Silver filtration

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Silver filtration

 S.A. Tarasova, Marketing Director

A.G. Kochkurov, Specialist of Marketing Department, Research-and-Manufacturing Enterprise Technofilter Ltd.

Nowadays, any manager realizes that to make the business develop, one should keep abreast of the times, follow up new technologies, take over positive experience from colleagues, constantly make efforts to improve product quality. With the abundance of distilllery products available at the market today, an average buyer expectably became more experienced and choosy. To prevail in stiff competition, distilleries now need new, efficient technologies that make the product better and more competitive and the manufacturing process more flexible, dynamic and sophisticated.

Our company has been working with distilleries for more than 10 years. As we were dealing with the problems of filtration, communicating with process engineers and managers of distilleries, we turned our attention to the problem of processing of water-alcohol mixtures. The dynamic method of producing vodkas, that involves filtration of the water-alcohol mixture through a 4-meter layer of active carbon (usually of the BAU-A grade) by using carbon columns, does not always make it possible to adapt quickly to the permanently changing situation on the market. This is due to the relatively slow processing rate of  water-alcohol mixtures, large labour input for operation of the columns and, first and foremost, the impossibility of running the column in the batch mode, which would inevitably result in the production of vodkas having high aldehyde content. In addition, the adsorptive function of the carbon column now became less relevant. By using alcohols of Extra and Lux grades and RO water, it is now possible to produce water-alcohol mixtures having virtually no organic contaminants. Thus, the functions of the carbon column were partly taken over by reverse osmosis and partly, by distilleries employing modern rectification methods.

Recent examinations of active carbon used to the end of its service potential in carbon columns show that in the course of operation carbon spends only one third of its sorptive properties, whereas its catalytic properties conducive to etherification, saponification and formation of esters are already exhausted. Regeneration with steam is not a solution to the problem, because it only restores sorptive properties of carbon. Consequently, the role of redox processes taking place on the surface of active carbon in the presence of oxygen, resulting in the formation of high MW compounds having a pleasant flavour and taste, has become much more important. This requires new approaches to the treatment of water-alcohol mixtures with active carbon.

Nowadays, coconut and stone-fruit carbons are no longer exotic, and there are examples of using these carbons in carbon columns. However, in these cases the cost of filtration is significantly higher, because such carbons have higher weights and bulk densities. As a result, the column contains up to 600 to 800 kg of carbon. In addition, all disadvantages of conventional carbon columns are retained: the wall effect, channelling, self-sorting of carbon. It turns out that the problems are not only related to what kind of carbon is used: extra volume and the design of the carbon column itself fail to solve these problems and make operation of the system more convenient.

Specialists at Research-and-Manufacturing Enterprise Technofilter Ltd tried to solve the problem in a comprehensive way. To accomplish this, it was necessary to select a carbon that would offer good catalytic properties while having a minimum volume, and to change the design of the carbon carrier, the column.

We tested modern active carbons impregnated with silver. It is well known that silver is an active catalyst. Silver catalyzes not only the reaction of alcohol oxidation into aldehyde but also subsequent reactions, the oxidation reaction into acetic acid and the reaction of ester formation, owing to the emerging electrochemical potential difference between carbon and silver.

Carbons having various concentrations of silver (0.04 to 4%), particle size distributions and origins were tested. Preference was given to granular active carbons produced from coconut shells, having concentration of silver on the surface of 0.4 to 0.5%. These carbons feature high hardness (>97%) and a large surface area (>1000 m2/g).

The tests confirmed that the processing rate of water-alcohol mixtures had considerably increased. It became possible to reduce the amount of carbon, i.e. switch from quantity to quality, carry out the chemical processes by taking advanatage of new capabilities of the carbon rather than of its large amount.

The original design of the EPSF.U Ag0,4 cartridge sorptive filter element was used as a basis for the technology. The cartridge is a carbon minicolumn: carbon is loaded between the outer and inner shells of the filter element, liquid is supplied through the lower opening in the outer shell and exits inside the cartridge through the upper opening in the inner shell (Fig.1). This design takes account of the ability of carbons to swell in the course of operation and rules out the possibility of channelling even at high filtration rates.


