CTM 9.10 A3 Chemical Tanker Manual
CTM
Styrene Monomer and polymerising cargoes 		Doc No.: CTM 9.10 A3
Revision: 01
Date: 15 Oct 2024
Issued by: DPA
Approved by: MD

1. STYRENE MONOMER

Chemical Family:

Olefins, USCG compatibility group 30

Physical Properties

Property Value
Density 906 kg/m³ (20 °C / 68 °F)
Dynamic Viscosity 0.7 mPa.s (25 °C / 77 °F)
Vapor Pressure 670 Pa (20 °C / 68 °F)
Boiling Point 145 °C / 293 °F
Melting Point -31 °C / -24 °F
Flash Point 32 °C / 90 °F
Appearance Colourless to yellowish oily liquid. Please see SDS for details.

Regulatory information:

Property Value
Marpol Annex II cat Y
IBC ship Type 3
IBC 16.2.6 No
IBC 16.2.9 No
Pre-Wash Required No
Hazards Flammable, self-reactive and static accumulator. Heat sensitive.

1.1 Preloading preparation


Note:


Info on Inhibitor used

4-TERT-BUTYLCATECHOL (TBC): Styrene is generally inhibited with Par-tertiary Butyl Catechol (p-TBC), typically at 10-20 ppm or more, depending on the duration of the voyage. TBC is typically added to styrene monomer to inhibit polymer formation and oxidative degradation during storage and shipment. Typically, the product is considered inhibited when TBC levels are between 10-15 ppm, but if long storage times or high temperatures are anticipated, the product is inhibited at a higher level, as per charterer’s instructions. The time required for TBC concentrations to fall to a dangerously low level varies greatly because of different storage and handling conditions. The depletion rates in actual storage may be appreciably faster or slower depending on the set of environmental conditions. Key factors that affect depletion of TBC are heat and oxygen.

1.2 During loading

1.3 After loading

After loading, when nitrogen blowing, or padding is done, the officer should remain aware of bubbling that can remove some of the dissolved oxygen from SM.

1.4 Monitoring and reporting

1.5 Styrene Monomer Polymerization

Styrene monomer is inhibited with TBC to reduce and control self-polymerization. Styrene monomer undergoes polymerization slowly at ambient temperatures, but polymerization will become rapid at elevated temperatures. Styrene monomer may experience rapid polymerization if TBC inhibitor and dissolved oxygen are depleted at elevated temperatures or if the product is contaminated with incompatible materials. If excess heat is not adequately dissipated, the product temperature will rise with a subsequent rise in the rate of polymerization. The following should be considered as typical indications of runaway polymerisation:


Note:


Vapours may erupt violently from tank vents or, if vents become plugged with polymer, excessive pressure can be generated that may rupture the cargo tanks of the vessel. Styrene monomer should be monitored regularly for TBC content. Styrene-containing vessels should be protected from external sources of heat.

1.6 Emergency actions

These should only be considered after discussion with charters and the company. The action to take will depend on how far the runaway polymerisation has proceeded. The higher the temperature, the further the runaway has progressed and the more difficult to stop. Typical mitigating actions that might be taken in discussion with all relevant stakeholders can be:

1.7 Discharge and tank cleaning

Oxygen, nitrogen pressure, and temperature log should be presented at the discharge port. Tank cleaning should be done with ambient water and lines, blind spots well flushed. In case of failure of the main cargo pump, the emergency cargo pump may only be used as per CTM 9.6 section 13. As a minimum, a risk assessment must be made and both the company as well as charterer permission taken. If the tank is to be inerted, then oxygen level should be maintained 4-8%.

1.8 Sampling

Refer to sampling procedures in CTM 9.8 section 4. Ensure samples are discharged within the duration of inhibitor validity in compliance with company sample disposal procedures.

2. OTHER POLYMERIZING CARGOES

In addition to Styrene monomer, there are many cargoes that self-react. Some of the examples are Vinyl acetate monomer, Acrylates, Cyanates, and so on. Polymerization is an irreversible chemical reaction in which small molecules (monomers) bind together into large molecules (polymers) resulting in a change of state from liquid to solid. The process is exothermic (gives off large amounts of heat) and is a chain reaction. Heating the monomer acts as a catalyst and can trigger off/speed up the polymerization process. Once polymerization starts, it is very difficult/impossible to stop the process.

2.1 Hazards and health information

The hazards of polymerizing cargoes are as follows:

2.2 Prevention

Polymerization and self-reacting cargoes may be somewhat stabilized by two means:

2.3 IBC code requirements

IBC 15.13.1 Certain cargoes with a reference in column o in the table of chapter 17, by the nature of their chemical make-up, tend, under certain conditions of temperature, exposure to air or contact with a catalyst, to undergo polymerization, decomposition, oxidation, or other chemical changes. Mitigation of this tendency is carried out by introducing small amounts of chemical additives into the liquid cargo or controlling the cargo tank environment.

IBC 15.13.7 mentions Crystallization or solidification of cargoes normally carried in the molten state can lead to depletion of inhibitor in parts of the tank’s contents. Subsequent re-melting can thus yield pockets of uninhibited liquid, with the accompanying risk of dangerous polymerization. To prevent this, care shall be taken to ensure that at no time are such cargoes allowed to crystallize or solidify, either wholly or partially, in any part of the tank. Any required heating arrangements shall be such as to ensure that in no part of the tank does cargo become overheated to such an extent that any dangerous polymerization can be initiated. If the temperature from steam coils would induce overheating, an indirect low-temperature heating system shall be used.

2.4 Inhibitor

Inhibition is achieved by the addition of a small quantity of an inhibitor which retards/inhibits the reaction process. Some inhibitors work independent of oxygen while some do not. For Styrene Monomer, TBC (4-Tertiary Butyl Catechol) is usually added as an inhibitor. Other cargoes use different inhibitors like MEHQ (hydroquinone monomethyl ether) for acrylates. The transport of monomers by sea usually involves the addition of inhibitors and at the same time, ensuring that the cargo temperature is maintained as low as possible. The inhibitor added to the cargo should have sufficient validity for the intended conditions of the voyage i.e., expected voyage duration and expected temperature during the voyage. When inhibitor is added to the cargo on board the vessel, the operation should be witnessed by the ship’s officers. The Master should obtain an inhibitor or stabilization certificate as required by the IBC code.


Note:


A certificate of inhibition from the manufacturer of the cargo should specify the following information:

The signs of polymerization can be recognized by a rise in the temperature of the cargo. For this reason, the temperature of the cargo tanks carrying self-reacting cargoes must be closely monitored. If polymerization is suspected, a sample from the tank must be drawn for analysis. White particles or a milky appearance of the sample would indicate polymerization. This is a potentially dangerous situation. The company must be immediately notified as the situation may require immediate action to prevent further threat to the safety of the crew and vessel.

2.5 Precautions for polymerizing cargoes

General precautions are the same as described in Styrene monomer procedures above. Namely:

For cargo-specific polymerization information, Company should be advised and Charterers and shippers will be contacted as appropriate.