EBTAX: The Conversion of Ethane to Aromatics via Catalytic Conversion

81 Pages·2016·1.67 MB·English

University of Wyoming
Wyoming Scholars Repository
Honors Theses AY 15/16 Undergraduate Honors Theses
2016
EBTAX: The Conversion of Ethane to Aromatics
via Catalytic Conversion
Emily Schwichtenberg
University of Wyoming, [email protected]
Aaron Cheese
University of Wyoming, [email protected]
Bridger Martin
University of Wyoming, [email protected]
Saud Alshahri
University of Wyoming, [email protected]
Follow this and additional works at:http://repository.uwyo.edu/honors_theses_15-16
Recommended Citation
Schwichtenberg, Emily; Cheese, Aaron; Martin, Bridger; and Alshahri, Saud, "EBTAX: The Conversion of Ethane to Aromatics via
Catalytic Conversion" (2016).Honors Theses AY 15/16.Paper 7.
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Ethane to Aromatics
5/6/2016
EBTAX Group
Saud Alshahri, Aaron Cheese, Bridger Martin, Emily Schwichtenberg
CHE 4080 PROCESS DESIGN II
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Table of Contents
I. Table of Tables..................................................................................................................................... 2
II. Table of Figures ................................................................................................................................. 4
III. Executive Summary (Emily)............................................................................................................ 6
IV. Scope of Work (Bridger) .................................................................................................................. 8
V. Introduction (Saud) .......................................................................................................................... 10
VI. Description of Base Case ................................................................................................................ 11
Section 100: Feed processing, reaction, and initial separation (Bridger) ....................................... 15
Section 200: Lights Separation Section (Emily) ............................................................................... 24
Section 300: Separation and Recovery of BTX and Heavy Aromatics Products (Saud) ................. 30
Section 400/500: Propane and Ethylene Refrigeration (Aaron) ...................................................... 34
VII. Design Alternatives (Bridger) ...................................................................................................... 43
Possible Reactor Alterations .............................................................................................................. 43
Product Recovery (Section 300) alternative designs ......................................................................... 44
Continuous Catalyst Regeneration .................................................................................................... 46
Fuel gas reallocation, C2 through C4 repurposing .......................................................................... 47
VIII. Permitting and Environmental Concerns (Emily) ................................................................... 48
IX. Safety and Risk Management (Emily) .......................................................................................... 52
X. Project Economics (Aaron) ............................................................................................................. 54
Equipment and Capital Cost .............................................................................................................. 54
Pricing, Revenue and Production Cost ............................................................................................. 62
Cash Flow Analysis ............................................................................................................................ 64
Sensitivities ......................................................................................................................................... 65
XI. Global Impacts (Saud) ................................................................................................................... 68
XII. Conclusions and Recommendations (Bridger) ........................................................................... 72
XIII. Future Work (Aaron) .................................................................................................................. 74
XIV. Acknowledgements (Saud) .......................................................................................................... 75
XV. References ...................................................................................................................................... 76
XVI. Appendices ................................................................................................................................... 79
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I. Table of Tables

Table 1: List of reactions, their respective conversions, and the heats of reaction/ ................................... 19

Table 2: Pressure, temperature and enthalpy data for propane .................................................................. 38

Table 3: Pressure, temperature and enthalpy data for ethylene ............................................................... 39

Table 4: Various operating conditions specified for the different refrigeration cycles involved along with
the Aspen unit operation or stream that it corresponds to. .......................................................................... 41

Table 5: This table shows the emissions of thermal NO with and without control measures. The emission
x
limit for needing a permit from the EPA is 100 tons/year, which can be obtained with control measures in
this process. ................................................................................................................................................. 50

Table 6: Specific information involved in sizing and costing compressors. .............................................. 55

Table 7: Specific information involved in sizing and costing turbines ...................................................... 55

Table 8: Specific information involved in sizing and costing furnaces ..................................................... 56

Table 9: Specific information involved in sizing and costing heat exchangers ......................................... 57

Table 10: Specific information involved in sizing and costing air coolers ............................................... 58

Table 11: Specific information involved in sizing and costing vessels ...................................................... 59

Table 12: Specific information for costing the PSA unit ........................................................................... 59

Table 13: Specific information for sizing and costing the amount of catalyst used ................................... 60

Table 14: Specific information for sizing and costing the amount of catalyst used ................................... 61

Table 15: Specific information for distillation column and tray sizing and costing .................................. 61
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Table 16: Fixed Capital Investment for the various equipment involved in the process along with the
resulting total .............................................................................................................................................. 62

