Top 8 Applications of Cobalt Phthalocyanine Desulfurization Catalysts

Sulfur removal is rarely just an emissions issue. Hydrogen sulfide can corrode piping, poison downstream catalysts, damage engines, create odour problems and block desulfurization towers with deposited sulfur.

Cobalt phthalocyanine desulfurization catalysts are used in alkaline wet oxidation systems to remove H₂S from industrial gases. They help regenerate the circulating solution and convert absorbed sulfides into separable elemental sulfur.

Selected cobalt phthalocyanine formulations are also used for mercaptan sweetening in LPG and petroleum fractions. However, gas-phase H₂S removal and liquid hydrocarbon sweetening are different duties and should be evaluated separately.

This article covers eight common industrial scenarios for cobalt phthalocyanine catalysts and the operating issues buyers should check before selecting a product.

How Does a Cobalt Phthalocyanine Desulfurization Catalyst Work?

In a wet oxidation desulfurization system, sulfur-bearing gas contacts an alkaline circulating solution inside an absorber. Hydrogen sulfide is absorbed into the liquid and then oxidised to elemental sulfur through a catalytic redox cycle.

Air introduced into the regeneration section restores the circulating solution so it can return to the absorber.

The usual process includes:

1. H₂S absorption in an alkaline solution
2. Catalytic conversion of dissolved sulfides
3. Oxidation to elemental sulfur
4. Air regeneration of the circulating liquid
5. Sulfur separation
6. Recycled solution returned to the absorber

A well-managed system can reduce H₂S loading while recovering sulfur and limiting chemical consumption. Actual performance still depends on inlet composition, alkalinity, pH, temperature, aeration, liquid-to-gas ratio and sulfur separation.

Honrel supplies a PDS-HY cobalt phthalocyanine desulfurization catalyst for wet oxidative gas purification and selected sulfur-treatment duties.

1. Coke Oven Gas Desulfurization and Decyanation

Coke oven gas can contain H₂S, HCN and other sulfur-bearing impurities. These contaminants must be controlled before the gas is used as industrial fuel, supplied as town gas or sent to another chemical process.

PDS wet oxidation is used in coking plants to absorb H₂S and promote sulfur formation in the circulating solution. Depending on the process arrangement, the same purification section may also support decyanation.

Common operating concerns include:

• High inlet H₂S
• HCN in the raw gas
• Sulfur deposition on tower packing
• Blocked piping and spray nozzles
• High suspended sulfur
• Foaming in the circulating solution
• Accumulation of thiosulfates and other by-product salts
• Falling regeneration efficiency

PDS-HY produces relatively large sulfur particles, making solid-liquid separation easier. Better sulfur removal can lower suspended solids in the solution and reduce the risk of tower packing and pipeline blockage.

Honrel recommends a catalyst concentration of at least 30 ppm for the stated coke oven gas conditions, with absorption at 30–35°C, regeneration at 35–40°C and solution pH between 8 and 9.

2. Crude Coal Gas and Town Gas Purification

Crude coal gas must often be cleaned before it enters a fuel network or downstream processing unit. Untreated H₂S can cause corrosion, unpleasant odour and sulfur emissions during combustion.

A cobalt phthalocyanine catalyst can be added to an ammonia-based or carbonate-based circulating liquid. It promotes oxidative regeneration while the absorber removes H₂S from the gas.

This treatment can support:

• Industrial fuel gas preparation
• Town gas production
• Coal chemical feed-gas cleaning
• Gas reuse within a coking facility
• Reduction of downstream sulfur load

The catalyst does not replace basic gas conditioning. Tar, dust and excessive condensate should be controlled before the gas reaches the absorber. Otherwise, contaminants may disturb gas-liquid contact, increase foaming or interfere with sulfur separation.

For older desulfurization units, the main purchasing question is usually compatibility with the existing circulating solution. Buyers should provide the current absorbent composition, catalyst dosage, gas flow and sulfur data before changing products.

3. Semi-Water Gas Purification in Fertiliser Plants

Semi-water gas is used as an intermediate feed in some fertiliser and ammonia production routes. H₂S must be reduced before the gas enters the shift, compression and synthesis sections.

