Nufarm DNBP as a Styrene Polymerization Retarder

DNBP (2,4-dnitro-6-sec butyl phenol) is the most commonly used polymerisation

control additive in the distillation of styrene monomer. It is used similarly in

divinylbenzene. Used on its own it is an effective and safe retarder that has been

proven over many years use, it can be used in all plant designs and at all

temperatures found in the distillation sections.

DNBP can be used as a direct replacement for 2,4-dinitrophenol (DNP), 2,4-dinitro-

o-cresol (DNOC) and 2,4-dinitro-p-cresol (DNPC). These other nitrophenols are

solids with very low solubility in styrene or ethylbenzene requiring manual handling of

the material on location. DNBP is a low melting point solid (35°C) and is very soluble

in ethylbenzene enabling it to be pumped from a container to bulk store tank with no

manual handling required.

Most widely used polymer control additive in styrene production.

A retarder that gives long lasting protection even under abnormal conditions

which can occur in plant outages such as pump failure, vacuum failure etc

Proprietary process that reduces residual free acid to very low levels

Nufarm DNBP can also be used in combination with Nufarm stable free radical

products for improved performance at reduced cost (see AHM 700 Series)

Nufarm registered DNBP under the European REACH regulations in November 2010

and will continue to support this useful and valuable product.

Nufarm DNBP is available in several different formulations. We are always ready to

evaluate new mixtures to suit specific customer plants.

H507A: DNBP technical, molten solid

H509A: 50% DNBP in Ethylbenzene

H510A: 70% DNBP in Ethylbenzene

H513A: 75% DNBP in Ethylbenzene

All Nufarm DNBP is produced at our own site in the UK and is quality controlled

before leaving site. It is available in 200L drums, 1000L intermediate bulk containers

(IBC) and in isotanks.

We aim for high quality at all times and in all areas; from production, through QC and

shipping, to technical service.

Nufarm AHM 700 Series Styrene Polymerization Inhibitors

The Inhibitor AHM 700 series are polymerization control additives specifically

designed to enable the most efficient trouble free operation of styrene monomer

production plants. They are a mixture of DNBP retarder with a true inhibitor that

offers greatly improved anti-polymerization performance compared to other

commonly used materials. The performance and economics have been proven at

many plant trials and conversion rate from plant trial to full time use is 100%.

Easily handled liquid products.

Superior polymer control, and can be used at a much lower dose, compared to

conventional nitrophenolic products

Reduced usage rate leads to superior economics and low NOx when residues

are burnt

Retarder and inhibitor properties in a single product so only one storage and feed

system is required

Nufarm AHM 700 series comprises several different formulations designed to suit a

variety of plant conditions and we can create bespoke formulations to suit specific

customer needs.

Inhibitors are selected from our range of stable free radical (SFR) products and

phenylenediamines.

The latest development from Nufarm is a liquid, solvent-free, mixture that reduces

shipping costs and the amount of product handling required.

Inhibitor AHM 700 series are available in 1000L intermediate bulk containers (IBCs)

and in isotanks.

Case History: Savings on plant >$500,000 per year

Parameter Pre-Trial With AHM700 % Change

DNBP in EB splitter, ppm 1250 900 -28

Polymer in EB splitter, ppm 3000 750 -75

DNBP in SM column, % 1.5 1.0 -33

Polymer in SM column, % 6.5 3.5 -46

Green Retarders as Styrene Monomer Polymerization Inhibitors

Retarder MB-1 is a Nufarm patented formulation for use in styrene in combination

with a true inhibitor.

Retarder MB-1 is not classified as toxic and offers a greener alternative to the

retarder DNBP.

The combination of Retarder MB-1 and a true inhibitor provides excellent control of

polymer during styrene distillation and is successfully used in several commercial

styrene distillation units.

Most effective at temperatures up to 110°C

Retarder MB-1 is not classified as toxic

Reduced NOx when distillation tars are burnt.

Easy to handle liquid product

H530A: Retarder MB-1, 55% solution in ethylbenzene

Retarder S450 (patent applied for) is a new retarder suitable for use in all styrene

monomer plants. It has been tested and shown to be effective up to 160°C and is

therefore ideal for plants operating at higher operating temperatures and those

operating with heat recovery systems.

Retarder S450 is not classified as hazardous for transport and offers a true Green

alternative to DNBP. Used in combination with a true inhibitor it offers excellent

performance.

This is a newly commercialised product and material is available for plant trials.

Nufarm’s experienced and skilled Technical Service Team will be on hand to guide

you through all aspects of a plant introduction.

Nufarm Crude C4 Inhibitors for Butadiene Units

Crude C4 cuts are produced by crackers and contain varying amounts of the

valuable monomer 1,3-butadiene. These can be processed on site but can also be

transported and traded for processing at sites remote from the crackers.

