17 Mineral Ultrafiltration Membranes in Industry DANIÈLE GERSTER1 and RENÉ VEYRE2 1
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Comission de l'Energie Atomique, 29 Rue de la Fédération, 75015 Paris, France SFEC, BP 33, 84500 Bollene, France The technology and components developed for gas phase separation and, more specifically, for isotopic enrichment of uranium by gaseous diffusion, have been adapted to separations in liquid media by SFEC, with the technical backing of the French Atomic Energy Commission. SFEC manufactures "Carbosep" the first mineral membranes in the world commercially available. The industrial use of the advanced membranes is discussed. The concept of "mineral membranes" and their specific properties and characteristics are summarized, and the corresponding industrial modules and ultrafiltration units are then described. Many industrial facilities based on Carbosep membranes are in operation in France and other European countries, treating a wide variety of compounds. This paper deals in particular with: • the food industries: milk, whey, cheese, fruit juices, alcoholic beverages, vinegar, eggs etc., • the biotechnology industries: membrane fermentation reactors, enzyme reactors etc. In these two fields, the ability of Carbosep units to withstand successive steam sterilizations unaffected is most welcome.
Apart from France, only a small number of countries, such as the USA, Japan, and more recently Holland, have tried to develop entirely mineral separation membranes. The most widely used materials are porous nickel, sintered stainless steel, carbon, alumina and zirconia. A few composite mineral/organic membranes have also been developed, of the zirconia/polyacrylate or zirconia/polyamide type. As a rule, the applications planned are related to hyperfiltration for mixed membranes, and microfiltration for ceramic membranes. Until very recently, however, the use of these mineral membranes expanded much less than that of organic membranes, and only rarely left the laboratories. On the other hand, the mineral ultrafiltration membranes manufactured and marketed under the Carbosep trade name by Soci6te" de fabrication d*Elements Catalytiques (SFEC), a CEA subsidiary, are well established in Europe today, 0097-6156/85/0281-0225$06.00/0 © 1985 American Chemical Society
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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particularly in the agri-foodstuffs and biotechnology fields. The different industrial references compiled in Europe since 1981 now foreshadows the worldwide commercial development of the process. Before presenting the process (and its applications), it should be pointed out that it results from the merger of American and French technological know-how in the area of mineral microporous substances initially developed for gas separation. The Carbosep process, which stems from the licence issued by Union Carbide to SFEC, has been developed and adapted by the company since 1979 mainly for agrifoodstuffs and biotechnology applications.
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The Carbosep Ultrafiltration Process Membranes. The microporous mineral membranes exhibit a composite morphology. The composite character is obtained by the superposition of several homogeneous microporous media: • a sintered carbon support, • an ultrafiltering layer of metallic oxide, usually zirconia. The geometry selected is tubular. The tube is 1200 mm long, has an outside diameter of 10 mm, and is 2 mm thick. Its main characteristics are given in the Table I, Table II and Table II. Table I.
Separation Characteristics of Carbosep Membranes
CUT OFF M4 membrane Ml membrane M6 membrane
20,000 daltons 50,000 daltons 2,000,000 daltons 180-600 l/m2*h
WATER FLUX (25°C, 4 bars)
Table II.
Mechanical Properties of Carbosep Membranes
BURST PRESSURE OPERATING PRESSURE CRUSH STRENGTH YOUNG MODULUS
Table III.
60 bars 15 bars 30 kgf/20 mm 1000
Operating Conditions of Carbosep Membranes
PRESSURE pH TEMPERATURE Membrane System STERILIZATION Oxidant Steam
15 bars 0 to 14 300°C 150°C
YES YES
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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The performance of these membranes offers outstanding industrial reliability. They can withstand the most severe stresses engendered by hot process fluids, and those of chemical and especially steam sterilization. Moreover, they accept the highest concentrations and viscosities hitherto reached in ultrafiltration. A number of original properties merit emphasis: • possibility of back-washing, • dry storage • long life time: some installations have been operating for over three years without any decrease in performance. Modules. The tubular membranes are assembled in parallel bundles in stainless steel housings. The steel grade is adapted to the specifications of the agri-foodstuffs and biotechnology industries. The type of assembly adopted allows the unit replacement of the membranes. The diffusing areas of the modules range from 0.02 to 5.73 m 2 (see Table IV). Table IV.
Carbosep Modules
REFERENCE (number of tubes) S S S S S
1 7 37 151 252
DIFFUSING AREA m2 0.02 0.16 0.84 3.43 5.73
Systems. The industrial systems are of the "multistage" type, operating in steady state conditions with a recirculation loop. The equipment is gradually approaching standardization, from laboratory units to industrial units with several hundred square meters of diffusing area. SFEC now has a total of 30 mobile pilot units performing in situ tests required for the design of industrial units. Industrial Applications The main industrial applications developed since 1981 concern different product lines of the agri-foodstuffs and biotechnology industries. Dairy industry. Due to the dimensions of milk proteins, the dairy industry is the privileged field of ultrafiltration applications. Since its commercial introduction in Europe, SFEC has established 25 installations which have not yet required membrane replacement. The different processes developed in the dairy field are the following: • Milk protein standardization: which serves to correct seasonal variations in milk protein content and to raise their average content, which tends to fall in certain areas. This process helps to achieve a higher cheese yield and to improve operating reliability.
