Mass Transfer and Hydrodynamic Aspects of Kinetics Studies in Light Oil Sweetening: A Review

Abstract

LPG (liquid petroleum gas) sweetening is a very important refining process in which mercaptans are extracted from LPG by caustic solution, resulting in mercaptide salts. Subsequently, these mercaptides are oxidized in the presence of air and catalyst to disulphides involving gas liquid (G‐L) reactions in an oxidizer. This review discusses design and operational aspects of a laboratory G‐L oxidizer which are essential for determination of intrinsic kinetic parameters of the mercaptide oxidation step. These kinetic parameters are subsequently used for scale‐up and design of grass root industrial scale oxidizers. The sweetening is categorized as a slow reaction. Hence, reaction takes place both in the film and the bulk. Transport of oxygen across the air to the aqueous alkaline phase in the oxidizer is critical and controlled by the liquid film mass transport term. Thus, oxygen transportation limitations need to be overcome and ensured before conducting kinetic studies. This paper fills the gap between laboratory reactor design and operational aspects by presenting a detailed review on chemical engineering analysis for maximization of the volumetric mass transfer coefficient using operational aspects of an agitated sparged G‐L reactor.

The Effect of Impeller–Sparger Geometry on the Gas Holdup in an Oxygen–Water System Using an Agitated and Sparged Tank Contactor

“…Volumetric mass transfer rates (K L S) are generally used to represent G-L mass transport rates across the G-L interfaces. 1,13 Accordingly, K L S, which is dependent on operating parameters, shown in eq 1, is expressed as a function of specific gassed power consumption (P g /V L ) and superficial gas velocity (u s ). 1,5 K S P V u…”

“…1,13 Accordingly, K L S, which is dependent on operating parameters, shown in eq 1, is expressed as a function of specific gassed power consumption (P g /V L ) and superficial gas velocity (u s ). 1,5 K S P V u…”

“…Consequently, G-L mixing enhancement by gas sparging and agitation is usually practiced to improve K L S. 1,2 Accordingly, an ASTC system consisting of a stirrer, sparger, and baffles is the desirable mode of contact for such applications. 2 In an ASTC, gas is introduced from a sparger beneath the impeller, and sparged bubbles are broken up by impeller action and uniformly dispersed throughout the system.…”

“…Previously Published Work. Five distinctive hydrodynamic regimes 1,4,6,7,11,12,18,19 in G-L systems have been characterized (Figure 1), and their descriptions are listed:…”

“…where exponent γ ranges from 3.92 to 5.06, α 1 ranges from 0.70 to 1.00, α 2 ranges from 2.11 to 3.02, β 2 ranges from 0 to 0.29, and θ ranges from 0.9 to 1.45. 1 From the discussions in section 1.2 above and eqs 3 and 4, mass transfer rates in G-L systems depend on both hydrodynamic conditions: ensuring intimate G-L contacting and vessel-impeller-sparger geometry. 1,4,15−17 We show that K L S is linearly reliant on ε g 4 and is, therefore, a reasonably sound basis for serving as an indicator of mass transfer rates.…”