Glyoxal and glyoxylic acid production

Glyoxal (ethanedial) (C2H2O2) is produced from oxidation of acetaldehyde (ethanal) (C2H4O) with concentrated nitric acid (HNO3). Glyoxal can also be produced from catalytic oxidation of ethylene glycol (ethanediol) (CH2OHCH2OH). Glyoxal is used as a crosslinking agent for vinyl acetate/acrylic resins, disinfectant, gelatine hardening agent, textile finishing agent (permanent-press cotton, rayon fabrics), wet-resistance additive (paper coatings) (Ashford, 1994; p.454).

Glyoxylic acid is produced by nitric acid oxidation of glyoxal. Glyoxylic acid is used for the production of synthetic aromas, agrochemicals and pharmaceutical intermediates (Babusiaux, 2005; p.1).

The basic reaction equation for the production of glyoxal from acetaldehyde is:

2C2H4O (Acetaldehyde) + 2HNO3 ^ 2C2H2O2 (Glyoxal) + N2O + H2O

The stoichiometric relationship indicates that complete reaction will result in 0.543 tonnes of N2O per tonne of glyoxal. Under commercial conditions, the yield of N2O per tonne of glyoxal is approximately 0.52 tonnes (Babusiaux, 2005; p.1).

Glyoxylic acid production is a batch process where nitric acid is reduced to NO and N2O with NO recovered as HNO3 in the process. N2O arises in the production process through a secondary reaction where glyoxal is converted to oxalic acid (COOH)2.

Default factors for glyoxal and glyoxylic acid production are shown in Table 3.6. Emissions can be estimated using the same approach as described in the foregoing for caprolactam. To use default destruction factors, inventory compilers should verify that the abatement technology is installed at individual plants and operated throughout the year.

Table 3.6

Default factors for glyoxal and glyoxylic acid production

Product

N2O Generation Factor

N2O Destruction Rate

N2O Emission Factor

Uncertainty

(tonnes N2O/tonne)

(%)

(tonnes N2O/tonne)

(%)

Glyoxal

0.52

80

0.10

±10

Glyoxylic acid

0.10

80

0.02

±10

Source: Babusiaux (2005)

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