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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REVERSE OSMOSIS AND ULTRAFILTRATION This process is applied to various cheese technologies, such as soft, blue-veined and pressed cheeses, and also to different goat's milk base technologies, particularly the freezing deferment process. • Extraction of serum proteins from whey: ultrafiltration represents the first upgrading of this by-product of the cheese industry. The protein concentrates are characterized by a protein/dry extract ratio of 0.4 to 0.9, and, after s^ray drying, they display very high nutritious value. They are intended for infant diets (maternized milks) and therapy diet (hyperprotein foods) as well as cured meat productions. The industrial installations are of the multistage type, and operation is fully automated. Constant protein content is guaranteed by refractometric or flow rate regulation. Daily cleaning is performed at 85°C in alkaline medium. From the hydrodynamic standpoint, the turbulence at every point of the installation yields protein concentrates of very satisfactory bacteriological quality. The permeate or deproteinated lactosed juice is either concentrated to 32% by evaporation for sale to pig breeders, or used as a substrate for protein production from single cell organisms. • Production of fresh cream cheeses by the ultrafiltration of curdled milk; this application is currently revolutionizing the French and German cheese industry, because it helps to produce fresh cream cheeses such as Petits Suisses, low-salt cheeses, and a variety of cream cheeses with a much higher cheese yield than obtained by centrifugation and thermocentrifugation.
Fruit juice clarification. In 1983, Carbosep mineral membranes witnessed further development with the construction of three industrial plants for apple juice clarification. A comparison of the conventional process with the ultrafiltration process immediately shows that: • the conventional batch process is vastly simplified by the elimination of operations such as cooling, fining, tank cleaning, and filtration through diatomaceous earth and cellulose plates. • passage from a batch process to a continuous process facilitates the operating conditions. • equipment: fewer tanks, elimination of the centrifugal separator and conventional filtration units. • products: less enzymation, elimination of gelatin, bentonite, kieselguhr, and cellulose plates. • manpower: reduction in transfer operations, possibility of bottling 2 hours after startup of the ultrafiltration unit compared to 30 hours in a conventional process. • material yield: evaluated as not less than 97%, against approximately 90 to 93% in conventional processing, depending on location. Despite closely comparable compositions, two specific characteristics may be noted. • Ultrafiltered juices preserve apple tannins, whereas they are partly complexed by gelatin fining in conventional processing.
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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• Ultrafiltered juices are more deeply colored than conventional juices, as the fining operation causes a loss in color. Moreover, taste tests are more favorable to juices clarified by ultrafiltration. Cross flow microfiltration of fermented alcoholic beverage. Since 1983, SFEC and CEA have launched a research and development program to step up the Carbosep process for the clarification of fermented alcoholic beverages. France's three leading beverages are: • wine 50 to 80.10 6 hi/year • beer 20 to 25.10 6 hi/year • cider 15 to 20.10 6 hi/year The advantage of the Carbosep process for this product line is: passage from a batch process to a continuous process and simplification of the operation of the conventional filtration system. The various constraints pertaining to wines, both qualitative and cost related, led us to the concept of cross flow microfiltration. A mineral microfiltration membrane was specially developed for this application and for the microfiltration of cider and beer (M6 membrane recently marketed in Europe). Eggs. Carbosep systems have witnessed original development in France for the concentration of whole eggs and egg whites, due to their capacity to convey viscous liquids with minimum mechanical shear of the product. Moreover, the lysozyme contained in the egg is now subjected to extraction/concentration. Biotechnologies. Mineral membranes offer a new tool for biotechnologies. Micro-organism separation, purification and concentration are ideally performed by Carbosep ultrafiltration units. The "product" yield is nearly 100%. Here also, Carbosep ultrafiltration, which serves to treat highly viscous liquids, due to its hydrodynamics, competes with centrifugation equipment. These units also allow the coupling of a bioreactor or a biofermentor with the ultrafiltration device. The ultrafiltration system forms an integral part of the fermentor. This coupling offers the following main functions: • joint sterilization of the fermentor and the ultrafiltration system, • continuous, controlled elimination by the ultrafilter of metabolites or of the sterile upgradable phase, • homogenization of the biomass by recirculation between the fermentor and the ultrafilter, • if necessary, purification of the biomass by continuous washing without exposure to air, • concentration of the residual biomass, whose value may be raised by the ultrafiltration system to levels of several hundred g/1, • sterile drainage and recovery. On the whole, bioreaction and biofermentation yields are boosted. Several ultrafiltration systems coupled with fermentors or reactors, are operational. They can be used for the concentration of micro-organisms, the synthesis of amino and enzyme compounds, the extraction of
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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biomolecules produced by fermentation, hydrolysis reactions of highly viscous complex media, the synthesis of organic acids resulting from a bioreaction, such as vinegar, the extraction of yeasts and the synthesis of different type of ferments, the sterile concentration of viruses and the extraction of specific toxins. The capacity to operate in a totally sterile environment also endows these new membranes with potential applications, such as the preparation of thermally fragile biochemical solutions, by "cold" sterilization by passage on the membrane wall. This property is of particular interest to the pharmaceutical industry.
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Conclusion The Carbosep ultrafiltration process, characterized by the use of so-called 3rd generation mineral membranes offers a high performance tool for the agri-foodstuffs and biotechnology industries. After three years of industrial and commercial expansion, its operating reliability has enabled the process to penetrate the industries discussed above successfully in Europe, and is now aimed at North America. Yet, the inherent virtue of every new technology is to require continued research and development activities to hold on to markets. To achieve this, each link in the "membrane separation" chain (membranes, modules, systems, applications) is the subject of sophisticated research, and development in our laboratories and our engineering design departments, or jointly with other French research institutions and industrial firms. RECEIVED February 22, 1985
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
