The application of basalt paper and board as filtration materials for the purification and sterilization of air

Abstract

Papers have appeared in recent years on the application of special types of paper and board for the sterilization of air by filtration [1-3]. The properties of these materials depend on many factors: the type of fibers used, methods of physicochemical treatment, the presence of sizing agents, etc. The structure of a sheet for air purification is that of a fairly porous interweaving of fibers of various lengths The most dependable method of preparing filter paper and board of uniform structure is the multilayer pouring method [4], since on superimposing thin leaves one upon the other, possible defects in individual layers are covered. Sterile air is used in the process of manufacturing antibiotics and is obtained by filtration through a layer of fibrous filtration material. Sterile air, which is supplied for aeration in the fermentation process, must have a defined temperature and moisture content. In the event of a drop in air temperature below the dew point, moisture separation occurs which wets the filtration material and leads to a reduction in its mechanical strength. Moreover, as a result of the swelling of cellulose fibers the pore size and consequently the air penetrability is reduced [4, 5]. To prevent the phenomenon mentioned and to impart hydrophobicity and ~-et strength to the paper and board, various polymeric binders are introduced into the fibrous mass which after special treatment confer stiffness on the paper fibers. The filtration materials obtained in this way are sufficiently tough, stable to the action of moisture, and retain their previous values of specimen porosity thus guaranteeing a high moisture penetrability. At the present time basalt superfine fiber (BSFF) (fiber diameter 1 p) is used as a filtration material in filters for the fine purification of air [6]. This material answers the requirements set for a material for sterilization by the filtration method, viz. a high effectiveness in retaining particles of contaminants (99.999 % of 0.3 p particles), sufficient vapor and thermal stability, and an extended service life. The comparatively small mechanical strength is a shortcoming of the material. This shortcoming also caused a search for a filtration material based on BSFF and more sturdy and convenient in operation. Specimens of materials in form of paper and board based on BSFF have been developed in the Ukrainian Paper Research Institute [7]. Pulverized cellulose fibers and latex were added to increase the durability of materials in manufacture. An investigation has been carried out in the All-Union Scientific-Resea rch Institute of Antibioties on specimens of basalt paper and board with the aim of possibly using them for the sterilization of process air in antibiotic manufacture. It is known that materials for air purification are evaluated according to the drop in pressure and the size retention of particles entering with the air [8]. An increase in the drop in pressure is energetically unprofitable; however, simultaneously with the growth of this parameter the efficiency of retaining particles is raised, and consequently it is necessary to find the size of the optimal ratio of the values mentioned. An investigation to find the optimum has been carried out with the aim of elucidating the interrelationshi p of the properties of the paper and the sizes of the characteristics mentioned. Tests on specimens of paper and board were carried out at afiltration rate ofl cm/sectaldng the highly effective materials for testing [9] The effectiveness of a material was verified on a test bed with an oil spray [I0]. Averaged results of several measurements are presented in Tables 1 and 2. In column 2 of Tables 1 and 2 the labelling of the basaltic materials submitted by the manufacturer is given. For example,