Decaffeination with supercritical

Of the various extraction processes the decaffeination with supercritical CO2 exhibits the most commercial advantages for bulk production. The process is a discontinuous one. Fig. 1.4-3 shows a number of serially arranged extractors (5) charged with the supercritical CO2 feed by the centrifugal circulation pump (1). 

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-... 

Figure 3.3.55 Decaffeination with supercritical CO2 (adapted from Viani and Petracco, 2007) ...

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 5.2 Zosel s second process for decaffeination with supercritical CO2 (extraction conditions as in Figure 5.1). In this process the caffeine is removed from the CO2 by adsorption on activated charcoal. Reproduced with permission from K. Zosel (see caption to figure 5.3).

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...

The article Caffeine in coffee its removal why and how by K. Ramalakshmi and B. Raghavan in Critical Reviews in Food Science and Nutrition, 1999, 39, 441 provides an in-depth survey of the physicochemical factors underlying decaffeination of coffee with supercritical CO2. 

Extraction with supercritical fluids (e.g., C02) 80-300 decaffeinated coffee (tea) spices, hops colours drugs oils, lecithine and fats tobacco (nicotine) perfumes... 

In contrast to the decaffeination of coffee, which is primarily executed with green coffee, black tea has to be extracted from the fermented aromatic material. Vitzthum and Hubert have described a procedure for the production of caffeine-free tea in the German patent application, 2127642 [11]. The decaffeination runs in multi-stages. First, the tea will be clarified of aroma by dried supercritical carbon dioxide at 250 bar and 50°C. After decaffeination with wet CO2 the moist leaf-material will be dried in vacuum at 50°C and finally re-aromatized with the aroma extract, removed in the first step. Therefore, the aroma-loaded supercritical CO2 of 300 bar and 40°C will be expanded into the extractor filled with decaffeinated tea. The procedure also suits the production of caffeine-free instant tea, in which the freeze-dried watery extract of decaffeinated tea will be impregnated with the aromas extracted before. 

Extraction with supercritical CO2 is a technical process of increasing importance. It provides a mild and rapid technique for the extraction of low- or medium-polarity substances. Supercritical CO2 is used for supercritical fluid extraction (SFE) in important technical processes such as the decaffeination of coffee and the extraction of hops, as well as the extraction of naturally occurring compounds from biomaterials. As many applications are performed in the pharmaceutical, polymer, environmental and nutritional fields, direct on-line SFE-NMR would be an ideal tool to monitor the various extraction processes. 

As reported in a lot of reviews, extractions with supercritical solvents have a very promising commercial potential. Until now the commercialization is mainly restricted to batchwise extraction of solids with carbon dioxide (e g. decaffeination of coffee and tea, extraction of hop). Laboratory experiments and operation of small-scale pilot plants gave favourable economic values for continuous extraction of liquids with C02 and other gases. Only a few extractions with C02 or C HS are performed already on a small industrial scale. For research purposes and product development a new high pressure counter-current extraction plant was erected. To get greater amounts of product the explosionproof plant was constructed in pilot scale using a special modular concept and an effective visual control system. 

Consequently, the vast majority of SCF applications are based on CO2 near the GL critical point, with a possible admixture to support the ability for solvating dipolar components. The extraction of carcinogenic aromatic hydrocarbons and their nitro derivatives from diesel particulates by CO2 + toluene or methanol SCF can serve as an example. CO2 based SCF also helps in cleaning polyethylene from undesired polymer additives. In a similar way one can consider technologies focused on so called h q)er-coal, an extremely pure and environment friendly fuel for turbines in power plants. Recently, the first power plants based on this idea are being constructed in China. The removal of pesticides from meat, decaffeinated coffee and denicotinized cigarettes are the next society-relevant applications. Noteworthy is the h q)er-oxidation with supercritical water and bitumens extraction based on supercritical toluene. The latter system is also used for the liquefaction of coal. ... 

Coffee decaffeination with carbon dioxide has been the object of a large amount of effort in research and development at the Max Planck Institute for Coal Research in Germany and at other academic and industrial laboratories in Europe and the United States. An indication of the intensity of effort applied to this process comes from a review article that lists the United States patents on decaffeination granted up to the end of 1981 (Paulaitis et al., 1983a). Several earlier patents were inadvertently omitted from that list a corrected version is given in table 10.1. Research activity on supercritical fluid extraction of stimulants from coffee, tea, and cocoa has continued, indicated by the number of United States patents granted since that review article was published some of them are listed in table 10.2. 

We summarize the data from one example of an early coffee decaffeination patent to highlight the specifics of the process (Roselius, Vitzthum and Hubert, 1974). Four hundred grams of rough-ground deoiled roast coffee is wetted with 200 ml of water and is treated with supercritical CO2 with an... 

Katz, S. N. 1989. Method for decaffeinating coffee with supercritical fluid. U.S. Patent... 

