are present in natural glycerin which are not detectably present in synthetic glycerin. That is, since the fats and oils of animals and vegetables consist of both saturated and unsaturated fatty acid esters (see, " Organic Chemistry ", Morrison et al, 3rd Ed., p. 1058 (1976)), residual unsaturated fatty acid esters may be present in natural glycerin owing, for example, to incomplete deesterification in the fat splitting stage and/or incomplete separation of the fatty acid esters from glycerin in subsequent refining stages employed in natural glycerin production. Likewise, unsaturated fatty acids may also be present in natural glycerin owing to incomplete separation in the refining stages during natural glycerin production. Residual unsaturated fatty acid esters and/or unsaturated fatty acids in the glycerin may then be oxidized (i.e., rancidified) at mild temperatures to form unsaturated (and possibly saturated) aldehydes which contain fewer carbons than their fatty acid precursors (" Fatty Acids (Their Chemistry, Properties, Production and Use) ", Part 5, pp. 3693-3697, 3701 (1968)). Such aldehydes are highly odoriferous and may render the resulting triacetin produced from natural glycerin unusable as a plasticizer, even if present in a few parts per million. Moreover, the sources of animal or vegetable fats vary widely, thereby precluding with any degree of certainty whether the triacetin produced will have acceptable odor for use as a plasticizer. Odor problems associated with glycerol obtained from the fats and oils of animals or vegetables and its related compounds are not new and have been the subject of various prior proposals to deodorize the same. For example, U.S. Patent No. 2,120,227 to Brant discloses deodorizing glycerol for use in regenerated cellulose film by agitating with the glycerol for at least six hours, (preferably 12-24 hours) activated charcoal and an oxidizing agent, preferably hydrogen peroxide. This oxidizing agent, in general, is disclosed as comprising any solution which yields hydrogen peroxide under the process conditions or, alternatively, ozone or oxygen under pressure. The patentee found the treatment of glycerol with hydrogen peroxide without the use of charcoal results in a product which is not improved and which, in many instances, is more odorous when used in regenerated cellulose film than glycerol which has not received such treatment. Moreover, low treatment temperatures (i.e., below 50°C) are used to avoid degradation of the hydrogen peroxide. Lee et al in U.S. Patent No. 2,368,669 disclose purifying and deodorizing "glyceride oils"; i.e., glyceryl esters, by vaporizing unwanted volatiles (aldehydes, ketones) via distillation but with the exclusion of oxygen from the system. Franzen et al in U.S. Patent No. 1,977,988 disclose recovering fatty acids from a crude mixture of volatile, non-aromatic hydrocarbons produced by destructive oxidation by the method of treating the mixture with a spray of water or inert organic materials at 150° - 300°C and 1333 to 6666 Pa (10-50 mm Hg) gauge. The crude mixture is thereby freed of hydrocarboxylic acids without the formation of; e.g., unsaturated acids. The fatty acids recovered only have a slight odor due to the action of the small drops of liquid. U.S. Patent 2,591,134 to Canariis discloses an apparatus and method for removing oxidizable taste-and-odor-producing material from liquids, such as water. Air is introduced into the liquid by means of the flow of liquid through, for example, a Venturi tube forming a part of the aeration member so that use of external sources of power; e.g., blowers, fans, compressors, etc., is avoided as well as the use of moving parts. BRIEF STATEMENT OF INVENTION It is one object of this invention to provide a method to produce a triacetin product from natural glycerin feedstock which exhibits acceptable odor qualities suitable for use as a plasticizer for cellulose acetate tow to produce cigarette filters. A further object of this invention is to produce triacetin of acceptable odor quality from a feedstock of natural glycerin by an effective, commercially economic process so as to enable triacetin manufacturers to utilize the more commercially plentiful supply sources of natural glycerin as opposed to synthetic glycerin, and as such, provide a commercially economical and viable alternative to the use of synthetic glycerin as a feedstock for the production of triacetin. These and other objects (which will become more clear to the reader after consideration of the following detailed description of the invention) are generally achieved by a process whereby natural glycerin is esterified to produce triacetin, the