Question

HCFC-123 (CHCl2CF3) has been proposed as a substitute for CFC-11 (CFCl3). How would you expect the following environmental properties of HCFC-123 to compare to those of CFC-11 (i.e., are they greater or less than and why):

(a) tropospheric lifetime?
(b) ozone depletion potential (ODP)?
(c) contribution to warming of troposphere (greenhouse gas properties)?
In each case, explain why the property would be greater or less than what it is for CFC- 11.

Answer 1

Answer:

(a) tropospheric lifetime

HCFC-123 is heavier / more dense, so will stay at higher concentration in the troposphere for any tonnage vented. But is more bioavailable too.

(b) combustibility

HCFC-123 will be more flammable, due to the presence of the carbon-carbon bond, and the not-completely bonded carbon atom (the carbon with the chlorines, has only 3 or 4 bonds formed. Will also be more bioavailable.

c) ODP-

Compounds such as CHCl2CF3 (HCFC-123) and CHClFCF3 (HCFC-124) are being used in commercial refrigeration units and have much shorter atmospheric lifetimes than the chlorofluorocarbons they replace. The HCFC-123 and HCFC-124 model-calculated atmospheric lifetimes of 1.3 years and 5.8 years are much shorter compared to the 45 years of CCl3F (CFC-11).

d) greenhouse gas properties

HCFC-123 reduces carbon dioxide (CO2) emissions, develop capture and storage technologies (CCS), as well as direct carbon dioxide removal (CDR) from the atmosphere.