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  • Technobell - Phthalic Anhydride

CHEMICAL PROCESS TECHNOLOGIES

PHTHALIC ANHYDRIDE

The Technobell technology that is used to produce Phthalic Anhydride (PA) is based on a well-known catalyst for oxidation of o-xylene to form Phthalic Anhydride.

Phthalic Anhydride molecule

Phthalic Anhydride is produced from two main sources: o-xylene and naphthalene. Both main technologies involve specific catalyst for selective oxidation of raw material to product.

Phthalic Anhydride main advantages

MAIN ADVANTAGES OF THE TECHNOBELL’S PHTHALIC ANHYDRIDE PRODUCTION PROCESS

  • HIGH YIELD OF PHTHALIC ANHYDRIDE
    High overall yield of Phthalic Anhydride product (up to 115 wt%).
  • LOWER INVESTMENT AND OPERATION COSTS
    High concentration of o-xylene in the feed gas results lower investment and operation costs.
  • NEAR-COMPLETE REMOVAL OF UNDESIRED BY-PRODUCTS
    Application of post-reactor shows near-complete removal of undesired by-products and minimisation of burning of Phthalic Anhydride.
  • OPTIMAL HEAT RECOVERY
    Careful and inventive process design allows optimal heat recovery from the reactor gases and production of medium pressure (MP) and low pressure (LP) steam.
  • USE OF ANY SUITABLE OXIDATION CATALYST
    Technology design allows using any suitable – commercially available oxidation catalyst.
  • NO OSCILLATIONS IN EXPORT STEAM QUANTITIES
    Technobell offers continuous thermal treatment and distillation of Phthalic Anhydride. Such design results in slightly smaller equipment requirements and greatly increased utilisation of uniform energy resources. There are no oscillations in export steam quantities, which regularly occur in batch distillation systems.
  • ENVIRONMENT CARE
    The environment is protected by incineration of liquid and gas pollutants.
  • FLEXIBLE OPERATION
    Fixed bed reactor(s) results in flexible operation.
  • HIGH EFFICIENCY
    High efficiency of switch condensers (up to 99,8%).
Phthalic Anhydride plant Phthalic Anhydride Technobell Phthalic Anhydride Technology Phthalic Anhydride - Salt pump

Phthalic Anhydride production process

Phthalic Anhydride unit consists of fixed bed reactor with a post-reactor, continuous gas cooling, continuous product recovery by switch condensation, thermal treatment / refining, flaker unit and incinerator system. It can also include waste water handling (depends on the customer requirements).

PROCESS SCHEME OF TECHNOBELL’S PHTHALIC ANHYDRIDE TECHNOLOGY

Phthalic Anhydride process scheme

PHTHALIC ANHYDRIDE PRODUCTION PROCESS DESCRIPTION

Chemical reaction

Main reaction:

Side reactions:

  • O-xylene thermal oxidation

C8H10  +  7 O2 →  3 CO2   + CO + 4 H2O

  • Maleic Anhydride formation (can be recovered as commercial product)
  • O -toluic aldehyde formation
  • Phthalide formation
  • Benzoic Acid formation
  • Citronic acid formation

Due to released reaction heat the available technology results as energetically self-sustaining and energy can be exported.

Typical temperatures of reaction are between:

  • Reactor (Salt) temperature:     350 – 400 °C.
  • Catalyst temperature (Hot Spot):     390 – 440 °C
Reaction section

Reaction sector

Liquid O-xylene is vaporized in vaporizer drum and then super-heated prior to mixing with compressed air. The mixture then passes over a specified catalyst installed in tubular fix bed reactor, cooled by eutectic salt mixture. There the chemical reaction takes place and o- xylene is transformed mainly to Phthalic Anhydride. Heat released by chemical reaction is removed through melted salts to heat exchanger where HP steam is produced. To increase the yield of reactor a post-reactor system is installed where almost 90 % of by-products are removed.

