Metrohm White Paper

Utilizing online chemical analysis to

optimize propylene oxide production

Alyson Lanciki, Ph.D.

Propylene oxide (PO) is a major industrial

product with a yearly global production
of more than 7 million tons. PO is used in
assorted industrial applications, though
mainly for the production of polyols, the
building blocks for polyurethane plastics.
Several production methods exist, with and
without co-products. This white paper lays
out opportunities to optimize PO produc-
tion for safer and more efficient processes,
higher quality products, and substantial
time savings by using online process analysis
instead of laboratory measurements.

Metrohm International Headquarters; Herisau, Switzerland

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 Metrohm White Paper
Propylene oxide

Introduction Various uses of propylene oxide

Propylene oxide (PO) is a colorless and extremely flammable PO is a major industrial product with a global production of
liquid known by several names—epoxypropane, methyloxi- more than 7 million tons per year.4 Approximately 70% is used
rane, and epihydrin, to list a few.1,2 to make polyether polyols, which are raw materials used in
production of polyurethane.1,3–6 Another 20% is utilized to
make propylene glycol, used as an additive in cosmetics and
refined foods,4–6 as well as in the production of unsaturated
polyesters.1,6 The final 10% or so is used to create propylene
glycol ether solvents and other products.2,6

Production methods
There are several production processes available, however the
majority of PO is still co-produced along with styrene mono-
mer (approximately one third of PO production worldwide).1
Other methods include the chlorohydrin process, epoxidation
of propylene with hydrogen peroxide, epoxidation of propyl-
ene with organic peroxides, and even epoxidation using mol-
ten salts.1–6
PO is derived from crude oil and is used in several industrial
applications, however it is mainly consumed for the produc-
Process depends on market needs
tion of polyols which are the building blocks for polyurethane
PO production methods are available both with and without
plastics. The primary reactant used is propene (propylene),
byproduct materials. Depending on the market for these by-
though there are several different production processes cur-
products, one or more processes may be in major use globally
rently in use on the market.1–6
at any one time.
Derivative markets
Many different markets utilize PO to manufacture other prod- Processes with co-products:
ucts. Some of the top derivative markets are: • Chlorohydrin (CH-PO)
• polyols • Styrene (SM-PO)
• propylene glycol • Methyl tert-butyl ether / Tert-butyl alcohol (MTBE-PO / TBA-PO)
• propylene glycol ethers
Derivative-free processes:
• Cumene (CU-PO)
• Hydrogen peroxide (HP-PO)

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 Metrohm White Paper
Overview of the major PO production processes

The chlorohydrin process (chlorine process)

The first large-scale process developed for the production of Waste from CH-PO process
propylene oxide was based on the chlorohydrin route in the Wastewater resulting from the chlorohydrin process needs
earlier part of the 20th century. The chlorohydrin process has complicated and elaborate treatment methods. Salt resulting
been in decline since the 1950’s, though it still accounts for from the dechlorination procedure can be disposed of in the
a significant proportion of PO production volume globally.3,4 wastewater as well, though it is possible through chlor-alkali
High costs are involved both on the environment from the electrolysis to recover caustic and chlorine (at increased cost).3
massive amounts of wastewater and for utilities to generate
the large amounts of electricity needed to produce the
feedstock. CH-PO – Byproducts produced per ton of PO:1–5
• 100–150 kg 1,2-dichloropropane
Production method • 2.1 tons NaCl or 2.2 tons CaCl2
This method of PO manufacture is shown in Figure 1 and • 40 tons wastewater
Figure 2. The selectivity for producing propylene oxide is near
90%, however hundreds of kilograms of byproducts without
any significant sales market are obtained per ton of PO.1–3

Cl OH

OH Cl
2 + 2 HOCl +
Propylene 2-Propylene chlorohydrin 1-Propylene chlorohydrin

Cl OH
O
OH Cl
+ + Ca(OH)2 2 + CaCl2 + 2 H2O
2-Propylene chlorohydrin 1-Propylene chlorohydrin Propylene Oxide

Figure 1. Chemical process behind the chlorohydrin route to produce propylene oxide. Adapted from Bernhard et al.3

Figure 2. Schematic process diagram outlining the chlorohydrin method for co-production of propylene oxide. Adapted from Nijhuis et al.2
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 Metrohm White Paper
The styrene process (organic peroxide process)

