15Design 2 Input-Output Structure.pdf

DESIGN METHODOLOGY II:
INPUT-OUTPUT DECISIONS
GOAL -- Choose the process chemistry and
feedstock most appropriate to the plant to be
designed and determine the associated
economic potential.
11/19/99 Input-Output Structure 1
BASIC LEVEL II DECISIONS
u Choice of reaction chemistry
u Choice of raw material feedstocks
u Determination of need for vapor recycle
u Evaluation of economic potential for process
11/19/99 Input-Output Structure 2
CHOICE OF REACTION CHEMISTRY
The choice of reaction chemistry involves the following
considerations:
u Source of the chemistry to be employed
ð Developed in-house
ð Freely available (patents expired)
ð Available only through a license
u Availability of feed stocks
u Choice of process type
u Environmental considerations
11/19/99 Input-Output Structure 3
EXAMPLE #1
Chemistries available to manufacture Vinyl chloride (from
Seider et al, Process Design Principles)
uDirect chlorination of Ethylene
C2H4 + Cl2 --> C2H3Cl + HCl
(Only half the Cl2 converted to vinyl chloride)
u Thermal cracking of Dichloroethane via
Oxychlorination of Ethyelene
C2H4 + 2HCl + 1/2 O2 --> C2H4Cl2 + H2O
C2H4Cl2 --> C2H3Cl + HCl
(Uses HCl instead of Cl2, but requires two reaction steps)
11/19/99 Input-Output Structure 4
EXAMPLE #1 (Cont’d.)
u Balanced Process for Chlorination of of Ethylene
C2H4 + Cl2 --> C2H4Cl2
C2H4 + 2HCl + 1/2 O2 --> C2H4Cl2 + H2O
2 C2H4Cl2 --> 2 C2H3Cl +2 HCl
(Converts all Cl atoms to Vinyl Chloride)
11/19/99 Input-Output Structure 5
EXAMPLE #2
Chemistries available for the manufacture of maleic
anhydride:
u From benzene
C6H6 + 3 1/2 O2 --> <(.CHCO)2>O + 2 CO + 2 H2O
C6H6 + 4 1/2 O2 --> 6 CO2 + 3 H2O
u From butane
C4H10 + 3 1/2 O2 --> <(.CHCO)2>O + 4 H2O
C4H10 + 4 1/2 O2 --> 4 CO + 5 H2O
C4H10 + 6 1/2 O2 --> 4 CO2 + 5 H2O
11/19/99 Input-Output Structure 6
EXAMPLE #2 (Cont’d.)
u Maleic Anhydride from Benzene
ð High selectivity at plete conversion - no
recy