temperature of the triacetin is subsequently elevated while an oxygen-containing gas (i.e., air or oxygen) is sparged into and intimately mixed with the elevated temperature triacetin for a time sufficient to substantially remove odoriferous compounds therefrom. The temperature of the triacetin is elevated between about 80°C to about 130°C, and preferably between about 90° to about 100°C. The triacetin is maintained at such elevated temperature during the continuous sparging with air or oxygen for between about 10 to about 36 hours, and more preferably between about 20 to about 24 hours. The triacetin during sparging is preferably gently agitated to ensure complete and intimate contact with the air or oxygen. Additionally, the air or oxygen that is sparged into the triacetin should be substantially dry (i.e., a dew point of less than about -40°C) to avoid degradation of the triacetin, thereby ensuring that the acetic acid content after treatment by the present invention is maintained within acceptable standards (i.e., less than about 0.005%, and preferably less than about 0.002% by weight acetic acid). Although the precise mechanism by which deodorization of triacetin is accomplished by means of the present invention is not fully understood at this time, it is surmised that the combined action of elevated temperature and air or oxygen sparging causes accelerated rancidification of residual unsaturated fatty acid esters and/or unsaturated fatty acids. The odoriferous aldehydes which are believed to be produced as a result of such accelerated rancidification are more volatile than their unsaturated fatty acid precursors since they have fewer carbon atoms per molecule. This increased volatility may therefore permit the formed aldehydes to be more readily stripped from the triacetin by means of the air or oxygen being sparged thereinto thereby resulting in a deodorized triacetin product. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Reference will hereinafter be made to the accompanying drawings wherein like reference numerals throughout the various figures denote like elements, and wherein; FIGURE 1 is a diagrammatic flowsheet showing a preferred processing sequence to produce deodorized triacetin from natural glycerin in accordance with this invention; and FIGURE 2 is a diagrammatic flowsheet of a triacetin deodorization system which forms a part of the overall process shown in FIGURE 1. DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT A diagrammatic flowsheet, showing a preferred processing sequence to produce deodorized triacetin from natural glycerin in accordance with this invention, is shown in accompanying FIGURE 1. As can be seen, natural glycerin and a source of acetic acid, e.g., acetic anhydride, are charged into reaction vessel 10 at a weight ratio of natural glycerin to acetic anhydride of between about .25:1 to about .29:1. The glycerin and acetic anhydride reactants are maintained in vessel 10 under triacetin-forming conditions, that is, a temperature of greater than about 130°C under atmospheric pressure for about 160 minutes. Esterification of the natural glycerin thus occurs in reaction vessel 10 so as to produce triacetin which exits in product stream 12 together with residual acetic anhydride and acetic acid formed during the reaction. Product stream 12 then passes on to the acid distillation unit 14 whereby a substantial portion of the acetic anhydride and acetic acid is volatilized and removed in vapor stream 16 to be subsequently reconverted to acetic anhydride for use in further processing. The bottoms stream 18 from acid distillation unit 14 will thus contain substantially no acetic acid (i.e., less than about 0.005% by weight acetic acid) with the remainder being raw triacetin product. Additional purification of the raw triacetin product occurs in triacetin evaporator 20 which removes carbonaceous material and other solid particulates therefrom and passes them on to waste treatment via stream 22. The vapor stream 24 from triacetin evaporator 20 will thus be substantially free of carbonaceous material and other solid particulates and will be condensed by means of heat exchanger 26 and passed on to holding vessel 28. Raw triacetin contained in holding vessel 28 is then withdrawn as needed and passed via stream 30 to triacetin deodorizing system 32 so as to remove odoriferous compounds therefrom and thereby produce a final triacetin product acceptable for use as a plasticizer in producing cigarette filters from crimped filamentary tow. Deodorized triacetin from system 32 is then passed via stream 34 to the final product storage tank 36. A more detailed diagrammatic flowsheet of the triacetin