Caustic Spending
The percentage of the original NaOH which has been consumed by the extraction reactions is known as
“spending.” Higher spending results in lower fresh caustic costs and smaller caustic disposal volumes.
Excessive caustic spending, however, has two important downsides. First, it increases the tendency for
caustic to carry-over into the hydrocarbon stream. Second, higher spending also leaves less margin for
maintaining the hydrocarbon product specifications when impurity levels swing outside of design limits.
For these reasons caustic spending should be kept as high as can safely contain the spikes or surges of
impurities seen during normal operations.