Butadiene can form polymers during storage and transportation, both poly-butadiene

rubber and, via reaction with oxygen, polyperoxides that are highly unstable and

hazardous.

Crude C4s are therefore stabilized during transport and the ideal product is one

which combines a phenolic anti-oxidant to remove poly-peroxides and a stable free

radical product that can prevent any polybutadiene formed from carbon radical

reactions.

Nufarm’s crude C4 stabilizer, Inhibitor AHM E870, is designed to perform these

functions and has been successfully used for several years.

Nufarm Polymerization Inhibitors for Butadiene Production

Butadiene is extracted and purified from a crude C4 stream using several different

technologies. The basic principle of them all is to use a solvent to extract 1,3-

butadiene from the other stream components, the solvent and butadiene are then

separated by distillation and finally polymer grade butadiene is purified in a final

distillation step.

There are two types of polymer that can form in a butadiene distillation unit

Polybutadiene rubber

o This is formed by carbon-carbon radical reaction and is characterised

by soft brown polymer. The process can be inhibited with stable free

radical inhibitors and Nufarm have been providing these compounds to

butadiene producers for over 10 years. It is normal to achieve 5 year

run-lengths between mandatory shutdowns using these products.

Nufarm can provide a bespoke product for your plant and advice is

available from our Technical Service Team.

o Products Available

Inhibitor AHM B238 (>10 years of commercial use)

Inhibitor AHM B247 (>7 years of commercial use)

Inhibitor AHM B239 (>5 years of commercial use)

Popcorn polymer

o This is formed when oxygen ingress occurs and is characterised by

white or yellow globular polymer that grows from the inside out and can

damage equipment through uncontrolled growth. Butadiene plants

rigorously exclude oxygen and operate under a positive pressure of

several bar. Excellent engineering and operator controls are required

to prevent oxygen ingress because there are no polymerization

inhibitors capable of preventing popcorn polymer growth once it has

seeded. The characteristic of the popcorn polymer of growing in the

vapour phase and containing internal radical sites means that

conventional inhibitors are ineffective. The Nufarm Technical Service

Team can advise on industry best practice to prevent popcorn polymer.

Nufarm Polymerization Inhibitors for Acrylonitrile

Acrylonitrile (ACN) is largely produced using the SOHIO process with propylene,

ammonia and air (oxygen) as the raw materials giving acrylonitrile, water and HCN

as products. The HCN can be recovered as a commercial product (a raw material

for MMA production) or incinerated. The purification of ACN is essentially split into

two sections (i) Recovery of ACN by quenching the gaseous reaction product in

water and (ii) Purification of ACN to give the polymer grade product. Purification of

the product includes a HCN column, a drying column and then the final product

column.

Fouling in the acrylonitrile plant can occur in the HCN column but this is largely

anionic polymerization of the HCN and cannot be controlled by free radical inhibitors.

It can be mitigated by addition of acids (usually acetic acid) and good engineering

techniques combined with dispersants are used to keep this column free of fouling.

Free radical polymerization occurs in the acrylonitrile, causing fouling of the column

plates and the reboiler, and can be inhibited using stable free radicals. Nufarm have

developed a proprietary product for acrylonitrile polymerization inhibition that has

provided excellent results as the case history below demonstrates.

2005: Hydroquinone/Phenylenediamine treatment

2008: Nufarm treatment, Inhibitor AHM N720

0

1

2

3

4

5

2005 2008

Frequency of Shutdowns

HCN

Drying

Product

The reduction in annual cleaning costs for this plant was in the order of US$570,000.

In addition to the reduced fouling, AHM N720 eliminated the need for manual

handling required for the previous treatment and reduced operator exposure to

acrylonitrile. The Nufarm treatment also increased ACN/water separation rates in

two decanters, thus increasing plant efficiencies.

Nufarm Polymerization Inhibitors for Acrylic Acid and Acrylic

Esters

Acrylic acid is a highly corrosive monomer that can polymerize extremely quickly and

violently. Thus the prevention of polymerization is not only critical to improving plant

efficiencies but also to the safety of the process. Polymerization is affected by many

competing influences including the metallurgy of the plant, the amount of water

present in different areas, temperature and the amount of air (oxygen) present, all of

which influence the tendency and rate of acrylic acid to polymerize.

Nufarm stable free radical inhibitors have been used in acrylic acid distillation and

through our own research, and working closely with our customers, Nufarm has

gained a high level of expertise in the prevention of acrylic acid polymerization in all

areas of the plant. Our Technical Service Team is available to give advice on the

best products for each area of the plant.

Acrylic esters are produced from the esterification of acrylic acid with a range of

different alcohols. Nufarm has products that will prevent polymer fouling in both the

esterification reactors and in the purification section.

The case history shown below shows what can be achieved with the correct

product selection.

Before treatment started with Nufarm, the customer had to clean the pump screens

many times per day, now the screens are checked only during plant maintenance.

