NZ203500A - Separating rubber from guayule resin/rubber mixtures - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £03500 20350 Priority D&te(s): O.. COQ'Cr^P.. I Complete Specification Filed: 7.~.

Class: c.p.sc;;..

Publication Date: JPflG ....

P.O. Journal. No: . I NO SBAlliSS N.Z.No.

NEW ZEALAND Patents Act 3953 COMPLETE SPECIFICATION " IMPROVED PROCESS FOR DERESINATION OF RESINOUS GUAYULE RUBBER." We, THE FIRESTONE TIRE & RUBBER COMPANY of 1200 Firestone Parkway, Akron, Ohio, United States of America, a corporation of the State of Ohio, in the United States of America do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - - . iy ^ r.

V 2 035 - l f\- IMPROVED PROCESS FOR DERESINATION OF RESINOUS GUAYULE RUBBER FIELD OF THE INVENTION This invention relates to processes for isolating pure rubber from resin/rubber mixtures derived from guayule plant material. More particularly, it relates to such processes wherein in relatively uniform, porous, spherical particles of resinous guayule rubber are 10 extracted to yield purified rubber. It further relates to the rubber and resin fractions obtained from such particles and the particles themselves as well as to systems comprised of such particles.

GENERAL BACKGROUND The guayule plant, Parthenium argentatum Gray, which grows principally in the southwest United States and Mexico, is known as a potential domestic source of rubber. This plant also contains organic resinous material which usually accompanies the rubber in many 20 isolation and processing steps. For many purposes, however, it is desirable to free the rubber of such resin 2 035 0 C by-products. The resins, by themselves, may also be useful in various applications.

The terms "guayule resin" and "resin" are used herein to refer to those constituents of the guayule plant 5 (and similar rubber-containing plants) obtained when the plant itself, or organic material prepared from it, is extracted with an oxygenated organic solvent such as acetone, ethyl alcohol and the like. These resinous components usually constitute about 6-9% of the dry weight 10 of the plant before processing. Material obtained by hydrocarbon solvent extraction of aged guayule shrub is also considered resin since it probably contains resin and resin-like low molecular weight rubber.

Since it is probable that guayule will be 15 cultivated in the future as a source of rubber and resin, and since resin-free rubber is desirable for many uses, increasing attention has been directed to methods for processing guayule to produce desired products in relatively pure form. In addition it is often desirable 20 for reasons of economy and convenience to process guayule plant material in two stages, first to produce relatively crude resin/rubber mixtures and then to further process these mixtures to make more highly-purified rubber and resin fractions. Such resin/rubber mixtures can be stored 25 and transported more conveniently than unprocessed plant material.

Generally resin/rubber mixtures contain at least about 25% rubber. Materials containing at least about 50%, and up to 85% or 90% rubber, with the substantial 30 remainder being resin, are termed, for the purpose of describing this invention, "resinous rubber." Resinous 2.0350C rubber is usually about 50-85% rubber, typically about 60-80% rubber and about 50-15%, typically about 40-20%, resin, with minor amounts (say 5-10%) of other guayule-derived materials such as sugars and other 5 water-soluble fractions. Both resinous rubber and other resin/rubber mixtures can be advantageously processed in the present invention.

PRIOR ART There are two basic procedures for isolating 10 guayule rubber in resin-free form (for example, less than 2% resin). In the first, as practiced in Saltillo, Mexico (see the book "Guayule, reoencuentro en el desierto," Consejo Nacional de Ciencia y Technologia, Mexico, 1978) resinous rubber is recovered by grinding the shrub in a 15 hammermill, preparing a water slurry of the ground shrub and then regrinding of the shrub/water slurry in a pulping mill, and finally recovering resinous rubber by water flotation. The resinous rubber is then contacted with hot acetone to remove guayule resin. The deresinated rubber 20 remaining is then dissolved in a hydrocarbon solvent, antioxidant added, filtered and the solution desolventized with hot water.

