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BIOCON’s membrane systems for ultra- and microfiltrtion. Application in various branches of industry.

 

The results of long-term developments in the field of installation designing for cross flow microfiltration and ultrafiltration are presented. As filter elements there are used tubular ceramic membranes from aluminum oxide with silicon carbide selective layer and roll membranes from polysulphonamide.

There are given many examples of application of these installations in pharmaceutical, food and dairy, fuel and energy industries and in water treatment.

There are shown some research results concerning concentration of cow and soybean milk and microfiltration of skim milk using new ceramic membranes.

 

Content:

1.   Introduction.

2.   Design and operating principles of the BIOCON membrane systems.

3.   Application of the BIOCON membrane systems.

3.1. Pharmaceutical and microbiological industries.

3.1.1.  Riboflavin.

3.1.2.  Erythromycin .

3.1.3.  Vitamin В2.

3.1.4.  Lysine.

3.1.5.  Enzymes.

3.2. Dairy industry.

3.2.1.  Milk concentration.

3.2.2.  Whey and lactose concentration.

3.2.3.  Milk microfiltration.

3.3. Food industry.

3.3.1.  Soybean milk.

3.3.2.  Drinks, extracts, syrups.

3.3.3.  Wines.

3.3.4.  Water treatment in beer production.

3.4. Fuel and energy industries.

4.   Conclusion.

      References.

 

1. Introduction.

The membrane filtration processes, particularly, ultrafiltration and microfiltration are separation processes, which go under pressure on porous polymeric or inorganic materials. For the last 30 years these processes have found application in different industries for liquids purification or concentration.

Sales of membranes and membrane equipment are increased continuously with approximately 10-12% annual rate of growth. For example, in 1986 the membrane market was $ 3,2 billion, in 1990 it was $ 6,1 billion and according to the experts at the end of 90-s it should be about $10-11 billion [1,2, 3].

Production of membranes and membrane equipment concentrated mainly in three regions: USA, Western Europe and Japan, a share of which ones is about 97 % in all production and 75 % in purchase concerning membrane technology. Now in these regions about 100 corporations and plants occupy membrane industry, and only 60 of them produce membranes and membrane units, others design equipment using membranes as elements of commercial installations (systems) [4,5].

        In 70 -s the ceramic membranes have appeared in the membrane market of Europe, USA and Japan. The ceramic membranes made usually on the base of oxides, nitrides and carbides of some metals were for micro and ultrafiltration of different liquids that are aggressive or require temperatures more than 100oC for effective separation, when polymeric (organic) membranes fail or lose their properties. Beyond their high thermal stability ceramic membranes have a series of properties, which allow to select them into independent commercial and technological activity named abroad as "ceramic membrane business".

       Among such properties first of all it should be noted:

- mechanical stability;

- stability to chemical and microbiological influence;

- stability of structural pores and possibility of their control during membrane production;

- possibility of using backflow through membranes;

- high flow rate through membranes;

- long service life.

       According to the above mentioned advantages of ceramic membranes, their using as compared to polymeric membranes allows to reduce maintenance costs (mainly due to their longer service life), to reduce overall dimensions and weight of filtering installation, that also lower capital outlays [6, 7].

      Despite of dominate position of polymeric membranes in sectors of West biotechnological industry, ceramic membranes start gradually expand into this industry due to their lesser effect on protein curdle on membrane surface, and also because they allow to sterilize them by steam repeatedly. Ceramic membranes are widely applied in filtration of industrial sewage, particularly in Germany, where the metalworking industry is highly developed.

      Sales of ceramic membranes in 1988 was $ 32 million, in 1993 it was $ 40 million. In 1991 the experts forecasted rough propagation of inorganic membranes sales in 90s. It was expected, that sales should be about $ 450 million in 1999 [8, 9]. However, it has not taken place, that was caused by high ceramic membrane price that was higher than polymeric membrane price in 3-5 times (ceramic membrane prices were $ 1800 - $ 2500 for 1 sq. meter of membrane surface). The consequent estimations were more conservative. They predict, that sales of inorganic membranes will be $ 228 million in 2003 at ceramic membranes share of 70 %. [10].

     Nowadays in Russia there are small productions (500 m2 per year) of ceramic membranes, competitive in quality, for example, RPE"Ceramicfilter" Co., Ltd. (Moscow, tubular ceramic membranes).