Start of Nufarm

Inhibitor treatment

Nufarm Polymerization Inhibitors for Methyl Methacrylate

Methyl methacrylate (MMA) has been made principally using the Acetone

Cyanohydrin (ACH) route developed in the 1930s. Recently Lucite have introduced

the Alpha Process and started the first operational plants using this technology.

Nufarm has provided inhibitors for plants operating using both technologies and our

Technical Service Team can offer advice on product selection depending on the part

of the plant to be treated.

One of the main fouling locations in the ACH route occurs in the reactor section. The

data below compares the efficacy of two Nufarm products under typical conditions

encountered in this section

Methyl Methacrylate 15%w/w

Methacrylic acid 2%w/w

Sulphuric acid (36%) 32%w/w

Ammonium Bisulphate 51%w/w

Inhibitor 1ppm

Temperature 100oC

0

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4

6

8

10

12

14

16

Inhibitor S4 P500 HQ

Po

lym

er

Inhibitor

1st Run

Data shows that both Inhibitor S4 and AHM P500 (a more acid stable inhibitor)

exhibit high efficacy in reducing MMA polymerization compared to the conventionally

used hydroquinone.

Nufarm Polymerization Inhibitors for Vinyl Acetate Monomer

Vinyl Acetate Monomer (VAM) requires inhibition to prevent polymerization in the

purification by distillation. Old inhibitor technology has now been displaced by the

use of stable free radical chemistry in this monomer.

Nufarm currently supplies inhibitor to a large VAM plant and can offer a range of

different inhibitor/solvent combination to suit your specific requirements.

0

1

2

3

4

5

TBC/BQ Inhibitor S4 P500

Po

lym

er

The above graph compares the efficacy of Nufarm inhibitor products (Inhibitor S4

and AHM P500) with the conventionally used treatment system of tert-butyl catechol

(TBC) and p-benzoquinone (BQ).

Both Nufarm products provide a significant reduction in the amount of polymer

formed.

Nufarm Inhibitors for the Ethylene Train

Naphtha or ethane are “cracked” to give the range of unsaturated monomers that are

used to produce many of our polymers used in everyday life. In various amounts,

ethylene, propylene and butadiene are produced and separated by distillation. C4s

including butadiene can be purified remotely and are often traded. C5+ materials are

also produced.

Stable free radicals are well established in the purification of ethylene and propylene.

They are also used in compressors to keep these clear of fouling. Nufarm staff have

many years of experience in the industry and can advice on dosing locations and

quantities to prevent fouling.

We currently supply products to both depropanisers and debutanisers.

Case History: In 2010 we were approached by a company with severe fouling

problems in their debutanizer unit. Typical run-lengths before shutting down to

clean the column were 150 days only. Nufarm treatment was started in September

2010 and to date there has been no indication of fouling, no pressure drops, no

change in steam valve settings etc.

Nufarm Inhibitors for Pygas and Pygas Hydrotreating

Pyrolysis gasoline (pygas) is the cut of heavier molecules (C5+) that is generated by

the cracking of naphtha or ethane. It is used as a feedstock for BTX units and is

transported and traded in bulk.

Nufarm supplies Pygas stabilisers that can be added to the pygas during transport to

prevent the formations of gums or polymer whilst in transit. These are particularly

useful if the pygas is to be stored for any significant time or transported through hot

climates.

Pygas can be hydrotreated (hydrogenated) to remove unsaturated compounds from

the stream. This process is hot, and fouling caused principally by styrene and

cyclopentadiene can occur in the reboiler and heat exchangers. Nufarm has been

supplying inhibitors to prevent fouling in this process for six years.

Nufarm Inhibitors for Chlor-Vinyls

Vinyl Chloride monomer (VCM) is a very large volume monomer whose polymers have a wide range of application in both flexible and rigid forms. The most common method of production is via ethylene dichloride (EDC).

EDC is prepared by reacting ethylene and chlorine. This process is very selective, resulting in high purity EDC and high yields. When the EDC is heated to 500 °C at 15–30 atm (1.5 to 3 MPa) pressure, EDC vapour decomposes to produce vinyl chloride and anhydrous hydrochloric acid.

Even though residence time and temperature are carefully controlled, it produces significant quantities of chlorinated hydrocarbon side products. In practice, EDC conversion is relatively low (50 to 60 percent). The furnace effluent is immediately quenched with cold EDC to stop undesirable side reactions. The resulting vapor-liquid mixture then goes to a purification system.

VCM itself does not cause significant fouling problems during purification but some of the by-products of the cracking process do so. Chloroprene can foul the Lights column and Nufarm can supply inhibitors to keep this column free of polymer and reduce the amount of valuable product lost to waste.

Vinylidene Chloride is produced by the alkaline de-chlorination of 1,1,2-trichloroethane and has a tendency to polymerize during purification. Nufarm Technical Services can offer advice on the best inhibitors to use to prevent this based on our past experiences in commercial units.