Green Styrene Manufacturing Plant Proposal¶
Copyright © Wei MEI, MLMS™—all rights reserved. 🀤¶
The aim of this plant design project is to provide critical insights into and recommendations of the available synthetic routes to styrene along with market, feedstock, economic, and sustainability analyses of the venture. This has culminated in a preliminary overview of the plant design and operation in the area of Ordos, China, produced for our clients at Bentham Corporation.
Project Description¶
Bentham Coporation requires the production of 100,000 te y-1 of styrene monomer at purity of 99.7 mol%. (See Project Specification for more details).
Styrene is a monomer used in the production of polymers including polystyrene, acrylonitrile butadiene styrene (ABS) and styrene-butadiene (SBR). Following fluctuations in the price of polystyrene the board would like a recommendation on which polymer should be produced from the styrene monomer.
Appraise¶
To begin, a process route review was conducted where various production routes of styrene manufacturing were critically evaluated to determine the synthetic route to styrene that is the most efficient in implementation, economics, and in styrene production rate. The selected route can be divided into 2 sections: The production of ethylbenzene through benzene alkylation with ethylene as well as ethylbenzene dehydrogenation to produce styrene. Various commercial process and innovative elements for each section were discussed leading to the final process route selection. In the alkylation section, commercial processes and reaction conditions was considered and it was concluded that the reaction should be done in liquid phase in the presence of a beta-zeolite catalyst; to this end, the Lummus/UOP EBOne method represented a solid choice for ethylbenzene production given the process constraints and feedstocks available. After further consideration, it was concluded that dehydrogenation process should be performed in a vapourphase adiabatic reactor in the presence of superheated stream and an iron (III) oxide-based catalyst; industrially known as the Lummus/UOP SMClassic process.
Section 1:
Section 2:
Subsequently, the feedstock market of styrene production was critically evaluated to determine the risks associated with production being affected by feed shortage, fluctuations in demand or price volatility. It was found that the feed prices and supply of benzene and ethylene in China are predicted to remain stable and hence will not influence production costs for at least the next 2-5 years. Additionally, the local and global markets for styrene were evaluated to determine which market(s) the styrene should be sold in to provide the highest profits. To sum up, industrial polystyrene production currently dominates the market of styrene, but due to the uncertain nature of the PS global markets the benefits were evaluated of synthesising product polymers and selling them instead. Upon analysing the markets of SAN resin, styrene-butadiene rubber and SB latex it was concluded the market for SB rubber would be of the greatest commercial interest to Bentham Corporation.
Next, the material and energy balance were also carried out. To do this, a BFD was constructed, and each major operating units’ function and conditions were identified. The mass balance was conducted to predict the required feed input, flowrates within the process, and the outputs of the plant which could then be used for preliminary analysis of the plant economics. The energy balance was done solely on the dehydrogenation part of the process, giving an approximate energy requirement overview and utility usage for this particular section.
Using the preliminary mass balance & ASPEN study, a basic economic study was done to provide an initial estimation of CAPEX and OPEX costs and the predicted profit of the plant. The plant CAPEX was calculated with the cost curve method and its results were further refined with the factorial method, giving a good indication of individual unit costs. The OPEX costs were calculated based on the available utilities and wages in China (2018). From the preliminary economics calculations, it was estimated that annual profit would be expected to be approx. US$23,800,000/yr.
Following this, an initial HAZID study was carried out in order to determine the process hazards and to get an idea of the magnitude of their associated risks. Many of the materials used and products/byproducts formed in this process are flammable/harmful/toxic. Some reactors and columns involved operate at elevated temperatures and pressures, increasing the risk to employees and the public.
To provide an in-depth look at the process route as a whole, it was modelled on ASPEN V10. Using the simulation, optimization and sensitivity analysis was performed in order to determine the profitable unit configurations and conditions, including modelling the effects of heat integration and feed excesses. Heat integration, done through the pinch analysis, was implemented on the final design of the plant to minimize utility costs. The preliminary mass and energy balance were subsequently compared to the simulation results, with the aim of identifying the cause of any differences. The overall profit was found to be US$21,788,100/yr.
