Carbon-mineral adsorbents — new type of sorbents? Part I. The methods of preparation

Materials Chemistry und Physics, 31

243

(1992) 243-255

Carbon-mineral adsorbents - new tvDe of sorbents? Part I. The methods of preparation ’ ’ R. Leboda Faculty

of Chemistry,

Maria Curie-Skiodowska

University, 20031 Lublin

(Poland)

(Received September 2, 1991; accepted October 17, 1991)

Abstract The methods of preparation of carbon-mineral adsorbents produced on the basis of typical sorbents (e.g. silica gels, alumina, titanum oxide, Celite 545) and other sorbents important in industry (mainly ahrminosilicates and natural silicates) are described. Among the methods of preparation have been distinguished mechanical mixing, incorporation, carburization of organic substances bonded chemically or physically with the surface of mineral adsorbent, as well as deposition of the carbon on catalyst and adsorbent surfaces during different adsorption and catalysis processes. The source of starting materials for preparation of complex adsorbents has been shown. The thermodynamic bases of the process of formation of carbon deposits are also discussed.

Introduction

Adsorption processes play a very important role in many fields of modern technolo~: exact drying and purification of gases and liquids; absorption of volatile solvents and harmful waste products polluting the atmosphere and water reservoirs; isolation and concentration of valuable components from gas and vapor mixtures, often in order to further chemical or biological treatment, and accumulation of gas fuels in reservoirs filled with adsorbent. Actually, for an example, it is estimated that about 70% of chemical analyses are performed using chromatographic methods. With these methods tens and even hundreds of different types of adsorbents are used for the separation of mixtures as well as the isolation and preconcentration of trace amounts of substances. Petrochemical, chemical, food and pharmaceutical industries could not perform without adsorbents and catalysts. Adsorption and catalysis are strictly connected with each other, and often the requirements made for adsorbents and catalysts are the same. In many cases the same porous solids can be used as adsorbents, catalysts supports and catalysts. To make up a complete list of the fields in which porous solids are used appears to be impossible. Further possibilities of utilization of surface phenomena in technology and other walks of life will be always connected with elaboration and

02.54-0584/92/$5.00

production of new types of adsorbents. In this case we can speak about some feedback. Carbonmineral adsorbents can be considered as a new type of sorbent. They were not so far described in any mono~aph. The number of reviews related to these adsorbents is not large [l, 21. The first article relates to the application of carbon-mineral adsorbents in the processes of water purification and the second article to the preparation, properties and application of these adsorbents in chromatography. In this connection a wider survey of such adsorbents, regarding the actual literature data, appears to be reasonable. This is the main purpose of this article. This articles includes all methods utilized so far for preparation of carbonmineral adsorbents and shows the sources of potential starting materials for preparation of adsorbents. Moreover the surface properties and application of these adsorbents in technology are also discussed. Preparation

methods

Carbon-mineral adsorbents are complex or mixed adsorbents consisting of two components: mineral and carbon. These components may be mixed in any way or the carbon substance may be a stable deposit on the surface of the mineral adsorbent. From the literature review the following methods of complex adsorbent preparation could be distinguished:

0 1992 - Elsevier Sequoia. All rights reserved

244

1. mechanical mixing of the graphitized carbon black particle or active carbon with the mineral adsorbent particles; 2. incorporation of the carbon adsorbent particles between the gel particles (usually silica gel or alumina) by the addition of carbon particles to the sol before gelation; 3. total or partial carbonization of organic substances previously bonded physically or chemically with the surface of the mineral adsorbent; 4. the process of carburization of adsorbents and catalysts. The adsorbents produced by the last two methods are the most interesting either from a practical or from a cognitive viewpoint. The processes of carbon matter formation from organic substances are in general very complex, and depend on many factors [3]. The most general picture of the carburization process can be presented by the following scheme of the cracking of hydrocarbons [4]: paraffins -

olefins -

high-molecular olefins and naphthenes unsaturated cyclic hydrocarbons aromatic hydrocarbons high molecular condensed aromatic hydrocarbons asphalt-like condensed substances -

carboids -coke.

Scheme 1.

The process of carbon deposit formation in complex carbon-mineral adsorbents may be initiated and terminated in any stage or stages of scheme 1. This is dependent on the chemical nature of the carbonized substance, porous structure and chemical nature of adsorption and catalytic centers of the mineral matrix, etc. For this reason the complex adsorbents prepared by the third and fourth methods have the carbon deposits consisting of the substances of differentiated chemical and physical structure formed during the defined stages of the scheme 1. Such deposits have different names. In heterogenous catalysis, for example, the carburization of the surface is spoken of using a variety of names for carboneous substances, eg. cokes, condensation products, carbons, tars, deposits [4]. This shows either some conventionality of these names or the morphologic complexity of the products of carbonization reactions. Some problems connected with this will be discussed successively in further sections.

