Caffeine extraction, coffee beans

Highly pure / -hexane is used to extract oils from oilseeds such as soybeans, peanuts, sunflower seed, cottonseed, and rapeseed. There has been some use of hydrocarbons and hydrocarbon-derived solvents such as methylene chloride to extract caffein from coffee beans, though this use is rapidly being supplanted by supercritical water and/or carbon dioxide, which are natural and therefore more acceptable to the pubHc. 

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 potential of supercritical extraction, a separation process in which a gas above its critical temperature is used as a solvent, has been widely recognized in the recent years. The first proposed applications have involved mainly compounds of low volatility, and processes that utilize supercritical fluids for the separation of solids from natural matrices (such as caffeine from coffee beans) are already in industrial operation. The use of supercritical fluids for separation of liquid mixtures, although of wider applicability, has been less well studied as the minimum number of components for any such separation is three (the solvent, and a binary mixture of components to be separated). The experimental study of phase equilibrium in ternary mixtures at high pressures is complicated and theoretical methods to correlate the observed phase behavior are lacking. 

Carbon dioxide, 4 an important green house gas,45 is obtained in combustion of carbon and hydrocarbons, calcination of CaC03, and so on. It forms complexes with transition metals (Section 7-14) and inserts into MH and other bonds (Section 21-3). The gas is very soluble in ethanolamines, which are used to scrub C02 from gas streams. Liquid C02 at pressures up to 400 bar is a solvent for some organic compounds and is used to extract caffeine from coffee beans many studies of other applications of supercritical C02 have been conducted.46... 

Solubilitiesattemperaturesand pressures above the critical values of the solvent liave important applications for supercritical separation processes. Examples are extraction of caffeine from coffee beans and separation of asplraltenes from heavy petroleum fractions. For a typical solid/vapor equilibrium (SVE) problem, tire solid/vapor saturation pressure P is very small, and the saturated vapor is for practical purposes an ideal gas. Hence 0 for pure solute vapor at this pressure is close to unity. Moreover, exceptfor very low values of the system pressure P, the solid solubility yj is small, and can be approximated by j, the vapor-phase fugacity coefficient of the solute at infinite dilution. Finally, since is very small, the pressure difference P — in the Poyntingfactor is nearly equal to P at any pressure where tins factor... 

The effects of this variable depend on both the matrix and the analytes. Thus, hydrophobic matrices facilitate penetration of supercritical CO, also, because the fluid is water-immiscible, the presence of moisture can make the analytes inaccessible to it. Figure 7.9A illustrates the influence of this variable on the kinetics of extraction of pyrene from natural sludge, both as collected (45 /o moisture) and after air-drying (2% moisture) [40]. However, water added to the sample can facilitate extraction (e.g. that of caffeine from coffee beans. Fig. 7.9B). Natural samples with a high moisture content can plug restrictors as a result of the water they contain freezing at restrictor tips. This problem can be overcome by raising the restrictor temperature, at the expense of losses in the more volatile analytes. 

Supercritical fluid extraction processes are particularly appropriate for the separation and isolation of biochemicals where thermal decomposition, chemical modification, and physiologically-active solvents are undesirable. Examples of these bioseparations include the extraction of oils from seeds using carbon dioxide (1), of nicotine from tobacco using carbon dioxide-water mixtures (2), and of caffeine from coffee beans again using carbon dioxide-water mixtures (3). 

Carbon Dioxide - Water - Crotalaria Spectabilis System. Water has been used as a CO-solvent in the extraction of caffeine from coffee and nicotine from tobacco. To extract caffeine from coffee beans, Zosel (3) recommended the pre-saturation of the carbon dioxide with water before passing the fluid through the coffee bean bed. In the case of nicotine from tobacco, Hubert and Vitzthum (2) first soaked the tobacco with up to 25 wt.% water and subsequently passed carbon dioxide through the tobacco bed. The water acted as a co-solvent as it saturated the fluid phase. Both of these processes have proven highly selective toward the alkaloids present in the plant material. Therefore, water was used as a co-solvent in the present study. 