Bulk sulfur removal at this stage can help:

• Protect downstream catalysts
• Reduce corrosion in compressors and piping
• Lower the load on fine-desulfurization beds
• Extend polishing adsorbent service life
• Stabilise later production stages

For semi-water gas, Honrel lists an absorption-temperature range of 25–35°C and a regeneration-temperature range of 35–45°C. The suggested solution pH is 8–9, with a catalyst concentration of at least 30 ppm.

The circulating liquid may use volatile ammonia or sodium carbonate, depending on the plant process. Solution composition should be checked regularly because low alkalinity weakens H₂S absorption, while uncontrolled operating conditions may increase side reactions and by-salt formation.

PDS wet oxidation is generally used for bulk removal. If the downstream process requires very low residual sulfur, an additional polishing stage may still be necessary.

4. Shift Gas and Synthesis Gas Cleaning

Sulfur compounds in shift gas or synthesis gas can shorten downstream catalyst life. Even when the main process can tolerate short-term fluctuations, repeated sulfur breakthrough often leads to unstable production and more frequent adsorbent replacement.

Cobalt phthalocyanine wet desulfurization can be used ahead of:

• Ammonia synthesis sections
• Hydrogen production systems
• Methanol units
• Carbon monoxide conversion stages
• Fine sulfur-removal beds

The commercial value is mainly upstream load reduction. Removing most of the H₂S before a polishing adsorbent can reduce replacement frequency and help maintain a more stable inlet sulfur level.

However, “organic sulfur” is a broad term. COS, CS₂ and mercaptans do not behave like H₂S, and their removal rate varies with gas composition and process conditions. Buyers should provide a sulfur-species analysis rather than only total sulfur.

Honrel reports an organic sulfur removal range of 50%–80% under applicable conditions. Actual results should be confirmed against the specific feed gas and required outlet specification.

5. Metallurgical Gas and Furnace Off-Gas Treatment

Steel, non-ferrous metal and industrial furnace operations may produce or reuse gases containing H₂S and other sulfur-bearing components.

Removing sulfur can help plants:

• Reuse gas as an internal fuel
• Reduce corrosion in gas lines
• Protect burners and downstream equipment
• Lower sulfur emissions during combustion
• Improve recovered-gas quality

Honrel’s PDS-HY catalyst can be considered for blast furnace gas and selected industrial furnace off-gas after suitable cooling and dust removal.

Metallurgical gases vary widely. Temperature, particulate loading, carbon monoxide, carbon dioxide and water content should be reviewed before choosing a wet oxidation process. Hot or dusty gas should not be sent directly into the desulfurization system.

The inlet gas should be conditioned to protect the absorber, circulation pump and regeneration section from solids and condensate-related problems.

6. Biogas and Landfill Gas Desulfurization

Biogas from anaerobic digestion and landfill gas may contain enough H₂S to damage engines, boilers, compressors, membranes and upgrading equipment.

Uncontrolled hydrogen sulfide can lead to:

• Corrosion in pipelines and storage equipment
• Lubricating-oil degradation
• Shorter engine maintenance intervals
• Damage to membrane and PSA systems
• Higher load on activated carbon or iron oxide beds
• SO₂ emissions after combustion

Wet oxidative desulfurization is suited to projects with continuous gas flow and a circulating liquid-treatment system. PDS-HY supports catalyst regeneration and sulfur formation, allowing the solution to be reused.

This route may be considered for:

• Agricultural biogas plants
• Food-waste digesters
• Wastewater treatment facilities
• Landfill gas projects
• Biomethane upgrading systems
• Industrial anaerobic digestion

The right process depends on gas volume, inlet H₂S, methane content, required outlet concentration and available operating staff. For small or intermittent systems, a dry desulfurizer may be simpler. Larger continuous plants may benefit more from a regenerative wet process.

7. Natural Gas and Oilfield Associated Gas Treatment

Natural gas and associated gas may contain H₂S together with carbon dioxide, water and light hydrocarbons. The gas must be treated before transportation, combustion or downstream processing.