Gas coolers

Gas coolers & switch condensers

The post-reactor effluent containing Phthalic Anhydride is cooled down by the Gas Cooler generating HP steam from condensate. Phthalic Anhydride is then routed to the switch condensers, which cool further the gases below the Phthalic Anhydride solidification point by use of cold oil. When the condenser starts to be full with solid Phthalic Anhydride, the reaction gas is connected to a spare and clean switch condenser. The oil in the by-passed switch condenser is heated up with steam till Phthalic Anhydride is melted. The recovered liquid crude Phthalic Anhydride is collected in the Crude Phthalic Anhydride tank.

Distillation/Refining

Distillation & refining system

The distillation and refining system consists of two phases. In the first column light-ends content of the crude Phthalic Anhydride are removed on the top (light cut acids), while the Phthalic Anhydride is routed to the second column from the bottom in which the pure Phthalic Anhydride leaves on the top, while small amount of heavy-ends is collected from the bottom.

Incinerator

Incinerator

Off-gas arriving from the switch condensers contains flammable, environmental polluter materials (like acids, CO) which are burned away with natural/fuel gas or oil while the generated heat can be used for steam producing. Also the residue from the distillation (light and heavy cut) is designed to incinerate.

Flaking

Flaking & packing

The drum flaker is used to transform the molten pure PA product into a solid. In the continuous process the product is transformed to easily processable flakes. The PA flakes are collected in a special silo, then routed to an automatized packing system to be dosed and packed into 25 kg bags or 1/1,25 tons big bags.

Additional

Additional sections of the plant

  • Steam system, with the task of careful energy transformation and recuperation,
  • Oil system providing hot and cold oil for switch condenser operation,
  • Demineralized water station,
  • Other Utilities system, like Instrumental air, nitrogen, Electrical Power stations.

PROCESS VALUES

Process values

O-xylene concentration in reactor feed80 – 100 gr/Nm3
High reactor yield (depends on catalyst)up to 115 wt% of o-xylene
Efficiency on SW. C.up to 99,8 wt% of condensable PA
Distillation residues2 – 3 wt%
Overall plant Yield (wt. %)*112 (SOR**) – 110 (EOR***)
The catalyst life time4 to 5 years.

*overall plant Yield → ton of product Phthalic Anhydride / tons of feed o-xylene in percentage.
** start of run / fresh catalyst.
*** end of run / after 4 years of operation.

Phthalic Anhydride Production Capacity

Production capacity

UP TO 40,000 MTPAUP TO 80,000 MTPA
Feed systems incl. o-xylene storage and vaporisation, air compression, and feed mixingFeed systems incl. o-xylene storage and vaporisation, air compression, and feed mixing
1 pc. of fixed bed reactor + 1 pc. of post-reactor2 pc. of fixed bed reactor + 2 pc. of post-reactor
Continuous gas cooling system + condensation (based on switch condensers)Continuous gas cooling system + condensation (based on switch condensers)
Continuous Phthalic Anhydride distillation and refining systemContinuous Phthalic Anhydride distillation and refining system
Incinerator for waste gases and liquidsIncinerator for waste gases and liquids
Phthalic anhydride product storage and flaking / packing systemPhthalic anhydride product storage and flaking / packing system

Phthalic Anhydride Product Characteristics

Product characteristics

PROPERTIESFORMUNITEXPECTED VALUEGUARANTEED VALUE
ColourMoltenHazen5max 10
Colour stability*MoltenHazen30max 40
Melting pointMolten°C131,5min 131,3
Colour stabilitySolidHazen40max 60
PurityMolten%99,9min 99,8

*Tested one hour at 150°C.

Contact our Chemical Process Technologies Team for more information

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Ferrarska ulica 10
6000 Koper, SLOVENIA

+386 5 63 98 276

info@technobell.eu

 

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201, Cervantes House
5-9 Headstone Road
Harrow HA1 1PD
Middlesex, UK

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