328 



THE INDIA RUBBER WORLD 



[June i, 1909. 



The Deresination of India-Rubber — II. 



By H. O. Chute. 



AMONG the earliest American patents in relation to the 

 deresination of rubber are those using processes which de- 

 pend on the action of alkali on the resins. No. 756 and 

 No. 757, issued to Austin G. Day, June 12, 1859, are a 

 reissue of patent No. 15,067, issued June 10, 1856. The patent 

 specification describes a process of purifying rubber gums by 

 treating them with alkaline solutions, but resins are not men- 

 tioned as being contained in rubber. In 1857 Robert Haerting 

 received patent No. 17,214 in which he states: "My invention 

 consists in submitting gutta-percha to the action of an alkaline 

 liquor, which dissolves out the etheric oil," which probably refers 

 to the resins. In 1893 a patent was granted to Paul Biersdorl, 

 (No. 508,560), for a process of treating gutta-percha, in whicU 

 the gutta was deprived of "the whole of its resinous contents by 

 solution in alcohol." The process of deresinating gutta-percha 

 seems to have been well known and largely practised in England 

 in 1897, for in that year in one of the "Cantor" lectures, pub- 

 lished in the Journal of the Society of Arts (December 6) there is 

 a good description and illustration of a deresinating plant. The 

 solvent used seems to have been cold gasoline. In igoi United 

 States patent No. 673,570 was issued to E. F. V. Wilmonsky for 

 a process of refining gutta-percha which consisted in dissolving 

 the entire gum in hot gasoline and cooling to 60° P., when, it i.^ 

 said, if four gallons of naphtha or more had been used for each 

 pound of gum, loose precipitate formed which consisted of 

 pure gum. 



It was not until 1903, however, that any patents for the extrac- 

 tion of resins from caoutchouc had been granted in the United 

 States, but in that year patent No. 741,260 was granted to Wil- 

 liam .^ppleton Lawrence, which patent was for a process of 

 treating crude rubber with alcohol. In the specification the 

 crude rubber referred to is guayule, which has been obtained 

 from the wood by extraction with naphtha and contains some 

 naphtha as an impurity. The extracting plant involved [see Th£ 

 Indi.\ Rubber World, October i, 1905 — page 3] consists of a 

 "chum," which is provided with a corrugated bottom, and cor- 

 rugated rollers passing over it, which serve to masticate the 

 gum in presence of the solvent. The saturated solvent is n- 

 moved to a still, and the solvent evaporated and condensed in a 

 condenser. The alcohol and naphtha are separated and run into 

 various tanks for reuse. 



The first claim of this patent covers "the process of refining 

 crude rubber gum, which consists in subjecting the gum to the 

 action of alcohol, which forms a solution of resin and naphtha 

 and alcohol, then evaporating the alcohol and naphtha and alcohol 

 from the resin, then condensing the vaporized alcohol and 

 naphtha and separating the same." It is to be observed that this 

 claim presupposes the presence of naphtha in the rubber, as 

 otherwise the steps relating to its separating could not be carried 

 out. This claim does not specifically state that the solution is 

 to be separated from the gum before evaporation, and in a 

 patent claim each step should be specifically mentioned. Clai;n 

 No. 2 covers "a process of refining crude rubber gum consist 

 ing in agitating the gum in alcohol, then vaporizing the alcohil 

 from the gum, and tlien refrigerating to separate the alcohol 

 from by-products." 



Here it is specifically stated that the alcohol is to be removed 

 from the gum by evaporation or vaporization, and while this 

 process would perhaps remove the naphtha, it would not remove 

 the resins. It may be mentioned here that alcohol is a poor sol- 

 vent of the resins when compared with acetone, and while this 

 process has been largely worked in the past, and while purified 



guayule is now on the market produced by this process, the sol- 

 vent used is acetone instead of alcohol. This patent may be 

 taken as representative of the processes which follow the analyti- 

 cal method which consists in dissolving up the entire gum in a 

 rubber solvent and then precipitating the gum by the addition of 

 a solvent in which the gum is insoluble. 



As representative of that class of processes which are sim- 

 ilar to the analytical methods which extract the resin by a 

 solvent which does not affect the gum, but leaves it in its 

 original condition, there may be cited United States patent 

 No. 821,934, issued in 1906 to Archie P. Eves, for "Process 

 of Treating Gum." This process involves the use of an ap- 

 paratus consisting of three distinct parts, with different func- 

 tions. First is a base, which is a vessel with a steam coil 

 for heating and evaporating the volatile solvent and removing 

 the resin. The vapors pass up to a car, which is rolled out- 

 side and filled with rubber and rolled back into the extract- 

 ing vessel. This car contains stirring arms, which are 

 worked by attaching a shaft and pulley. The hot vapor goes 

 to the top after heating the car and rubber, and is condensed 

 by the cooling coils and drips down into the car, dissolving 

 the resin. Claim 5 of this patent reads: 



"A method of purifying rubber which consists in passing 

 alcoholic vapors through and around the material to be 

 treated to a condenser, and at the same time causing the con- 

 densed solvent to descend through the rising vapors upon 

 the gum, whereby the heat of the vapor is utilized and the 

 gum and solvent made to undergo treatment at as high a 

 temperance as is practicable." It is stated in the specifica- 

 tion that acetone is the preferred solvent. 



Dr. Weber says ["Chemistry of India-Rubber," page 240]: 

 "I very much prefer a form of extractor in which an inner 

 tube which receives the thimble (containing the gum) fits 

 into an inner jacket so that there remains a free annular 

 space between them, through which the vapor of the extract- 

 ing liquid may pass up into the reflu.x condenser, thus keeping 

 the material to be extracted always at the temperature of the 

 boiling liquid." On page 239 he speaks of the alcoholic 

 solvents but states that "acetone is, however, the solvent 

 which is free from any objections." As this publication was 

 made in 1902 it would seem to be an anticipation of the claim 

 of the Eves patent already quoted. 



This patent is, however, the basis of several atttcmpts to 

 purify rubber by the processes which extract the resin by a 

 solvent which in no way affects the gum, and at least one 

 large plant was erected under it and is now in successful 

 operation, having treated several hundred tons of crude 

 rubbers and used it successfully, and presumably at a 

 profit. 



But it is a fact that most of the solvents for rubber resins 

 which will not dissolve the gums also are liquids which are 

 soluble in water and cannot be separated therefrom without 

 elaborate separating machinery, and all the crude gums, no 

 matter how well dried, still contain some water, and after 

 repeated use these solvents become so charged with water 

 that they will not further dissolve the resins, so that if used 

 in the apparatus suggested by the Eves patent it is necessary 

 to dry the rubber most carefully, and then to have another 

 apparatus which will separate the water from the solvent and 

 at the same time work with a minimum loss. Such an ap- 

 paratus, installed by the writer, will in the case of acetone 