2.   Design and operating principles of the BIOCON membrane systems.

      Base BIOCON filtering systems are two kinds of duplicate products: filtering modules and filtering units, that differ, mainly, by scale parameters (dimensions and weight).

       As filtering material (filter element) the polymeric membranes in the form of roll membrane elements (ERU-100-1016 type, JSC «Vladipor», Vladimir) or ceramic membranes in the form of single-channel tubular ceramic elements (CMFE type, RPE"Ceramicfilter" Co., Ltd. Moscow) are used. Pore size or retain ability of filtering materials is the following:                                                                                    

    for ceramic membranes: 0.05 microns,  0.2 microns, 0.8 microns, 

     for polymeric membranes: 500, 50000, 10000, 20000, 50000 Dalton.

      Ceramic membranes CMFE-150/80 type (see Fig.1) are porous tubes of 800 mm length with inner diameter of 6 mm and outer dia of 10 mm or multi-canal tubes made from aluminum dioxide with a selective layer made from silicon carbide on their inner side.

 Polymeric membranes ERU - 100-1016 type (see Fig.2) are roll membrane elements of 1016 mm length and with outer diameter of 100 mm with membrane from polysulphonamide.

  

     The filtration module (see Fig. 3) consists of a cylindrical housing with the face flanges made from stainless steel. Tubular ceramic or roll membrane filter elements are inserted into the housing. The hermetic sealing of filtering elements in the module is made in the face flanges by rubber rings.

There are nipples and connecting pipes on the housing and face flanges of filtering module for liquid feeding, for filtrate and concentrate removing.

      The filtration unit (see Fig. 4) consists of one or several filtration modules, circulating pump (centrifugal type), feeding pump, heat exchanger, inlet and outlet collectors, platform, valves, pressure gauges, flowmeters, auxiliary tank (by necessity), connecting quick-detachable fixture, control desk. 

         The filtration unit is constructed by circulating loop principle for creation of cross flow mode of filtration (tangential filtration).

 Liquid for filtration moves in the apparatus by feeding pump. Inside the apparatus the filtered liquid under circulating pump is continuously pumped through the flow circuit formed by several filtrating modules, heat exchanger and circulating pump, that are connected in series (for ceramic membranes) or connected in parallel (for polymeric membranes).

 Part of liquid and particles, which size is less than pore size are passed through membrane surface of ceramic elements under pressure of (0,5 - 3,5 bars) and continuously removed from the apparatus. This part of liquid is named as permeate. Constant supplying with new liquid for filtration fills up the deficiency of liquid in the module.

The particles, which size is more than pore size, are retained by selective layer and collected inside the flow circuit. This part of flow is named as concentrate. Circulating flow, which rate is 4-7 m/sec for ceramic membranes and 1-1.5 m/sec for polymeric membranes, continuously washes off the deposit formed above a membrane.

Fig.4

 
          The BIOCON industrial systems are designed from several filtration units, control valves and system of automatic control. The company BIOCON possesses "know-how" on designing of large industrial systems in the context of membrane type optimum choice and scales of filtering system for the given product.

The company BIOCON produces wide spectrum of filtering systems.

 

 

       Filtration surface of the base units is:

-      for ceramic membranes: 0,5; 1,1; 4; 8; 10; 20 m2;

-      for roll membranes:  5, 10, 20, 40, 80, 100 m2.

       To the present time the multistage installations with the maximal area of a surface of a filtration 360 m2 - for polymeric membranes and 320 m2 - for ceramic membranes are issued.

      Stored knowledge of ceramic and roll filter elements using shows that most effective at the following temperatures:

-      for ceramic membranes: 40-90 0 С;

-      for roll elements:  40-55 0 С,

service life for ceramic membranes makes 3-5 years and for roll elements makes 0,5 - 1 year.

3.    Application of the BIOCON membrane systems.

3.1.                  Pharmaceutical and microbiological industries.

3.1.1. Riboflavin. The culture broth of vitamin В12 (riboflavin) producer is subjected to microfiltration on ceramic membranes with pore size of 0.2 micron at temperatures more than 1100С for biomass separation from vitamin В12 dissolved at this temperature. The rate of filtration is 400 l/m2/h. The installation of 20 m2 filtration surface is used.