deodorizing system 32 can be seen by reference to accompanying FIGURE 2. The triacetin deodorizing system 32 preferably includes multiple closed treatment vessels 40a, 40b, each provided with a mechanical vane agitator 42a, 42b, driven by suitable motor means 44a, 44b, respectively. Raw triacetin is introduced into treatment vessels 40a, 40b from holding vessel 28, (see FIGURE 1) via line 30 and its manifold lines 30a, 30b. It should be understood that although two treatment vessels 40a, 40b happen to be shown in FIGURE 2, as many treatment vessels as are necessary will be required to accommodate the production of raw triacetin while yet permitting between about 10 to about 36 hours (preferably about 20 to 24 hours) resident treating time in each treatment vessel and the necessary time cycles for filling and draining of the treatment tanks. In addition, a single treatment tank could be provided without departing from the scope of this invention but is less than desirable since such a system would require a much larger holding vessel 28 and/or multiple holding vessels 28 in order to accommodate the time necessary to cyclically fill/treat/drain the triacetin utilizing a single treatment tank. When the raw triacetin has filled either tank 40a, 40b (depending on the tank being used for a particular cycle) to a predetermined level, a corresponding steam valve 46a, 46b, respectively, is opened so as to pass steam (preferably 50 psig) from steam header 48 to steam coils 48a, 48b, located within treatment tanks 40a and 40b, respectively. In such a manner, the raw triacetin in treatment tanks 40a, 40b is heated to a temperature between about 80°C to about 130°C, and preferably to a temperature within the range of about 90° to about 100°C. Condensate is collected in traps 50a, 50b and routed to the condensate return system (not shown). With the raw triacetin elevated in temperature and under influence of gentle agitation provided by means of mechanical agitators 42a, 42b, air or oxygen is then introduced via air supply line 52 connected to air distribution manifolds 52a, 52b within treatment tanks 40a, 40b, respectively, so as to sparge air into the heated and gently agitated raw triacetin being treated. Prior to being introduced into the treatment tanks 40a, 40b, the air or oxygen is filtered so as to remove, for example, particulate matter, oil and other contaminants therefrom and is dried to a dew point of less than about -40°C and more preferably between -40°C and -100°C. Dry air is very important to the successful practice of this invention as otherwise residual water in the air or oxygen may degrade the triacetin to form acetic acid in the treatment tanks 40a, 40b. The triacetin is maintained at an elevated temperature as mentioned previously while air is continuously sparged thereinto via distribution manifolds 52a, 52b and is gently agitated by means of mechanical agitators 42a, 42b. Such conditions are maintained for a time period sufficient to deodorize the triacetin, and particularly for a time period between about 10 to about 36 hours (preferably between about 20 hours to about 24 hours). Sparging should be accomplished utilizing a sufficient quantity of air or oxygen to ensure that complete and intimate contact with the triacetin under treatment conditions is achieved so as to ensure adequate rancidification of residual fatty acids and/or fatty acid esters and also to ensure that the more volatile and odoriferous aldehyde compounds thus formed are entrained in the air or oxygen and removed as a vapor stream from the triacetin. Agitation of the triacetin during air or oxygen sparging will facilitate intimate contact between the air or oxygen and triacetin. Under preferred treatment conditions, at least 0.002832 m³ per hour (measured at standard temperature and pressure, that is, 25°C and 101.325 kPa) (.01 scfh) of air or oxygen per each 0.4536 Kg (per pound) of triacetin being treated (and more preferably at least 0.01416m³ per hour (.05 scfh) of air or oxygen per each 0.4536Kg (per pound) of triacetin) is sufficient to adequately deodorize the triacetin. Lesser quantities of air or oxygen may be used, however, under conditions of more vigorous agitation, for example. Moreover, excess quantities of air or oxygen may also be utilized and is limited by the practical considerations of unacceptably large quantities of triacetin product being lost due to entrainment with the air or oxygen. The now deodorized final triacetin product is emptied from treatment tanks 40a or 40b via lines 54a or 54b, respectively, and is cooled to ambient temperatures by means of triacetin cooler 56. The cooled and deodorized triacetin is then