This multi-stage procedure is generally effective in producing high-quality rubber, but difficulties may be 25 encountered. Specifically, depending upon the variety of guayule shrub processed, the "rubber worms" released by the pulping step may or may not agglomerate to a mass which can be conveniently handled in the subsequent deresination step. For example, the final report of the 30 U.S. Natural Rubber Research Station; Salinas, California entitled "Natural Rubber Extraction and Process Investigations" dated April 30, 1953 on pages 26-28, 2035 00 summarized the milling characteristics of the different strains of guayule shrub as well as yields of rubber obtained by a standard procedure. Milling characteristics of the different strains varied significantly in buoyancy 5 (ability of the rubber to float) and tendency of rubber worm to agglomerate. Several guayule strains released rubber worms of very fine size during processing which would not agglomerate and were difficult to recover by the conventional skimming processes. Other strains, such as 10 "Strain 4265-1", released buoyant rubber worms which readily agglomerated. The reported yields of recovered rubber varied from 45.6% for "Mariola X's" to 100.0% for strain 4265-1. On page 32 of the final report, it was reported that frequently during deresination many fine 15 worms floated in the deresinating solvent and were lost.

At the other extreme, Clark and Feustel reported in U.S. Patent 2,665,317 that guayule rubber worms can clump or cohere to form relatively large and impervious aggregates or masses which cannot be extracted because the 20 resin solvent cannot penetrate them. Clark and Feustel determined that an insoluble soap film deposited on the rubber worms impedes the clumping of the rubber worms.

In any event, it is believed that the process of the present invention will minimize the loss of finely 25 divided rubber worms and prevent formation of compacted resinous guayule worms so that efficient solvent deresination is possible.

The second basic approach to obtaining resin-free guayule rubber is through extraction of ground shrub with 30 a solvent specific for resin which essentially does not dissolve the rubber fraction present. Acetone is reported to be such a solvent (U.S. Natural Rubber Research Station IIP 2035 Report, page 32). This approach, of course, requires subsequent processing to recover the rubber left in the plant material. The efficiency of this processing is sometime decreased by the large amounts of inert plant 5 material, such as bagasse, present. Also such procedures necessitate handling of bulky guayule shrub material twice. The ground shrub must be deresinated, dried and then further processed either by water flotation or solvent extraction to finally produce resin-free rubber.

SUMMARY OF THE INVENTION Unexpectedly, it has now been found that the difficulties previously encountered in guayule rubber recovery can be overcome to a significant extent by the process which comprises: (a) forming an aqueous suspension 15 of spherical resin/rubber particles, about 90% of which are about 0.8-13 mm. in diameter; (b) extractively deresinating the particles with oxygenated resin solvent; and (c) recovering the deresinated rubber, wherein the suspension is formed by removing organic solvent through 20 vaporization from a solution of a resin/rubber mixture in the solvent, said removal occurring in the presence of water containing one surfactant for aqueous systems.

Typically, the oxygenated solvent for resin is acetone or a similar solvent, the organic solvent for the 25 resin/rubber mixture is a hydrocarbon mixture such as commercial hexane and the surfactant is a metal salt of a fatty acid such as a sodium or calcium soap.

An advantage of this inventive process is that porous resin/rubber particles of relatively uniform, 30 spherical shape are obtained consistently which can be effectively deresinated to resin-free rubber containing 2035 less than about 2%, often, less than 1% or 0.5% resin. The rubber is recovered either as small spherical particles or the particles can be agglomerated to bulk rubber in the form of baled rubber used in the rubber 5 industry.

DETAILED DESCRIPTION OF THE INVENTION As noted above, the resin/rubber mixtures used in the present invention can be obtained by water flotation or by extraction of ground guayule shrub with a solvent 10 that dissolves both resin and rubber. Depending upon the procedure used for recovering the mixture, it may be desirable to further purify by forming a solution which is filtered to remove insoluble material. Other purification steps known to those of skill in the art, such as 15 decolorization, stabilization with additives and the like may also be used at this stage, but they are optional and not essential to the invention.