It can be argued that the first supercritical fluid extractions (SFE) were performed in 1879 when Flannay and Hogarth investigated the solvating capabilities of ethanol.28 However, it took roughly 100 years before supercritical fluids made any significant impact on industrial processes. The removal of caffeine from coffee beans was reported in the 1970s29 and led to... 

Certain important industrial processes are based on the high solubility of organic species in supercritical carbon dioxide. For example, this medium has been employed to extract caffeine from coffee beans to produce decaffeinated coffee and to extract nicotine from cigarette tobacco. 

A large body of experimental data has been accumulated on the solubility and extractability of natural products, such as steroids, alkaloids, anticancer agents, oils from seeds, and caffeine from coffee beans, in various SCF solvents such as CO2, ethane, ethylene, and N2O. Carbon dioxide is probably the most widely investigated SCF solvent since its critical temperature T = 31.1°C) makes it an ideal solvent for extracting materials that are thermally labile. Also, CO2 is nontoxic, nonflammable, environmentally acceptable, and inexpensive. 

Many of these properties of C02 have been known for years,2 but aside from some small specialty applications such as the extraction of caffeine from coffee beans and the fractionation of some polymeric compounds, C02-based processes have not made major inroads in industry. Over the last decade, interest in the use of C02 as a solvent has seen a great resurgence as a result of the discovery of some unique solubility properties associated with C02 that have enabled the synthesis of fluoropolymers in carbon dioxide as well as the rational design of surface-active materials that are soluble in C02. 

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. 

Fig. 12.4. Simple diagram of the extraction of caffeine, from coffee beans Wo SCCO2 extraction.

Animal studies showing that methylene chloride becomes a carcinogen when inhaled caused some concern because methylene chloride was the solvent used to extract caffeine from coffee beans in the manufacture of decaffeinated coffee. However, when methylene chloride was added to drinking water fed to laboratory rats and mice, researchers found no toxic effects. They observed no toxicological responses of any kind either in rats that had consumed an amount of methylene chloride equivalent to the amount that would be ingested by drinking 120,000 cups of decaffeinated coffee per day or in mice that had consumed an amount equivalent to drinking 4.4 million cups of decaffeinated cof-... 

Ouid. Whereas a neat compound may be soluble in SC-CO2. it may not be extractable from its matrix without the addition of an entrainer. This phenomenon is demonstrated in the decaffdnation of coffee (iO) neat caffeine is soluble in dry SC-C02. but moist SC-CO2 or moist coffee is necessary for the extraction of caffeine from coffee beans. This same phenomenon occurs with decuffeinaiion by traditional organic solvents. Investigators have hypoihesiwd that water frees the chemically bound" caffeine in the coffee matrix. 

In literature very little is published on the extraction of alkaloids on an industrial scale. The few papers available were published between 1950 and 1970 and concern the isolation of alkaloids from whole plants or plant parts 168,169). The extraction of catharanthine and vinblastine from C. roseus leaves on a pilot plant scale is described by Atta-ur-Rahman et al. (170). Svoboda developed a method for the extraction of ajmalicine, vinblastine, and vincristine which has been used by Eli Lilly Co. (169,171-173). Supercritical fluid extraction is a method which is used for the extraction of caffeine from coffee beans. This method also seems of interest for further studies of other alkaloids. 

A large amount of research has been concentrated on the decaffeination of coffee by SC-CO2. Thus, it is not surprising that this was the first process that was commercialized in early 1978, whose primary step is supercritical extraction. Liquid CO2 cannot extract caffeine from dry coffee effectively, so the beans should be prewetted by water. Soaking of about 2 h is necessary for efficient extraction of caffeine from coffee beans by supercritical CO2. Conunercial processes for decaffeination of coffee have been first patented by General Foods Corporation in the United States [27]. 