3.1.2. Erythromycin. The culture broth of erythromycin producer is diluted twice with water and then subjected to microfiltration on ceramic membranes with pore size of 0.2 micron at the temperature of 400С. The rate of filtration is 60-80 l/m2/h. The antibiotic yield at the stage of microfiltration is 17-21 % higher as compared to using of filter-presses according to previous plant technique. The duration of ceramic membranes washing and regeneration makes 30 min. Now the installation of 112 m2 filtration surface is used (fig.5). Gross rated capacity of the installation will be 320 m2. 

3.1.3. Vitamin В2. The culture broth solution purified of biomass is concentrated in 40 times by nanofiltration with using of roll elements ERU-100-1016. The rate of filtration is 8-10 l/m2/h.

3.1.4. Lysine. To make crystalline lysine the culture broth of lysine producer is subjected to the process of preliminary clearing from biomass by microfiltration on ceramic membranes with pore size 0.2 micron at the temperature of 500С. The rate of filtration is 120-160 l/m2/h. According to technology 75 % of purified solution goes for crystalline lysine production and the biomass concentrate (25 %) goes for production of feed lysine. Gross rated capacity of the installation is 160м2.

3.1.5. Enzymes. Alcoholic (70 %) extract of protein and enzymes is purified in installation with filtration surface of 1.1 м2 using ceramic membranes with pore size of 0.2 microns. The rate of filtration is 130 l/m2/h (fig.6).

 

 

3.2.Diary industry.

 

      Ultrafiltration (UF) is the most popular membrane process at processing of dairy raw material. Whole milk, skim milk, previously clabbered milk and also whey are subjected to UF.

Tasks of ultrafiltration are the following:

        а) Preliminary concentration of milk proteins for production of traditional sorts of cheese;

        b) Significant change of ratio between proteins and other ingredients for creation of new cheese sorts;

        c) Normalization of milk on protein for maintenance of homogeneity and reproducibility of cheese properties beyond any dependence on seasonality;

        d) Separation of whey proteins to receive protein concentrates and lactose solution.

 

 

3.2.1. Milk concentration.

      Preliminary concentration of milk by UF increases fraction of total mass of dry substances on average from 12,5 % up to 16 % and allows to double productivity of subsequent stages. At concentration of whole milk in 2 times the processing line includes only UF system and the basic operations of cheese manufacturing are carried out by standard technology.

      Further concentration of milk up to concentration factor of 3-5 (up to 40 % of solids) for receiving and processing of protein coagulum requires special equipment.

        Using of ultrafiltrated milk increases cheese yield. For example, in Fet cheese production the consumption of milk is reduced from 8,5 down to 6,5 kg/kg of cheese. Besides, UF concentrating allows to reduce consumption of milk coagulating enzyme (up to 60 %) and bacterial ferment, to accelerate cheese ageing and manufacturing process, and also to automize production and control processes.

      In pilot experience the whole cow milk from milk plant was heated up to 600С then cooled down to 500С. The average composition of milk is the following:

n     Solids ....... ………… …………             10,5  %

n     Protein ...............…………..                     2,8  %

n     Fat .......................... …………                  3,1 %

n     Ash ........................…………. ..                0,6 %

n     Lactose ………….. ....... ……….…          4,0  %

 

      In the experiment the BIOCON pilot membrane installation (Fig.7) was tested. It consists of the following:

 

n     Filtration module АRS-5 type with ultrafiltration roll element of ERU-100-1016 type, filtration surface of 5 m2, polysulphonamide membrane, cut off of 50 kD.

n     Centrifugal circulating pump (flow rate 5 m3/h at  pressure of 5 kg/сm2);

n     Feed pump;

n     Circuital tank (30 l)

n     Heat exchanger.

 

 

    In each experiment in the beginning milk was concentrated up to the concentration factor (CF) of 3 or 5 times in volume, then permeate was returned in the circuital capacity and the process of ultrafiltration was carried out at constant CF during 5 hours. Temperature of the ultrafiltration process was 42-550С. The results of the experiments are given in Table 3.1.

 

 

 

      Cleaning and regeneration of membranes was carried out up to primal water permeability of  membrane element (210 - 240 l/m2 h) by standard procedure, routine for cow milk using solution of caustic soda with sodium hypochlorite adding.

