What Is THPS?
THPS (tetrakis(hydroxymethyl)phosphonium sulfate), CAS 55566-30-8, is a water-soluble organophosphorus biocide, supplied as an acidic aqueous solution (typically about 75% active). It is a broad-spectrum antimicrobial used mainly in industrial water systems – above all in oilfield water injection, where controlling bacteria is essential – and in cooling water, process water and pulp/paper systems. THPS is also a key intermediate in flame-retardant chemistry.
This guide covers the chemistry, specification, properties, production, biocide mechanism and applications of THPS, its comparison with other water-treatment biocides, dosage, safety and supply. PolyBlueChem supplies THPS to the specification below with per-batch COA and SDS.
| CAS number | 55566-30-8 |
| Chemical name | Tetrakis(hydroxymethyl)phosphonium sulfate |
| Synonyms | THPS; bis[tetrakis(hydroxymethyl)phosphonium] sulfate |
| Formula unit | [(HOCH2)4P]2SO4 |
| Molecular weight (formula unit) | About 406.3 g/mol |
| Form | Aqueous solution (~75% active) |
Chemistry and Structure
THPS is the sulfate salt of tetrakis(hydroxymethyl)phosphonium: a central phosphorus atom bearing four hydroxymethyl (-CH2OH) groups, as the phosphonium cation, balanced by sulfate anions. The structure explains its behaviour:
- The phosphonium centre carries a positive charge – the basis of its antimicrobial action against negatively charged microbial surfaces.
- The four hydroxymethyl groups make the molecule highly water-soluble and reactive (they are the handle for further chemistry, such as crosslinking in flame-retardant finishing).
- The sulfate counter-ion makes the commercial product a stable, water-soluble salt rather than a chloride (compare THPC, the chloride analogue).
THPS is a non-oxidising biocide: unlike chlorine or peroxide biocides, it works by a chemical (not oxidising) route, which is why it is favoured in systems where oxidising biocides would corrode metal, damage membranes or react with process chemicals.
Specifications
THPS is supplied as an aqueous solution to the following specification:
| Parameter | Specification |
|---|---|
| Content (as [(HOCH2)4P]2SO4) | 75.0% min |
| Viscosity (25 °C) | 30.0 – 40.0 mPa·s |
| Relative density (25 °C) | 1.350 – 1.420 |
| Iron (Fe) | 20 ppm max |
| pH | 2.5 – 5.5 |
| Parameter | What it controls |
|---|---|
| Content (75.0% min) | Active strength of the solution; dosing is set on the active content |
| Viscosity / relative density | Consistency of the solution; assists dosing and quality control |
| Iron (20 ppm max) | Metal content, important in systems sensitive to iron fouling |
| pH (2.5 – 5.5) | Acidity of the solution; characteristic of THPS and relevant to dosing and materials compatibility |
A specification sheet and a per-batch certificate of analysis (COA) are available on request.
Physical and Chemical Properties
| Property | Behaviour |
|---|---|
| Form | Aqueous solution (about 75% active) |
| pH | Acidic (2.5 – 5.5) |
| Solubility | Fully miscible with water |
| Type | Non-oxidising organophosphorus biocide |
| Compatibility | Not an oxidiser; used where oxidising biocides are unsuitable |
| Handling | Acidic and irritant; keep away from alkalis and strong bases |
Two points matter in use: THPS is water-soluble and acidic (so dosing and materials compatibility must account for the pH), and it is non-oxidising (so it complements, rather than competes with, oxidising biocides).
How THPS Is Produced
THPS is made from phosphine chemistry. Phosphine (PH3) is reacted with formaldehyde in the presence of sulfuric acid to build the tetrakis(hydroxymethyl)phosphonium cation, which forms the sulfate salt:
- Addition of formaldehyde to phosphine – phosphine reacts with formaldehyde to form tetrakis(hydroxymethyl)phosphonium species.
- Salt formation – sulfuric acid provides the sulfate counter-ion, giving the water-soluble THPS.
- Adjustment and filtration – the solution is adjusted to the required content, pH and clarity, and filtered to the finished product.
The same chemistry gives the chloride analogue (THPC), used mainly in textile flame-retardant finishing; THPS is the sulfate form chosen for water treatment and other applications where the sulfate is preferred. Because the product is a solution, the specification fixes the content, viscosity, density, iron and pH rather than a melting point.
How THPS Works as a Biocide
THPS is a non-oxidising, broad-spectrum biocide active against bacteria (including sulphate-reducing bacteria), fungi and algae.