transferred to triacetin storage tank 36 (see Figure 1) for shipment to customers for use as a plasticizer for cigarette filters. Of course, after the treatment cycle is complete and prior to emptying the triacetin from tanks 40a, 40b, the steam supply, air supply and agitation are each terminated. The deodorized triacetin may alternately be allowed to gradually cool by allowing it to stand within vessels 40a or 40b. If the triacetin is expected to stand for prolonged periods of time, it is preferred that the vessel which contains the triacetin be charged with, for example, nitrogen so as to displace substantially all air from the vessel. Such a precautionary practice ensures that the triacetin does not undergo any degenerative changes which may otherwise occur if it was maintained in contact with air for prolonged periods of time. The present invention will be further understood from the following non-limiting examples. EXAMPLE NO. 1 Approximately 27240Kg (60,000 pounds) of triacetin was produced in a triacetin production facility by the esterification of a natural glycerin feedstock. About 13620Kg (30,000 pounds) of the triacetin was subsequently air sparged in a pilot plant facility for 21 hours at 95°C at an air flow rate of 660 scfh. Two samples of the triacetin were obtained before the air sparging treatment (designated below as Sample Nos. 1 and 2) while one sample was obtained after the air sparging treatment (designated below as Sample No. 3). Triacetin Sample Nos. 1 through 3 produced from natural glycerin and a triacetin control sample produced from synthetic glycerin (designated below as Sample No. 4) were submitted to a panel for odor evaluation. The results of the evaluation were as follows: EXAMPLE NO. 2 Two groups of cellulose acetate cigarette filter plugs using, as plasticizer, the triacetin of Sample No. 3 and Sample No. 4, respectively, were prepared. The filter plugs of king-size filter cigarettes obtained commercially in the retail market were removed and replaced with either a filter plug using the triacetin of Example No. 3 as plasticizer or a filter plug using the triacetin of Example No. 4 as plasticizer thereby providing trial and control lots, respectively, of filtered tip cigarettes. The trial and control lots of filter tip cigarettes were then submitted to a smoking panel for evaluation in multiple, blind comparisons of the two lots of cigarettes. No consistent differences between the trial and control lots of cigarettes were detected by the smoking panel. EXAMPLE NO. 3 Approximately 945g (750 ml) of natural glycerin was air sparged in a laboratory facility for 25.25 hours at 93-101°C at an air flow rate of 0.00708m³ per hour (0.25 scfh). Subsequent to the air sparging, 645g of the natural glycerin was reacted with acetic anhydride to form triacetin and the thus formed triacetin sample was then submitted to a panel for odor evaluation with the following results: The above data demonstrate that triacetin produced from natural glycerin and treated according to the present invention is deodorized to a degree comparable to triacetin produced from synthetic glycerin. Particularly, it should be noted that the detected odor for the triacetin of Sample No. 3 treated according to this invention is comparable to or is less than the triacetin of control Sample No. 4, the latter representing a triacetin product now in commercial use as a plasticizer for filamentary crimped tow in the production of cigarette filters. Neither Sample No. 3 nor the control Sample No. 4 evidenced a detectable "sour buttermilk" note which is significant in determining whether triacetin is suitably deodorized for use as a tow plasticizer for cigarette filters. Without treatment according to this invention, however, a "sour buttermilk" note is detectable in the triacetin produced from natural glycerin thereby rendering such triacetin unsuitable as a tow plasticizer for cigarette filters. Moreover, Example 3 above demonstrates that treatment of natural glycerin by air sparging at elevated temperatures has no effect upon the odor quality of triacetin subsequently formed therefrom. Thus, it is only when the triacetin produced from natural glycerin is treated according to this invention that the beneficial deodorization thereof occurs to levels comparable to triacetin produced from synthetic glycerin. While the present invention has been described in terms of what is presently considered to be the most preferred embodiment thereof, those in this art may recognize that many modifications may be made, which modifications shall be accorded the broadest scope of the appended claims so as to encompass all equivalent methods and/or processes.