Furthermore, a sustainability analysis was performed to determine the best course of action for dealing with each waste stream. It was found that the byproduct effluent streams were hydrocarbon dense and are therefore combusted to provide energy to the plant, save for benzene and toluene side products. This method reduces the amount of natural gas required by the plant. It was found that it was more profitable to sell the benzene and toluene mixture as BTX used as a feedstock in petroleum production, than to combust them or separate them and sell them individually. Combusting these side products, however, will increase the overall carbon dioxide footprint of the plant. Within the plant design, sustainability measures were taken such as heat integration and water recycling which was found to be more environmentally friendly as water with minor impurities from the plant is not disposed into the environment. These 2 measures also increase overall profits of the plant making it more economically viable to implement these designs.
Lastly, the preliminary plant layout was drawn. This was a key part of plant design as it plays an important in ensuring the safest plant operation possible along with plant longevity and economic viability. To generate a preliminary plant layout, all the units were sized. The factors that were taken into consideration include availability of raw materials and utilities, availability of land and labour, socioeconomic and environmental impacts of plant construction and operation, transportation, and political, legislative, and legal considerations. This was done by converting the PFD into a plant layout and sizing each process unit.
Summary¶
The aim of this plant design project is to provide critical insights into and recommendations of the available synthetic routes to styrene along with market, feedstock, economic, and sustainability analyses of the venture. This has culminated in a preliminary overview of the plant design and operation in the area of Ordos, China, produced for our clients at Bentham Corporation.
Process Route Review¶
Three Methods for Ethylbenzene Manufacture:
Alkylation of benzene with ethylene(favoured):
\(C_6 H_6+ CH_2=CH_2\Longleftrightarrow C_6 H_5CH_2CH_3\)
Recovery of mixed C8 aromatics by Superfractionation: Very small fraction
Production of ethylbenzene from butadiene
Methods for Styrene Manufacture:
Dehydrogenation-the dehydrogenation of ethylbenzene to styrene takes:
\(C_6H_5CH_2CH_3\Longleftrightarrow C_6H_5CH=CH_2+H_2\)
PO-SM Coproduction Coproduction (Propylene oxide and Styrene monomer):
a). Oxidation of ethylbenzene to ethylbenzene hydroperoxide
\(C_6H_5CH_2CH_3+O_2\longrightarrow C_6H_5CH(CH_3)OOH\)
b). Epoxidation of ethylbenzene hydroperoxide with propylene to form α-phenylethanol and propylene oxide
\(C_6H_5CH(CH_3)OOH+CH_2=CHCH_3\longrightarrow C_6H_5CH(CH_3)OH+CH_2OCHCH_3\)
c). Dehydration of α-phenylethanol to styrene
\(C_6H_5CH(CH_3)OH\longrightarrow C_6H_5CH=CH_2+H_2O\)
See Process Route Review for more details.
Feedstock and Market Review¶
Benzene
- Key component in petrochemical industry global demand 46 million tonnes.
- 50% used to make ethylbenzene.
3. Not produced directly but as a by-product of other industries - oil refineries, steam cracking of naphthalene, coal used in steel production.
- North East Asian Market 40% of Benzene market.
- China is the largest producer and consumer of Benzene.
- Price of Benzene in China 5,300-5,350 Yuan/te (Q3 2018).
- Direct routes to obtain benzene now being explored.
- Converted from other aromatics and dehydro-aromatisation reaction with ethane.
Ethylene
- Ehtylene importance unparalleled in industry/Largest petrochemical by volume in 2018.
- Wide variety of uses including in surfactants and plasticisers as well as to produce Ethylbenzene.
- Obtained from distillation of natural gas and oil.
