S1

Supporting Materials

Comparative Economic and Environmental Assessments of H2O2-based and

Tertiary Butyl Hydroperoxide-based Propylene Oxide Technologies

Madhav Ghanta1,2, Darryl Fahey1, Daryle Busch1,3, Bala Subramaniam1,2,* 1Center for Environmentally Beneficial Catalysis, 2Department of Chemical & Petroleum

Engineering, 3Department of Chemistry, University of Kansas, Lawrence, Kansas 66045-7609.

Number of Pages: 22

Number of Tables: 7

Number of Figures: 3

S2

Section A. Assumptions common to the simulations of the conventional PO/TBA, HPPO and

CEBC-PO Processes.

Table S1. Summary of Assumptions

PFD Specification Description

Catalysts and

Solids

Estimated using the property estimator tool embedded in Aspen HYSYS®

software

Catalyst Synthesis

and Regeneration

Neglected in comparison to capital costs of unit operations

Direct Costs(1)

(estimated as a %

of purchased

equipment cost)

Purchased-Equipment Delivery (10%), Concrete Foundation (6.6%),

Painting (1.3%), Instrumentation and control (13.5%), Piping (61.4%),

Steel support (5%), Equipment Setting (5%), Freight (3%), Electrical

(14.5%), Building (43%) and Yard Improvement (11%)

Indirect Costs(1)

(estimated as a %

of direct costs)

Engineering and Supervision (16%), Construction Expenses (26%), Legal

Expenses (3%), Contingency (15% for conventional PO/TBA and HPPO

process, 30% for the CEBC process), Contractors Fees (17%)

Utility Costs(1), (2),

(3)

Steam ($ 10/1000 lbs), Electricity ($ 0.0655/ KWh), Cooling Water ($

0.10/1000 gal), Refrigeration (-50 °C, $ 60/GJ & -30 °C, $ 30/GJ)

Labor Costs(4), (5) Skilled Labor (46.9 $/person/h), Unskilled Labor (35.6 $/person/h)

Working Capital(1) 18% of fixed capital investment

Miscellaneous

Costs(1)

Distribution, Marketing, research and development (10% of production

cost), Depreciation Rate (10% per year), Tax Rate (2% of total fixed

capital), Operating Supplies (10% of labor costs), Plant Overhead (80% of

labor costs), Maintenance Material (3% of purchased cost)

S3

Section B. Process Description of the Conventional PO/TBA Process

This process may be viewed in two parts (Figure S1) i-butane oxidation and propylene

epoxidation.

i-Butane oxidation reactor (Section A of Figure S1): Table S1 summarizes the mass flow rates of

the components entering and leaving i-butane oxidation and propylene epoxidation reactors and

the mass flow rates of components in the recycle streams. In Section A, recycled gases (i-butane,

butane) and make-up raw materials (i-butane and oxygen) are fed into six continuous stirred tank

reactors (CSTR) in parallel (total volume = 2143 m3).(6) i-Butane undergoes non-catalytic liquid-

phase oxidation to form t-butyl hydroperoxide (TBHP). Typical reaction conditions are 3 MPa at

135 °C with an average residence time of 10 h. Under optimized conditions, the i-butane

conversion is 37%, and the TBHP selectivity is 53 mol% based on i-butane consumption. A

major co-product of this step is t-butyl alcohol (TBA), with a selectivity of 41 mol% (based on i-

butane conversion).(7) The oxygen concentration in the liquid phase is kept below 4-7 mol%,

primarily for safety reasons.(8) Temperature control in the TBHP reactor is achieved by re-

circulating the liquid reaction mixture through a series of coolers.(7)

The liquid phase containing product TBHP, t-butanol and dissolved i-butane and n-butane

exit the reactor from the bottom. The unreacted oxygen, nitrogen, undissolved i-butane and n-

butane exit the reactor through the overhead stream (vent gases). The vent gases are partially

condensed to recover and recycle (R1) the butanes (i-butane and n-butane) whereas the non-

condensable gases (nitrogen and small quantities of oxygen) are sent to a flare where the oxygen

is used to burn off the unrecovered light hydrocarbon gases. The liquid effluent stream exiting

the reactor is sent to the butanes column (P = 0.2 MPa, T = 78-134 °C) where the light ends (i-

butane, n-butane) and byproducts (acetone and methanol formed by the decomposition of TBHP)

