CHE446: Chemical Process Design and Simulations
Batch: FA17-CHE Section: A
Name: Roll No.: FA17-CHE-
Date Assigned: April 30, 2021
Due Date: June 04, 2021
Instructor: Engr. M. Haris Hamayun
Assignment Statement
Question # 1 (CLO # 4, C6, PLO # 3): (10 + 10 + 10)
Fig. 1: Outline of phthalic anhydride flowsheet
Phthalic anhydride is an intermediate for the plastics industry, which is manufactured by
the controlled oxidation of o-xylene or naphthalene. The most common route uses o-xylene. The
following reactions take place in the setup:
Main Reaction: C8 H10 + 3O2 = C8 H4 O3 + 3H2 O
Side Reaction: C8 H10 + 5⁄2 O2 = 8CO2 + 5H2 O
The reaction uses a fixed-bed vanadium pentoxide–titanium dioxide catalyst that gives
good selectivity for phthalic anhydride, providing the temperature is controlled within relatively
narrow limits. The reaction is carried out in the vapour phase with reactor temperatures typically
in the range 380 to 400 °C. The reaction is exothermic, and multi-tubular reactors are employed
with direct cooling of the reactor via a heat transfer medium. Various heat transfer media have
been proposed to carry out the reactor cooling, such as hot oil circuits, water, sulfur, mercury, and
so on. However, the favoured heat transfer medium is usually a molten heat transfer salt, which is
a eutectic mixture of sodium-potassium nitrate–nitrite. The process flowsheet for o-xylene
production is presented in Fig. 1.
Air and o-xylene are heated and mixed in a venturi, where the o-xylene vaporizes. The
reaction mixture enters a tubular catalytic reactor. The heat of the reaction is removed from the
reactor by recirculation of molten salt. The temperature control in the reactor would be difficult to
maintain by methods other than molten salt. Heat is removed from the molten salt by generating
high-pressure steam. The gaseous reactor product is cooled first by boiler feedwater before
entering a cooling water condenser. The cooling duty provided by the boiler feedwater has been
fixed to avoid condensation. The phthalic anhydride forms a solid on the tube walls in the cooling
water condenser and is cooled to 70 °C. Periodically, the on-line condenser is taken off-line, and
the phthalic anhydride melted off the surfaces by recirculation of high-pressure hot water. Two
condensers are used in parallel, one on-line performing the condensation duty and one off-line
recovering the phthalic anhydride. The non-condensable gases contain small quantities of
byproducts and traces of phthalic anhydride and are scrubbed before being vented to the
atmosphere.
The crude phthalic anhydride is heated and held at 260 °C to allow some byproduct
reactions to go to completion. Purification is by continuous distillation in two columns. In the first
column, maleic anhydride and benzoic and toluic acids are removed overhead. In the second
column, pure phthalic anhydride is removed overhead. High-boiling residues are removed from
the bottom of the second column. The reboilers of both distillation columns are serviced by a fired
heater via a hot oil circuit. Various hot and cold utilities are available within the plant premises,
i.e., for hot (saturated steam, superheated steam, furnace oil), and cold (water, air, and refrigerant).
Your general manager (GM plant) has called a meeting to discuss the process flow diagram
of the process. After a detailed meeting, the manager wants the process engineering department to
work on this flowsheet and make a comparatively efficient design. In this regard, being the head
process engineering department, you are assigned the task to do the heat exchanger networking to
see its impact on the overall process.
You are required to do a comprehensive literature review to find the parameters, which
are important towards process improvement – heat exchanger networking. Based on the literature
review, you are required to design the heat exchanger networks (do hand-written
calculations/design and use Aspen Energy Analyzer to depict the design).
Question # 2 (CLO # 3, C4, PLO # 2): (05 + 05)
With reference to the calculations performed in Question # 1, analyze the system, and
identify the best network design. Furthermore, you are required to identify the value of the
parameter(s) at which the problem is turned from threshold to pinched.
Groups Detail:
Groups Students Names and Registration Numbers
Asif Alvi (FA17 – CHE – 004)
Muhammad Shoaib (FA17 – CHE – 045)
A1
Ahsan Khan (FA17 – CHE – 087)
Aakash Shabbir (FA17 – CHE – 106)
Rana Gohar Naeem (FA17 – CHE – 08)
A2 Ghufran Arif (FA17 – CHE – 014)
Muhammad Abdullah (FA17 – CHE – 091)
Muhammad Sufyan (FA17 – CHE – 028)
A3 Muhammad Hamza (FA17 – CHE – 039)
Muhammad Sohaib Maqsood (FA17 – CHE – 077)
Syed Ashmal Hashmi (FA17 – CHE – 015)
A4 Ali Irfan Khan (FA17 – CHE – 053)
Muhammad Arslan Majeed (FA17 – CHE – 090)
NOTE:
The marks of Question # 1 will be allocated to Assignment # 3 (CLO # 4), while marks of
Question # 2 will be allocated to Assignment # 4 (CLO # 3).
- The End -
