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Licensed Unlicensed Requires Authentication Published by De Gruyter June 1, 2020

Optimization studies of low-density polyethylene process: effect of different interval numbers

Ashraf Azmi, Suhairi Abdul Sata ORCID logo, Fakhrony Sholahudin Rohman and Norashid Aziz


The highly exothermic nature of the low-density polyethylene (LDPE) polymerization process and the heating-cooling prerequisite in tubular reactor can lead to various problems particularly safety and economic. These issues complicate the monomer conversion maximization approaches. Consequently, the dynamic optimization study to obtain maximum conversion of the LDPE is carried out. A mathematical model has been developed and validated using industrial data. In the dynamic optimization study, maximum monomer conversion (XM) is considered as the objective function, whereas the constraint and bound consists of maximum reaction temperature and product melt flow index (MFI). The orthogonal collocation (OC) on finite elements is used to convert the original optimization problems into Nonlinear Programming (NLP) problems, which are then solved using sequential quadratic program (SQP) methods. The result shows that five interval numbers produce better optimization result compared to one and two intervals.

Corresponding author: Norashid Aziz, School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, Nibong, Tebal, Seberang Perai Selatan, 14300, Pulau Pinang, Malaysia, E-mail:

Funding source: Ministry of Higher Education, Malaysia

Award Identifier / Grant number: 203/PJKIMIA/6071368


The financial support from Kementerian Pengajian Tinggi (KPT) through Grant No. 203/PJKIMIA/6071368 and MyBrain15's Fund to the first author are greatly acknowledged.

List of symbols



Mass flow rate of x component (kg/h)






Input variable of x component


Live radical with chain length x


Live radical with chain length x




Temperature (°C)


Reactor inlet temperature (°C)


Reactor jacket temperature (°C)


Maximum reaction temperature (°C)


Overall heat transfer coefficient (cal/cm2.s.K)

  1. Author contribution: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: None declared.

  3. Employment or leadership: None declared.

  4. Honorarium: None declared.

  5. Conflict of interest statement: The authors declare no conflicts of interest regarding this article.


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Received: 2019-11-19
Accepted: 2020-04-01
Published Online: 2020-06-01

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