June 1, 1916.] 



THE INDIA RUBBER WORLD 



471 



After the gas has been cooled to the required temperature, 

 it is admitted into the benzol washers, where it is brought into 

 intimate contact with wash oils which at low temperatures are 

 capable of dissolving out of the gas all the constituents, which 

 go to make up what is commercially known as crude or 50 per 

 cent benzol. The wash oil containing the benzol will again 

 release these constituents after being heated to about 266 degrees 

 F., and further separation takes places by distillation. 



Scrubbing or VV.\shi.\c. — The wash oil, called "straw oil" at 

 the works, is a petroleum product which is virtually a light ma- 

 chine oil. free from water, having a low naphthalene content, 

 and a Hash point of 300 degrees F.. or more. The gas is passed 



E.xzoL Stills. 



through one or more water tanks, then through several scrub- 

 bers, consisting of tall iron towers, through which the gas 

 passes upward and encounters a downflow of straw oil. The 

 oil may be sprayed, or spread out over the hurdles or trays 

 contained in the towers. By thorough scrubbing it is possible 

 to remove practically all of the benzol, etc., from the gas. 



The scrubbed gas is passed through a drip tank, and then 

 sent to the gas manufacturing division of the works to be 

 burned under the ovens, sent to gas enriching plant or direct 

 to gas holders. The saturated wash oil, or "charged oil," is 

 delivered to near-by storage tanks, from which it is pumped to 

 a storage tank on the roof of still house at the recovery plant. 



ExTR.ACTiNG OR RECOVERY. — The processes in this plant are 

 essentially the heating of tjie wash oil to drive off the absorbed 

 benzol constituents, the recovery and cooling of the wash oil, 

 and the separation by distillation of these benzol constituents to 

 a greater or less degree. There may or may not be present 

 an elaborate rectification plant for recovering benzol of 90 per 

 cent or more purity. In the ordinary separation of a light oil, 

 or primary oil, 80 per cent benzol may be attained, and the 

 secondary or heavy oil will contain toluol, xylol, etc. These 

 oils may be shipped away for further refining at the plant 

 where they are to be used. 



The detailed methods of recovery vary, and an exact account 

 of any one plant would not apply to all. The process is rather 

 involved, but the fundamental features are about as follows: 



In order to use as small an amount of steam as possible for 

 heating the charged oil, methods of preheating are used. The 

 cold wash oil enters a preheater, where it is heated to about 

 175 degrees F., by benzol and steam vapors issuing from the 

 still. This oil now passes through a second preheater in which 

 it is preheated to a temperature of about 212 degrees F., by 

 means of the hot debenzolizcd wash oil issuing from the still. 

 The lighter products of benzol begin to vaporize and leave the 

 oil. It is then heated to about 266 degrees F., by means of live 

 steam in one of the superheaters, for the purpose of driving off 

 the water contained in it and thus rendering it possible to sepa- 

 rate the naphthalene. The naphtlialene is washed from the gas 



and absorbed by the oil in a manner similar to washing out 

 benzol in the scrubbers. 



.■\t the temperature of 266 degrees F., in the superheater, all 

 benzol, toluol and water is expelled, and the oil with its remain- 

 ing burden, x.\ lol, solvent naphtha and naphthalene, now enters 

 the still. The oil flows through the lower portion of this ap- 

 paratus, the steam being lilowii directly into the lowest part of 

 the still, thence traveling in a direction counter to that of the 

 oil, thus driving oflf all xylol, solvent naphtha, and most of the 

 naphthalene from the wash oil. 



The resultant mixture of benzol and water vapors passes 

 through the upper portion of the still, where crude rectification 

 is performed and where all entrained wash oil particles are sep- 

 arated from the vapors. The benzol and water vapors issuing 

 from the superheater enter the upper portion of the still, where 

 they are rectified in conjunction with the other vapors. 



These vapors now issue from the top of the still at a tem- 

 perature of about 220 degrees F., and enter the first superheater, 

 previously mentioned, where they are nearly all condensed and 

 the wash oil receives a preliminary heating. The remaining 

 vapors and the condensates formed in the superheater then en- 

 ter a water cooler, where the vapors are completely condensed^ 

 and all condensates, water and light oils, enter a separator on 

 decanter, where they are separated due to their difference in, 

 specific gravity. 



The wash oil, which has been freed from benzol, etc., leaves 

 the still at a temperature of about 257 degrees F., and enters the, 

 superheater previously referred to, where it transfers a portion; 

 of its heat to the charged wash oil, after which it enters the oil 

 cooler, where it is cooled by water to a temperature below 17 

 degrees F. It may pass over a series of circulation coils through 

 wliicli cnld water is passing, arranged nne alune the •nhcr ver- 



Tar Extractors and Gas E::hai 



on tlie left are bell washers for remo 

 e elevated tanks arc for liquor storage 



nd feed. 



tically: the oil flows down over the whole coil, being caught in a 

 trough at the bottom. 



A further distillation may take place and the various benzol 

 products be separated and sent to their respective storage tanks. 

 Purification of benzol, etc., is accomplished by washing with 

 sulphuric acid, caustic soda, and washing and then distilling, for 

 ,T final separation of the products, in their desired state of purit}'. 

 This is generally done, where necessary, at the plant using these 

 materials. I' rom the usual by-product coke oven gases, about 

 the following proportions of hydrocarbons are recovered : 

 Benzol 67 per cent, toluol 16 per cent, xylol 8 per cent, and 

 solvent naphtha 9 per cent. 



The United States Geological Survey reports 14.000.000 

 gallons benzol and other light oils produced in the I'nited 

 States in 1915. In connection with these oils 761,256 pounds 