Fig.1. EPSF.UAg0,4 filter element

This design of the filter element and the use of carbon containing silver for the production of vodkas was patented by Technofilter Ltd as the Silver filtration method for processing of water-alcohol mixtures and vodkas and the cartridge filter (Patent No 2222586 of 19.06.2002).

The weight of carbon in the standard 250 mm high EPSF.U Ag0,4 element (carbon minicolumn) is 300 to 330 g, the content of silver is 0.4%. The filter elements are thermally welded together into candles 500, 750 or 1000 mm high and are installed into the filter holder accomodating 3 to 24 elements depending on required processing rate. Technofilter specialists have developed and certified a line of USF Silver filtration systems offering flow rates of 40 to 1000 dal/h.

Research performed in cooperation with All-Russian Research Institute of food biotechnology on experimental-industrial scale at the factories of Vladalkko JSC (Vladimir), The first wine blend factory Ltd (Tula), SPI-RVVK JSC (Kaliningrad) and Alkon JSC (Great Novgorod) has proved that a new technique for cleaning water-alcohol mixtures had really been developed. As a result of the tests, the Silver filtration technology was included into the Manufacturing process regulation for the production of vodkas and distillery products (revision No 1 of PTR10-12292-99 of 07.11.2005, section 8.5.9).

We will not include diagrams and tables for the numerous tests and experiments, because they have been already extensively discussed. What is important is the fact that Silver filtration ensured in all cases successful volumetric structurization of water-alcohol mixtures, making it possible to produce vodkas that are not inferior in quality to vodkas produced from a similar alcohol by using columns incorporating BAU-A carbon. In addition, problems that are typical of conventional carbon columns were solved, including accumulation of aldehydes in the cases when the processes of water-alcohol mixture treatment are stopped, owing to the fact that the volume of the water-alcohol mixture coming into contact with carbon has been drastically reduced.

Just because of this, new possibilities, techniques and, in some enterprises, even new secrets have emerged in the vodka production technology. It became convenient to handle the product, conduct experiments on its quality. For example, by changing the processing rate of the water-alcohol mixture it is possible to produce vodkas having various organoleptic properties that suit the tastes of various buyers. Low-capacity enterprises now can operate in the batch mode, because the process can be stopped at any moment and, if required, resumed without losing time or expensive raw materials. It also became possible to produce the required amount of wine blend within one shift, and then allow it to assimilate and ‘rest'.

The process engineer has been given a tool helping him to solve his problems and to present his product to the customer.

Major vodka producers focus their attention on other advantages of Silver filtration technology.

1.Compactness. Compared to conventional carbon columns, the new units have a smaller footprint: one Silver filtration system having a flow rate of 500 dal/h (1430x970x1920 mm in size) replaces 10 carbon columns (Fig.2). In addition, the new system requires no pressure containers.


Fig.2. A Silver filtration system (a) replaces a stack of carbon columns (b,c) in the cleaning section (Vladalko JSC, Vladimir)

2. Reduced time cost. There is no need to unload tons of carbon from the columns and fill them with fresh carbon (some major factories have up to 90 carbon columns!), spending human resources and, first and foremost, time for the handling and clean-up operations. There is no need to work up the column to the required mode, losing expensive raw materials and time. One should only replace the filter elements.

Treatment of water-alcohol mixtures by Silver filtration technology is also used in continuously working Ruchei systems (Fig.3). These systems contain a water-alcohol mixture treatment unit with a filter holder for 24 1000 mm high EPSF.U Ag0,4 elements. The Ruchei system has a modular design. To increase the processing rate of the system, more modules should be added. The system requires no containers for water-alcohol mixtures, because it has a module for preparation of the water-alcohol mixture having required strength, where a unique injector is used as the mixer.


Fig.3. Ruchei system (produced by Altair Ltd) having processing rate of 1200 dal/h installed at Topaz distillery

The whole system, including the water-alcohol mixture preparation unit and water-alcohol mixture treatment modules incorporating EPSF.U Ag0,4 elements is very compact and occupies an extremely small area.

