Caffeine carbon dioxide decaffeination process

Carbon dioxide gas is a normal component of air. In the carbon dioxide decaffeination process, the gas is raised to a temperature of at least 32°C. Then it is compressed to a pressure of about 7400 kPa. At this pressure, it resembles a liquid but can flow like a gas. The carbon dioxide penetrates the coffee beans and dissolves the caffeine. When the pressure returns to normal, the carbon dioxide reverts to a gaseous state. The caffeine is left behind. 

A third method, the carbon dioxide decaffeination process, is being used with increasing frequency. The raw coffee beans are moistened with steam and water, and they are then placed into an extractor where they are treated with carbon dioxide gas under very high temperature and pressure. Under these conditions, the carbon dioxide gas is in a supercritical state, which means that it takes on the characteristics of both a liquid and a gas. The supercritical carbon dioxide acts as a selective solvent for caffeine, thus extracting it from the beans. 

Process for the direct decaffeination of aqueous coffee extract solutions Process for extracting caffeine from solutions thereof in carbon dioxide under high pressure Process for the extraction of caffeine supercritical solutions Decaffeination process Method for decaffeinating coffee with a supercritical fluid Method for decaffeinating coffee with a supercritical fluid... 

In some cases, the solids themselves are subjected to extraction by a solvent. For example, in one process used to decaffeinate coffee, the coffee beans are mixed with activated charcoal and a high-pressure stream of supercritical carbon dioxide (carbon dioxide at high pressure and above its critical temperature) is passed over them at approximately 90°C. A supercritical solvent is a highly mobile fluid with a very low viscosity. The carbon dioxide removes the soluble caffeine preferentially without extracting the flavoring agents and evaporates without leaving a harmful residue. 

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. 

In the process depicted in figure 1.2, coffee beans charged to the extractor, 10, via line (18) are decaffeinated with supercritical carbon dioxide. The caffeine-laden CO2 stream leaving the extractor is passed into the bottom of a water-wash column where the caffeine is removed from the CO2. (Chapter 8 describes the thermodynamic equilibrium situation for the water-wash column.) The caffeine-free CO2 is recycled to the coffee bean column, and decaffeinated coffee beans leave the extractor via line 20. Let s now follow the water stream leaving the bottom of the CO2 scrubbing tower. The caffeine-... 

Each patent has somewhat different features and claims. We select one patent for more detailed discussion to highlight certain technical facets of the process. First we explain the (often misunderstood) effect of water on the extractability of caffeine by selective supercritical carbon dioxide. A number of references report that dry carbon dioxide cannot extract caffeine from dry coffee, either green or roasted, but moist carbon dioxide can. The inability of dry carbon dioxide to extract caffeine from coffee should not be misconstrued to mean that dry carbon dioxide cannot dissolve neat caffeine. This same moist-versus-dry effect is experienced if, for example, methylene chloride is used to extract caffeine from coffee. Dry methylene chloride cannot decaffein-ate dry coffee but moistened coffee can be decaffeinated. It is thought that the caffeine is chemically bound in a chlorogenic acid structure present in the coffee bean. Thus, water somehow acts as a chemical agent it frees caffeine from its bound form in the coffee matrix in both the carbon dioxide and the methylene chloride processes. 

Let us proceed to some of the technical facets of the decaffeination process. Figure 10.1 is a graph of the solubility of neat caffeine in ctu-bon dioxide (Krukonis, 1981a). The solubility of caffeine is about 0.2 wt% at 60°C and 300 bar. The caffeine content of most coffees is about 1 wt%. If, during the extraction process, the caffeine in coffee dissolves to the solubility limit during extraction at, say, 60°C and 300 bar, the amount of carbon dioxide required to decaffeinate coffee is easily calculated. It is 5.0 pounds per pound of coffee. 

Consider the chemistry required to decaffeinate coffee. Most techniques use an extraction process to remove the caffeine from the green coffee beans before they are roasted. One method starts by steaming the green beans and then rinsing them with an organic solvent (usually dichloromethane) to pull the caffeine molecules out of the beans. The other method uses supercritical carbon dioxide to extract caffeine. The latter obviously avoids the use of toxic solvents, but is energy-intensive. With all extraction techniques,... 

Much of the commercial interest has been in the food and pharmaceutical industries. Here, the major driving force is the desire to have conpletely natural processes, which cannot contain any residual hydrocarbon or chlorinated solvents tHumphrey and Keller. 19971. Supercritical carbon dioxide has been the SCF of choice because it is natural, nontoxic, and cheap, is conpletely acceptable as a food or pharmaceutical ingredient, and often has good selectivity and capacity. Currendy, supercritical CO2 is used to extract caffeine from green coffee beans to make decaffeinated coffee. Supercritical CO2 is also used to extract flavor conpounds from hops to make a hop extract that is used in beer production. The leaching processes that were replaced were adequate in all ways except that they used solvents that were undesirable in the final product. 

Swollen raw coffee can also be decaffeinated with supercritical CO2 (crit. point 31.06 °C 73.8 bar) at 40-80 °C and a pressure of 200-300 bar. The high vapor pressure of carbon dioxide under normal conditions guarantees a product that is free from solvent residues. Apart from the extraction of caffeine, this process can also be applied in the extraction of odor- and taste-active substances from hops and other plant materials. 

Figure 5 1 Zosel s first process for the decaffeination of green coffee beans with supercritical CO2. (Operating conditions are 90°C, 160-200 atm, carbon dioxide density in range 0.4-0.65 g cm ). In this process the caffeine is removed from the CO2 by washing with water. Reproduced with permission from K. Zosel (see caption to Figure 5.3).

An alternative process based on the use of liquid CO2 to extract the caffeine from the milled roasted coffee has been described by Gehring et al. [40]. Extraction pressures between 50 and 200 bar and temperatures between 5 and 31°C are cited. Very short extraction times (less than 4 hours) are claimed. The recirculating carbon dioxide stream is decaffeinated by passing it through an ion exchange unit (cf. section 5.4.3.1). 

Suppose the requirement is to reduce the caffeine content from 1 to 0.05%, which is typical of commercial decaffeination processes. The task is to calculate the ratio G/S kg C02/kg coffee required to achieve this reduction. The carbon dioxide is assumed to be devoid of caffeine initially. The equilibrium content in the gas at the end of the operation is given by... 

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