Production of Maleic Anhydride

UNDERGRADUATE LEVEL / Project Description: The main objective of this maleic anhydride production plant is to produce 25,000 tons of MA per year. The process flow diagram modelling the process was simulated by HYSYS, where Peng Robin Stryjek Vera (PRSV) was used as it is recommended for most hydrocarbon and moderately non-ideal systems (Sjauw and Lam 1994). The feed to the fluidized bed consisted of pure n-butane and air feed (mixture of inert gases) which were compressed then mixed and fed into the reactor to obtain the required temperature of above 250 °C and pressure of 1.614 bar_g. The reactor was modelled by three plug flow reactors (PFR-100, PFR-101, and PFR-102), where the oxidation reaction of n-butane and oxygen in the presence of a VPO catalyst took place following a heterogeneous catalytic reaction.


The kinetic data used achieved an n-butane to maleic anhydride conversion of 81.21%, which meets the requirement of above 80% (Dente et al. 2003). The reactor product was then fed into a cooler (E-101) to cool down to a temperature of 160 °C and enter the absorber (T-100). Solvent feed (mixture of fresh and recycled solvent) also entered T-100. The solvent used was dibutyl phthalate to recover MA from the reactor product feed (stream 15) which is in vapour form, where MA leaves from the bottom of T-100 and inert gases are released at the top as emission. The emission (stream 18) is further purified to extract n-butane from the inert gas by a membrane separator, which is modelled as a component splitter (x-100) in HYSYS. Then, the extracted pure n-butane (stream 20) is stored in a storage tank and the offgas (stream 19) is sent to an incinerator. Having a mass flowrate of 3044.93 kg/hr, the MA (stream 23) from T-100 enters the first distillation column (T-101) in liquid phase, which used a partial condenser, where gas and MA were released from the top and a reboiler, where almost 100% pure solvent was recycled back to T-100. The MA released from the condenser had a purity of 94% and a mass flowrate of 2982.3181 kg/hr. To further purify MA and achieve a purity of 99%, a second distillation column (T-102) was used, where the overhead outlet (stream 30) consisted of mostly water and the bottoms liquid outlet (stream 31) consisted of almost 99% of MA with a mass flowrate of 2968.69 kg/hr. Hence, 23,512.03 tons of MA per year can be produced.

The simulation modelled the ALMA process for producing MA via the oxidation of n-butane. However, the innovation made was in how the n-butane from stream 18 of T-100 was extracted. A membrane separator was used in order to separate the un-reacted n-butane amounting 655 kg/hour from the offgas in stream 18. Other separation attempts include: recycling the n-butane and mixing it with the air and n-butane feed, and then inserting it into the reactor, using a distillation column, and using an adsorption column with fresh water as solvent. Next, the simulation file was compared with the manual calculation for validation of results and the percentage of error received was less than 10%; hence, it was concluded that the HYSYS simulation was capable of modelling the production of MA process efficiently. Lastly, the utilities required prior to heat integration were found using the HYSYS energy analyser, where it was found that the cold utilities included MP Steam and air, while hot utilities included LP Steam, HP Steam, Hot Oil, and fired heat (1000).

Dente, Mario, Sauro Pierucci, Enrico Tronconi, Marco Cecchini, and Federico Ghelfi. 2003. “Selective Oxidation of N-Butane to Maleic Anhydride in Fluid Bed Reactors: Detailed Kinetic Investigation and Reactor Modelling.” Chemical Engineering Science 58 (3–6): 643-648. doi:

Sjauw, Koen Fa, and W.S. Lam. 1994. “The Production of Maleic Anhydride by Selective Catalytic Oxidation of N-Butane.” Delft University of Technology.

Important Remarks: This page only includes Project Description. The full document is available upon request. [Project Duration: August 2013 – November 2013]

Acknowledgement: This work was fully guided by Dr. John Lau (project supervisor) with the support from Curtin University, Miri Campus, Sarawak, Malaysia.