Batch Fractionation (1855-1880)

Batch Fractionation (1855-1880)

In the first refineries of the United States, Pennsylvania crude was easily distilled to produce kerosene for lamps (which burned cleanly without producing much smoke because of the paraffinic composition of Penn crude) and lubricating oil for steam engines. Lighter fractions obtained from distillation such as naphtha, propane, and butane were largely considered a nuisance and were flared for disposal because of their high vapor pressure and low flash points that would cause difficulties with storage. Figure 11.1 shows a typical batch distillation process in early refineries of the 1850s used primarily to produce kerosene, labeled as “product” from the separator in the diagram. For the distillation process, crude oil feed was filled into a kettle heated by burning gas, or other fuels in a fire box and the residual tar was removed after the distillation was over. The Dephlegmator Tower worked as a distillation column and as the crude boiled in the still, the vapor fraction from the dephlegmator was condensed and sent to the separator [2]. The separated kerosene fraction often went through a second distillation process to control the flash point for the safe use of fuel in lamps and reduce odor. The residue fraction was also distilled using vacuum to produce lubricating oil and grease for the steam engines and wax for making candles.

Charging the kettle with crude oil and emptying the residue left over from distillation took a lot of time and effort, making the batch distillation highly inefficient. In most cases, the recovered overhead fraction was fed back to the same still to drive off more hydrogen sulfide and lighter fractions to control the flammability (flash point) of kerosene. Driving off hydrogen sulfide and other light sulfur species also reduced the odor of kerosene and of the products obtained from burning kerosene in gas lamps. As the demand increased for kerosene, the refiners began to use two stills, one for the first fractionation of a kerosene cut and the second one to redistill the kerosene for purification. Using two stills in series marked the beginning of the continuous stills [2].

Figure 11.1. An early batch distillation process to produce primarily kerosene as product [2].