As noted above, the resin/rubber mixtures used in this invention may be resinous rubber (as defined above) 20 or they may be mixtures containing a predominance of resin such as mixtures of about 50-75% resin. In any event, the suspension of resin/rubber particles is made from a solution of resin/rubber mixture in organic solvent. This solvent can be a hydrocarbon solvent, typically one of 25 about 5 to 9 carbon atoms. Aliphatic, alicyclic and aromatic hydrocarbons can be used; specific useful hydrocarbons include pentane, hexane, heptane, octane, nonane (all isomers of each), cyclic analogs of these, e.g., cyclohexane, methyl cyclopentane), and aromatics 30 such as benzene, toluene, xylenes and the like. Mixtures of these hydrocarbons are useful and commercial hexane is typically used. 2.03500 Non-hydrocarbon solvents can also be used, particularly those consisting of mixtures of the previously specified hydrocarbons with polar organic solvents such as the deresinating solvents described 5 below. Usually such mixtures contain at least about 50% hydrocarbon solvent. They are capable of dissolving essentially all the resin/rubber mixture to be processed except for hydrocarbon insoluble impurities. A specific example is a mixture of hexane/acetone containing about 10 50-80% hexane. Usually, however, purely hydrocarbon solvent is used.

The resin/rubber mixture solutions used in the inventive process contain about 0.5-50% solids (by solvent evaporization), usually about 1-25% solids, often 5-10% 15 solids.

The aqueous suspension of resin/rubber particles is formed by removing organic solvent from the aforedescribed solution through vaporization in the presence of water containing at least one surfactant for 20 aqueous systems. Thus, a mixture of resin/rubber-organic solution and water is prepared with surfactant present in the water (added before or after formation of the mixture). The organic solvent is then removed from the solution/ water mixture through vaporization, usually with the aid 25 of heat. The vaporization process provides agitation which may be supplemented by mechanical or other means. As vaporization proceeds, spherical particles of resin/ rubber are formed which are suspended in the water. The surfactant acts to keep the particles in a size range such 30 that at least 90% are of about 0.8-13 mm. in diameter.

Usually at least 90% of the particles are of about 1.5-5.5 mm., typically 2.5-3.5 mm. diameter. These particles are relatively uniform, porous and of spherical shape.

-Z.035DO The resin/rubber organic solution-water mixture is usually used in the proportions of about 1 part resin/ rubber solution to about 1-100 parts water. More water, in the form of liquid or steam can be added during the removal of the organic solvent. As solvent is removed, the proportion of water naturally increases until there is little or no organic solvent left. At this point, there is effectively the desired suspension of resin/rubber particles in water with, at most, only traces of organic solvent left.

The aqueous surfactants useful in the spherical particle forming step are usually anionic in nature.

Typically they are soaps, that is, metal salts of long chain fatty acids. These acids are often carboxylic but they can also be sulfur-containing (sulfonates, sulfates) or phosphorous-containing (phosphonates, phosphates). The organic portions of all these types of acids contain at least one organic chain of at least 6 carbon atoms interrupted by no more than one pendant group. Typically, the chain has no more than one methyl group; often no pendant groups are present. These chains have up to about 22 carbon atoms. The metals in these surfactants (soaps) are in their mono-, di- or trivalent states and of groups IA, IIA, IB, IIB, IIIA and IIIB of the periodic table. As used herein, reference to groups of the periodic table refer to the periodic table as it appears in authoritative texts such as "Advanced Inorganic Chemistry: A Comprehensive Text", Interscienve Publishers (1962). Examples are sodium, potassium, lithium, calcium, barium, magnesium, aluminum and the like. Usually the surfactants are fatty carboxylic acid soaps of 12-20 carbons and a group IA or IIA metal. Mixtures of soaps can often be used to advantage. Nonionic and cationic materails can also be used as long as they function as surfactants in aqueous systems. Many such anionic, cationic and nonionic surfactants are known; see, for example, the discussion in "Surfactants and Interfacial Phenomena," by Milton J Rosen, published by John Wiley and Sons, N.Y., (1978) 2035 pages 5-26, which are incorporated herein by reference. These surfactants are used in surface-active concentrations. Usually about 0.25-10, typically 0.5-5.0 parts surfactant are used per 100 parts of resin/rubber (phr) 5 processed.

The oxygenated deresinating solvent used in the present invention is a polar organic solvent. Usually these deresinating solvents contain one to about eight carbon atoms and are chemically classified as alcohols, 10 ketones, esters, or ethers. Specific examples include methanol, ethanol, propanol, acetone, methyl ethyl ketone, ethyl acetate, methyl propionate, diethyl ether, etc. Combinations of oxygenated solvents can also be used.