Following the successful commercialization of decaffeination with SCCO2, further applications of sc-fluids in the fleld of separation/purification of natural products have been investigated. In addition, product purification in synthetic processes also came into focus. The major challenge was to specifically exploit the unique physical properties of supercritical fluids to solve those separation problems which are difficult by classical approaches. 

An important stimulant for many is a fully methylated pitrlne present in tea and coffee— caffeine. Caffeine is a crystalline substance easily extracted from coffee or tea with organic solvents. It is extracted industrially with supercritical COj (or, if you prefer, nature s effervescence ) to make decaffeinated tea and coffee. 

In the food industry, commercial plants with supercritical fluids have so far only been used with supercritical CO2 as solvent. The first plant was opened in 1981 in Bremen (Germany) for decaffeination of coffee, by a process invented in the 1970s by Zosel (1973). Plants for the production of hop extract and for the decaffeination of tea are today also in operation, for example, in Germany, England, and Australia (Voeste et al., 1997). Supercritical hydrocarbons such as propane are also used, for example, for deasphalting of heavy oils or for the removal of triglycerides from fish oils. 

Processing of natural products with supercritical fluids-based technologies has been an extensive area of research during the past two decades. In fact, since many valuable products occurring in natural compounds, such as vitamins, aromas, natural pigments or essential oils, are soluble in supercritical fluids, their extraction from natural materials is one of the most widely studied applications of supercritical fluids. To date, SFE technology is used at industrial levels in economically relevant processes such as decaffeination of both colTee and tea and extraction of hop constituents and spices [19]. 

Many solvents have been suggested for use in these decaffeination processes. Initially benzene was used but it is never used today because of its toxicity and flammability. When chlorinated solvents first became available at low prices, trichlorethylene was sometimes used but this solvent also has now been superseded. Methylene chloride is the only chlorinated hydrocarbon currently used as a decaffeination solvent. Other commercially used solvents are ethyl acetate, coffee oil and other triglycerides [12]. In addition to the decaffeination processes outlined above, which are based on conventional solvent extraction with organic solvents, water decaffeination and supercritical carbon dioxide extraction have now become well-established processes. It is still necessary in these processes to humidify the beans before extraction (step 1) and to return them to their initial humidity afterwards (step 4), but the remaining steps in the extraction process differ substantially from those in the conventional solvent extraction processes. Steam stripping (step 3), for example, is only necessary in processes using organic solvents. 

Decaffeination of roast coffee extract. Thin film absorber used Decaffeination of roast coffee with subcritical CO2. Regeneration by ion exchange Decaffeination of coffee extracts with supercritical CO2 Supercritical CO2 extractant with temperature gradient... 

In the following, we divide continuous-contact operations into two distinct categories. The first deals with classical packed-column operations in countercurrent flow. We revisit the packed-gas scrubber we first saw in Chapter 2 and provide a general survey of packed-gas absorption operations. Packed-column distillation is addressed next and, in a somewhat unusual departure from the norm, we reexamine coffee decaffeination by supercritical extraction. 

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. 

Methylene chloride is probably the most generally used solvent for decaffeination processes, but others, some of which are already found in small amounts in coffee beans, are coming into use. For example, ethyl acetate,8 formaldehyde-dimethylacetal, ethanol, methanol, acetone,9 propane,10 benzyl alcohol,11 carbon dioxide,12 and supercritical carbon dioxide with an acid13 are used. Generally the pressure and temperature of the system are adjusted to keep the solvent in the liquid state. Coffee oil itself is even described for this use in one patent.14... 

SCFs will find applications in high cost areas such as fine chemical production. Having said that, marketing can also be an issue. For example, whilst decaffeina-tion of coffee with dichloromethane is possible, the use of scCC>2 can be said to be natural Industrial applications of SCFs have been around for a long time. Decaffeination of coffee is perhaps the use that is best known [16], but of course the Born-Haber process for ammonia synthesis operates under supercritical conditions as does low density polyethylene (LDPE) synthesis which is carried out in supercritical ethene [17]. 

A significant development in supercritical fluid extraction was Zosel s patent for decaffeination between 1964 and 1981, which reported a procedure for the decaffeination of coffee beans with C02 [6-10]. Also, a number of patents of some food companies have been reported that concern the decaffeination of coffee [11]. The American Food Company, for example, has constructed an extraction vessel 7 ft in diameter and 70 ft tall for supercritical C02 decaffeination of coffee at the Houston, Texas plant. The current annual U.S. market for decaffeinated coffee is 2- 3 billion [4]. 

Below the critical temperature, a phase transition occurs when compressing a gas. The formation of a liquid phase is usually first noted by the formation of droplets on the walls of the container. At temperatures above the critical temperature, a substance can be continuously compressed without a separate liquid phase forming. Under such conditions, the substance is a gas, because it continues to fill its container. However, because densities comparable to those of the liquid can be reached by such compression, it is customary to call a substance above its critical temperature a supercritical fluid, where the term fluid (from flow) refers to either liquid or gas. Supercritical fluids, with densities comparable to liquid and high thermal energy, can be exceedingly good solvents and have found use recently in processes such as decaffeination of coffee. 

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