Table 17: Income or cost of each of the materials consumed or produced ................................................ 63

Table 18: Cost of utilities ........................................................................................................................... 64

Table 19: Various fixed costs associated with the design .......................................................................... 64

Table 20: Results of the cash flow analysis conducted on this design ....................................................... 65

Table 21: Sensitivities run, along with the resulting IRR .......................................................................... 66
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II. Table of Figures

Figure 1: Overall Process Flow Diagram. Part A: Section 100, 200, and 300 up to M301. Part B:
Remaining portion of section 300. Part C: Section 400 and 500. ........................................................... 14

Figure 2 : Feed and reactor (Section 100). Feed ethane is mixed with hydrocarbon and hydrogen
recycles. The presence of hydrogen significantly reduces catalyst coking. The flash tank, D101, sunders
gaseous C1-C5 to section 200 and C6-C9 to section 300. .......................................................................... 15

Figure 3: Section 200, the Lights Separation Section. This section consists of a mixer to combine the
vapor stream from the flash drum and a recycle from the product recovery section, two distillation towers
and a pressure swing adsorption (PSA) unit to separate the product and recycle streams, one splitter to
allow for the hydrogen sale stream to be separated, and two compressors to pressurize the recycle streams
to appropriate pressures to be mixed with the feed stream ......................................................................... 24

Figure 4: Section 200 Up To T201. From the flash drum, the vapor stream is mixed in M201 with a
vapor recovery stream in the product recovery section before being sent to a distillation tower (T201) to
remove hydrogen and methane from the product stream as the vapor distillate (S203), with the remainder
exiting the tower in the bottoms stream (S206). ......................................................................................... 25

Figure 5: Section 200, T201 Distillate Path After T201. The hydrogen and methane stream is sent to a
heat exchanger to warm it up to room temperature before being sent to the pressure swing adsorption
(PSA) unit, where the methane is removed to a fuel gas stream and the hydrogen stream is sent to a
splitter (S201). This splits the hydrogen stream into a sale product stream and a recycle stream, which will
be sent compressed and sent back to the reactor to prevent coking of the catalyst..................................... 26

Figure 6: Section 200, T201 Bottoms Path. The bottoms of T201 is sent to T202, where C2 and C3
hydrocarbons are distilled off and sent to a compressor before being recycled back to the recycled to
increase the overall conversion of the reactor. The bottoms stream is sent to a mixer in the product
recovery section to recover any BTX products that could have been lost .................................................. 28

Figure 7: Heavy Separation (Section 300). From flash tank D101, the heavy stream is separated
remaining light hydrocarbons. The remaining heavies are separated into Benzene, Toluene, and Xylene
product and TMB byproduct. ...................................................................................................................... 30

Figure 8: Heavies Separation (Section 300). From flash tank D101, the liquid stream is separated fed
into the first distillation column (T301) to remove the remaining light hyrdrocarbons as well as recover
TMB as a product. The aromatic rich stream is sent on for further processing by S302. .......................... 31
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Figure 9: Purge Stream. BTX rich streams are fed into tower T302, one of which comes from the lights
separation section, and one of which come from the previous tower, T301. T302 separates out any
remaining lights and purges them from the system. The bottoms of the tower is sent on for product
recovery as it mainly consists of BTX. ....................................................................................................... 32

Figure 10: Benzene Recovery. Benzene is recovered from the BTX rich stream leaving T302. The
bottoms of the tower is sent on to recover the remaining Toluene and Xylene. ......................................... 33

Figure 11: Toluene and Xylene Recovery. T304 separates toluene from para-xylene that is fed to the
tower from T303. ........................................................................................................................................ 34

Figure 12: Propane and Ethylene Refrigeration. Section 400 consists of two propane refrigeration cycles
operating at different pressures. Section 500 consists of only one ethylene refrigeration cycle. For each
cycle the refrigerant is compressed, condensed, expanded, and evaporated in order to complete the
cycle. Propane refrigeration is used in condensing the process fluid in T202 along with condensing the
ethylene in section 500. Ethylene refrigeration is only required to condense the process fluid in T201. 35

Figure 13: Tornado Diagram. This plot chose the change on IRR based on different variation of various
uncertain parameters. .................................................................................................................................. 67

Figure 14: Industry Rivalry. This figure illustrates the possible industry pressure associated with a new
competitor ................................................................................................................................................... 69
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III. Executive Summary (Emily)