Resin micella containing about 4-30% resin and one or more 15 of the aforedescribed oxygenated solvents are also useful. For reasons of economy and convenience, the preferred deresinating solvent is an oxygenated organic solvent such as ethanol, acetone or propanol or mixtures thereof.

The deresinating, oxygenated organic solvent is brought in contact with the above-described spherical particles after the bulk (for example, 90-99%) of the resin/rubber solvent and water are removed. As explained previously, the resin/rubber solvent is removed by 25 vaporization. The water can be removed by decantation, centrifugation, filtration or any other convenient technique. The wet spherical particles usually form a sponge-like mass which is conveniently deresinated. The high surface area, small size and porous nature of these 30 particles permit very effective contact between the resin/rubber and deresinating solvent. This contact can be effected by any convenient, conventional technique such as column elution, counter current elution, trituration 20350 and the like. Ratios of deresinating solvent to resin/ rubber mixture in the particle form such as about 1-100 parts solvent to one part resin/rubber mixture are used.

An added benefit of the present invention is that 5 the typical deresinating solvents, ethanol, propanol and acetone, are miscible with water and can very effectively remove the remaining of the water present in the rubber. Because of the relatively low normal boiling point and low heat of vaporization of ethanol, propanol and acetone 10 (compared to water) the drying of the deresinated rubber via vacuum or extruder is thus facilitated. The deresinated rubber can be recovered by any conventional technique. Similarly, removal of the deresinating solvent leaves as a residue relatively pure resin which can be 15 used for a variety of purposes.

In one convenient embodiment of the invention, the spherical particles are formed by removing the organic solvent with steam in the presence of the above-described surfactant to obtain resinous rubber of relatively uniform 20 spherical particle size with about 90% having a diameter of 0.8-13 mm.; said particles being of highly-porous nature. In this embodiment, steam is added to the mixture of organic solvent and water containing soap, with the steam providing both heat and agitation.

The inventive process is particularly useful in processing resin/rubber mixtures having resin contents of greater than 50%. It has been determined experimentally that the resin content of resin/rubber mixtures obtained by direct hydrocarbon extraction of ground guayule shrub 30 will vary considerably but can be as high as 60-70%.

Relatively immature guayule shrub at a stage in growth at which the rubber content has not developed to the extent 2,03 50 C expected in a mature shrub (or plants that have not been treated with bioregulators to stimulate rubber development) can be extracted with a hydrocarbon solvent to recover such mixtures of very high resin content. Unexpectedly, 5 it has been found that by the practice of the present invention, porous spheres of resin/rubber mixture of very high resin content can be prepared. Surprisingly, although the resin is a very sticky material, these spheres will not agglomerate to a mass if suspended in 10 water and/or a deresinating solvent such as acetone. The resin/rubber porous spheres are more dense than acetone; therefore, gentle agitation of an acetone suspension of the resin/rubber spheres, preferably heated to the normal boiling point of acetone, effects a rapid, thorough 15 extraction of the resin. Under these general conditions, the deresinated spheres do not agglomerate to a mass of rubber.

EXAMPLES The practice of the present invention is 20 illustrated by the following examples which do not in any way limit the scope of the invention. In these examples, as elsewhere in this specification and the appended claims, all parts and percentages are by weight unless expressly indicated otherwise. Comparative examples bear 25 letter designations (A, B, etc.) while those of the invention, a Roman numeral (I, II, etc.) Example A: Desolventization Without Surfactant This example describes an attempt to desolventize a hydrocarbon solution of guayule rubber containing about 8% 30 resin in the absence of surfactant. The desolventized rubber rapidly agglomerates even during the solvent 2 035 0- removal step thus making the complete removal of hydrocarbon solvent difficult and subsequent deresination almost impossible. The guayule rubber is obtained from the water flotation process using non-deresinated shrub.

The resinous rubber is partially deresinated via contacting rubber worms with acetone.

A hexane solution of resinous guayule rubber (about 8% resin) is prepared at 10.2% concentration of the resinous rubber. The hexane/solution of resin/rubber is 10 filtered through a 100 micron filter, demonstrating the ease with which non-hydrocarbon material such as cork, dirt and bagasse can be removed. The hexane solution is then heated to 93° F. and then pressured through the 100 micron filter by applying a 14 psig pressure head to the 15 inlet of the filter. The outlet of the filter registers 12 psig indicative that the pressure drop across the filter is not excessive using a relatively concentrated resinous/rubber solution.

