Removing caffeine

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

The basic process outline is depicted in Figure 5.2 moist un-roasted coffee beans and CO2 are fed counter-currently into the extractor under supercritical conditions. Caffeine is selectively extracted into the CO2 and this stream is led to a water-wash column to remove caffeine at a reduced pressure, the CO2 being recycled back to the extraction column. Extraction of the caffeine into water is necessary to avoid dropping the CO2 pressure too low, since compression is energy-intensive. There is now the problem of separating the caffeine (which is used in soft drinks and pharmaceu-... 

Another challenge is to develop methods to replace the volatile organic solvents that are used in many industrial procedures. One choice is water as a solvent it is easily repurified, and has a harmless vapor. Another choice is supercritical carbon dioxide, a good solvent for many organic substances. It is not as innocuous as is water, but carbon dioxide can be easily recovered and reused. It is currently used to remove caffeine from coffee, and is being developed as a dry-cleaning solvent to replace organic solvents (Chapter 9). 

Figure 5.8 Coffee is decaffeinated by constantly irrigating the ground beans with supercritical carbon dioxide schematic representation of a Soxhlet apparatus for removing caffeine from coffee...

D. J. Adam, J. Mainwaring and Michael N. Quigley have described a simple experiment to remove caffeine from coffee with a Soxhlet apparatus see Journal of Chemical Education, 1996, 73, 1171. Their solvent was a chlorinated organic liquid rather than supercritical CO2. The abstract is available at http //jchemed.chem.wisc.edu/ journal/issues/1996/Dec/absll71.html. 

In Table 10.2, a comparison is made of the antioxidant power of various teas brewed identically and then fractionated to remove caffeine and pigments and to concentrate the catechins. The purified catechin fractions were all very similar in their antioxidant power, but green tea produced more than twice as much catechins. Comparatively, green tea drinkers receive approximately twice the antioxidants that drinkers of oolong or black tea drinkers receive. 

Dichloromethane is used as a solvent to remove caffeine from coffee beans. 

Dichloromethane, CH2C12, is an organic solvent used for removing caffeine from coffee beans. The following table gives the vapor pressure of dichloromethane at various temperatures. Fill in the rest of the table, and use the data to plot curves of Pv ... 

Food and Drug Administration (FDA) proposes to remove caffeine from its Generally Recognized As Safe list. Subsequently, the FDA concluded in 1992 that, after reviewing the scientific literature, no harm is posed by a person s intake of up to 100 milligrams (mg) of caffeine per day. 

Because of its low cost, nonhazardous chemical nature, and low critical temperature, carbon dioxide has been used in many applications. A commercial process to remove caffeine from coffee, using supercritical C02 as the solvent, is shown in Fig. 17. While actually a liquid-solid extraction process, it demonstrates principles involved in SCFE. A commercial SCFE process has been reported for recovery of hydrocarbon liquid from heavy oil. As compared with conventional propane deasphalting, this SCFE process can reduce capital and energy costs. 

All the methods of extracting caffeine take place before the beans are roasted. Caffeine and the other organic compounds that give coffee its taste are mainly non-polar. (Caffeine does contain some polar bonds, however, which allows it to dissolve in hot water.) Non-polar solvents, such as benzene and trichloroethene, were once used to dissolve and remove caffeine from the beans. These chemicals are now considered to be too hazardous. Today most coffee manufacturers use water or carbon dioxide as solvents. 

With some screening tests we tried to verify the findings summarised above. It turned out that none of the procedures described in the cited literature is feasible for the demand removal of the xanthines without a reduction of cacao butter (being a valuable component of the cacao mass). According to our investigations it is possible to remove caffeine from swollen nibs but it is not possible to reduce theobromine by simply using Carbon dioxide. The procedure of Li et al. [2] is not suitable because of the coextraction of cacao butter. Only with a combination of the approaches cited above the scope claimed already in the patent specification EP 61 017 [1] can be achieved ... 

Supercritical CO2 is used to remove caffeine from coffee beans. First, the green coffee beans are soaked in water. The beans are then placed in the top of a column that is 70 ft high. Supercritical CO2 fluid at about 93 °C and 250 atm enters at the bottom of the column. 

