Industrial Production Of Citric Acid

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CITRIC ACID

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Citric acid Citric acid is a weak organic acid found in citrus fruits(lemon). It is a good, natural preservative and is also used to add an acidic (sour) taste to foods and soft drinks. More than million tonnes are produced every year by fermentation.

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Properties At room temperature, citric acid is a white crystalline powder. It can exist either in an anhydrous (water- free) form or as a monohydrate. The anhydrous form crystallizes from hot water, whereas the monohydrate forms when citric acid is crystallized from cold water. The monohydrate can be converted to the anhydrous form by heating above 78 °C. Citric acid also dissolves in absolute (anhydrous) ethanol at 15 °C. When heated above 175 °C, it decomposes through the loss of carbon dioxide and  water.

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Occurrence Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits (about 47 g/L in the juices). The concentrations of citric acid in citrus fruits range from0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes.

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Discovery The discovery of citric acid has been credited to the 8th century Muslim alchemist Jabir Ibn Hayyan (Geber). Citric acid was first isolated in 1784 by the Swedish chemist  Carl Wilhelm Scheele, who crystallized it from lemon juice.  Industrial-scale citric acid production began in 1890 based on the Italian citrus fruit industry. In 1893, C. Wehmer discovered Penicillium mold could produce citric acid from sugar. However, microbial production of citric acid did not become industrially important until World War I  disrupted Italian citrus exports.

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In 1917, the American food chemist James Currie discovered certain strains of the mold Aspergillus niger could be efficient citric acid producers, and the pharmaceutical company  Pfizer began industrial-level production using this technique two years later, followed by Citrique Belge in 1929.

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WikipediaCitric Acid Production by Aerobic Bioprocesses

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Microorganism: Aspergillus niger (mainly), Candida yeast (from carbohydrates or n-alkanes) Citric acid production is mixed growth associated, mainly take place under nitrogen and phosphate limitation after growth has ceased. Medium requirements for high production: - Carbon source: molasses or sugar solution. - Na-ferrocyanide is added to reduce Iron (1.3 ppm) and manganese (<0.1ppm). - High dissolved oxygen concentration - High sugar concentration - pH<2 - Temperature: 30oCIndustrial Production of Citric acid

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Bioreactor: batch or fed-batch (100m3) - 5-25×106 A. niger spores/L may be introduced to the fermentor. - Aeration is provided to the fermenter by air sparging (0.1-0.4 vvm) - Temperature is controlled by cooling coil. - Agitation: 50-100rpm to avoid shear damage on molds. - Fed-batch is used to reduce substrate inhibition and prolong the production phase one or two days after growth cessation. - Volumetric yield: 130 kg/m3 Industrial Production of Citric acid

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Separation: - The biomass is separated by filtration - The liquid is transferred to recovery process: - Separation of citric acid from the liquid: precipitation calcium hydroxide is added to obtain calcium citrate tetrahydrate → wash the precipitate→ dissolve it with dilute sulfuric acid, yield citric acid and calcium sulfate precipitate → bleach and crystallization → anhydrous or monohydrate citric acid.Industrial Production of Citric Acid

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Microorganism: S. cerevisae for hexose Candida sp. for lactose or pentose Genetically modified E. coli Ethanol production is growth-associated with S. cerevisae. Medium requirements for high production - Carbon source: sugar cane, starch materials (e.g. corn, wheat), cellulosic materials (?!). yield: 0.51 g ethanol/g glucose. - N, P, minerals. - Anaerobic - 100g/L glucose are inhibitory for yeast. - 5% (v/v) of ethanol are inhibitory for yeast. - pH:4-6 for 30-35 oC. Industrial Production of Citric Acid

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Bioreactor: batch, continuous or with cell recycle 95% conversion of sugars with a residence time of 40 h in batch reactor 21 h in continuous reactor without cell recycle 1.6 h in continuous reactor with cell cycle By-products: glycerol, acetic acid, succinic acid.Industrial Production of Citric AcidSeparation: - Distillation to obtaining 95% (w/w) of ethanol-water mixture, followed by - Molecular sieves to removing water from the mixture to get anhydrous ethanol.

