Fumaric acid is a common organic acid widely used in the food, feed, pharmaceutical, resin, unsaturated polyester, and cleaning agent industries. With increasing demand, various synthetic routes have emerged in different countries. Different processes vary significantly in terms of raw material sources, yield, energy consumption, and environmental requirements. Below is a summary of the current mainstream production processes from an industrial perspective.
1. Hydrogen Distillation Method (Phenylic Anhydride → Maleic Acid → Fumaric Acid)
This is currently the most common industrialized route globally, with mature technology, high output, and high product purity.
Process Flow:
Butane or benzene is oxidized to produce maleic anhydride;
Massic anhydride is hydrolyzed to produce maleic acid;
Maleic acid is then converted to fumaric acid via catalytic hydrogenation or isomerization;
The product is obtained through filtration, decolorization, crystallization, and drying.
Advantages: Mature technology, high degree of continuity, suitable for large-scale production.
Disadvantages: Raw material costs are affected by fluctuations in petrochemical prices, and a tail gas treatment system is required.
2. Catalytic Isomerization Method (Maleic Acid → Fumaric Acid)
This method uses maleic acid as the main raw material, directly obtaining fumaric acid through a catalytic isomerization reaction. Alkali metal salts, weakly acidic resins, and molybdenum-based catalysts are commonly used.
Characteristics:
Mild operating conditions;
High conversion rate, low impurities;
Suitable for large and medium-sized enterprises to expand production or for co-production with maleic anhydride plants.
The key here is reaction control, requiring optimization of catalyst formulation, pH value, and temperature to avoid the formation of byproducts such as malic acid.
3. Malic Acid Dehydration Method (L-Malic Acid → Fumaric Acid)
This route relies on the dehydration reaction of malic acid to produce fumaric acid under the action of an acidic catalyst (such as sulfuric acid, activated carbon supporting acidic groups, or solid acid).
Advantages:
Simple route, controllable reaction;
Suitable for the production of food-grade or pharmaceutical-grade fumaric acid (high purity).
Disadvantages:
Raw material prices are higher than maleic acid, making it less cost-competitive;
Mostly used in small to medium-sized factories or for special applications.
4. Bio-fermentation Method (Renewable Carbon Source → Fumaric Acid)
With the promotion of sustainable chemistry, bio-based methods have become a global research hotspot. Common microorganisms include filamentous fungi such as *Rhizopus oryzae* and *Rhizopus arrhizus*.
Production Process:
Uses glucose, starch hydrolysate, molasses, or lignin-cellulose sugars as raw materials;
Controlling pH, dissolved oxygen, and calcium salt concentrations promotes fumaric acid accumulation;
Uses membrane separation, crystallization, or electrodialysis to extract the product.
Advantages:
Uses renewable resources;
Green process with low carbon emissions;
No need for high-temperature oxidation and exhaust gas treatment as in petrochemical routes.
Disadvantages:
Yield and scalability are still limited;
Industrial-grade bio-based routes have not yet been fully adopted in some countries.
Bio-based methods are an international trend, particularly attracting attention in the food and feed industries because their natural source label has greater market value. 5. Chemical Oxidation Method (Massene → Maleic Anhydride System)
Some plants use butene and n-butane as raw materials, selectively oxidizing them to produce intermediate products, which are then further hydrolyzed and isomerized to obtain fumaric acid. This is part of the traditional petrochemical system, similar to the hydrogen distillation method, only the raw materials in the oxidation stage are different.
Characteristics:
Relies on a mature petrochemical raw material system;
Suitable for extended processing in conjunction with maleic anhydride plants;
Lower cost, but requires high energy consumption and strict waste treatment.
6. Other Emerging Routes (Experimental or Small-Scale Stage)
Electrochemical Synthesis: Utilizes electrocatalysis to directly convert maleate salts into fumaric acid; still in the laboratory and semi-industrial testing stage.
Solid Catalyst Continuous Flow Process: Improves yield and safety through fixed-bed or microchannel reactors; suitable for future intelligent factory development.
Photocatalytic Route: Utilizes photosensitive materials to promote conversion; still in the exploratory stage.
Industry Trends and Future Directions
From a global market perspective, fumaric acid production is trending towards greener, lower-energy-consumption, higher-purity, and more sustainable raw materials:
The petrochemical route will remain dominant due to its lower cost;
The bio-based route will expand into the food, pharmaceutical, and high-end materials sectors;
Catalyst technology and continuous production equipment will significantly reduce energy consumption and wastewater discharge;
New processes will place greater emphasis on the circular economy, such as integrating symbiotic systems, catalyst recovery, and byproduct utilization.