A PDS liquid-phase oxidation system can be considered where the process requires:

• Bulk H₂S removal
• Regenerable desulfurization liquid
• Elemental sulfur separation
• Continuous gas treatment
• Reduced load on downstream purification

For gas with a high CO₂-to-H₂S ratio, selectivity becomes important.

8. LPG and Petroleum Fraction Sweetening

Cobalt phthalocyanine derivatives are also used in alkaline systems that treat mercaptans in LPG and selected petroleum fractions.

Typical streams include:

• LPG
• Propane and butane fractions
• Natural gas liquids
• Light naphtha
• FCC gasoline
• Kerosene
• Jet fuel
• Selected fuel oils

In these duties, the catalyst promotes the oxidation of mercaptans into disulfides:$$4RSH + O_2 \rightarrow 2RSSR + 2H_2O$$

The objective is usually to improve odour, reduce corrosiveness and help the product meet mercaptan-related specifications.

Mercaptan extraction and fixed-bed sweetening are not the same process. In extraction units, mercaptans move into a caustic phase and the resulting disulfide oil is separated during regeneration. In direct sweetening, disulfides may remain in the hydrocarbon product.

As a result, sweetening does not always mean deep total-sulfur removal. It changes more aggressive mercaptans into less troublesome compounds.

Before using PDS-HY in an LPG or petroleum stream, confirm the existing process, catalyst form, alkali system and compatibility requirements. A catalyst designed for wet H₂S removal should not automatically be treated as a drop-in replacement for every Merox-type unit.

Wet Gas Desulfurization vs. Hydrocarbon Sweetening

Process point	Wet oxidative gas desulfurization	Hydrocarbon mercaptan sweetening
Main feed	Industrial gas	LPG or liquid petroleum fraction
Main sulfur compound	H₂S	Mercaptans, RSH
Primary purpose	Remove H₂S from gas	Convert or extract mercaptans
Main sulfur product	Elemental sulfur	Disulfides
Typical equipment	Absorber and regeneration unit	Liquid-liquid extractor or fixed-bed reactor
Circulating medium	Ammonia or alkaline solution	Usually caustic or another alkaline medium
Main operating concern	Sulfur separation and solution regeneration	Mercaptan conversion and caustic regeneration
Product selection	Based on gas composition and wet-process conditions	Based on feedstock and licensed process requirements

This distinction should be made before requesting a sample or quotation.

PDS-HY Product Specifications

Honrel provides three product grades for different catalytic-activity and composition requirements.

Элемент	Единица	Superior Grade	First-Class Grade	Qualified Grade
Появление	—	Blue-grey powder	Blue-grey powder	Blue-grey powder
Размер частиц	μm	≤850	≤850	≤850
Плотность	g/cm³	≤0.80	≤0.80	≤0.80
Insoluble Matter	wt%	≤5.0	≤8.0	≤10.0
Каталитическая активность	min⁻¹	≥0.040	≥0.030	≥0.020
Cobalt Content	wt%	≥3.0	≥2.70	≥2.50
Dichloroporphyrin Cobalt Sulfonate	wt%	≥70.0	≥65.0	≥60.0

The superior grade provides higher specified catalytic activity, cobalt content and active-component content, along with a lower insoluble-matter limit.

Grade selection should reflect the current process, target dosage, solution condition and plant performance requirements. A higher grade is not a substitute for poor aeration, inadequate gas-liquid contact or ineffective sulfur separation.

Reference Process Conditions

The following conditions apply to the coke oven gas and semi-water gas duties listed by Honrel.

Process Parameter	Единица	Coke Oven Gas	Semi-Water Gas
Volatile Ammonia, Ammonia Process	g/L	6.0–8.0	6.0–8.0
Sodium Carbonate, Alkali Process	mol/L	0.4–0.6	0.4–0.6
Catalyst Concentration	ppm	≥30	≥30
Absorption Temperature	°С	30–35	25–35
Regeneration Temperature	°С	35–40	35–45
Solution pH	—	8–9	8–9
Regeneration Tank Aeration	m³/m²·h	35–110	35–110
Regeneration Tower Aeration	m³/m²·h	110–130	110–130
Regeneration Efficiency	%	≥80	≥80
Liquid-to-Gas Ratio	L/m³	≥12	≥12
Suspended Sulfur	g/L	≤1.5	≤1.5
By-Product Salts	g/L	≤250	≤250

These are reference conditions rather than universal settings. Gas composition, absorber design and existing operating procedures should be reviewed before adjusting a running unit.