Hydroperoxide process for PO production Production method: Styrene Monomer and PO

The hydroperoxide process involves oxidation of propylene The SM-PO process, which is outlined in Figure 3 and
to PO via use of an organic hydroperoxide, with a resulting Figure 4, creates styrene, with propylene oxide as the major
alcohol as a co-product. Commercially, there are two different co-product.2–5 Recovered feedstocks are recycled back into
hydroperoxides in use: ethylbenzene hydroperoxide (SM- the process. This method produces 2–2.5 tons of styrene
PO process) and tert-butyl hydroperoxide (TBA/MTBE-PO monomer per ton of PO.3–5
process).

Manufacturing styrene monomer Principal sources of emissions to water:4

Styrene monomer is one of the most important large-volume • acid purge from the oxidation unit
commodity chemicals, with more than 27 million tons • aqueous stream from epoxidation caustic wash
produced worldwide each year.4 Two major production routes • aqueous stream from styrene monomer production and
are in use—the ethylbenzene (dehydrogenation) process, purification
which is the most common, and via co-production with
propylene oxide (SM-PO process).1–5 The SM-PO process along
with the TBA/MTBE-PO process account for more than 40%
of the global total capacity of PO.3

+ O2
OOH
Ethylbenzene Ethylbenzene Hydroperoxide

OOH + + OH
Ethylbenzene Hydroperoxide Propylene Propylene Oxide 1-Phenylethanol

Al2O3
+ H2O
OH
1-Phenylethanol Styrene (monomer)

Figure 3. Chemical process behind the styrene (SM-PO) route to produce propylene oxide.3,4

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 Metrohm White Paper

Figure 4. Schematic process diagram outlining the styrene method for co-production of propylene oxide. Adapted from Nijhuis et al.2

SM-PO process conditions Related application note:

• Primary reactor conditions: 120–150 °C, 2–3 bar1–4 Monitoring of 4-tert-butylcatechol in styrene in
• Intermediate (EBHP) reaction conditions with propene accordance with ASTM D4590: AN-PAN-1027
over catalyst: between 90–130 °C, 15–60 bar1–4 https://www.metrohm.com/en/applications/AN-PAN-1027
• Total selectivity with respect to PO: 90% or more1–3
• 2.2–2.5 tons styrene produced per ton of PO3,5
• Process water condensate is stripped, organics recycled
back in to process, purified water as boiler feed
• Crude epoxidate stream is washed with caustic then
distilled to recover more PO from the process

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 Metrohm White Paper

The TBA / MTBE process (organic peroxide process)

Co-production with TBA

The second commercial hydroperoxide process in use today OH
+ O2 O
is the propylene oxide–tert-butyl alcohol (PO-TBA) process,
also known as TBA-PO or MTBE-PO / PO-MTBE. Figure 5 and Isobutane Oxygen tert-butyl hydroperoxide (TBHP)

Figure 6 summarize the production process.

Uses of tert-butanol and methyl tert-butyl ether

OH +
Tert-butanol (TBA) is used as a solvent and as a denaturant in O
ethanol. It is also used as an intermediate in the production tert-butyl hydroperoxide (TBHP) Propylene
of methyl tert-butyl ether (MTBE), which is the reasoning
behind the many names for this process. The TBA co-product
is converted directly to MTBE with methanol in the presence O
of a catalyst. +
OH
Propylene Oxide tert-butanol (TBA)
The majority of MTBE is utilized by refineries to increase
the octane number in gasoline as an additive (oxygenate)
to extend the lifespan of engines, especially in heavy- Figure 5. Chemical process behind the PO-TBA (also known as TBA-
duty machinery.1–5 Further processing of MTBE leads to PO or MTBE-PO / PO-MTBE) route to produce propylene oxide.1
the production of isobutylene,1,5 which is used to make
polyisobutylene (synthetic rubber) and the acrylic resin methyl TBA / MTBE (TBA-PO / MTBE-PO) process conditions
methacrylate (MMA). • Primary reactor conditions: 95–150 °C, 25–55 bar1–3
• Intermediate (TBHP) reaction conditions with propene
Regulations around the contamination of groundwater over catalyst: between 90–130 °C, 15–60 bar1–3
threaten the estimated market growth for MTBE. • Total selectivity with respect to PO: 90–95%1,3
• 2.5–3.5 tons tert-butanol produced per ton of PO3
• Process water condensate is stripped, organics recycled
back in to process, purified water as boiler feed