Thermodynamics of the formation (carbon deposits)

of cokes

Formation of coke from hydrocarbons is determined by different thermodynamic factors and by kinetic characteristics of the process. The characteristics of the process indicate the reality of the process and its general trends consisting in the shift of the process towards formation of defined condensation products including graphite-like structures. Kinetic characteristics determine not only the rate of the process but also its curiosities, accumulation of different intermediate products as well as the full course of the reaction. Kinetic curiosities of the process of gradual condensation of hydrocarbons and formation of cokes are dependent on the structural-energetic characteristics. Two main ways of formation of carbon deposits can be distinguished: 1. by a complex sequence of successive reactions leading to gradual condensation and dehydrogenation of starting hydrocarbons until the formation of solid substances characterized by their high percentage of carbon; 2. by simple decomposition of hydrocarbons to carbon and hydrogen or to carbon and more light hydrocarbons; this way of preparation can be realized by periodic interactions of the hydrocarbons with the catalyst. Both above ways can be performed as catalytic, non-catalytic or thermal processes. Independently of the mechanism of formation of the coke, the course of this process is determined by the transition of the system to a more thermodynamically stable state which is characterized by a lower numerical value of isobaric thermodynamic potential: AGO= AH0 - TASO

(1)

which is connected with the equilibrium constant of the reaction by the equation of the isotherm of chemical reaction AGO=-RTlnK,

(2) where AH0 and AS0 denote the changes in enthalpy and entropy (during the chemical reaction) respectively, T = absolute temperature, R = universal gas constant, I(p = equilibrium constant of the reaction. Simultaneously with the decrease of AI-P, AS0 also decreases during the process of condensation losses

of hydrocarbon which is connected of some oscillation and rotation

with

the

degrees of freedom as the starting substances transform gradually to the products of the condensation. For the

235

processes of formation of cokes during catalytic and non-catalytic processing of hydrocarbons i.e. in the conditions of preparation of carbon-mineral adsorbents, detailed thermodynamic estimation of individu~ stages of the process by means of known methods is very difficult because of poor knowledge of the process, including a lot of simultaneous and successive reactions. For the processes of formation of the cokes, however, the evaluation of nonstability of hydrocarbons and the possibilities of their thermal decomposition to carbon and hydrogen is univocal. This is possible by means of the control of the changes of free enthalpy of formation of chemical compounds from the atoms AGO with the changes of the temperature of the process. Figure 1 presents the dependence of AGO of formation of a chemical compound calculated for 1 gram-atom of carbon on the temperature, determined by Fitzer et at. 131. It can be seen that the stability of the compound increases with the increase of negative value of AGO. Thus the greater the positive value of AGO, the easier the decomposition of the compound. Decomposition of the compound will be dependent also on the energy of formation of reaction products. The higher this energy (lower negative AGO value) the easier the decomposition of the compound.

Figure 2 presents the dependences of free enthalpies of formation of hydrogen and carbon monoxide on the temperature of the process. Numerical values of these enthalpies were calculated for 1 mole of hydrogen (in the case of CO for l/2 mole of 0,). From this figure it results that HF is the most stable compound, and the stability of CO is only slightly lower. For this reason the fluorine-contained compounds may decompose at relatively low temperatures. One among the methods of preparation of porous active carbons consists in the reduction of polytetrafluoroethylene (PTFE) at room temperature [5]. Oxygen-containing compounds e.g. carboxylic acids will decompose with the evolution of COZ. Pyrolysis of alcohols often will lead to formation of water which is very stable until 600 “C. Similarly the decomposition of organic substances containing halogen atoms will lead to the fo~ation of substances containing halogen and hydrogen atoms but not containing carbon (e.g. HCI). This is connected with the high energy of formation of hydrohalogenes. Figure 1 shows that the stability of the paraflins decreases with the increase of chain length. At higher temperatures the same rule relates to the olefines. The stability of aromatic hydrocarbons containing aliphatic chains is lower than that of aromatic hydrocarbons not containing such chains. Contrary to this, the stability of aromatic hydrocarbons increases with the increase of the number of rings in the molecule.

a

-80 -

0

100

-.L._1500

500 TEMPERATURE

Fig. 1. The free enthalpy of carbon compounds formation. values are referred to 1 g-atom of carbon 131.