- Alternative non fossil fuel methods of production.
- Prices in China 9,978-10,254 Yuan/te (Q2 2014).
Styrene
Asia:
Supply rose in most parts of northeast Asia as plants in Japan restarted from turnarounds and South Korean manufacturers were running at higher rates, on better margins in comparison with Q1. Only Taiwan saw a drop in production because of maintenance. Western supply levels were higher on the opened arbitrage window and rising run rates after Q1 maintenance plans. Import demand from China and northeast Asia were both healthy owing to healthy importer margins for most of Q2, and wider downstream production margins especially in the ABS and PS sectors respectively.
Europe:
Europe styrene was oversupplied during the second quarter. Supply was in abundance as demand was sharply reduced as lockdown measures were enforced across the region to control the spread of the coronavirus. A near halt in end-use automotive and tyre manufacturing and consumption destroyed demand for derivative ABS and SBR. Low PO demand resulted in reduced SM/PO output, but supply was still long because of low demand. Europe styrene demand fell sharply in the second quarter, as manufacturing along the supply chain, and end-use consumption were drastically impacted by enforced lockdowns to contain the spread of the coronavirus. The key end-use automotive sector was particularly affected, destroying demand for styrene derivatives such as ABS and SBR. PS and EPS demand was also slow, but packaging and single-use plastic demand picked up slightly.
US:
Supply was tighter in Q2 as US producer AmSty had some equipment issues while restarting its 953,000 tonne/year plant in Saint James, Louisiana, after planned maintenance. Producer INEOS Styrolution began a turnaround in mid-March at its 455,000 tonne/year plant in Texas City, Texas. The company has yet to restart the plant, likely because of demand destruction associated with the pandemic. The tight supply had minimal effect on the market because demand was soft. Overall demand was soft in Q2 as much of the country shut down to prevent the spread of the coronavirus. The North American auto industry shut down in March after an employee at a plant in Michigan contracted the virus. There were some pockets of improved demand related to the pandemic, including for some styrene derivatives such as including ABS for use in ventilators and PS as bans on single-use plastics were eased.
See Feedstock and Market Review for details.
Define Phase¶
Summary¶
The purpose of this report is to find the optimal dimensions and the optimal operating variables of two dehydrogenation reactors. More specifically, the height and diameter, catalyst amount and characteristics, heat exchange strategy of reactors need to be determined optimally. The operating conditions include temperature and pressure as well as the steam-to-ethylbenzene ratio.
Codes¶
- Install Wolfram Mathematica (version 11.0 or higher) or Wolfram Cloud (App or Online Version);
- Or run codes within the software interface, e.g., you can run the published codes to get concentration profiles for reactor 1;
- Or you can scan the QR code to take a glimpse at these codes:
- And to get an overview of how temperature, pressure, steam to ethylbenzene ratio on the ethylbenzene conversion, run these codes:
Manipulate[
K[T_] := Exp[A1 + B1 / T + C1 Log[T] + D1 T];
A1 = -13.2117277;
B1 = -13122.4699;
C1 = 4.353627619;
D1 = -0.00329709;
F0 = 152.2;
Fsteam = ratio F0;
Conv[T_] := 1/(2 F0 (P + K[T]))*(-K[T] Fsteam + Sqrt[(K[T] Fsteam) ^ 2 + 4 F0 (P + K[T]) K[T] (F0 + Fsteam)]);
Conv1[T_] := 1/(2 F0 (P + K[T]))* (Sqrt[4 F0 (P + K[T]) K[T] (F0)]);
Show[Plot[Conv1[T], {T, 500, 1500}, Frame → True, FrameLabel → {"temperature", "conversion"},
AxesOrigin→ {500, 0}, PlotLabels → {Callout["Without steam", {Scaled[0.25], Right}]},
PlotStyle → {Thick, Green}], Plot[Conv[T], {T, 500, 1500}, Frame → True,
FrameLabel → {"temperature", "conversion"}, PlotLabels → {Callout["With steam", {Scaled[0.25], Left}]},
AxesOrigin→ {500, 0}, PlotStyle → {Thick, Red}], ImageSize → {500, 350}],
{{P, 1.37, "total pressure in bar"}}, 1, 1.7, 0.01,
Appearance → "Labeled"}, {{ratio, 10, "steam to EB flow rate ratio"}}, 0, 20, 0.5, Appearance → "Labeled"},
TrackedSymbols⧴ {ratio, P}]
Here is what you can get:
Appraise¶
Thermodynamic Limitations and Side reactions¶
The first step in the production of commercial EB is the reversible reaction between benzene and ethylene forming EB.
