June i, 1909.] 



l.IE INDIA RUBBER WORLD 



329 



recover more tlian 99 per cent, on each operation and will 

 concentrate to 99 per cent, purity. 



Those who are familiar with the working of rubber gums 

 know that no solvent can properly act on them without some 

 means whereby the gum is constantly stirred, torn, or re- 

 worked through rolls, or some means of constantly supplying 

 fresh surfaces of the gum to the solvent is provided. Patents 

 Ko. 821,716 and Xo. 821,717 were granted to F. C. Hood, of 

 Boston, in 1906, the first for a machine for washing rubber 

 and the second for a process of purifying rubber. These 

 patents were noted in The Indi.\ Rubber World at the time of 

 issue, though their object was not fully disclosed. 



The working of the two patents is similar. There is a set of 

 ordinary rubber washing rolls mounted in a watertight covered 

 casing and the "washing rolls are immersed in liquid, so that 

 the level of the liquid in the tank rises to a height above the 

 nip of the rolls so that the rubber as it passes tlic nip of 

 the rolls is flooded with the washing liquid . . . and the 

 sheet itself rises automatically toward the surface of the 

 liquid, where it pa.sses over and is caught by and carried 

 througli the rolls." The sheet is directed toward the roll.-; 

 by a spider wheel. The specification further says: "I use 

 the term 'liquid' because, while water alone is generally used, 

 it may be desirable to add chemicals to the water, or to sub- 

 stitute for the water other liquids having a specific solvent 

 or chemical eflfect."' A steam pipe allows the heating or 

 boiling of the liquid in the machine. 



One of the claims of the Hood process patent reads; "The 

 herein described process of purifying rubber, which consists 

 in passing it between co-acting rolls while submerged in the 

 purifying liquid, and automatically returning the sheet issu- 

 ing from the rolls to the nip of the rolls for a fresh pass, 

 substantially as described." 



It is plain that the Hood apparatus is well adapted to the 

 treatment of rubber gums for deresination by solvents which 

 do not attack the rubber, and that, with the enclosed tank 

 containing the rolls and having automatic means of feeding, 

 such solvents as alcohol and acetone can be thoroughly 

 contacted with the rubber while heated and without loss of 

 the solvents. It is understood that this apparatus is now in 

 successful operation. 



It is to be observed that at the present time acetone is used 

 almost universallj' as the solvent in deresinating rubber. 

 While the resins may be completely removed by this process, 

 yet as acetone will, while hot, dissolve, for example, only 

 18 per cent, of Pontianak resin, a large amount of the solvent 

 must be used and it must be kept hot, or the resin will crystal- 

 lize out. Acetone is also rather expensive, and even a slight 

 loss of such valuable material becomes worth considering. 

 Moreover, the crude and unsystematic methods of applying 

 the solvent to the rubber required that much more than the 

 theoretical amount be used to obtain an extraction anywhere 

 near complete. 



The writer's attention, therefore, was directed to finding, 

 if possible, cheaper and more efficient solvents and a more 

 methodical method of application, combined with the most 

 complete recovery of the solvents for reuse. It was found 

 that the esters of methyl and ethyl alcohol were better 

 solvents than acetone for the resins, while not attacking the 

 gums. These esters can also be produced cheaper than 

 acetone. E.xperiments showed that while only 18 per cent. 

 of resin was dissolved by acetone, methyl acetate would dis- 

 solve 25 per cent., and ethyl acetate would dissolve 50 per 

 cent, resins. 



The discovery that these esters were excellent resin sol- 

 vents was considered valuable, and it was sought to protect 

 the discovery through patents No. 845,616 and No. 890,217, 

 while the methodical treatment which secured a good ex- 

 traction, and the methods of complete solvent recovery which 



made the economical operation of the process possible, were pro- 

 tected by patent No. 890,216. 



This invention relates (l) to a method of extracting im- 

 purities from crude rubber by certain compound solvents 

 exercising selective action upon certain constituents, and used 

 in regulated amounts and in a regulated way, and (2) to an 

 apparatus comprising structures adapted to selectively extract 

 various impurities from rubber. The apparatus comprises a 

 series of extractors provided with heating means and in- 

 ternally with masticating devices. The solvent is admitted 

 to the extractors successively with a view to treating the 

 rubber in each four or more times, the nature of the solvent 

 undergoing a change in its constituent parts as it passes 

 through the apparatus during the various steps of treatment. 

 Four steps are usually desirable, two for drying the rubber 

 and two for removing the remaining impurities. With a bat- 

 tery of five extractors, four may be in use at one time while 

 the fifth is being charged or discharged. The apparatus 

 einbraces means of introducing the solvent and for its re- 

 covery later, and also for the wilhdraw.il of tlie matters 

 removed from the rubber. 



This process allows of the treatment direct of crude rub- 



^ lyj 



Chute's I^eresination System (Patent No. 820,316.) 

 In the center is shown a battery of fine extractors, with macerating 

 apparatus, and connected to three kettles at the bottom into which the resin 

 laden solvent is run. The kettles are connected to refining columns on the 

 right, in w-hich the solvent vapor arising from the steam heated kettles 

 is purified and condensed, passing to storage tanks shown at the top on the 

 left. The circulating jnimp is shown at the bottom [on the left]. 



bers without drying, and it has been found cheaper to re- 

 move the tvater by the use of solvents than by drying in any 

 of the ordinary ways. It is believed that this process repre- 

 sents the best practice at the present day. 



As to cost of operation and products: Assuming that Ponti- 

 anak can be bought for 5 cents per pound, and that it will 

 yield one pound of purified gum from 10 pounds of the crude 

 raw-, then the materials' cost for rublier will be 50 cents 

 per pound for the finished product. If one gallon of solvent 

 per pound of crude gum is used, and the solvent is worth 

 75 cents per pound, and the loss is i per cent., then the cost 

 for loss of chemicals calculated on the finished product 

 would be 7.5 cents per pound. The cost for labor and other 

 factory costs cannot be figured closely imless the particular 

 factory conditions are known, but with a moderate sized 

 ])lant the factory costs should not exceed 5 cents per pound 

 of finished product. This would give a total cost per pound 

 of purified gum of 62.5 cents per pound. This is a wide dif- 

 ference from the price at which the higher grades of rubbers 

 are selling, and it must be remembered tha.t this finished 

 product must be compared with the washed and dried product, 

 as there is no further shrinkage before use. 