The other cleanup method utilizes the adsorptive properties of activated carbon to remove caffeine from the carbon dioxide before recycle (Zosel, 1981). An adsorption isotherm of the carbon dioxide-caffeine-activated carbon system, shown in figure 10.3, indicates that it is possible to adsorb the caffeine in the carbon dioxide-rich stream onto activated carbon (Krukonis, 1983a). In this industrial application an activated carbon bed is used to remove a component from a supercritical carbon dioxide-rich stream rather than having the activated carbon regenerated by the supercritical carbon dioxide. It is perhaps no surprise that spent activated carbon is difficult to regenerate with carbon dioxide, as discussed in chapter 8. 

A variant of the use of activated carbon to remove caffeine from carbon dioxide is described in this patent. A mixture of activated carbon and coffee beans is placed in a vessel, the vessel is pressurized with CO2 to some supercritical condition, and the contents held statically at those conditions for a period of time. At the end of this period, the CO2 is vented and the activated carbon is separated from the coffee bean by sieving. 

The abstract on the patent face page describes tbe use of liquid propane or butane as a decaffeinating solvent. In tbe abstract tbe patentee uses the phrase selectively remove caffeine from moistened green coffee. To describe how effective liquid propane is as a decaffeinating solvent, it is most informative to reproduce Example 3 from the patent. 

The solubility of naphthalene in supercritical carbon dioxide at 60.4 C increases from a mole fraction of 0.00240 at 1 bar (Illustration 12.1-4) to 0.098 at 291.3 bar. This illustrates the large increase in the solubility of a solute that may occur with increasirvg pressure, which is the basis of supercritical extraction to. for example, remove caffeine from coffee beans or fragrances and oils from plant material. 

For safe and long-term storage, carbon dioxide must be injected more than 800 m below the Earth s surface. At that depth, the gas becomes a supercritical fluid. Such fluids have the gas-like characteristic of low viscosity and the liquidlike characteristic of high density. Supercritical behaviour exists only when temperature and pressure both reach, or exceed, their respective values at the so-called critical point . Every substance has its own critical temperature, above which the gas cannot be liquefied no matter how high the pressure. For carbon dioxide, the critical point lies at 31 °C and 7.4 MPa. Supercritical fluids have properties similar to those of liquid solvents and are employed commercially to extract soluble substances. For example, supercritical carbon dioxide is used to remove caffeine from coffee. 

These are used in the processing of food. For instance, there are defoamers used in fruit juice. There are solvents used to remove caffeine from coffee, and antibacterials used to prevent bacterid growth in... 

Caffeine is usually absorbed rapidly, especially in the small intestine, and overcomes the blood/brain barrier without problems. The bioavaUability is greater than 90%. The drug is deactivated in the liver by cytochrome P 450 enzymes. The methyl groups are an essential part of the pharmacophore. After their oxidative removal, caffeine loses its activity. The primary metabolites are theophylline, theobromine and 1,7-dimethylxanthine. 

Caffeine-free tea is available in the supermarkets today. This is made by removing caffeine with an organic solvent. Biotechnology already works on genetically modified caffeine-fiee tea, not without some success. 

Removal of pollutants or unwanted components from the product by extraction (for example, to remove caffeine from coffee beans, separation of nicotine from tobacco)... 

Experiment 12B makes use of reverse phase chromatography to remove caffeine from a tea or coffee solution. The technique is simple. See Technique 12, Figure 12.14, for a diagram of the apparatus that you will use. The procedure involves the following steps ... 

Another green approach involving technology is the use of solid-phase extraction (SPE) columns (see Technique 12, Section 12.14). Using SPE columns, extractions such as removing caffeine from tea can be carried out more quickly and with less-toxic solvents. In other applications, SPE columns can be used to carry out the synthesis of organic compounds more efficiently with less use of toxic reagents. 

The following steps are used with an SPE tube to remove caffeine from tea or coffee (see Figure 12.18) ... 

The physiological effects of caffeine are not beneficial nor are they tolerated by everyone. Hence, many processes have been developed to remove caffeine (<0.1%) from coffee. The following process steps are normally used ... 

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