Reactive Absorption Technology - Process Intensification for Green Chemistry - page 291

11.4.2 Sour Gas Treatment

Natural gas and other industrial gases containing hydrogen sulfide (H 2 S) are called sour
gases. As H 2 S is a known poison that leads to catalyst deactivation, its removal from sour
gases is crucial to natural gas processing and to gas cleaning for the synthesis of ammonia
and methanol. Petroleum refining is a major source of sour gas with low concentrations of
CO 2 . Another key application of the sour gas treatment is in coke oven gas purification. The
gas, produced during the carbonization of coal to form coke, consists mainly of CO, H 2 ,
CH 4 ,H 2 S and CO 2 - but it is also contaminated with other components that must be
removed. Sour gases are industrially cleaned using a similar amine scrubbing process, as
previously described (Figure 11.2, right).
The most widely used amines for sour gas treatment are MEA (10-20% concentration),
DEA (10-30%), di-isopropanolamine (DIPA) (30-50%), N-MDEA (30-50%) and digly-
col amine (DGA) (40-70%) [28]. Sour gas removal can also be carried out using hot
potassium carbonate or the Benfield process [27]. In the purification of coke oven gas
contaminated with various substances, an aqueous ammonia solution is usually used as a
solvent. 'Ammonia hydrogen sulfide circulation scrubbing' is also applied in industry for
coke oven gas purification [24].

11.4.3 Removal of Nitrogen Oxides

Nitrogen oxide is a highly reactive gas that contains varying amounts of nitrogen and
oxygen. NO x is formed during the combustion of fuel at high temperatures. According to
Chung et al. [29], the primary sources of nitrogen oxides are transportation (61%), the
energy industry (18%), the chemical processing industry (14%) and others (7%). The
applied removal processes can be subdivided into dry processes (catalytic or noncatalytic
denitrification) and wet processes (which make use of water or aqueous nitric acid for NOx
scrubbing in RA columns). Note that the wet process based on RA is also used for the
production of nitric acid, described in a later section. During NOx absorption, the following
main reactions in gas- and liquid-phase occur [24]:

2NO þ O 2 ! 2NO 2 ð gas phase Þ (11.3)

2NO 2 ! N 2 O 4 ð gas phase Þ (11.4)

þ

NO 2 !

ð Þ

NO N 2 O 3 gas phase (11.5)

2NO 2 þ H 2 O ! HNO 3 þ HNO 2 ð liquid phase Þ (11.6)

N 2 O 4 þ H 2 O ! HNO 3 þ HNO 2 ð liquid phase Þ (11.7)

N 2 O 3 þ H 2 O ! 2 HNO 2 ð liquid phase Þ (11.8)

3 HNO 2 ! HNO 3 þ H 2 O þ 2NO ð liquid phase Þ (11.9)

2NO þ 3H 2 O 2 ! 2 HNO 3 þ 2H 2 O ð liquid phase Þ (11.10)

HNO 2 þ H 2 O 2 ! HNO 3 þ H 2 O ð liquid phase Þ (11.11)