Against the backdrop of the global chemical industry’s transition towards green and sustainable development, the biodegradable material PBS (Polybutylene Succinate) has garnered significant attention due to its excellent performance and environmental benefits. The quality of succinic acid, the key monomer for PBS synthesis, directly determines the quality and conversion rate of the final PBS product.

Currently, the catalytic hydrogenation of maleic anhydride has become one of the mainstream industrial routes for producing succinic acid. The fixed-bed liquid-phase hydrogenation process, favored for its mild reaction conditions, high selectivity, and ease of continuous production, is widely used. To achieve long-term, table operation and obtain high-purity product, alongside mastering the core thermodynamic and kinetic purification, catalyst retention, and product separation-play an indispensable role.

Reaction Characteristics of Maleic Anhydride Hydrogenation to Succinic Acid

The essence of producing succinic acid via maleic anhydride hydrogenation is the addition of hydrogen atoms to the carbon-carbon double bond (C=C) in the maleic anhydride molecule, catalyzed to form succinic anhydride, which is then hydrolyzed to yield succinic acid.

Schematic Diagram: RuCl₃/PPh₃Catalyzed Hydrogenation of Maleic Anhydride to Succinic Acid  

RuCl₃／PPh₃

▶ Fluid Uniformity and Thermodynamic Control

Maleic anhydride hydrogenation is a typical highly exothermic reaction (reaction enthalpy ΔH ≈ -128 kJ/mol). In a liquid-phase environment, the fluid possesses high specific heat capacity and thermal conductivity, effectively removing reaction heat and preventing “runaway temperatures” or hot spots in the catalyst bed. However, this superior heat transfer performance is predicated on the fluid flowing uniformly through the catalyst bed. If mechanical impurities in the feed or worn catalyst fines clog the bed pores, it can lead to fluid bypass or channeling, causing local hot spots that trigger side reactions.

▶ Kinetic Characteristics

From a kinetic perspective, as the reaction is first-order with respect to maleic anhydride and zero-order with respect to hydrogen, the rate equation can be written as:

Where kis the reaction rate constant, and C_MA is the concentration of maleic anhydride. k = k₀* exp(-Ea/(R*T)), where k₀is the pre-exponential factor, Ea is the activation energy, Ris the ideal gas constant, and T is the absolute temperature.

For fixed-bed reactors, maintaining a uniform residence time distribution of reactants within the bed is crucial for high efficiency and conversion. Solid particulate impurities disrupt this uniformity, reducing the effective utilization of the catalyst and potentially shortening its lifespan.

▶ Zero Impurity” Requirement  

Liquid-phase reactions typically occur at relatively low temperatures (40℃~ 100°C) and moderate pressures (1.0 ~ 4.0 MPa), effectively suppressing side reactions like over-hydrogenation to γ-butyrolactone (GBL) or 1,4-butanediol (BDO). However, to obtain polymer-grade succinic acid, it is essential to prevent trace amounts of catalyst fines (e.g., nickel, ruthenium) from entering the subsequent crystallization system. If these heavy metal ions or fines contaminate the product, they can increase the color index and ash content of the succinic acid, directly leading to failure in downstream PBS polymerization.

Therefore, constructing an efficient filtration system deeply aligned with the reaction principles is not merely physical purification; it is a process core that ensures the stability of chemical reaction kinetics and compliance with product chemical specifications.

Challenges Faced by Fixed-Bed Liquid Phase Hydrogenation Technology

In the fixed-bed liquid-phase hydrogenation process, filtration technology primarily faces the following three major challenges:

✗Bed Clogging Risk: If mechanical impurities entrained in the raw maleic anhydride and solvent, or pipeline corrosion products, are not intercepted, they will deposit in the bed voids, causing a surge in pressure drop, uneven fluid distribution, and severely impacting reaction efficiency.