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A typical method used for purification of citric acid from a fermentation broth involves two major purification techniques: precipitation and filtration. The following schematic displays a generic citric acid purification scheme: ffffPrecReact citric acid with calcium carbonateFilter precipitateReact precipitate with sulfuric acidFilter precipitatePurified Citric AcidPurification of Citric acid

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The citric acid broth from the production fermenter is highly contaminated by leftover biomass, salts, sucrose, and water. First, the citric acid must be reacted with calcium carbonate to neutralize the broth and form the insoluble precipitate calcium citrate. Calcium citrate contains about 74% citric acid. The stoichiometric equation is as follows: CaCO3 + Citric Acid → CO2+ Calcium Citrate Kirk 15 Calcium Carbonate, CaCO3Contaminated Citric AcidCalcium Citrate as a precipitate plus contaminantsCSTRPurification of Citric acid

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The calcium citrate is then washed, heated, and filtered to remove any number of the contaminants. Depending on the specific design of the purification scheme, filters can be placed before the first reaction with calcium carbonate, in series between the two precipitation reactions or in any other combination that works. Also, it is important to choose the best kind of filter for what is being removed. For simplicity, the filters here will remove larger contaminants first (sucrose and salts) and the smaller contaminants later. Filter Ex. Plate filter, Rotary presses, rack-and-frame presses Calcium Citrate as a precipitate plus contaminantsCalcium Citrate, biomass, waterPurification of Citric acid

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To crack the calcium citrate precipitate, sulfuric acid is needed. The temperature of this reaction should stay below 60ºC. The reaction will produce free citric acid and a new precipitate, calcium sulfate, which will need to be removed later. The stoichiometric coefficients for this reaction are all one. Sulfuric Acid, SO4Calcium sulfate as a precipitate, free citric acid, biomass, waterCSTRCalcium Citrate, biomass, waterPurification of Citric acid

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In this filter, the calcium sulfate is washed away from the citric acid and the leftover biomass is removed. Again, the contaminants that were present in the fermentation broth can be removed by additional filtration means, such as microfiltration or ultra filtration. Calcium sulfate as a precipitate, free citric acid, biomass, waterCitric acid, waterFilter Ex. Plate filter, Rotary presses, rack-and-frame presses Purification of Citric acid

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Further Purification Citric acid can be produced in two forms – monohydrate and anhydrous. These forms may require additional purification steps to reach the desired purity. 1. Monohydrate contains one water molecule for every citric acid molecule Requires repeated crystallization until water content is approx. 7.5-8.8% 2. Anhydrous Processed to remove all water from end product Prepare by dehydrating the monohydrate citric acid product at a temperature above 36.6ºC Purification of Citric acid

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Once the product has been brought to the desired purity, it would be sent to packaging and distribution. PurificationCitric AcidPurification of Citric acid

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Applications Food Used as flavoring and preservative in food and beverages. Can be added to e.g. ice cream as an emulsifying agent to keep fats from separating, to caramel to prevent sucrose crystallization, or to recipes in place of fresh lemon juice. Citric acid is used with sodium bicarbonate in a wide range of effervescent formulae, both for ingestion (e.g., powders and tablets) and for personal care (e.g., bath salts, bath bombs, and cleaning of grease). Citric acid is also often used in cleaning products and sodas or fizzy drinks. Cleaning and Chelating agent Used to remove scale from boilers and evaporators. Can be used to soften water, which makes it useful in soaps and laundry detergents. In industry, it is used to dissolve rust from steel. Can be used in shampoo to wash out wax and coloring from the hair.

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Cosmetics and pharmaceuticals Citric acid is widely used as a pH adjusting agent in creams and gels of all kinds. Citric acid is commonly used as a buffer to increase the solubility of brown  heroin. Citric acid is used as one of the active ingredients in the production of antiviral tissues. Dyeing Citric acid can be used in food coloring to balance the pH level of a normally basic dye. It is used as an odorless alternative to white vinegar for home dyeing with acid dyes. Photography Citric acid can be used as a lower-odor stop bath as part of the process for developing photographic film. 

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Last Updated: 8th March 2018