- Interaction with microbial surfaces – the positively charged phosphonium centre interacts with the negatively charged microbial cell surface and cell membrane.
- Membrane disruption – this interaction disrupts membrane integrity and function, inhibiting growth and killing the cells.
- Non-oxidising route – because it does not work by oxidation, THPS is effective in systems where oxidising biocides would corrode equipment, damage membranes, or react with process chemicals.
THPS is therefore used both on its own and in biocide programmes where a plant alternates or blends a non-oxidising biocide with an oxidising one to prevent resistance and cover all conditions.
THPS vs Other Water-Treatment Biocides
| Biocide | CAS | Type | Character | Typical use |
|---|---|---|---|---|
| THPS | 55566-30-8 | Organophosphorus (non-oxidising) | Broad-spectrum; water-soluble; acidic | Oilfield water injection, industrial water, paper |
| Glutaraldehyde | 111-30-8 | Aldehyde (non-oxidising) | Fast-acting; broad-spectrum | Oilfield, water treatment, disinfection |
| DDAC / quaternary ammonium | 7173-51-5 | Quaternary ammonium (non-oxidising) | Surface-active biocide | Water treatment, cooling systems |
| Chloramine T / chlorine | 127-65-1 | Oxidising | Oxidising disinfectant | Water and process disinfection |
| DBNPA | 10222-01-2 | Non-oxidising (halogenated) | Fast-acting; degrades quickly | Cooling water, paper |
Guidance: choose THPS where a stable, non-oxidising, water-soluble biocide is wanted – especially in oilfield water injection and systems where oxidisers are unsuitable; choose glutaraldehyde where a fast-acting aldehyde biocide fits; use quaternary ammonium or oxidising biocides where their specific strengths apply – often in a rotating programme with THPS.
Applications
| Industry | Role of THPS |
|---|---|
| Oilfield water injection | Control of bacteria (incl. sulphate-reducing bacteria) in injection and produced water |
| Industrial cooling water | Microbial control in recirculating systems |
| Process water | Broad-spectrum antimicrobial treatment |
| Pulp and paper | Slime control in papermaking |
| Flame-retardant chemistry | Precursor for THP/THPC textile flame retardants |
| Other | Leather treatment and antimicrobial applications |
- Oilfield – THPS is one of the main biocides for injection-water systems: bacteria such as sulphate-reducing bacteria cause reservoir souring and corrosion, and a stable non-oxidising biocide is essential.
- Industrial water – cooling and process water systems use THPS where its non-oxidising action and compatibility are valuable.
- Paper – slime control in papermaking, where it controls biofilm-forming organisms.
- Flame-retardant chemistry – THPS/THPC chemistry is used in durable flame-retardant finishing of textiles.
Dosage and Use
| Application | Starting-point guidance |
|---|---|
| Oilfield injection water | Dosed on the water volume and the bacterial load; set by field testing and a biocide programme |
| Cooling / process water | Dosed periodically or continuously, set by microbial monitoring |
| Paper | Fed into the system at a point giving good mixing |
Biocide dosing is set on the active content and the measured microbial load, not on a fixed figure; the level is confirmed by microbial testing (for example, bacterial counts) and by the plant’s biocide programme. Because THPS is acidic, dosing points and materials must be chosen accordingly.
Safety, Handling and Storage
- Corrosive/irritant – THPS solutions are acidic and can irritate or burn skin and eyes; use protective equipment and avoid contact.
- Keep away from alkalis – contact with strong bases can cause decomposition; store and dose separately from alkaline chemicals.
- Ventilation – handle in a well-ventilated area; avoid breathing mists.
- Materials – select tanks, pumps and lines compatible with an acidic solution (e.g. suitable plastics or corrosion-resistant alloys).
- Storage – keep sealed and cool, away from oxidisers, alkalis and food/feed.
Regulatory and Documentation
| Point | Note |
|---|---|
| Biocide use | Biocidal products are regulated; the use, registration and permitted claims depend on the market |
| Transport | Classified as a corrosive/acidic solution; transport and labelling follow the applicable rules |
| Documents | Per-batch COA and SDS; further regulatory documents on request |
Confirm the registration and permitted use for your market and application before ordering.
Packaging, Logistics and Supply
| Item | Standard options |
|---|---|
| Packaging | IBCs, drums or as agreed |
| Documentation | Per-batch COA and SDS |
| Incoterms | FOB and CIF |
| Storage | Sealed, cool, away from alkalis and oxidisers |
THPS price tracks the phosphine/formaldehyde feedstock and the cost of handling an acidic solution. Buying on committed tonnage gives the best terms.