The filtered hexane solution is then charged at a 20 rate of about 0.3 gallons/minute into a reactor containing about 12 gallons of water heated to 175° F. to volatize the hexane and recover the guayule rubber. The temperature of the water is maintained at about 175° F. via controlled addition of steam to the jacket of the 25 reactor. The total time to charge and desolventize the resinous rubber/hexane solution is about 20 minutes.

After the bulk of the hexane has been removed as an azeotrope with water, the reactor is cooled to ambient temperature, the reactor opened and examined. The 30 recovered rubber is a light greenish-cream color and is a solid globular, relatively impervious mass with smaller masses adhering to the vessel walls. 2 035 0 C Deresination of the mass of guayule rubber is impractical because of its bulk and the consequent low surface area that would be exposed to a deresinating solvent.

EXAMPLE B For the sake of complete disclosure, Example A is repeated using a hexane solution of 5.15% resin/rubber in an attempt to prevent agglomeration of the rubber. The temperature of the water in the hexane-stripping tank is 10 increased to 200° F. After the bulk of the hexane has been removed, the reactor is cooled and the rubber inspected. As in Example A, the recovered rubber is essentially one large mass and the odor of hexane from it indicates that this clumping of the rubber prevents 15 complete removal of the hexane solvent.

Example I: Desolventization With Aqueous Surfactant Essentially, the conditions of Example A are repeated with the exception that 1.0 phr (parts per hundred resin/rubber) of sodium soap (Ivory brand, Proctor 20 and Gamble, Cincinnati, Ohio, U.S.A.) is added to the water in the hexane-stripping reactor. The rubber used is the same as in Example A. The recovered rubber agglomerated to some extent but is not as compacted as that in Examples A and B. The rubber recovered in this 25 example is a spongy mass with considerable void spaces.

This indicates that approximately 1.0 phr of a surfactant in the water produces high-surface resin/rubber particles which can subsequently be easily deresinated. Low concentration of surfactant can be used with increased 30 agitation and/or slower charging of the hexane/resinous rubber solution to produce the desired spherical 2035 resin/rubber. The size of these particles is such that 90% of them have diameters of about 0.8-13 mm. Determinations of particle sizes can be made by microscopic examination, filtration, photographic 5 techniques and other conventional means.

Example 11j Desolventization With Aqueous Surfactant Example I is repeated except that the concentration of resinous rubber in hexane is 7.14% and 5.0 phr of surfactant in the hot water is used. The 10 recovered resin/rubber is of fine particle size and free-flowing even when the bulk of the water is removed. To demonstrate the high surface area of this resin/rubber crumb and its porous nature, a water-wet sample of it is placed in a laboratory hood and after about 20 hours, 34% 15 of the original weight is lost. An additional 24 hours of air-drying resulted in a total 48% weight loss. Such losses upon simple air drying can only occur with very small particles of high porosity.

Example III: Desolventization With Aqueous Surfactant The techniques of Example I are repeated in a series of experiments in which the soap concentration in the hot water stripping reactor is varied from 1.5 to 2.0 and finally to 2.5 phr. The resin/rubber particles recovered using 1.5 phr of soap generally have average 25 particle sizes larger than the sample recovered using 2.5 phr of soap. The resin/rubber particles recovered using 2.0 phr soap have a uniform intermediate size. These results indicate that the size of recovered resin/rubber particles can be controlled to a significant extent by the 30 amount of soap added to the hot water solvent-stripping 2035 reactor. The greater the concentration of soap, the smaller the particle size rubber recovered. All resin/rubber particles from these experiments can be easily deresinated with hot acetone.

Example IV: Recovery of High-Resin Content Rubber This example demonstrates use of the invention with resin/rubber mixtures of very high resin-content. A resin/rubber hexane solution is obtained from hexane extraction of guayule shrub which contains 10.16% resin 10 and 12.19% rubber by prior analysis. The anticipated resin content of the resinous rubber, therefore, is 45.5% ((10.16/10.16 + 12.19) 100 = 45.5% resin).