S4

are separated from the TBA+TBHP mixture, which is sent to the propylene epoxidation

reactor.(9) The low concentration of methanol byproduct in the reactor effluent stream containing

TBHP may pose a safety concern. By preventing the build-up of methyl hydroperoxide in the

butanes column, the risk associated with distillation of the mixture of

TBHP+methanol+acetone+i-butane+n-butane is minimized.(10) The light ends recovered in the i-

butane column (P = 0.6 MPa, T = 118-140 °C) are recycled whereas acetone and methanol are

separated by extractive distillation with water as the separation solvent.(11) Acetone is recovered

in the acetone column (P= 0.1 MPa, T= 56-84 °C) while methanol and water are separated by

simple distillation in methanol column (P= 0.1 MPa, T= 65-91 °C). In all these columns, cooling

water is used in the condensers.

Propylene Epoxidation (Section B): In the second step, the oxidant (TBHP dissolved in TBA,

from section A), make-up enriched propylene feedstock (propylene/propane ratio is 9:1), and

recycled gases (propylene/propane) are fed into four stirred tank reactors (total volume=1080 m3)

in parallel.(12), (13) Propylene is selectively epoxidized by TBHP in the presence of a

homogeneous molybdenum-based catalyst at 121 °C and 3.5 MPa. For a residence time of 2 h,

the reported TBHP conversion is 98%, and the PO selectivity is 98.4% (based on converted

TBHP).(14), (15) Temperature control in the propylene epoxidation reactor is achieved by

vaporizing and reflux-condensing the reaction mixture.(13) The non-condensable vapors from the

reflux condenser are sent for product separation to the propylene stripper.

The reactor effluent stream containing the unreacted reactants and products are recovered in

a train of distillation columns. The spent catalyst solution is recovered as bottom product from

the separation column (P = 0.4 MPa, T = 9-140 °C). The overhead stream from the separation

column is sent to a propylene stripper (P = 0.6 MPa, T = 3-70 °C) where propylene and propane

S5

are separated from PO, t-butanol and TBHP. The mixed propylene/propane stream is sent to a

propane stripper (P = 20 MPa, T = 50°C). The enriched propylene stream is recycled back to the

reactor (R2). PO is separated from the t-butanol and TBHP in the crude PO column (P = 0.2

MPa, T = 5-85 °C). The crude PO is further purified by distillation in a PO purification column

(P = 1.9 MPa, T = 54 °C). The condensers in the propylene stripper and crude PO column are

cooled with chilled water whereas the condensers in the separation column, propane column and

PO purification columns are cooled with ordinary cooling water. The byproduct/product weight

ratio for the PO/TBA process is 2.4.

Figure S1: Process flow diagram for the conventional PO/TBA process: (A) i-Butane

oxidation; (B) Propylene oxide production. (7), (13), (12) Table S2 lists the simulation

parameters employed in this simulation and the compositions of the recycle (R1-2)

S6

Table S2: Simulation parameters for the conventional PO/TBA process.(7), (15), (16), (14)

Input/Output stream flow rates (lb/h) from the TBHP and PO reactors obtained from

HYSYS® simulation

TBHP production

Reaction

Conditions

Reactor: Six CSTRs in parallel

P= 3 MPa, T= 135 °C; Conversion (i-butane)= 36.9 mol%,

LHSV (Liquid Hourly Space Velocity)= 2.5 h-1

Catalyst Non-Catalytic

Product Selectivity TBHP= 53.4 mol%; TBA= 40.2 mol% (based on i-butane fed)

Propylene Epoxidation

Reaction

Conditions

Reactor: Four CSTRs in parallel

P= 3.5 MPa, T= 121 °C; Conversion (TBHP)= 98 %

Liquid Hourly Space Velocity (LHSV)= 5 h-1

Feed Composition : Propylene/Propane: 9/1

Catalyst 1.5% Mo Solution in TBA (165 ppm Mo in reaction mixture)