      The concentrating milk experiments on pilot installation were carried out within 3 months on the same roll element with periodicity of 1 time per week. Thus the results obtained were similar to the results given above.

      For milk concentration in 2-5 times the filtration installations with roll membrane elements of  50 kD cut off are used.

Fig.8

 
      The installations have filtration surface of 240 m2, consist of two stages (150 m2 and 90 m2), work in automode and ensures productivity on initial milk 5000 l/h (fig.8).

 

 

3.2.2.                     Whey and lactose concentration.

 The experiments concerning concentrating of cheesy whey and lactose solutions obtained in the previous process of ultrafiltration, were carried out on the pilot installation described above in item 3.2.1. For whey concentration the roll membrane elements ERU - 100-1016 with cut off of 20 kD were used, and for lactose concentration the roll membrane elements ERU - 100-1016 with cut off of 400-500 Dalton were used.

The calculation of ultrafiltration process for production capacity of 100 tons whey per day based on the test data obtained is given below.

      3.2.2.1. Calculation of ultrafiltration process at whey concentrating.            

       А) Membrane type: roll polymeric membrane of ERU - 100-1016 type (cut off of  20 kD)

       B) Source data:       Whey volume per day            -    100000 l;

                                        Process time: filtration          -     20 h;

    Regeneration                         -     4 h;

                                        Operation cyclogram: 10 h + 2 h (washing)

     Productivity:   -  whey     -  5000   l/h;

                                          -   permeate ( with allowance for waters for diafiltration)      -  5625 l/h;

                                          -   concentrate   -   125 l/h

                                         Concentrate and filtrate yield –  continuous.

                                         Concentration factor: 40 as compared to initial volume.

                                         Temperature of the process:  50-520С.

 

       During a multistage ultrafiltration at the last 4-th stage is made diafiltration process for decrease of the contents lactose and salts.

 

 

      Liquid concentrate of whey proteins is a result of ultrafiltration at CF=40. After that the concentrate obtained is dried on a spray drier and the powder with the contents of whey proteins 80 % is received. This process can be executed using the ultrafiltration installation UFS/5000WPC80 type

 

Fig.9

 
      Permeate, obtained after whey ultrafiltration is highly refined lactose solution, which can be concentrated in 2-2.5 times using of roll membranes for nanofiltration (retainability of 400-500Dalton) to lactose content of 9-10 % and solids content of 10.6-11.0 %, the filtration rate at that is 7 -10 l/m2/h. After that the concentrate obtained is dried on a spray drier and can be used in food industry at production of drinks, ice cream or in pharmaceutical industry for nutrient mediums.

 

3.2.3.                     Milk Microfiltration.

        Microfiltration of milk is rather new for milk membrane process, that as well as ultrafiltration, separates milk ingredients under pressure in flowing mode at 5 - 7 m/sec rates of liquid above membrane.

        Application of ceramic membranes with pores of 0.2 - 0.8 microns allows to delete bacteria from milk. At whole milk microfiltration most part of fat is deleted simultaneously, at this membranes with pore size of 0.2 microns delete 99.9 % of fat particles, and membranes with pore size of 0.8 microns delete 90-98 % of fat. Bacteria content in milk filtered through membranes with pore size of 0.8 microns is decreased in 200 times without noticeable retention of proteins.

        Microfiltration of nonfat milk goes at much higher rate as compared to the similar process for whole milk. For example, at using of ceramic membranes CMFE-150/80 with pore size of 0.8 microns microfiltration of whole milk (at 550С) goes at the rate of 500 - 700 l/м2/h, and for nonfat milk it goes at the filtration rate of 2500 - 3500 l/m2/h, 99.6 % of bacteria are deleted from the skim milk.

        The Microfiltration of skim milk can be used for high-yield sterilization of milk, especially in the cases of strong milk contamination.

       The corporation "Alpha-Laval" (Sweden) has developed the process of milk sterilization named "Bactocatch", at which nonfat milk is subjected to microfiltration using ceramic membranes with pore size of 0.8 – 1.4 microns, and the concentrate obtained in the process, that makes 5-10 % of total milk volume, is mixed with fat concentrate and heat treated at the temperature of 1300С for 4 sec, then it is mixed with milk microfiltrate in the necessary proportion /11/. The given technique allows to increase pasteurization level of milk considerably and decrease protein denaturizing as compared to standard thermal pasteurization.

