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 is produced from two main sources: o-xylene and naphthalene. Both main technologies involve specific catalyst for selective oxidation of raw material to product.
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 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 PRODUCTION PROCESS DESCRIPTION
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 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 & 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 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
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 & 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 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 feed | 80 – 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 residues | 2 – 3 wt% |
| Overall plant Yield (wt. %)* | 112 (SOR**) – 110 (EOR***) |
| The catalyst life time | 4 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.
Production capacity
| UP TO 40,000 MTPA | UP TO 80,000 MTPA |
|---|---|
| Feed systems incl. o-xylene storage and vaporisation, air compression, and feed mixing | Feed systems incl. o-xylene storage and vaporisation, air compression, and feed mixing |
| 1 pc. of fixed bed reactor + 1 pc. of post-reactor | 2 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 system | Continuous Phthalic Anhydride distillation and refining system |
| Incinerator for waste gases and liquids | Incinerator for waste gases and liquids |
| Phthalic anhydride product storage and flaking / packing system | Phthalic anhydride product storage and flaking / packing system |
Product characteristics
| PROPERTIES | FORM | UNIT | EXPECTED VALUE | GUARANTEED VALUE |
|---|---|---|---|---|
| Colour | Molten | Hazen | 5 | max 10 |
| Colour stability* | Molten | Hazen | 30 | max 40 |
| Melting point | Molten | °C | 131,5 | min 131,3 |
| Colour stability | Solid | Hazen | 40 | max 60 |
| Purity | Molten | % | 99,9 | min 99,8 |
*Tested one hour at 150°C.