Food and luxury goods industry (e.g., extraction of vegetable fat and oil from oil seeds, production of hops and spices extracts, extraction of caffeine from coffee beans and nicotine from tobacco, by using hygienically safe supercritical gases as the solvent, such as carbon dioxide)... 

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

For the design of extraction processes of mostly high boiling liquid or solid compounds with the help of supercritical fluids, for example, the extraction of caffeine from coffee beans using carbon dioxide the phase equilibrium behavior as a function, of the pressure without or in the presence of co-solvents is required. As in the case of all other phase equilibria, the isofugacity condition has to be fulfilled ... 

Figure I /. Flow scheme of a multistage extraction of caffeine from coffee beans [2].

Snpercritical CO2 tluid extraction of caffeine from coffee beans is nsed by an Increasing nnmber of companies fo prodnce decaf coffee. After tbe coffee beans are soaked In water to bring tbe caffeine cioser to tbe snrface, they are placed nnder approximately 35 atm of CO2 at room temperatnre. This selectively extracts more than 98% of the caffeine from the beans with minimal effect on flavor and aroma. The caffeine Is soluble in the supercritical CO2, but precipitates when the pressnre Is lowered to convert the supercritical fluid to gaseous CO2. 

Extract substances using supercritical CO2 (e.g. caffeine from coffee beans, hop extracts)... 

However, because of the initial concern, researchers sought alternative methods for extracting caffeine from coffee beans. Extraction by CO2 at supercritical temperatures and pressures was found to be a better method because it extracts caffeine without simultaneously extracting some of the flavor compounds, as dichloromethane does. This was one of the first green (environmentally benign) commercial chemical processes to be developed. After the caffeine has been removed, the CO2 can be recycled, whereas dichloromethane is not a substance that should be released into the environment (Section 7.12). 

SFE is common in the food, pharmaceutical and cosmetic industries, where it extracts caffeine from coffee beans, bitter from hops, tar and nicotine from tobacco, and other natural compounds from spices, flowers, aromatic woods, and medicinal plants. 

Examples that fall into the first category include the extraction of natural oils from crushed oil seeds [4, 77-80,153], toxic organic chemicals from soils [81, 82] and hop extracts from hops (see Figure 8.7). This behaviour has also been observed when spices are extracted [83-85] and when alkaloids are extracted from ground seeds [86]. Examples that fall into the second category include the extraction of caffeine from coffee beans [77], lignin from wood [87, 88] and peanut oil from peanuts. 

If, on the other hand, the equilibrium solute concentration C is very low, leading to a correspondingly low value for Cj in equation (10.1), the energy and capital costs associated with the recompressor can become major factors in determining the separation cost. This will be seen to be the case, for example, in the hypothetical process for extracting crushed rape seed with subcritical carbon dioxide which is considered in section 10.6. It would also be true of the extraction of caffeine from coffee beans if pressure reduction was used to recover the caffeine. In cases such as these the most economic flow conditions and tower dimensions will be such that Ct is quite close to the equilibrium value C. ... 

Decaffeination by Supercritical Extraction The Freundlich Isotherm The data of Figure 6.16 showing the equilibrium distribution of caffeine between coffee beans and supercritical carbon dioxide can be fitted by a power relation termed the Freundlich isotherm ... 

Researchers are interested in supercritical fluids because of their unique properties. A supercritical fluid has properties of both liquids and gases—it is in some sense intermediate between the two. Supercritical fluids can act as good solvents, selectively dissolving a number of compounds. For example, supercritical carbon dioxide is used as a solvent to extract caffeine from coffee beans. The caffeine dissolves in the supercritical carbon dioxide, but other substances—such as those responsible for the flavor of coffee—do not. Consequently, the caffeine is removed without substautially altering the coffee s flavor. The supercritical carbon dioxide is easily removed from the mixture by simply lowering the pressure below the critical pressure, at which point the carbon dioxide evaporates, leaving no residue. 

---