All

1°C

_..~

I

Fig. 2. The free enthalpy of hydrogen compounds, and carbon monoxide formation. All values of the hydrogen compounds are referred to 1 g-mole of hydrogen, that of carbon monoxide to the equivalent of l/2 g-mole Oz 131.

246

Qualitative considerations of thermodynamic stability lead to the following general rules relating to the regularities of the pyrolysis process: 1. decomposition of all non-aromatic hydrocarbons runs initially towards the formation of smaller molecules; 2. in secondary processes the cyclization of all hydrocarbons to the aromatic forms takes place; 3. the final process runs towards the condensation of aromatic hydrocarbons to polyaromatic ones. The above three rules relate to all processes connected with the formation of the carbons by pyrolysis reactions. In the conditions of preparation of carbon-mineral adsorbents the course of the above processes and their thermodynamics depend also on the nature of the mineral matrix i.e. adsorbent or catalyst. Although the ‘rules’ present here permit the rational choice of the substance carburized for preparation of complex adsorbents, it cannot expect however that these rules may be always utilized in practice. In practice we will meet very often with a ptioti given mineral adsorbentorganic compound systems. For this reason among others the necessity arises of extensive studies relating to carbon-mineral adsorbents. The number of ‘model ways’ of preparation of carbon-mineral adsorbents including the series of simple schemes of chemical reactions is so far relatively small.

Preparation

of complex adsorbents

800-1000 “C. On the surface of the so-produced material is deposited additionally 10% of carbon obtained by the carbonization of light or heavy oils, kerosene or crude oil at temperature of 800 “C. A more complex mode of preparation of such adsorbents consists in the mixing of active carbon with the solution of metal salts or their sols, followed by the precipitation of metal hydroxides ( - 30%) on the surface of carbon material. In this way selective ion-exchangers [9] are produced. For purification of edible oils and greases, the mixture of fuller’s earth (clay, natural or activated with acids) and active carbon in the proportion of 4:1[6] is often used. Incorporation

The effectiveness of utilization of a complex adsorbent in the process of adsorption purification of substances may be increased by working with one mechanically stable carbon-mineral adsorbent. Such an adsorbent should combine the favorable properties of active carbons and porous mineral materials. Moreover both components, i.e. carbon and mineral material, should be bonded stably by adhesion-chemisorption forces. Apart from active carbon, the most widespread technical adsorbents are silica gel, alumina gel and in a smaller degree titania gel. Combination of these mineral adsorbents with the active carbons gives the possibilities of obtaining three types of complex adsorbents.

Mechanical mixing

Carbon-silica gels

In the literature special attention is paid to rational ways of mechanical preparation of the mixtures of carbon and mineral adsorbents. For example, in order to prevent formation of dusts during transport and loading of the mixture of bentonite and active carbon it is formed in special granules. They are’utilized for the purification of wines in order to remove compounds causing a nasty taste [6]. In order to obtain rapid and uniform distribution of hydrophobic carbon particles in the whole volume of mineral adsorbent, the pulverization of active carbon (particle size 10-40 pm) on the surface of particles of clays characterized by greater size (70-150 pm) is proposed [7]. This permits finally a significant intensification of purification of the mixtures by means of such a mixed adsorbent. Another patent [8] has described the method of production of carbon-mineral adsorbents by preliminary mixing of coke, charcoal or pit-coal with diatomite, followed by the heating in an at temperatures of oxygen-free atmosphere

One of the first attempts at preparation of a complex carbon-mineral adsorbent was made at the end of the twenties by Shilov et al. [lo] who saturated birch shavings with water glass. The saturated shavings were then treated with concentrated ZnCl, solution and then heated, obtaining gel. Organic components of this gel have suffered carbonization at elevated temperature. It has been stated that the adsorbent obtained in this way (carbosilica gel) is characterized by high adsorption capability which is higher than theoretically predicted on the basis of the parameters of individual components of such a gel, assuming the additivity of the properties of the complex adsorbent. Carbosilica gels are very interesting adsorbents from the viewpoint of their application in industry. The possibilities of utilization of active carbons in industrial practice are often limited because of their inflammability, while the carbon contained in a mixed adsorbent keeps its good adsorption properties but its ignition temperature is now

247

significantly higher. The methods of preparation of carbon-mineral adsorbents by incorporation are described in detail in the monograph of Nejmark