✗Catalyst Loss: Micron-or submicron-sized catalyst fines generated from abrasion or disintegration can escape the reactor with the product stream. This leads to the loss of expensive catalyst, potential product contamination, and poses separation challenges downstream.

✗Product Purity Compromise: Inadequate removal of fine solids, impurities, or catalyst residues can directly cause the final succinic acid to fail polymer-grade specifications (e.g., color, ash content), reducing its commercial value and affecting downstream polymerization.

Shinkai’s Filtration Technology Solution for Maleic Anhydride

Addressing the complex operating conditions of the fixed-bed liquid-phase process for maleic anhydride hydrogenation to succinic acid, Shinkai Filtration has developed a comprehensive, full-process filtration solution spanning feed, reaction, and separation, ensuring process efficiency and stability:

▶ Feed Protection: Efficient Interception with Metal Membrane Cartridges

Acting as a “protective screen” for the catalyst bed, Shinkai recommends using high-precision metal membrane filter cartridges before the feed enters the reactor.

✓High-Precision Interception: Filtration precision covers 0.5~10μm

▶ Feed Protection: Efficient Interception with Metal Membrane Cartridges

Acting as a “protective screen” for the catalyst bed, Shinkai recommends using high-precision metal membrane filter cartridges before the feed enters the reactor.

✓ High-Precision Interception:​ Filtration precision covers 0.5~10 μm, accurately removing mechanical impurities and corrosion products from the feed liquid, addressing both solid impurity filtration and safety filtration needs.

✓ Extreme Environment Tolerance:​ The metal membrane material offers极强的 corrosion resistance (resistant to solvents, acids, alkalis), perfectly adapting to the complex chemical environment of maleic anhydride feedstock.

✓ Core Asset Protection:​ Prevents bed clogging and pressure drop increase, ensuring clean fluid enters the reactor, safeguarding catalyst activity and reaction efficiency.

▶ Product Stream Safeguarding: Catalyst Filtration

For the fine catalyst dust in the reactor effluent and pressurized conditions, Shinkai’s catalyst filtration system and fully automatic backwash filtration system play a key role.

✓ Ultra-High Pressure Tolerance: Metal membrane cartridges have extremely high mechanical strength, withstanding forward pressures up to 50 bar, easily handling the high-pressure fluid impact from the reactor outlet.

✓ 100% Zero Leakage: Utilizing depth filtration mechanisms, achieves absolute interception of fine catalyst dust, ensuring no leakage and preventing heavy metal contamination of downstream products.

✓ Extended Service Life: Combined with fully automatic backwashing technology, the cartridges offer excellent backwash performance, with a service life of up to 10 years, significantly reducing maintenance costs by minimizing frequent replacements.

✓ Safety & Environmental Compliance: Suitable for precious metal catalyst filtration, reducing the risk of costly catalyst loss, while minimizing hazardous waste generation, aligning with green production requirements.

▶ Crystallization & Separation: System Closure with Cross-Flow Filtration

Shinkai utilizes cross-flow filtration systems in conjunction with fully automatic backwash filtration systems to completely resolve impurity accumulation challenges.

✓ Thorough Impurity Removal: Efficiently intercepts fine crystals, byproduct polymers in the mother liquor, and residues after activated carbon decolorization, achieving efficient product purification filtration.

✓ Closed-Loop Stability:​ Through full-process impurity control, ensures the quality of recycled mother liquor, maintains system material balance, and prevents equipment scaling and heat exchange efficiency decline.

✓ Purity Assurance:​ Ultimately ensures that succinic acid product indicators like color index and ash content meet polymer-grade standards, enhancing product market competitiveness.

Nanjing Shinkai is committed to providing precise and reliable core components and systems for the chemical and new materials sector through high-standard specialty filtration technology, helping your maleic anhydride hydrogenation and fixed-bed reaction processes achieve safer and more efficient operation. If your company is facing filtration challenges related to catalyst retention, impurity control, or product purity enhancement, please feel free to contact us. Let’s explore the optimal solution together.