Maleic Anhydride process details
Process diagrams of Technobell technologies
|Water based MA recovery systems||Solvent based MA recovery system|
|Semi-automatic dehydrating-refining technology||Continuous distillation technology||Continuous distillation technology|
Maleic anhydride is produced by the partial oxidation of butane with air over a vanadium/phosphorus catalyst. Low concentration (PPM range) of stabilizer (SAS) is added to the feed gas stream to stabilize catalyst activity and selectivity. Water (in the form of steam) is also added under some conditions to modify the catalyst performance.
Technobell has in collaboration with one of the world leading catalyst suppliers developed a reactor with double separated eutectic salt mixture circulation system in order to optimize the catalyst performance by enhancing the control and achieving excellent temperature profile in the catalyst tubes resulting in higher conversion and selectivity, and so to achieve better reaction yield and minimize by-product formation.
- Butane thermal oxidation
C4H10 + 6.5 O2 → 4 CO2 + 5 H2O
C4H10 + 4.5 O2 → 4 CO + 5 H2O
- Minor reactions forming by- products like acetic or acrylic acids
C4H10 + 2.5 O2 → 2 CH3COOH + H2O
C4H10 + 2.5 O2 → 4/3 CH2CHCOOH + 7/3 H2O
Typical temperatures of reaction are between:
- Reactor (Salt) temperature: 400 - 440°C.
- Catalyst temperature (Range): 440 - 485°C
Technobell has several types of technologies for recovery of Maleic Anhydride fromprocess gases coming out from oxidation section of the plant. Depending on the end use of product Maleic Anhydride and availability/price of local utilities and solvents, optimal MA recovery system can be defined:
Reactor off-gas from the fixed bed reactor(s) flows through a gas cooling system and then min. 50% of the Maleic Anhydride is condensed in the partial condenser, the other cca. 45-50% feeds to the scrubber and forms Maleic Acid (MAc) solution by reaction with treated Boiler Feed Water.
- Recovery system
The molten pure Maleic Anhydride (product) is recovered from the condensed (called: crude) Maleic Anhydride and Maleic Acid solution in a semi-automatic dehydrating-refining procedure. Solvent used in this step of the process is xylene.
In case of higher capacity requirement process with continuous distillation and refining system is recommended.
The off-gas leaving the top of the scrubber contains not reacted n-butane and other flammable and environmental polluter materials. The whole amount of off-gas can be eliminated by burning away its flammable components while the generated heat can be used for steam generation.
Recovered heat of the exothermic reaction and back-cooling of the reaction gases are used for steam generation. In case of requirement, the system can produce high pressure (HHP) steam, which can be used for operation of the air compressor steam-turbine driver(s) or to generate electric energy.
As an option Technobell has a system for valuable n-butane recovery as it can be partly used again as feed to the reactor by installing an off-gas recycling system.
This part of the plant contains 1-4 Pastillator(s) depending on the required capacity. Each Pastillator has a capacity of max. 12,500 MTPA solid Maleic Anhydride production. Pastillators are equipped with several trays internally, which are cooled with cold water generated in a refrigerator unit. Molten Maleic Anhydride drops onto the surface of trays and forms solid Maleic Anhydride pastilles immediately on the cold surface. Solid pastilles are removed from the trays by knifes and collected in a bin.
An automatic packing system is weighing and dosing the pastilles into 25 kgs plastic sacks, then forms 1 ton of palettes to be ready for supply out the final MAn product.