Propene
Co-products
Hypochlorite Chlorohydrin
production formation epoxidation

tert-Butanol separation

Water
Chlorine

Caustic
purification

Brine
Electrolysis
Treatment

Propylene Oxide
Hydrogen

Figure 6. Schematic process diagram outlining the propylene oxide-tert-butyl alcohol (PO-TBA, also TBA-PO, MTBE-PO, or PO-MTBE in
literature) co-production method. Adapted from Trent.1
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 Metrohm White Paper
Byproduct-free methods to produce PO

The following processes utilize (organic) peroxides for the

epoxidation of propylene to produce PO with only water as
a byproduct.

The cumene process (organic peroxide process)

The cumene process (organic peroxide process) Cumene in the chemical industry
The cumene to propylene oxide process (CU-PO) was Cumene is an aromatic hydrocarbon which is mainly used (in its
developed by Sumitomo Chemical. This PO production purified form) to produce cumene hydroperoxide (CMHP) —a
method is shown in Figure 7 and Figure 8. valuable intermediate for several other industrially processed
chemicals. Among these are phenol and acetone, detailed
Advantageous production method more in the related process application note, and later on in
Besides not being dependent on a separate co-product the applications section of this paper.
market, yet another advantage for CU-PO over SM-PO (and
other methods of PO production with byproducts) is the
stability of the hydroperoxide intermediate (CMHP).5 Related application note:
Determination of sulfuric acid in acetone and phenol:
AN-PAN-1008
https://www.metrohm.com/en/applications/AN-PAN-1008

Air
OOH

Cumene
Cumene Oxidation Hydroperoxide
(CMHP)

H2O
Hydrogenation Epoxidation Propylene
OH

H2
O Propylene
Oxide
α,α-dimethyl benzyl alcohol
Cumyl Alcohol (CMA)

Figure 7. Chemical process behind the cumene route to produce propylene oxide.5,7

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 Metrohm White Paper

Cumene (CU-PO) process conditions

• Oxidation conditions: atmospheric pressure (or up to 7
bar with autocatalysis)4, atmospheric O2, 80–120 °C3–5
• Cumene is purified and recycled within the process2,4,5
• Unreacted propene is also recovered and recycled5
• Temperature must be regulated (heat exchangers) to
avoid secondary reactions & runaway epoxidation
• Total selectivity with respect to PO: over 90%2

light ends H2O, Propylene

oxygenated Oxide light
compounds ends

N2, light ends

Crude
epoxidation

Propene
Propene
recycle

Crude
PO
Make-up extractor
Cumene
H2O, light
CMHP lights, O2,
NaOH ends
Cumene H2O
Air Propene
light
Cumene recycle ends CMA

extractor
Cumene Heavily Propylene
Heavies H2O heavies oxygenated
H2 Oxide
Recycle compounds

Figure 8. Schematic process diagram outlining the cumene-propylene oxide (CU-PO) method for byproduct-free production of PO. Adapted
from Nemeth and Bare.7

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 Metrohm White Paper
The hydrogen peroxide process

Harnessing the oxidation potential of H2O2

It was not until the 1990’s that hydrogen peroxide (H2O2)
could be used directly as an oxidizing agent in the production
of propylene oxide (now known as the HP-PO process).3
Conventional catalysts were found to be insufficient, and
thus a new catalyst (titanium silicalite-1, TS-1, Figure 9) was
synthesized to limit and suppress any secondary reactions.1–3

Epoxidation of propene with hydrogen peroxide

The details of the HP-PO process are shown in Figure 10 and
Figure 11. Unreacted propene is recycled to the main reactor Figure 9. Structure of TS-1, Si (grey) and Ti (black) tetrahedral con-
after removal of any traces of O2 for safety reasons. nected via oxygen bridges (white).8