        The test data obtained by BIOCON at microfiltration of nonfat milk using ceramic membranes CMFE with different nominal size of pores is given below. The experiments were carried out on the pilot installation similar in consist to the installation given in item 3.2.1, instead of modules with roll membranes, there were used two modules with single tubular ceramic membrane CMFE-150/80 (filtration surface of 0.015 m2).

        The results of the experiments are given in Table 3.3. The results given in  Table 3.3 show that ceramic membrane with pore size of 0.2 microns deletes considerable quantity of the solids from nonfat milk, that is connected with large retention of casein proteins (about 90-95%). The ceramic membrane with pore size of 1.2 microns shows rather strong drop of filtration rate during 2 hours of operation and, besides many bacteria can by-pass in the filtrate at such pore size. With relation to filtration rate and bacteria retention the optimum pore size of ceramic membrane for milk is 0.8 microns.

 

Note. There are given mean data of 2-3 repeated experiments.

For removal of microorganisms from skim milk the filtration installations with ceramic membranes CMFE-150/80 (pore size of 0.8 microns) with filtration surface of 8 m2 are used, productivity of installation is 5000 l/h (see Fig.10).

 

 

 

 

 

 

 

3.3.              Food industry.

3.3.1.                     Soybean milk (vegetable extract of soy). Soymilk base

Fig.10

 
      The soybean milk is produced by high-temperature extraction (900C) of soybeans in water. The hot extract obtained is centrifuged using screw decanting vessel for separation of brews (residual soy beans). The soybean milk contains valuable high molecular substances: vegetative protein (2.2-3.7 %) and  fats (1.1-2.5 %), and also undesirable low molecular substances, the content of which is about 2.4 % (phytic acid, trypsin inhibitor, lipoxidase). The low molecular substances can be deleted by ultrafiltration of soybean milk in combination with diafiltration.

      Ultrafiltration is rather new process for industry of soybean products. In contrast to traditional concentrating methods, for example, vacuum evaporation, the ultrafiltration allows to get various component combinations in soybean products. During ultrafiltration the high molecular substances are retained by membrane and concentrated, and the low molecular substances move with permeate, thus solids content (TS) in soybean milk rises from 7.5-8 % up to 12 - 22 %. Adding of water during ultrafiltration (so-called diafiltration process) allows to reduce concentration of low molecular substances to required level, for example, 1.1-1.2 %. The concentrate of soybean milk with protein content of 57-60 % and fat of 30 -34 % obtained during ultrafiltration can be used in production of cottage cheese, mayonnaise, cream, cheeses of different fat content and other products.

The concentration of soybean milk was carried out using ceramic membranes with pore size of 0.2 microns and 0.8 microns on a pilot installation described in item 3.2.1.

Filtration surface of ceramic membranes was 0.28 m2 in each module. Initial milk volume was

60 l, it was concentrated twice in the volume (CF=2) at the temperature of 700С, then 30 l distilled water was added and then concentrated from 2.5 up to 4 times in different experiments. Soybean concentrates were produced with concentration of the solids  = 12.4 % (CF=2.5), = 16.4 % (CF=3),  = 20.2 % (CF=4). Solids content in permeate was decreased down to 1.16-1.24 % by diafiltration.  Filtration rate for ceramic membranes with different pore size differed and made as concentration advanced 69 – 27 l/m2/h (for pore size of 0.2 microns) and  99 – 41 l/m2/h (for pore size of 0.8 microns) at the temperature of 60-80 0С and transmembrane pressure of 1.1 kgf/m2.

For installations of 1000 l/h and 2000 l/h productivity the calculations of different technological schemes for concentration/diafiltration of soybean milk using ceramic membranes were made.  

 

3.3.2. Drinks, extracts, syrups.

        In microfiltration a filter supply stream (raw juice for instance) is divided into a stream of filtrate (clear juice) and a stream of concentrate. The concentrate stream contains all turbidity-forming solid components such as proteins, pectin fragments, macromolecular tanning agents, cellulose and others in a concentrated form. The clear juice which is available as the filtrate stream (permeate) contains the typical components of a clarified juice in their natural percentages.