\(C_{6}H_{6}+C_{2}H_{2}\Longleftrightarrow C_{6}H_{5}CH_{2}CH_{3}\)
EB can react further to form polyethylbenzenes (PEBS) such di-ethylbenzenes (DEBs) and Tri-ethylbenzenes (TEBs). An excess of benzene is typically used to shift the thermodynamic equilibrium to the right-hand side, thereby limiting the available ethylene for further alkylation to PEBs. In addition to transalkylation, isomerization and polymerization may occur producing xylenes and oligomers; these side reactions occur at negligibly low rates because modern industrial catalysts are highly selective for monoalkylation and seldom partake in these side reactions. Alkylation catalysts will be discussed later on in SECTION 2.2.2. To further increase conversion of ethylbenzene, polyethylbenzenes are transalkylated to EB via a transalkylation process:
This reaction should also be done in the presence of excess benzene to shift the thermodynamic equilibrium to the right and increase conversion of PEB. Although alkylation and transalkylation can be carried out in the same reactor, higher EB yield and purity are achieved with a separate alkylator and transalkylator, operating under different conditions optimized for the respective reactions. EB production with 2 separate reactors is optimal for the highest possible yield of EB. Due to the thermodynamic limitations as described above, benzene excess dictates, in both alkylation and transalkylation reactors, the conversion of EB1,3,4,5,6. Having too much benzene excess, however, leads to a large benzene recycle flowrate, increasing feedstock, capital, and operating costs. It is therefore important to strike a balance between the benefits gained from increased conversion and additional costs incurred due to benzene excess.
Benzene Alkylation Catalysts¶
Commercial production of EB is primarily achieved using two distinct routes of exothermic catalyst-aided alkylation: the traditional method makes use of aluminium chloride catalysts (Friedel-Crafts reaction) and newer methods use more contemporary synthetic zeolite catalysts.
Aluminium Chloride Catalyst¶
In the 1950s, approximately 40% of the global commercial EB production was done though the Friedel-crafts reaction with aluminium chloride (AlCl3) catalysts7. In addition to AlCl3, a wide range of Lewis acid catalysts, including AlBr3, FeCl3, ZrCl4, and BF3, have been used. These catalysts are extremely corrosive and toxic, capable of corroding storage and disposal containers. Additionally, the disposal of unavoidable side products such as the production of hydrogen chloride and oxidation has raised serious environmental concerns8. It is therefore imperative that AlCl3 traces in the reactor effluent streams are removed and recovered for reuse, adding complexity in both the plant design and operation procedures. In the 1980s, however, a new alkylation method using zeolite-based catalysts process was commercialized. These zeolite catalysts boast improved selectivity of EB and lower toxicity and corrosiveness, overcoming the main drawbacks of AlCl31,6,9. Zeolite catalysts are therefore considered advantageous for modern EB production processes.
Zeolite Catalysts¶
Over the years, many production processes involving zeolite catalysts have been developed. Each of these processes use their own variation of zeolite catalysts resulting in different operating features. The conventional production processes used today were first developed in the 1990s, including the Mobil-Badger (1990), CD TECH EB (1994), EBMax (1995), and the Lummus EBOne (1996) process. A critical analysis of these process is detailed below.