The HP-PO process is nearly quantitative in producing PO

Hydrogen peroxide (HP-PO) process conditions
from a complete conversion of H2O2. The selectivity for PO
• Epoxidation conditions: < 90 °C and up to 30 bar2–4
in this process has been measured at more than 98%.2,3
• Methanol solvent is purified and recycled3,4,6
The effluent from this process must be monitored for traces
• Unreacted propene is also recovered and recycled to
of substances such as methoxypropanols and glycols prior to
primary reactor after removal of O2 (safety reasons)3,4
being discharged to a wastewater treatment plant (WWTP).
• Temperature must be regulated (heat exchangers) to
avoid secondary reactions and runaway epoxidation6
• Total selectivity with respect to PO: 94–99%2–4,6

H2
OH O
Hydrogenation
R R

R-anthraquinone
OH O
(R-AQ)
R-hydroxyanthraquinone
(R-HAQ) Air Oxidation H2O2
Propylene

Epoxidation

O
H2O

Propylene
Oxide
Figure 10. Chemical process behind the hydrogen peroxide route to produce propylene oxide.5

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 Metrohm White Paper
Environmental benefits Related application note:
The HP-PO process has the smallest environmental footprint Online analysis of peroxide in HPPO process: AN-PAN-1007
compared to all other existing technologies which produce https://www.metrohm.com/en/applications/AN-PAN-1007
propylene oxide at an industrial scale.4
• Wastewater reduction: 70–80%
• Energy savings: up to 35%
• Smaller industrial footprint
• Simpler raw material integration
• No byproducts, only H2O created beside PO

Quinones cycle Propylene Oxide

reactor

Makeup xylene

separation
reactor

& quinones
Oxygen
purge

flash
Hydrogen
L/L separation

epoxidation

Diluted

separation
H2O2

Propene Makeup
methanol
purge Methanol recycle Propene glycols

Figure 11. Schematic process diagram outlining the hydrogen peroxide-propylene oxide (HP-PO) method for byproduct-free production of
PO. Adapted from Nijhuis et al.2

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 Metrohm White Paper
Benefits of online process analysis

Typically, laboratory analysis for several key process parameters Inline and online process analysis also tie into closed-loop
is the norm to keep the production facility running smoothly control which brings production back in specification automat-
and safely. Manual sampling from various points along the ically with feed-forward chemical replenishment. Out-of-spec-
process is a necessity, which takes up valuable time. Delays in ification readings immediately trigger a warning at the control
sampling, analytical measurement, and data sharing due to room, ensuring the fastest response times. Analysis occurs at
these offline measurement strategies can have serious detri- the sampling point, leading to more accurate and reproducible
mental effects on production efficiency and overhead costs. results by the elimination of human bias and sample degra-
dation from transport delays. Reduction of manual sampling
lowers costs, saves time, and increases the safety of plant
operations.

Sampling Point
Process
Laboratory
$
SAVE
MONEY

Utilization of more effective methods which increase process Several online and inline application solutions exist for the
efficiency leads to higher productivity. Improvement of product production of propylene oxide. Titration, photometry (colo-
quality can be achieved much easier with the implementation rimetry) and even reagent-free spectroscopy all play signifi-
of automated process analysis, which increases profitability cant roles in these production processes.
for manufacturers.
Each PO production method is unique and requires a com-
bination of analytical techniques to cover the entire process,
from monitoring the raw material purity and environmental
ITY
TIV contaminants in the effluent up to and including stripping and
UC
OD recovery of reactants from the different process streams.
PR

Advantages of online analysis for PO production:

• 24/7 analysis for difficult to sample, hazardous
substances
Time-consuming manual sampling and long distances to the • Fast and reliable measuring techniques available
laboratory are eliminated by utilizing online, inline, or atline (including reagent-free spectroscopic methodology)
process analyzers. Samples are more representative and re- • No manual intervention necessary for analysis
producibility of results is increased as the measurements are • Protection of company assets with built in alarms at
performed exactly the same, every time. Chemical analysis specified warning limits, less downtime
performed directly at the most critical process points reduces • Safer working environment for employees: no manual
the potential for unforeseen plant shutdowns by providing sampling necessary (Cl2, exothermic epoxidation, high
data in real-time to the central computing system. temperature/pressure, autopolymerization, ATEX)
• Saving of chemicals and labor with faster response
times
• Byproduct storage control options (e.g. TBC in Styrene)
• Tighter specifications for impurities in recycled
reagents
• Increased product yield with an optimized production
process: more profitability
• Accurate, real-time moisture analysis in hygroscopic
sample matrix
• Purity analysis in final product made easier: higher
quality
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 Metrohm White Paper
Online and inline process application solutions for
the production of propylene oxide
There are numerous applications for this sector which can be
elevated from time-consuming manual techniques to auto-
mated online or inline process analysis solutions. A selection
of these applications for the production of PO is described
below.

