CHAPTER III. PRODUCTION OF CREOSOTE FROM TARS. 



In commercial practice creosote is to a considerable extent a by- 

 product of the manufacture of other materials. The details of the 

 process, therefore, vary somewhat with the end product obtained. 

 The process of manufacturing creosote consists, essentially, of the 

 distillation of the tar and is in general the same, no matter what 

 the end products may be. 



The size and shape of the stills used for the purpose of commercial 

 distillation vary somewhat according to the needs of the producer. 

 In England and Germany, according to Lunge {10) and Warnes ill), 

 the vertical still with a concave-upward bottom is preferred. Figure 

 9, taken from Lunge's Coal Tar and Ammonia, shows a cross-section 

 of a 25-ton vertical still. Many stills of this general design are used 

 in this country, but the horizontal still is more common. Figure 10 

 shows a battery of horizontal stills in use in this country. 



The stills are filled to the proper level with crude or settled tar, 

 preferably already heated by means of a preheater, and a slow fire is 

 started under the still. In the early stages of the distillation extreme 

 caution must be exercised, because most coal tar contains water, which 

 can not readily be separated by standing. Too rapid heating will 

 cause foaming or priming, with a loss of nearly the entire contents, 

 unless the priming can be controlled. 



In the United States it seems to be considered good practice to 

 stir the contents of the still by using either air or steam, the former 

 being preferred. This stirring aids in the prevention of foaming 

 over during the early part of the distillation and results in a more 

 rapid distillation when it is produced during the latter part of the 

 process. A slight chemical reaction is also probably obtained. In 

 Europe it is customary to inject steam into the still during the dis- 

 tillation of the anthracene oil. The number and graduation of 

 fractions taken from coal tar depend largely on the markets for the 

 various products. Warnes {11), an English writer, states that by far 

 the greatest amount of tar distilled is divided into the following 

 fractions: Crude naphtha, light oil, carbolic oil, creosote oil, anthra- 

 cene or "green oil," and pitch. Lunge {10), in general, makes the 

 same separation and gives the following temperatures as the cutting 

 points of the various fractions: 



Crude naphtha Up to 105° or 110° C. 



Light oils From crude naphtha up to 165° or 210° C. 



Carbolic oils From light oil to 230° or 240° C. 



Creosote oil From carbolic oil to 270° C. 



Anthracene oil Above 270° C. 



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