Pll*

Paper [12] describes carbon-mineral adsorbents by the dissolution of cane sugar in hydrochloric acid and the mixing of this solution with a solution of silicic .acid. After coagulation of the sol and its transformation into gel this was heated in conditions allowing the carburization of the sugar. In other investigations [13-151, peat, filtration paper and finely divided carbon were used as the carboneous materials. In this way different adsorbents containing different amounts of carbon may be obtained. The adsorbents obtained by means of the above methods are characterized by better adsorption properties than each individual component of the adsorbents. Carbo-alumo gels These adsorbents are mixtures of hydrophilic alumina gel and hydrophobic carbon. They can be obtained by the saturation of wooden sawdusts with aluminum salts followed by carbonization at high temperature or by the introduction of finely divided carbon to the suspension of alumina gel [6]. To a vigourously stirred solution of aluminium salt, finely divided carbon is added and then the suspension is heated and ammonia is added with continuous stirring. The precipitate of aluminium hydroxide absorbing small particles of carbon is formed. Then the precipitate is filtered, ground and washed in order to remove the residues of the salts and hydroxide and then dehydrated. After these operations the solid adsorbent is obtained.

Titanium-carbons Yermolenko and Yacewskaya [17] have obtained such adsorbents by the saturation of charcoal with Tic& followed by hydrolysis by means of water vapor.

Physical

and chemical

bonding

with the surface

This mode of preparation of complex carbonmineral adsorbents is described widely in the literature. An organic substance deposited previously on the surface of a given adsorbent or bonded chemically with its surface is carbonized, which leads to the formation of the complex adsorbent. The properties of such an adsorbent depend on the chemical nature of the matrix, its porous

structure, the nature of the organic substance and on the operational conditions. In this connection the above method creates wide possibilities of preparation of adsorbents of very differentiated surface properties. This results, among others, from scheme 1, illustrating the general process of formation of carbon materials during hydrocarbon cracking. In the given conditions of a carburization process different adsorbents of differentiated chemical nature can be obtained starting from different stages of scheme 1. Contrary e.g. to olefines the formation of carbon deposits from the paraffins is usually difficult [3, 41. The alcohols usually undergo dehydratation and form the olefines which can next proceed to complex polycondensation reactions. The nature of the carbonized substance and mineral matrix as well as the mode of realization of the carburization process depend on the destination of the adsorbent. If the final product will be used in industry e.g. as a catalyst, plastics filler or purifying matrix i.e. in cases where great amounts of the adsorbent are used, the starting materials must be low-cost, easily available and the process of preparation of such adsorbents should be realized in relatively simple technical conditions. In the case of more subtle applications of the adsorbent (chromatography, isolation and concentration of trace amounts of substances), i.e. when the amounts of adsorbent used are relatively small, the above requirements have lesser significance, but in this case a new problem appears connected with the reproducibility of prepared adsorbents, their energetic homogenity and the suitable chemical and physical structure of carbon deposits. For the above reason we will discuss now the different ways of preparation of complex adsorbents for technical purposes (mainly for purification of water) as well as for the laboratory (chemical analysis).

Preparation

on technical

scale

In the world this problem is solved in two ways. One consists in the utilization of these mineral adsorbents or catalysts which are used earlier in other technical processes and which contain now the substances capable to form carboneous compounds during the thermal treatment. Food, celulose-paper and petrochemical industries are potential sources of starting materials utilized for the production of carbon-mineral adsorbents. In the second case the carburized substances are sprayed on the surface of the mineral adsorbent.

248

For example, in the purification of wines and juices bentonite clays are usually used. The bed of consumed clay contains, among others, proteins, pectins, tanning agents, dyes, sugars, organic acids and other compounds. The content of these substances may attain 15-20% w/w. After appropriate thermal treatment a complex carbon-mineral adsorbent can be obtained which can be used successfully in water purification technology [18, 191. Utilization of clays for the purification of liquid confectioneries appears to be very promising [20]. The cited papers describe the utilization of palygorskite for these purposes. After long-time exploitation this material contains some amount of saccharose, the products of its caramelization, melanization and other substances [18] which are capable of carburization. In an other paper [21] are shown the possibilities of utilization of askan bentonite consumed during the process of purification of cane sugar solution. After the purification this adsorbent is heated at 500 “C, which produces a microporous carbon-mineral adsorbent characterized by the following parameters: specific surface area S= 130 m2 g-l, total pore volume pore radius 0.10 cm3 gg’ and predominant r=2-3 nm. It has been suggested earlier that some byproducts of the celulose-paper industry may be utilized for the production of carbon-mineral adsorbents. This is connected very often with the problems of environmental protection. In Bilitewski’s publication [22] it was shown that from an economical viewpoint, utilization of the slimes contained in waste waters of the celulose-paper industry is useful for production of porous carbonizates. He has prepared the carbonizates, characterized by high dispersion (ca. 65%) and relatively low specific surface area (S = 100’ g-l). In the paper industry strongly dispersed cellulose fibers pass through the gauzes of paper producing machines and then to the waste waters, from which they are then isolated by means of some chemicalcolloidal methods utilizing bentonite clays [23]. By the thermal treatment of this mechanical mixture of cellulose fibers and bentonite an effective adsorbent can be obtained. The absence of chemical bonds between the particles of cellulose fibers and the clay particles does not allow to obtain the granulated material and in this connection some species must be added to this mixture. For this reason in order to obtain an active carbonizate about 20% of mineral admixtures (perlite) and chemical activator (ZnCl,) were added to the solid wastes of the cellulose-paper industry before heating. In the literature many particles can be found