The Mobil-Badger uses catalyst ZSM-5, a medium pore modified Y zeolite, in a vapour fixed bed reactor for alkylation and transalkylation. Vapour-phase benzene alkylation in Mobil-Badger requires a high benzene/ethylene molar ratio, and high reaction temperatures, around 400oC. This results in high capital costs from larger vapour-phase reactors and high energy costs10,11. Unlike vapour phase alkylation, liquid phase alkylation reduces both the operating temperature (to 240-270oC) and the size of the reactors. Zeolite catalysts for liquid phase operations also have a longer lifetime and are more selective, decreasing the required benzene excess. These characteristics make liquid-phase alkylation more commercially favourable than vapour-phase.
EBOne and EBMax utilize liquid phase alkylation; The EBMax process performs benzene alkylation in liquid phase but transalkylation in vapour phase. EBMax uses a zeolite catalyst known as MCM-22 in the alkylation reactor and ZSM-5 in the transalkylation reactor. MCM-22 has an increased lifetime of 3 years and has a much higher ethylbenzene selectivity than Y zeolites, lowering the required feed ratio of benzene/ethylene to only 4/111. Similarly, Lummus EBOne alkylates benzene in liquid phase while transalkylation is performed in liquid phase. Lummus EBOne uses a modified beta zeolite in both alkylation (EBZ-500) and transalkylation (EBZ-100) reactors. Beta zeolites have a comparable selectivity to MCM-22 while giving a higher ethylbenzene yield than both Y and MCM-22 zeolites11,12,13. Using beta zeolites catalyst, the required feed ratio of benzene/ethylene is 4-6/1 with a lifetime of 2 years10,13 .Overall EBMax and EBOne have a comparable performance and costs. EBOne may operate both reactors in liquid phase but requires a higher benzene excess than EBMax resulting in similar reactor sizing and operating costs. The main difference is that the overall yield of EBOne is 99.6%, 0.1% higher than EBMax10, hence EBOne was the process that was chosen for the Bentham Cooperation venture.
In addition to the ethylbenzene processes above, other techniques have been used in industry such as ‘catalytic distillation’ using Y zeolites, also known as the CDTECH EB process. While CDTECH EB has a comparable performance to Lummus EBOne, can use dilute feedstocks, has increased catalyst lifetime of 6 years, and a high yield of 99.7%10, this technique has many limitations that makes a fixed bed reactor more favourable. The segregation of ethylene in vapour phase and benzene in liquid phase hinder the mass transfer of ethylene to the catalyst. This lowers the conversion of ethylene to ethylbenzene, thus requiring a large catalyst volume and complex reactor system, substantially increasing capital costs1. The characteristics of each process are summarized in Table 1.
Team¶
This project is part of Advanced Design Project and is developed by an international student team. The maintenance service is assisted by Wei MEI .
Team Members
This project team members are listed in alphabetical order, with affiliation, and main areas of contribution:
- Alastair Dixon (LinkedIn Profile Alastair Dixon)
- Alex Kearns (LinkedIn Profile Alex Kearns)
- Dusita De Hoop (LinkedIn Profile Dusita De Hoop)
- Dhrupal Godhaniya (LinkedIn Profile Dhrupal Godhaniya)
- Ernest Chu (LinkedIn Profile Ernest Chu)
- Wei MEI (LinkedIn Profile Wei MEI)
Note
This project is done with great help from two Personal Tutors and Prof. Haroun Mahgerefteh:
- Richard Porter (Personal Profile Richard Porter), Module Coordinator, Senior Research Associate and Teaching Fellow at Department of Chemical Engineering, University College London.
- Martynov Sergey (Personal Profile Martynov Sergey), Bentham Corporation Representative, Research Assoicate at University College London.
- Haroun Mahgerefteh (Personal Profile Haroun Mahgerefteh), Bentham Corporation Representative, Professor of Chemical Engineering, University College London.