Product Selectivity PO= 98.4 mol% (based on TBHP consumed), 100 mol% (based on C3H6

consumed)

i-Butane Oxidation Propylene

Epoxidation

Mass Flow Rates Input Output Input Output R1 R2

Top Bottom

i-Butane 307340 757 193172 - - 193172 -

n-Butane 2640 167 2406 - - 2574 -

Oxygen 51700 440 - - - - -

Nitrogen 176 176 - - - - -

Methanol 33 - 3750 - - - -

Acetone 66 - 6765 - - - -

t-Butyl Alcohol 352 - 57590 136840 224940 350 -

t-Butyl

Hydroperoxide

572 - 99770 99770 1995 570 -

Propylene - - - 155980 110264 - 110264

Propane - - - 18898 18898 - 18898

Propylene Oxide - - - 1716 55200 - -

Refer to Figure S1 for stream identification (Rj)

S7

Section C. Process Description of the HPPO process

Due to the lack of published information on the amylanthraquinone process, this analysis

assumes that the oxidant (H2O2) is procured from an external supplier. The process flow diagram

of the modified HPPO process (hereafter referred to as HPPO process) is shown in Figure S2.

Propylene epoxidation: A mixture of 50 wt.% H2O2/H2O, methanol, make-up reactants

(propylene/propane feed ratio of 1.5:1)(16), (17) and recycled gases (propylene/propane) are fed

into three fixed-bed catalytic reactors connected in parallel (total volume = 900 m3).(18) The mass

flow rates of components entering and leaving the reactor are summarized in Table S3. A

titanium silicate (often referred to as TS-1) catalyzes propylene epoxidation by H2O2 at 40 °C

and 2 MPa (Figure S2). The activity of the TS-1 catalyst gradually declines from an initial H2O2

conversion of 96% to 63% after two weeks, necessitating catalyst regeneration.(19) In this

analysis, roughly 90% of the H2O2 is utilized in the reactor for epoxidation while the remaining

10% unreacted H2O2 is safely decomposed. The selectivities toward PO and propylene glycol

(PG) are 95.5% and 4.5%, respectively.(16) In addition to PG, trace quantities of acetone, acetic

acid and formaldehyde are also formed as byproducts.(19) Temperature control in the PO reactor

is achieved by re-circulating part of the reaction mixture through a series of heat exchangers.

The bulk of the unreacted propylene and propane is recovered by simple depressurization in

propylene stripper 1. This propane-rich stream may be dehydrogenated to produce a mixture of

propane and propylene. The value of this enriched propane stream is credited in this analysis.

The presence of unreacted H2O2 in the reactor effluent stream poses safety concerns. Methanol

and H2O2 mixtures can form an explosive vapor phase mixture during distillation. For purposes

of this economic analysis, we assume that the unreacted H2O2 (10 mol%) is safely decomposed

to H2O and O2 post-reaction at approximately 50 °C immediately following the propylene

S8

stripper 1. The effluent from the decomposer is a gaseous mixture of oxygen and propylene

whose composition (1 wt% propylene) lies below the lower flammability limit (LFL) of the

mixture.(8) The liquid effluent stream from the H2O2 decomposer containing PO, propylene

glycol, methanol, water and dissolved propylene/propane is fed to a propylene stripper 2 (P = 1.2

MPa, T = 50 °C) where propylene and propane are recovered. The liquid phase from this unit is

sent to a PO stripper (P = 1.2 MPa, T = 47 °C). The methanol recovery column (P = 0.4 MPa, T

= 66 °C) and the wastewater column (P = 0.5 MPa, T = 94 °C) help with the separation of

methanol and propylene glycol. The condensers in all the distillation columns utilize cooling

water. It is believed that the commercial process incorporates a proprietary H2O2 recovery and

recycle technology, details of which are not yet available in the public domain. H2O2 recovery

obviates the need for deliberate H2O2 destruction and should improve the process economics.

S9

Figure S2: Process flow diagram for the HPPO Process.(17), (16) Table S3 lists the simulation

parameters employed in this simulation and the compositions of the recycle (R1-2).