THPS in Oilfield Water Injection
Oilfield water injection is the largest single use of THPS, and it shows why a stable non-oxidising biocide matters.
| Problem | How THPS helps |
|---|---|
| Sulphate-reducing bacteria (SRB) | Broad-spectrum activity against the bacteria that cause reservoir souring |
| Microbially influenced corrosion (MIC) | Controls the biofilms that drive corrosion of pipework |
| Non-oxidising requirement | Does not corrode equipment or react with process chemicals like an oxidiser |
| Water-soluble dosing | Fully miscible with injection water; easy to dose |
In injection systems, bacteria such as SRB produce hydrogen sulphide, which sours the reservoir, corrodes steel and forms sulphide scales. A non-oxidising biocide is essential because oxidising biocides are impractical in these systems; THPS is dosed into the injection water, often in a programme that alternates biocides to prevent resistance.
THPS in Cooling and Process Water
| System | Role of THPS |
|---|---|
| Recirculating cooling water | Microbial control of bacteria, fungi and algae |
| Process water | Broad-spectrum antimicrobial treatment |
| Membrane systems | Where non-oxidising biocides are preferred to protect membranes |
| Pulp and paper | Slime control in the wet end |
In cooling and process water, THPS is valued because it does not work by oxidation: it will not attack metal surfaces, degrade membranes, or react with the other treatment chemicals (corrosion inhibitors, scale inhibitors) as an oxidising biocide might. Dosing is set by microbial monitoring of the system.
THPS as a Flame-Retardant Intermediate
Beyond water treatment, THPS is an important building block in flame-retardant chemistry. The reactive hydroxymethyl groups make tetrakis(hydroxymethyl)phosphonium salts ideal for reacting with nitrogen compounds (for example urea) to form durable flame-retardant finishes.
| Product | Relationship |
|---|---|
| THPS (this product) | Sulfate salt of tetrakis(hydroxymethyl)phosphonium |
| THPC | Chloride analogue, used in textile flame-retardant finishing |
| THP-urea / THP-ammonia condensates | Flame-retardant finishes for textiles (e.g. cotton) |
In this role THPS/THPC chemistry gives durable, wash-resistant flame-retardant finishes, and is used in technical textiles, workwear and other applications where flame resistance must survive laundering.
Biocide Programmes and Resistance Management
Single-biocide dosing can lose effectiveness over time, so industrial systems usually run a biocide programme rather than one product.
- Rotation/alternation – switching between biocides with different modes of action reduces the chance of resistance and the build-up of tolerant populations.
- Blends – THPS is often blended or alternated with glutaraldehyde or quaternary ammonium biocides for a broader, harder-to-evade attack.
- Oxidising + non-oxidising – a plant may use an oxidising biocide (for general control) alongside a non-oxidising one such as THPS (for biofilm and SRB control).
- Monitoring – dosing is set by microbial testing (plate counts, ATP, specific tests) so the programme stays effective.
THPS is attractive in these programmes because it is water-soluble, broad-spectrum, non-oxidising and easy to dose – a reliable partner to other biocides rather than a stand-alone answer.
Frequently Asked Questions about THPS
What is THPS used for?
As a non-oxidising, broad-spectrum biocide in industrial water systems – notably oilfield water injection – and in cooling water, process water and paper; also as a flame-retardant intermediate.
What is the CAS number of THPS?
55566-30-8 (tetrakis(hydroxymethyl)phosphonium sulfate).
Is THPS an oxidising biocide?
No – it is a non-oxidising biocide, which is why it is used where oxidisers (chlorine, peroxide) would corrode equipment or damage membranes.
Is THPS the same as THPC?
No – THPC is the chloride analogue, used mainly in textile flame-retardant finishing; THPS is the sulfate form used in water treatment.
What is the active content?
75.0% min here (as [(HOCH2)4P]2SO4), supplied as an acidic aqueous solution.
How should THPS be stored?
Sealed and cool, away from alkalis, oxidisers and food/feed; it is acidic, so use compatible materials.
Related reading
- THPS for oilfield and industrial water treatment
- THPS vs glutaraldehyde and other water-treatment biocides
- Glutaraldehyde (CAS 111-30-8): properties, manufacturing and applications
- Water treatment chemicals: coagulants, flocculants and disinfection
- THPS (CAS 55566-30-8) – product page
PolyBlueChem supplies THPS (CAS 55566-30-8) to the specification above, with per-batch COA and SDS and FOB/CIF delivery. Contact us with your application, tonnage and delivery port.