Hexane is removed from the resinous rubber solution by using essentially the same technique used in 15 Examples I — 111; the soap concentration used is about 2.5 phr. The recovered resin/rubber particles are of very small size. It is observed that the particle size of the resinous rubber recovered is much smaller than that obtained in Example III where 2.5 phr of soap is used. 20 This difference suggests that the presence of a considerable amount of resin in the starting resin/rubber mixture does not significantly increase the amount of soap required to obtain small, high-surface resinous rubber particles. The resinous rubber spheres obtained are 25 easily deresinated via agitation in acetone to provide a rubber with a resin content of 2.07%.

This example demonstrates that the inventive process is effective using relatively high resin-content mixtures. These results are unexpected because of the 30 sticky nature of guayule resin. Because of this stickiness, it is expected that the resin/rubber mixture 2 0 35 would agglomerate and form a difficultly processable mass. Instead, it is found when the recovered particles are submerged in water and/or deresinating solvent, surprisingly they retain their physical integrity and can 5 be easily deresinated.

Example V: Processing of Resin/Rubber Misture from Aged Guayule Plants Cultivated guayule shrub approximately two years old is treated with hexane to simultaneously extract both 10 resin and rubber. Based on prior analysis, the shrub contained (on a dry basis) 5.54% resin and 2.37% rubber; therefore complete extraction would give a resin/rubber mixture containing 70.0% resin. Because of experimental difficulties, complete extraction of the resin and rubber 15 is not achieved. A resin/rubber mixture containing 43.6% resin is recovered. This mixture is processed by the general procedure of Examples I — 111 using 2.0 phr soap. The resinous rubber recovered is green in color and of relatively uniform spherical particle shape. The 20 spherical particles are relatively easily deresinated with hot acetone to provide a rubber containing 2.43% resin.

In summary, the Examples I-V demonstrate that resin/rubber mixtures typical of those obtained by conventional processing of guayule shrub can be treated by 25 the process of the invention to give relatively uniform, spherical resin/rubber particles. These particles are porous and can be effectively deresinated with a deresinating solvent such as acetone. ao350D

Claims (10)

WHAT WE CLAIM IS:

1. A process for separating rubber from guayule resin/rubber mixtures which comprises: (a) forming an aqueous suspension of spherical resin/rubber particles, at least 90% of which are 0.8-13 mm. in diameter; (b) extractively deresinating the particles with oxygenated resin solvent as hereinbefore defined on page 9; and (c) recovering the deresinated rubber, wherein the suspension is formed by removing organic solvent through vaporization from a solution of a resin/rubber mixture in the said organic solvent, said removal occurring in the presence of water containing at least one surfactant for aqueous systems.

2. The process of claim 1 wherein the organic solvent is at least one hydrocarbon of 5 to 9 carbon atoms. 15

3. The process of claim 2 wherein the surfactant is a soap of an organic carboxylic, sulfur-containing or phosphorous-containing acid having at least one straight chain of at least 6 carbon atoms and a mono-, di- or trivalent metal cation of a Group IA, IB, 20 IIA, IIB, IIIA or 11 IB metal of the periodic table.

4. The process of claim 3 wherein the acid is a carboxylic fatty acid of 12-20 carbon atoms and the metal is an alkali or alkaline earth metal.

5. The process of claim 4 wherein the 25 oxygenated resin solvent is ethanol, propanol (both isomers), acetone, or mixtures thereof.

6. The process of claim 1, 2, 3, 4 or 5 wherein the surfactant is present in a concentration of 0.25-10.0 parts per hundred parts resin/rubber 30 mixture. o\ «<\\\ •nil - 18 - Z0350D

7. The process of claim 1 wherein the resin/rubber mixture contains 25 to 90% rubber, at least 90% of the particles are 1.5-5.5 mm. in diameter, the oxygenated resin solvent is acetone, the organic solvent is at least one hydrocarbon of 5 to 9 carbon atoms or a mixture of at least 50% such hydrocarbon with acetone and .25-10.0 part surfactant per hundred parts resin/rubber mixture is present.

8. Guayule rubber containing less than 20% of guayule resin made by the process of claim 1.

9. Guayule rubber containing less than 20% of guayule resin made by the process of claim 7.

10. A process according to claim 1 substantially as herein described with reference to the Examples I - V. THE FIRESTONE TIRE & RUBBER COMPANY By Their Attorneys HENRY HUGHES LIMITED