Why Sulfur Separation Matters

High H₂S removal alone does not guarantee stable plant operation. The sulfur produced during regeneration must also be removed efficiently.

Very fine sulfur particles can remain suspended and cause:

• Higher solution viscosity
• Foam formation
• Filter overload
• Spray-nozzle blockage
• Packing fouling
• Increased tower resistance
• Reduced gas-liquid contact

PDS-HY is formulated to promote larger sulfur particles with easier separation. This can help control suspended sulfur and limit sulfur deposition in the tower and circulation system.

The catalyst can also support tower cleaning and resistance reduction, but mechanical fouling, tar and severe solids loading still require proper maintenance and upstream treatment.

Stability in Alkaline Circulating Solutions

PDS-HY remains stable below 95°C and has good solubility in ammonia water and alkaline solutions. It is designed to remain chemically stable across the applicable acid–alkali range encountered in desulfurization-liquid preparation and operation.

Its practical characteristics include:

• Simple solution preparation
• Low dosage
• Low catalyst consumption
• Good alkaline solubility
• Limited insoluble material
• Low side-reaction formation
• Non-corrosive operation under recommended conditions
• Easier sulfur separation

The stated stability below 95°C should not be confused with the recommended absorber temperature. Honrel’s reference absorption conditions are considerably lower, generally between 25°C and 35°C.

What Information Should Buyers Provide?

For a useful product recommendation, provide more than the industry name.

Required information	Why it matters
Gas or liquid feedstock	Separates H₂S removal from mercaptan sweetening
Gas or liquid flow rate	Defines process load
H₂S concentration	Indicates bulk desulfurization duty
Organic sulfur species	Shows whether COS, CS₂ or mercaptans are present
HCN concentration	Important for coke oven gas
CO₂ concentration	Affects alkalinity consumption
Current absorbent	Confirms ammonia, carbonate or caustic compatibility
Existing catalyst	Supports replacement comparison
Operating temperature	Checks solution and catalyst conditions
Solution pH	Affects absorption and regeneration
Required outlet sulfur	Determines whether polishing is needed
Current operating problem	Identifies foaming, sulfur blockage or low regeneration

Honrel can review this information before confirming the appropriate product grade and initial dosing reference.

Selecting a Cobalt Phthalocyanine Catalyst

The right choice depends on the job being done.

For coke oven gas, semi-water gas, synthesis gas, biogas and similar streams, focus on:

• H₂S removal
• Solution compatibility
• Regeneration efficiency
• Sulfur particle separation
• By-salt control
• Tower resistance
• Catalyst consumption

For LPG or petroleum fractions, focus on:

• Mercaptan type
• Extraction or fixed-bed process
• Catalyst solubility
• Caustic compatibility
• Disulfide separation
• Existing unit requirements

Honrel supplies additional industrial catalysts for gas purification and chemical processing. Related raw materials and other industrial products are available through the complete product catalogue.

Заключение

Cobalt phthalocyanine desulfurization catalysts serve several industries, but their duties fall into two main groups: wet oxidative H₂S removal from industrial gases and mercaptan sweetening of selected hydrocarbon streams.

PDS-HY is principally suited to wet desulfurization in coking, fertiliser, chemical, metallurgical, biogas and related gas-treatment systems. Its high catalytic activity, alkaline solubility, low dosage and larger sulfur-particle formation address common plant problems such as weak regeneration, suspended sulfur and tower blockage.

For petroleum sweetening, the catalyst must be checked against the feedstock and existing process before use.

Онрел supplies PDS-HY in three specification grades. To request product data or discuss an existing desulfurization unit, submit the feed composition, operating conditions and outlet target through the contact page.