HP-PO: High concentration H2O2 in effluent of the pri- heads and must be measured accurately. The measurement
mary reactor (reaction outlet line) is performed online with photometric titration, with all data
In the HP-PO process, hydrogen peroxide present in a metha- sent immediately to the control room for immediate process
nol solvent is used as the sole oxidizing agent and is the criti- adjustment measures in case of higher H2O2 concentrations.
cal feedstock and parameter to measure the complete con-
version rate to PO. Thus the high demand for accurate and Related application note:
robust online process monitoring throughout the whole reac- Online analysis of peroxide in HPPO process: AN-PAN-1007
tion process. https://www.metrohm.com/en/applications/AN-PAN-1007

Hydrogen peroxide can be accurately monitored in the efflu-

ent of the primary reactor using an online analysis solution
Primary Circulation: Measuring base in the primary cir-
designed for extremely hazardous areas. Explosion-proof
culation tank
(ATEX) process analyzers are especially suitable—compliant
Caustic (sodium hydroxide, NaOH) is necessary in several
with all electrical safety requirements, and specifically de-
processes which manufacture propylene oxide, especially
signed for high throughput processing in a hazardous
in the chlorohydrin (CH-PO) process. The concentration of
industrial environment. Strict safety precautions must be
NaOH is important to monitor in recirculating caustic streams
implemented with all production and process equipment.
feeding the primary circulation tank.
Measuring the H2O2 concentrations in the primary reaction
Analysis of sodium hydroxide content is easily performed
tank plays a vital role to ensure high PO yields throughout the
online with an industrial process analyzer configured for auto-
conversion process while reducing costs with low feedstock
mated titration. With a wide range of caustic concentrations
consumption. This application can be performed online with
able to be accurately measured, the recirculating feed streams
photometric titration. With 24/7 automated online analysis,
can be quickly adjusted to reach optimal levels.
alarms for out-of-specification values can be sent directly to
the control room for fast response.
NaOH Titration
Related application note:
Online analysis of peroxide in HPPO process: AN-PAN-1007
https://www.metrohm.com/en/applications/AN-PAN-1007
pH

HP-PO: Hydrogen peroxide in the finishing reactor

(upstream of propene recovery section)
Analyzing the residual H2O2 concentrations in finishing
reactor overheads upstream of the propene recovery section
ensures that unreacted hydrogen peroxide is closely moni-
tored for control measures after the epoxidation reactor. Titrant Volume (mL)

Considering the dangerous nature of this area of the process, Figure 12. Titration curve for the determination of caustic soda
online measurement techniques are key. Hydrogen peroxide (NaOH) in a chemical manufacturing process. Data provided by a wet
is present in low concentrations in the finishing reactor over- chemical process analyzer from Metrohm Process Analytics.

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 Metrohm White Paper

SM-PO: Monitoring TBC levels accurately in the styrene Performing this measurement online with titration in an in-
storage tank according to ASTM D4590 dustrial process analyzer allows the control room to monitor
In the SM-PO process, styrene is manufactured along with the long-term trends, optimize the process, and keep a close
propylene oxide. Styrene is a monomer, which polymerizes to watch on concentrations of these chemicals outside of their
form polystyrene, used in a wide array of industrial and con- programmed warning levels.
sumer goods. The stabilizer 4-tert-butylcatechol (TBC) plays
a crucial role in preventing premature polymerization during
storage and transport of styrene, butadiene, vinyl acetate, and
other reactive monomers. Cumene: sulfuric acid in acetone & phenol (cleavage
reactor)
TBC is a free radical inhibitor which requires oxygen to pre- The CU-PO process requires cumene as a reactant. Cumene
vent the monomers from polymerizing. In the presence of the is produced from benzene and propylene, and can be used
correct amount of TBC, peroxide radicals are scavenged. Oth- as an intermediate in the production of other basic chemi-
erwise, the peroxide radicals react with styrene monomers to cals. Phenol, one of the products from the cumene produc-
form peroxide chains (polyperoxides) until the oxygen is com- tion process, is a precursor for the production of bisphenol A
pletely depleted. (65%) which is used to make polycarbonates. Other products
are phenolic resins and cyclohexanol. The production process
These radical species are especially hazardous during purifica- has three stages:
tion processes (distillation) due to the instability of peroxides
at increased temperatures. In order not to compromise the • production of cumene from benzene and propylene
product quality, the TBC concentration in styrene must stay • conversion of cumene to cumene hydroperoxide (same
above 10–15 mg/L. To control TBC depletion and ensure opti- process as in CH-PO)
mal storage conditions, close monitoring of its concentration • decomposition of cumene hydroperoxide to phenol and
is required. acetone