But the main advantage of the Silver filtration, common to all producers, is the improved quality and organoleptic properties of the product, confirmed by numerous awards from exhibitions and specialized wine testing events. Let us quote several comments.

Svetlana Nikolayeva, Sinergiya Group, extract from the article ‘Silver filtration and no paradoxes!':

- Silver filtration was received at Alviz as a necessity, rather than a luxury. For Sinergiya, Silver filters are by no means an exotic thing. A Silver filtration system has been successfully installed and put into operation in Arkhangelsk.

An additional effect from Silver filtration was obtained immediately, at the stage of production tests and then confirmed by comparative analysis and trials performed by Alviz accredited laboratory.

Vladimir Ivanov, first deputy General Director of the Russky Alkogol Group on the Topaz factory:

- Our new regulation includes the Silver filtration technology. So far two lines using this technology have been installed. The technology ensures a steadily high quality at the modern level. Silver filtration significantly softens the taste of the product, making it integral and the perception of the taste harmonical.

Sergei Kardapoltsev, General Director of Valuyevsk distillery JSC:

- We have now completely given up the use of carbon columns, because the new technology is more convenient. We can produce the amount of vodka we need, without night shifts and overfilling of storages. At the same time we managed to significantly improve product quality. The Silver filtration technology is undoubtedly relevant and saleable. We are grateful to Technofilter for their innovative activities and continue to cooperate with them.

Elena Zhukova, Chief Process Engineer of Vladalko JSC:

- Our company has recently celebrated centenary since the date of its foundation. A company of that age undoubtedly has sufficient experience and knowledge. Nevertheless, in cooperation with Technofilter and All-Russian Research Institute of food biotechnology, we decided to look for more advanced techniques for treating water-alcohol mixtures that can ensure the highest product quality. At present we use two Silver filtration systems. One is used instead of carbon columns, and the other, as an extra stage of carbon filtration for vodkas of the Premium grade.

It should be pointed out that consumers are talking about Silver filtration not as a promotional fetish, but as an advanced technology assisting in production of high-quality products and making it possible for companies not only to survive in competition, but also consolidate one's positions on the vodka market.

In addition to the treatment of water-alcohol mixtures, the Silver filtration technology can also be used for aftertreatment of vodkas (Manufacturing process regulation for the production of vodkas and distillery products (revision No 1 of PTR10-12292-99 of 07.11.2005, section 8.5.10 "Postfiltration of vodkas"). This option is used in two cases:

- when a distillery remains committed to the dynamic method of water-alcohol mixture treatment (through carbon columns), reserving Silver filtration as an extra processing stage;

- when an enterprise uses a Silver filtration system instead of carbon columns, but finds it desirable to additionally modify organoleptic properties of the product by adding one more filtration stage.

In both cases, if there is an urgent need for increasing the production rate, the system being used for aftertreatment can be used for treatment of water-alcohol mixtures.

In addition to convenience and good quality of the product, a major advantage of the Silver filtration technology is the high throughput of filter elements.

When used for the treatment of water-alcohol mixtures, the throughput of one 250 mm high EPSF.U Ag0,4 element is 3500 to 5000 dal. When used for aftertreatment of vodkas, its throughput is 7000 to 10000 dal.

For example, when the required processing rate is 500 dal/h (with the recommended processing rate of water-alcohol mixtures being 3 to 7 dal per one 250 mm high element), the average throughput of a set consisting of 24 1000 mm high elements or 96 minicolumns is up to 500,000 dal.

In the aftertreatment mode, the recommended rate per one 250 mm high element is 8 to 15 dal/h. With maximum processing rate being 1000 dal/h, the throughput of the set is 1,000,000 dal.

Calculations show that the cost of using Silver filtration for a 0.5 l bottle is only 1 to 1.5 Kopecks.

In conclusion, we would like to add that ‘analogues' of Silver filtration have now emerged. These not only violate the rights of Technofilter Ltd as a patent holder but, first and foremost, compromise the regulated technology of Silver filtration. Therefore, we have to conclude with a familiar phrase: ‘Beware of counterfeits!'



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