       The fruit juice industry uses only the so called tubular membranes.

       At clarification of drinks, fruit and berry extracts and syrups the ceramic tubular membranes with pore size of 0.2 microns are used. The BIOCON installations have filtration surface of 2 m2, 4 m2, 20 m2 (fig.11).

        Microfiltration of fruit and berry extracts and syrups goes at the temperatures of 70 - 800С. Depending on product the filtration rate is 60 - 100 l/m2/h. Microfiltration is used in production of viburnum, dogrose, cranberries, sea-buckthorn, haw and etc. syrups.  

       For purification of vegetative extracts on maize base in production of red dyes the filtration installation with filtration surface of 4 m2 and pore size of 0.2 microns is used. The productivity of the installation on permeate is 700 - 800 l/h.

Fig.11

 
       After microfiltration refined solution is subjected to concentration in 3-8 times by nanofiltration using roll membranes ERU-100-1016. The filtration surface of the installation is 80 m2. Average productivity of nanofiltration installation is 700 l/h (fig.12).

Fig.11

 
       Clearing of mineral water obtained from a slit goes using the installation with ceramic membrane surface of  2 m2 with productivity on permeate of 1800 l/h.

       Research-and-Production Organization of brewing, nonalcoholic and wine industries has made a conclusion that after microfiltration iron ions are deleted from mineral water and chemical composition remains constant.

 

3.3.3. Wines.

There were tested more than 20 different dry, fortified and table wines, and also brandy drink (about 360) for microfiltration of wine materials using ceramic membranes with pore size of 0.2 microns. According to main laboratory data and estimations of wine-makers (joint-stock company "Agrofirm"Abrau-Derso", "Crymsovhozvinprom" and other factories) quality of filtration is very high, the organoleptic indexes completely meet requirements for the grades. Sugar and alcohol content does not vary, the removal of 99.99 % micro-organisms is ensured. For wine clearing the installations with filtration surface of 4 m2, 10 m2 and 20 m2 are used. Mean filtration rate (8 hours of operation) for dry wines is 150 - 250 l/m2/h, for fortified wine is 60-100 l /m2/h, for brandy drink is 300 -500 l/m2/h.

3.3.4. Water treatment in beer production.

      Purification efficiency of water from admixtures, microorganisms, iron and hardness salts is of great importance in beer production. In small power production with water use of 5-6 m3 per day at one shift operation the complex water-purification installation is used (fig. ). It includes microfiltration block with ceramic membranes (filtration surface of 5 m2) and blocks for water softening. Using of microfiltration is necessary in the cases, when artesian water has heightened content of microorganisms and iron. Ceramic membrane regeneration goes due to filtrate backflows during filtration process and periodic (1-2 times per week) washing by alkaline solution with sodium hypochlorite adding.

      The block of softening ensures soft water volume between regeneration cycles of 5.25 m3 at total hardness of 8 mg-equivalent. The regeneration of the block for water softening is carried out by 10 % solution of common salt in automode.

 

3.4.              Fuel and energy industries.

3.4.1. Regeneration of waste transformer oil.

      Utilization of waste transformer oil is a major problem for energy industry.

      Using microfiltration process on ceramic membranes it is possible to refine waste transformer oil from suspended particles and water and to bring up parameters of transformer oil purity to the required norms concerning specific resistance.

      The installation for regeneration of transformer oil includes the microfiltration block with ceramic membranes (filtration surface of 4 m2) and block of dehydration (fig.13).Water elimination from transformer oil goes under expansion pressure in permeates outlet zone above developed outer surface of tubular ceramic filters. The installation allows to increase purity of reclaimed transformer oil from 14  to 7-th class, to reduce humidity content from 3000 g/t  to 20 g/t and increase essentially electrical resistance of oil from 0 up to 24.5 kW/cm. Productivity of the installation for purification of transformer oil is 1200 l/h.

 

4.  Conclusion.

      A wide spectrum of domestic filtration installations using roll organic and tubular ceramic membrane filter elements was produced as a result of long-term developments of micro- and ultrafiltration equipment in cross flow mode. The examinations of these installations in new areas of application are carried out. The membrane systems developed find wide spread application in pharmaceutical, food and diary, fuel, energy and other industries.

 

 

       

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