Manufacturing Processes of Fumaric Acid
The two main industrial routes for the production of Fumaric acid are the established Petrochemical Route (chemical synthesis) and the emerging Biotechnological Route (fermentation).
1. Petrochemical Route (Isomerization of Maleic Acid)
This is the most common and current industrial method. It relies on the conversion of maleic acid (the cis-isomer) into Fumaric acid (the trans-isomer).
Step 1: Production of Maleic Anhydride
The process begins with the catalytic oxidation of a suitable hydrocarbon feedstock, which has historically been benzene but is now predominantly n-butane or n-butene mixtures, in the gas phase over a fixed-bed or fluidized-bed reactor. The catalyst is typically based on vanadium and phosphorus oxides (VPO).
- Reaction:C4H10+3.5O2→C4H2O3+4H2O(n-butane → Maleic Anhydride)
Step 2: Hydrolysis to Maleic Acid
The hot gaseous maleic anhydride product is absorbed, often by water, leading to hydrolysis that produces maleic acid.
- Reaction:C4H2O3+H2O→C4H4O4 (Maleic Acid)
Step 3: Isomerization to Fumaric Acid
The maleic acid is then isomerized from its cis configuration to the more stable trans configuration, Fumaric acid. This isomerization is typically conducted by heating the maleic acid solution in the presence of a catalyst. Common catalysts include:
- Halogen Compounds: such as bromates (KBrO3) or chlorates.
- Strong Mineral Acids: such as hydrochloric acid (HCl) or sulfuric acid (H2SO4).
- Thiourea
The reaction is typically carried out at elevated temperatures (∼100−105 °C), and the resulting Fumaric acid, due to its low solubility, precipitates out of the solution.
- Reaction:Maleic Acid→Fumaric Acid
Step 4: Separation and Purification
The precipitated solid Fumaric acid is separated from the mother liquor through filtration or centrifugation, washed, and then dried to obtain the final product.
2. Biotechnological Route (Fermentation)
This method, which was actually used commercially in the 1940s before being replaced by the cheaper petrochemical route, is now being revisited as a bio-refinery perspective due to rising petroleum prices and sustainability benefits.
Process Overview
Fumaric acid is produced by the fermentation of a carbohydrate source, typically glucose (or other biomass-derived sugars), using specific microorganisms, most notably filamentous fungi from the genus Rhizopus (e.g., Rhizopus oryzae).
Key Metabolic Pathway
The fungi use the reductive carboxylation pathway (an offshoot of the TCA cycle) to produce Fumaric acid. This pathway involves the fixation of carbon dioxide (CO2) during the metabolism of glucose, leading to a more sustainable process.
- Starting Material: Glucose and nutrients.
- Microorganism: Rhizopus species.
- Key Reaction/Benefit: CO2 fixation.
Separation and Recovery
After fermentation, the fermentation broth is filtered, and the Fumaric acid is typically recovered by acidification, followed by crystallization and drying of the precipitated product.
🎯 Intellectual Challenge: Petrochemical vs. Fermentation
You might consider which of these processes holds the future advantage.
| Feature | Petrochemical Route | Fermentation Route |
| Feedstock | n-Butane (Fossil Fuel, ↑ Price Volatility) | Glucose (Renewable, ↓ Price Volatility) |
| Sustainability | High CO2 emissions | CO2 Fixation (More Sustainable) |
| Purity | High purity is easily achievable | Impurities (Malic acid, ethanol) are common byproducts, complicating separation |
| Cost (Current) | Lower initial unit cost (currently) | Higher capital cost, but potential for lower raw material cost |
| Yield | Very high (typically 90%+ from Maleic Acid) | Lower (typically around 85% from Glucose) |
While the petrochemical route is currently the industrial standard for its high yield and efficiency, the fermentation route presents a compelling challenge to this dominance. Given increasing regulatory pressure on fossil fuels and the search for sustainable chemical production, the Rhizopus-based process, with its renewable feedstock and ability to fix CO2, could ultimately prove the more economically and environmentally sound long-term solution. The main logical hurdle for fermentation is increasing product concentration and reducing the formation of unwanted byproducts to simplify downstream processing.
🧪 Fumaric Acid Manufacturing Process Steps
The process detailed in your notes combines the conversion of Maleic Anhydride to Maleic Acid (hydrolysis) with the catalytic isomerization of Maleic Acid to Fumaric Acid.
1. Preparation of Weak Maleic Acid Solution (Hydrolysis)
The process begins by converting the Maleic Anhydride raw material into Maleic Acid by reacting it with water.
- Raw Materials Used: Maleic Anhydride (3000 kg), Water (300 L), Sulphuric Acid (catalyst/acidifier), Sodium Bisulphate (catalyst/isomerization agent), and Thiourea (catalyst/isomerization agent).
- Initial Dissolution & Reaction:
- Mix Maleic Anhydride (3000 kg) with water (300 L) up to 70°C. The Maleic Anhydride reacts with water to form Maleic Acid (hydrolysis).
- The notes mention to “take a weak maleic acid solution and cool to 15 to 20∘C then filtrate it.” This suggests the formation of a solution of Maleic Acid, likely followed by an initial filtration step to remove any insoluble impurities.
2. Isomerization Reaction (Maleic Acid to Fumaric Acid)
This is the key step where the cis-Maleic Acid is converted into the stable trans-isomer, Fumaric Acid.
- Catalyst Addition: The notes list Sulphuric Acid, Sodium Bisulphate, and Thiourea as raw materials. These serve as catalysts for the isomerization reaction.
- The addition of Ammonium Persulphate (1.200 gm) and Potassium Bisulphate (0.800 gm) is mentioned later, which are also often used as isomerization catalysts or promoters.
- Heating and Reaction:
- The “weak maleic acid solution” (filtrate from step 1) is transferred to a reaction tank.
- Heat the solution and add Sodium Bisulphate and Thiourea simultaneously.
- The notes specify a reaction temperature range of 70∘C to 80∘C (“Heat the solution up to 70∘C to 80∘C”). The isomerization reaction is an equilibrium process where temperature drives the formation of the less soluble Fumaric Acid.
- The notes also mention checking the density of the solution, which monitors the concentration.
3. Separation and Purification (Crystallization and Solid Collection)
Since Fumaric Acid is significantly less soluble in water than Maleic Acid, it precipitates out of the solution, allowing for easy solid-liquid separation.
- Precipitation and Filtration:
- Filter the hot solution after the isomerization reaction. The solid precipitate collected is crude Fumaric Acid.
- “Maintain up to 48∘C to 50∘C temperature range.” This likely refers to maintaining a controlled cooling or washing temperature to ensure maximum Fumaric Acid yield while keeping soluble impurities dissolved.
- Final Solid Isolation:
- Centrifuge the material (crude Fumaric Acid). Centrifugation is a mechanical process to separate the solid Fumaric Acid from the remaining liquid (mother liquor), which contains unreacted maleic acid, catalyst, and impurities.
- Collect the wet quantity of fumaric acid.
- Pack the product (e.g., 25 kg HDPE bag).
Note: The final line mentions “a sudden endothermic reaction seen at final product Fumaric Acid,” which is an interesting observation—Fumaric Acid crystallization is typically exothermic, but the final cooling or drying steps might involve endothermic processes.
The initial steps of hydrolyzing Maleic Anhydride into Maleic Acid, followed by catalytic isomerization into Fumaric Acid, are key to this process. You can see a general overview of this chemical conversion in the video below.
For more information on the chemical isomerization process of maleic acid to fumaric acid, you can watch this video: Experiment II – Isomerization of maleic acid to fumaric acid.