Team EBTAX was formed with the goal of taking ethane from natural gas refineries and
processing it into various aromatics, including benzene, toluene, and para-xylene (BTX). The market for
BTX chemicals is fairly stable, as they can be converted into larger molecules that are critical components
in polymer synthesis, producing plastics, textiles, and other consumer goods. The glut of natural gas in
the US has caused ethane prices to drop to around half of what they were at the beginning of 2014. This
makes it an ideal feedstock for our process, which includes a catalyzed reaction and several separation
units to separate the reaction products into pure component products. The plant will be located on an
existing oil refinery in the gulf coast area. This will provide easy allocation of products, as well as access
to the oil refineries and chemical plants that would purchase and further process the products.
To catalyze the reactor, a platinum-zeolite catalyst was chosen for its high selectivity toward
BTX compared to similar catalysts. US Patent 7745675 B2 only provides conversion and reaction
information for this catalyst from lab scale tests. The unfamiliarity with this catalyst and the lack of
information at diverse conditions led to several assumptions when modeling the process. Firstly, the
amount of catalyst required for the process scales linearly and ideally with the reactor inlet. Secondly, the
conversion of the reactions would not depend strongly on pressure. The patent also provides a functional
pressure for the catalyst specified from 20 to 2000 psia without providing correlations for pressure and
conversion. Catalyst lifetime use is assumed to outlive the life of the plant, and regeneration is assumed to
recover 100% of the catalyst. Regeneration alone will keep the catalyst active for the lifetime of the
project.
The process is broken down into five sections. To begin, the reactor section (Section 100),
consists of an ethane feed stream and two recycles from the separation sections. The feed is mixed with
the recycles and then heated before entering a gas-phase, fixed-bed, catalytic reactor at 1150°F. The
reactor houses 26 separate reactions. C2 and C3 hydrocarbons (HCs) undergo multiple equilibrium-based
reactions to form C1 through C5 linear and C6 through C9 aromatic HCs and hydrogen. After the stream
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has reacted, it is cooled before being sent to the separation sections. An initial flash tank separates the
reactor effluent into light and heavy HC streams, which are sent to sections 200 and 300, respectively. In
the lights separation, two distillation columns and a hydrogen pressure swing adsorption (PSA) unit are
used. The four product streams from the light separation section are high purity hydrogen (99.5 mol%),
methane fuel gas, and a C2-C3 HC recycle. The hydrogen stream will be split into a sale stream and a
recycle stream, which will prevent coking of the catalyst. Sections 400 and 500 are propane and ethylene
refrigeration, respectively, which will be used to cool the condensers in the lights separation to allow the
small hydrocarbons to condense. The liquids from the initial flash tank are pumped to the product
separation (Section 300). Four distillation towers are used in this section. The first tower (T301) functions
as a light HC recovery unit, with the remaining light vapors entering section 200. The liquids enter the
next distillation tower (T302) to remove TMB. The last two towers separate the BTX into its components
to be sold.
The fixed capital investment for this project is $320 million, which is largely due to the many
compressors needed for the refrigeration section. With a 20 year project life, this project yields an IRR of
30.3%, with a payback period of 2.6 years.
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IV. Scope of Work (Bridger)

The preliminary mission on team EBTAX is to design an industrial plant that takes advantage of
the abundant natural gas supplies in order to produce benzene, toluene, and xylene. Research into the
natural gas industry, along with common natural gas refinery processes, revealed ethane to be the most
probable feedstock. This was due to a number of contributing factors, including the recent practice of
ethane rejection, where ethane is allowed to flow with methane into the pipe gas stream. Ethane rejection
further lowers the cost of inexpensive ethane feeds.
US Patent US20130324778A1 was provided to team EBTAX as a starting point for the
conversion of ethane into valuable aromatics, including benzene, toluene, and xylene. This catalyst
became the basis for the plant design and created many constraints that had to be met by the plant.
Constraints
The primary design constraints are equilibrium constraints within the reactor. The catalyst
conversion is highly specific and creates the high volume reflux of C2 and C3 hydrocarbons. The catalyst
operating conditions also set the reactor temperature at 1150°F. These high temperatures can also ignite
the HCs if oxygen is present in the system. All process streams are run above atmospheric to prevent
oxygen from entering the system in the case of a leak.
The reactions taking place are exothermic. This creates the opportunity for a runaway reaction if
released heat and built up pressures go beyond controllable conditions. This creates additional safety
constraints, such as the inclusion of cooling systems, which will also be considered in more detailed
designs.
Thermodynamic constraints are present outside the reactor as well. To separate the C1-C9 HC
stream, extremely low temperatures are required for the lighter components. Two types of refrigeration
were included to reach the low temperatures. These refrigeration systems will be discussed in the Section
400/500 below.