Claims: In a process for producing triacetin from a glycerin feedstock by means of reacting the glycerin feedstock with a source of acetic acid under triacetin-forming conditions, the improvement comprising utilizing as the feedstock natural glycerin having its origin in the fats and oils of animals or vegetables, and deodorizing the triacetin produced therefrom, wherein said step of deodorizing includes the steps of elevating the temperature of the triacetin within a range between about 80° to about 130°C and maintaining the triacetin at said elevated temperature for a treatment period between about 10 hours to about 36 hours while continuously sparging air or oxygen thereinto during the treatment period, thereby to produce a triacetin product of deodorized quality which is at least comparable to the deodorized quality of a triacetin product produced from synthetic glycerin and thus is suitable for use as a plasticizer in the production of cigarette filters. A process as in Claim 1 wherein the elevated temperature of said triacetin is in the range of between about 90°C to about 100°C. A process as in Claim 1 wherein said treatment period is between about 20 hours to about 24 hours. A process as in Claim 1 wherein dry air is utilized in said step of sparging and has a dew point of less than about -40°C. A process as in Claim 4, wherein the dry air has a dew point of between -40°C and -100°C. A process as in claim 1 wherein said step of sparging is practiced utilizing air at a rate of at least 0.002832m³ per hour (0.1 scfh) for each 0.4536Kg (per pound) of triacetin. A process as in claim 1 wherein said step of deodorizing further includes the step of agitating said triacetin during said treatment period to ensure complete contact between the triacetin and the air being sparged thereinto. A process for deodorizing triacetin produced by the esterification of natural glycerin, said process comprising the steps of elevating the temperature of said triacetin, sparging said triacetin, while maintaining said elevated temperature thereof, with air or oxygen for a time sufficient to substantially remove odoriferous compounds therefrom whereby said triacetin is deodorized. Process for producing deodorized triacetin comprising subjecting glycerin, which contains at least 95% glycerol and which is produced from the fats and oils of animals or vegetables, to esterification with a source of acetic acid to form said triacetin, elevating the temperature of the triacetin to within the range between about 80°C to about 130°C, and introducing dry air into the triacetin while maintaining said elevated temperature thereof for a period of time between about 10 hours to about 36 hours so as to remove odoriferous compounds therefrom, whereby said triacetin is deodorized to a degree at least comparable to triacetin formed from synthesized glycerin. Process as in claim 9 further comprising agitating the triacetin concurrently with said step of introducing dry air thereinto. Process as in claim 9 wherein said dry air has a dew point of less than -40°C. Process as in claim 11 wherein the air is introduced into the triacetin at a rate of at least 0.002832m³ per hour (.01 scfh) for each 0.4536Kg (per pound) of triacetin. Process as in claim 11 wherein the air is introduced into the triacetin at a rate of at least 0.01416m³ per hour (.05 scfh) for each 0.4536Kg (per pound) of triacetin. Process as in claim 9 wherein the triacetin is elevated to a temperature within the range of about 90°C to about 100°C and is maintained at said elevated temperature for a period of time between about 20 hours to about 24 hours.

Inventors: HOWELL, CARL, J. JR., MC WILLIAMS, DAVID R., STEINER, THOMAS L.
Applicants: CELANESE CORPORATION
Application year: 1987
Main classification: C07C67
IPC codes: C07C29, C07C67, C11B3, C07C31, C07C69