(*) The C3H8-rich stream exiting from the overhead of the propylene stripper 1

and propylene stripper 2 is sent to a propane dehydrogenator to produce

propylene. Hence, the propane is assigned a value as a co-product.

S10

Table S3: Simulation parameters for the Hydrogen Peroxide/Propylene Oxide (HPPO)

Process.(17), (20), (16), (21) Input/output stream flow rates (lb/h) for the PO reactor

obtained from HYSYS® simulation

Propylene Epoxidation

Reaction

Conditions

Reactor: Three Fixed Beds in parallel

P= 2 MPa; T= 40 °C; Conversion (H2O2)= 90%

Liquid Hourly Space Velocity (LHSV)= 5 h-1

Feed Composition : Propylene/Propane: 1.5/1

Catalyst Titanium Silicate (TS-1)

Product

Selectivity

PO= 95 mol%; PG= 4.5 mol% (based on H2O2 consumed in the reactor)

PO= 95.4 mol%; PG= 4.6 mol% (based on C3H6 consumed)

Propylene Epoxidation Reactor

Mass Flow Rates Input Output R1

Hydrogen

Peroxide (H2O2)

35924 3566 -

Water 35924 53054 220

Methanol 22968 22968 22968

Propane 29608 29608 -

Propylene 44413 4441 -

Propylene Oxide - 55200 -

Propylene Glycol - 3676 -

Refer to Figure S2 for stream identification (Rj)

S11

Section D. Process Description of the CEBC-PO Process

Propylene Epoxidation: Table S4 lists the mass flow rates of components entering and leaving

the reactor. Along with fresh (99.99%) and recycled propylene, nitrogen, aqueous H2O2, make-

up catalyst, promoter and methanol are fed into a continuous stirred tank reactor (total volume =

1057 m3) fitted with a nano-filtration membrane.(22) The assumption of a nearly pure propylene

feed is based on the fact that our initial tests with the MTO/H2O2 system utilized pure propylene.

While this assumption would appear to handicap the CEBC-PO process economics, it

nevertheless helps in assessing to what extent the use of pure propylene feed affects the

economics. The CSTR volume for 90% H2O2 conversion is estimated from reported kinetic

parameters and PO selectivity (based on propylene) values of 99% (see Section F of the

Supporting Materials for details).(23), (22) The liquid hourly space velocity (LHSV) is estimated to

be 5 h-1. We assume that the total volume is divided equally into four reactors connected in

parallel. It is further assumed that the Re-based catalyst is bound to a soluble polymer support

and that the activity and selectivity of the polymer-bound catalyst are similar to the unbound

MTO catalyst. The size exclusivity of the nanofiltration membrane effectively retains the

polymer-bound catalyst in the reactor while allowing only the passage of smaller components

[such as PO, unreacted propylene, unreacted H2O2, water, and methanol].

The bulk of the unreacted propylene is recovered by simple depressurization from the reactor

pressure of 2 MPa to 0.4 MPa in propylene stripper 1 (Figure S3). The H2O2 in the reactor

effluent stream (approximately 10%) is safely decomposed at 50°C to avoid flammable vapors in

the distillation columns prior to secondary recovery of the remaining unreacted propylene (in

propylene stripper 2), product PO and methanol. The effluent from this decomposer is a gaseous

mixture of oxygen and propylene whose composition (2 wt% propylene) lies below the lower

S12

flammability limit (LFL).(8) The effluent from the decomposer is sent to a PO stripper where the

product PO is recovered (P = 1.2 MPa, T = 56 °C). Methanol is separated from water in the

wastewater column (P = 0.3 MPa, T = 27 °C). The condensers in all the distillation columns

utilize cooling water.