ASTM D4590 describes the specifications required to In this last stage, small amounts of sulfuric acid (H2SO4) are
accurately measure TBC inhibitor in styrene monomer within used to catalyze the reaction. Since the last reaction is very un-
this range, using colorimetry.9 Automated online photomet- stable, the cleavage reactor must operate under strict temper-
ric analysis of TBC is possible 24/7 with an explosion-proof ature and acidity control with a high level of acetone reflux. To
industrial process analyzer. Accurate data is provided around prevent the formation of color bodies and other undesirable
the clock, warning operators immediately if TBC levels are too byproducts, and to minimize corrosion, it is then necessary to
low. remove these traces of sulfuric acid prior to downstream dis-
tillation and purification. Therefore accurate and timely mea-
surement of sulfuric acid plays an important role in cumene
Related application note: production (found concurrently with the CU-PO process).
Monitoring of 4-tert-butylcatechol in styrene in
accordance with ASTM D4590: AN-PAN-1027 This analysis can be performed online via titration with a
https://www.metrohm.com/en/applications/AN-PAN-1027 process analyzer for both the cleavage effluent (lower con-
centrations) and for downstream production stages (higher
concentrations).

CU-PO: Determination of hydroquinone and hydrogen

peroxide content in cumene production Related application note:
During the hydrogenation process when producing cumene Determination of sulfuric acid in acetone and phenol:
from cumyl alcohol (CMA, Figure 7), the oxidized stream AN-PAN-1008
returning to the hydrogenator, as well as the reduced stream https://www.metrohm.com/en/applications/AN-PAN-1008
exiting the hydrogenator, must be monitored for both hydro-
quinone and hydrogen peroxide content. These impurities can
be detrimental to the production process for PO, affecting
product quality and yield.

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Finished Product: Analysis of low-level moisture in Polyols: Measuring OH in filter feed tank discharge
propylene oxide Approximately 70% of PO produced globally is used to make
Propylene oxide is a hazardous, flammable substance and polyether polyols, important raw materials for polyurethane
therefore must be treated with extreme caution. Measure- production. Hydroxyl (OH) is an important functional group
ment of moisture and other impurities in the final product and knowledge of its content is required in many intermediate
(as well as along the manufacturing process at critical points) and end-use products such as polyols.
is necessary to overcome unwanted side reactions or poor
yields. Manual laboratory analysis methods can be quite cum- Analysis of KOH in the production of polyols is necessary in
bersome and can introduce bias depending on the analyst. order to more tightly control the process and avoid unwanted
reactions from occurring. Manual sampling and analysis can-
The hygroscopic nature of PO necessitates inline or online not accurately monitor hydroxyl levels on a regular, contin-
analysis of water content for the most precise results. Addi- uous basis. Data transfer is slow and in the meantime, the
tionally, «real-time» analysis is a requirement for high through- uncorrected production process leads to suboptimal product
put PO production because this gives short response times in quality or lower yields.
case of process changes or increased water content in the
final product. Online measurement of OH concentrations is made simple us-
ing, for example, an explosion-proof (ATEX) industrial process
Fast, inline analysis of low moisture content is possible with analyzer configured for conductivity measurements. Time is
reagentless techniques such as near-infrared spectroscopy saved with the elimination of manual sampling procedures,
(NIRS). Suitable NIRS process analyzers are available for use and process optimization can be achieved more quickly when
in dangerous ATEX environments with robust stainless steel precise measurements of the hydroxyl content are consistently
flow cells. performed.

