Diisopropanolamine systems

Diisopropanolamine Systems. Diisopropanolamine (DIPA) is a secondary amine used in the Shell ADIP process to sweeten natural gas. DIPA systems are similar to MEA systems but offer the following ad an-tages carbonyl sulfide (COS) can be removed and regenerated easily and the system is generally noncorrosive and requires less heat input. 

These theoretical results are confirmed experimentally. In attempts to prepare a resin with a ratio of the starting materials of HHPA diisopropanolamine 2.3 1 the mixture gelated. This is reflected in Scheme 1, example 1 (n = 2). If a ratio of HHPA diisopropanolamine 3.2 1 is chosen (Scheme 1, example 2, n = 5/6), the system does not gelate. By GPC analysis it was verified that the theoretical assumptions made in Scheme 1 are valid for this system. Besides the hyperbranched material, the presence of hexahydrophthalic acid is demonstrated. The quantity of the acid is in close agreement (29 %) with the calculated value (28%). 

A minor variant to the amine scrubbing process described above is the Sulfinol process, which still uses an alkanolamine base, diisopropanolamine (35%), but in a solvent consisting of a mixture of sulfolane (40%), tetramethy-lene sulfone (CH2)4S02, a good hydrogen sulfide solvent) and water [29]. Other processes are based on hydrogen sulfide absorption in aqueous alkaline carbonate solutions, such as the Catacarb and Benfield systems (Eqs. 9.16 and 9.17). 

The Sulfinol gas conditioning process of Shell uses diisopropanolamine in a sulfolane solvent system. This system also increases gas capacity with improved efficiencies (152). 

As coabsorption of CO2 leads to an increase in the size of the combined Claus and Scot system, it might be desirable to remove H2S as selectively as possible. Selective amine solutions are therefore used, normally diisopropanolamine (Dipa), or methyl-diethanolamine(MDEA) if CD2 contents are very high. 

The simultaneous absorption of two gases that react with the solvent at different rates has been studied by Ouwerkerk. The specific system which he selected for analysis was the selective absorption of HjS in the presence of CO2 into amine solutions. This operation is a feature of several commercially important gas purification processes. Bench scale experiments were conducted to collect the necessary pi sico-chemical data. An absorption rate equation was developed for H2S based on the assumption of instantaneous reaction. For CO2 it was found that the rate of absorption into diisopropanolamine (DIPA) solution at low CO2 partial pressures can best be correlated on the l is of a fast pseudo-first-order reaction. A computer program was developed which took into account the competition between H2S and CC>2 when absorbed simultaneously, and the computer predictions were verified by experiments in a pilot scale absorber. Finally, the methodology was employed successfully to design a large commercial plant absorber. 

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