Figure S3: Process flow diagram for the CEBC-PO Process.(24), (22), (23) Table S4 lists the

simulation parameters employed in this simulation and the compositions of the

recycle (R1-2)

S13

Table S4: Simulation parameters for the CEBC-PO Process.(22), (23) Input/Output stream flow

rates (lb/h) for the PO reactors obtained from the HYSYS® simulation

Propylene Epoxidation

Reaction Conditions Reactor: Four CSTRs in parallel

P= 2 MPa; T= 40 °C; Liquid Hourly Space Velocity (LHSV)= 5 h-1

Conversion (H2O2)= 90%

Catalyst Methyltrioxorhenium (MTO)

Product Selectivity PO= 99+ mol% (based on H2O2 consumed in the reactor), PO= 100 mol%

(based on propylene consumed)

Propylene Epoxidation

Mass Flow Rates Input Output R1

Nitrogen 11370 11370 11370

Hydrogen Peroxide

(H2O2)

35780 3578 -

Water 1760 18808 -

Methanol 190608 190608 190608

#Pyridine-N-Oxide 8420 - -

*MTO (catalyst) 1866 - -

Propylene 40340 4044 4044

Propylene Oxide - 55200 -

Refer to Figure S3 for stream identification (R1)

*Represents the initial catalyst loading that is retained substantially by the nanofiltration

membrane. The catalyst make-up rate is dictated by the assumed catalyst leaching rate. #Represents initial loading of promoter in the reactor attached to the catalyst. The promoter

make-up rate is dictated by the assumed catalyst leaching rate

S14

Section E. Impact Categories considered in this analysis and their descriptions

Table S5. Impact Categories considered in this analysis and their descriptions

Impact Category Description

Greenhouse Gas

Emissions

Change in atmospheric temperatures caused by the buildup of chemicals that

trap heat from the reflected sunlight that would have otherwise passed

out to earth’s atmosphere

Acidification Quantifies the potential emissions (such as SO2 and NOx) that increase the

acidity of water and soil systems

Ecotoxicity Quantifies the potential ecological harm of unit quantity of chemical released

into an evaluative (soil, water and air) environment

Eutrophication Estimates the potential release of chemicals containing N or P to either air or

water

Human Health

Cancer

Estimates the potential of a chemical released into an evaluative environment

to cause human cancer effects

Human Health

Non-Cancer

Estimates the potential of a chemical released into an evaluative environment

to cause human non-cancer effects

Smog Air Estimates the potential of a chemical released to air to cause smog via

photochemical reactions

Ozone Depletion

Potential

Estimates the potential of chemical released to air to destroy ozone based on

chemical’s reactivity and lifetime

S15

Section F. Estimation of reactor volume for the CEBC-PO Process

The reactor is modeled as a CSTR and epoxide formation (represented by the following

stoichiometry) is assumed to be the only reaction.

)()()()( 2632263 DOHCOHCBOHAHC +→+

The rate of hydrogen peroxide (limiting reagent) consumption at the operating conditions is

given by(25)

VCkr BB

'=− (1)

The steady state conversion of hydrogen peroxide (XB) is obtained from a material balance as

follows:

( )BB

Xk

vXV

−=

1' (2)

Volumetric feed rate (v) = 5.59 m3/h

Hydrogen peroxide conversion (XB) = 0.90

Pseudo first order rate constant for the propylene epoxidation (k’) = 0.04752 h-1

Volume of the reactor (V) = 1057 m3

S16

Section G. Methodology to extract the Environmental Impact Factors for TRACI from GaBi

The potential adverse environmental impacts caused by the fugitive emissions at the plant

are estimated using empirical equations available in literature. TRACI, environmental impact

factors used in the estimation of environmental impacts are extracted from GaBi® software using

the following methodology:

1. Create a new plan.

2. Create a new process in the plan rather than using the existing USLCI datasets.

3. Define the various components that constitute as fugitive emissions as process streams in the

process.