Summary

Propylene oxide is a key industrial product, manufactured via Manual sampling and laboratory analysis methods are slow
several different methods for use in various industries. With and can introduce human error and bias, which puts em-
global production of more than 7 million tons per year, PO is ployees at risk (health and safety). Additionally, the liberated
a major necessity for our modern lives. End products such as samples are no longer completely representative of the man-
polyester, polyurethane, and several types of solvents would ufacturing process, as many factors differ from the process
be much more difficult to manufacture without this raw after manual sampling such as temperature or pressure.
material.
Online and inline analysis techniques performed with
PO production is achieved either with or without the creation robust and rugged industrial process analyzers can overcome
of marketable co-products. The chlorohydrin process (CH-PO) many challenges which face every industry. There are several
was the first large-scale production route developed, however automated solutions currently available on the market to
large volumes of wastewater are produced and utility costs provide these services 24/7. When utilizing online titration,
are exorbitant, which has led to a decline in the popularity of photometry, ion chromatography or even inline spectroscop-
this method. Styrene (SM-PO) and methyl tert-butyl ether / ic techniques such as NIR analysis, companies can increase
tert-butyl alcohol (MTBE-PO / TBA-PO) production routes have the efficiency of their operations and reduce downtime due to
grown in popularity relative to the demand and sale price of unforeseen events. Results are more reliable and accurate
the byproducts created during manufacture. With the grow- with automation, as human error is removed from the equa-
ing pressure to become more environmentally friendly, deriv- tion. Company assets are protected through automated
ative-free processes such as cumene (CU-PO) and hydrogen process control and direct data transfer for immediate
peroxide (HP-PO) have been developed and are fast growing adjustments in critical situations. Improvement in the safety of
in this sector. the employees is an added bonus through the elimination of
manual sampling and analysis.

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References

[1] Trent, D.L. Propylene Oxide. Kirk-Othmer Encyclopedia of Chemical Technology; online edition, John Wiley & Sons, Inc.:
New York, 2001. doi:10.1002/0471238961.1618151620180514.a01.pub2

[2] Nijhuis, T.A.; Makkee, M.; Moulijn, J.A.; Weckhuysen, B.M. The Production of Propene Oxide: Catalytic Processes and
Recent Developments. Ind. Eng. Chem. Res., 2006, 45, 3447–3459. doi:10.1021/ie0513090

[3] Bernhard, M.; Anton, J.; Schmidt, F.; Sandkaulen, F.; Pascaly, M. Vom Chlor zum Sauerstoff: Über den Technologiewandel in
der Propylenoxid-Herstellung. Chem. Unserer Zeit, 2017, 51, 198–209. doi:10.1002/ciuz.201700764

[4] Best Available Techniques (BAT) Reference Document for the Production of Large Volume Organic Chemicals; European
Integrated Pollution Prevention and Control Bureau (EIPPCB), Publications Office of the European Union: Luxembourg City,
Luxembourg (2017). http://eippcb.jrc.ec.europa.eu/reference/

[5] Tsuji, J.; Yamamoto, J.; Ishino M.; Oku, N. Development of New Propylene Oxide Process; Technical report translated from
"Sumitomo Kagaku" volume 2006-I: Sumitomo Chemical Co., Ltd., 2006.

[6] ThyssenKrupp Uhde. Propylene Oxide. The Evonik-Uhde HPPO technology: Innovative - Profitable - Clean. ThyssenKrupp
Industrial Solutions AG: Dortmund, Germany, 2015.

[7] Nemeth, L.; Bare, S.R. Science and Technology of Framework Metal-Containing Zeotype Catalysts. Advances in Catalysis,
2014, 57, 1–97.

[8] To, J.; Sokol, A.A.; Bush, I.J.; Catlow, R.A.; van Dam, H.J.J.; French, S.A.; Guest, M.F. QM/MM modelling of the TS-1 catalyst
using HPCx. J. Mater. Chem., 2006, 16, 1919–1926.

[9] Standard Test Method for Colorimetric Determination of p-tert-Butylcatechol In Styrene Monomer or AMS
(α–Methylstyrene) by Spectrophotometry; ASTM D4590-18; ASTM International: West Conshohocken, PA (2018).
https://www.astm.org/Standards/D4590.htm
WP-048EN by Metrohm, published 08-2019

Contact: 041-info@metrohm.com

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