4. Input the estimated quantitative data in the process and execute the plan.

The differences in the predicted and reported data (total waste generated) may be attributed

to the increase in fugitive emissions with the aging of flanges and other connections. Such

temporal variations in fugitive emissions from various unit operations is not accounted for by the

empirical equations available in the literature. 26

S17

Table S6. Comparison of emissions obtained from Toxic Release Inventory data for

LyondellBasell’s Bayport, TX facility and those predicted by GaBi® software.(27)

Impact Units LyondellBasell PO/TBA Process

GaBi®,

gate-to-gate

millions

EPA Toxic Release

Inventory (gate-to-gate),

millions

Total

Waste

Released

Waste

Acidification [mol H+ Eq.] 0 N/A N/A

Ecotoxicity-Air [kg 2,4-DCP Eq.] 1.29(10-3) 2.4(10-2) 0.35(10-3)

Ecotoxicity- Surface Soil [kg Benzene Eq.] 0 0.27(10-6) 0.27(10-6)

Ecotoxicity Water [kg 2,4-DCP Eq.] 1.72 2.73 0.49

Eutrophication [kg N Eq.] 0 N/A N/A

Greenhouse Gas Emissions [kg CO2 Eq.] 1.32(10-2) N/A N/A

Human Health Cancer-Air [kg Benzene Eq.] 0.25 N/A N/A

Human Health Cancer-SS [kg Benzene Eq.] 0 0.36 6.2(10-3)

Human Health Cancer-Water [kg Benzene Eq.] 0.96 0.96 0.012

Human Health Criteria- Air

Point Source

[kg PM 2,5 Eq.] 0 N/A N/A

Human Health Non-Cancer Air [kg Toluene Eq.] 0.052 0.10 0.17(10-2)

Human Health Non-Cancer SS [kg Toluene Eq.] 0.94 0.71 0.012

Human Health Non-Caner

Water

[kg Toluene Eq.] 0.67 0.41 0.007

Ozone Depletion Potential [kg CFC-11 Eq.] 0 N/A N/A

Smog Potential [kg NOx Eq.] 0.0051 0.032 0.2(10-3)

DCP: Dichlorophenoxyace, Eq.: Equivalent, N/A: Data not available in the toxic release

inventory

S18

Section H. Predicted cradle-to-gate environmental impact assessment

Table S7. Predicted cradle-to-gate environmental impacts for producing propylene oxide by the

conventional PO/TBA, HPPO and CEBC-PO processes

Impact Units Conventional

PO/TBA

Process,

millions

HPPO

Process,

millions

CEBC-PO

Process,

millions

Acidification [mol H+ Eq.] 572 465 493

Ecotoxicity-Air [kg 2,4-DCP Eq.] 18.2 3.33 3.42

Ecotoxicity Surface Soil [kg Benzene Eq.] 6.3(10-2) 4.0(10-2) 4.0(10-2)

Ecotoxicity Water [kg 2,4-DCP Eq.] 212.6 132.9 138.2

Eutrophication [kg N Eq.] 0.32 0.21 0.30

Greenhouse Gas Emissions [kg CO2 Eq.] 3561 2598 2827

Human Health Cancer-Air [kg Benzene Eq.] 0.38 0.62 0.67

Human Health Cancer-SS [kg Benzene Eq.] 0.22(10-3) 0.12(10-3) 0.12(10-3)

Human Health Cancer-

Water

[kg Benzene Eq.] 0.315 0.227 0.23

Human Health Criteria- Air

Point Source

[kg PM 2,5 Eq.] 3.75 3.02 3.21

Human Health Non-Cancer

Air

[kg Toluene Eq.] 5031 946 954

Human Health Non-Cancer

SS

[kg Toluene Eq.] 4.88 3.19 3.08

Human Health Non-Caner

Water

[kg Toluene Eq.] 8444

6317 6569

Ozone Depletion Potential [kg CFC-11 Eq.] 4.11(10-5) 7.4(10-5) 7.7(10-5)

Smog Potential [kg NOx Eq.] 5.61 (10-3) 4.7(10-3) 4.5(10-3)

DCP: Dichlorophenoxyace, Eq.: Equivalent

S19

Notation

CB concentration of hydrogen peroxide in the liquid phase, kmol m-3

k’ pseudo first order constant for propylene epoxidation includes catalyst concentration, h-1

-rB rate of hydrogen peroxide consumption, kmol m-3 h-1

v volumetric flow rate of the reactor effluent stream, m3 h-1

V volume of the reactor, m3

XB steady state hydrogen peroxide conversion in the reactor

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