relating to the preparation of complex sorbents on the basis of active clay i.e. of a material widespread in nature [25-271. It appears that this trend is advantaged because it solves completely the problems of purification and utilization of the precipitates contained in waste waters. Stiecenko and Tarasevich [28] have described the preparation of a carbonizate from active clay obtained by the mixing of the precipitates collected in settling tanks of the first and second steps of purification of waste waters from a cellulose-paper factory. The mixture was concentrated, then 10% of ferric chloride and 20% of lime were added and the mixture was dehydrated until the relative humidity equal led 75-80%. The material prepared in this way contained 39% of cellulose fiber, 27% of active clay and 34% of mineral compounds. After the carbonization of this mixture (at 600700 “C, for 1 hour) the material contained about 45% of carbon. Other authors [29] have added to the clays, apart from active carbon, also aluminosilicate catalysts or zeolite X. The low cost of carbon-mineral adsorbents combining the advantageous elements of active carbons and dispersed aluminosilicates creates possibilities of their utilization as agents improving the sedimentational properties of active clay. Montmorillonites are also very interesting materials because of their packet structure. It is well known that glucose and saccharose can penetrate the interlayer spaces of montmorillonite [30]. The other substances may behave in a similar manner. By the introduction of large organic cations into the interpacket spaces [32] the hydrophilic properties of the mineral can change to hydrophobic. The exchange of an inorganic cation for an organic one cause the increase of interpacket distances in the montmorillonite bed, and owing to this the sorption of large organic molecules, e.g. paraffins or aromatic hydrocarbons, becomes possible. Owing to appropriate preparation of the sorbents even the selective sorption of hydrocarbons is possible. The above facts have stimulated many authors to attempt preparation of carbon-mineral adsorbents on the basis of montmorillonites. It has been assumed that these adsorbents should be characterized by some specific properties in that the organic substance introduced between the montmorillonite packets should form some specific ‘pillars’ after the carburization. Such ‘column’ sorbents should possess open pores and the carbon clusters of different size should be localized between these pores. Data published in the papers [33, 341 show however that the coke formed by carburization of

249

glucose and saccharose forms a continuous layer which fills completely the interpacket spaces of montmorillonite, eliminating them from the adsorption processes. More promising results were presented by Krzyianowski and iyla [31] who have carburized and methyl polymetacrylate glycol, glycerine sprayed previously on the montmorillonite bed. The pyrolysis was made at three different temperatures i.e. 623, 773 and 873 “C. From the investigations of these authors it results that, by proper choice of activation as well as of temperature of pyrolysis, the modification of sorption properties of clay minerals is possible. The most advantageous changes can be obtained in this case when the activating agent penetrates the interpacket spaces and forms so-called interlaminar complexes, as well as in the case when the above substance easily undergoes destruction leading to the formation of great amounts of carbonaceous products. In the experimental conditions used by these authors the best results were obtained for glycerine. Significantly earlier however (1979) Loeppert and co-workers [35] have described the first trials of production of ‘column’ clays containing the carbon clusters in inter-packet spaces. The conception of formation of such adsorbents consists in the formation, in the interlayer space of a silica matrix, of cationic complexes containing the neutral organic ligands following by the carburization of formed compounds at a temperature of 4505.50 “C. For trapping oils contained in ship wastes a carbonized sorbent is often prepared on the basis of clay [36]. The clay is dried, ground, and then saturated with vegetable oil. The vegetable oil diffuses partially into the interior of the clay and then the granules undergo a two-stage thermal treatment at 160 “C for 2 hours and then at 220 “C until partially carburized products are obtained. Utilization of consumed sorbents and other products such as consumed oils is a problem requiring reflection, either because of economical or of ecological reasons [37, 381. The scale of the problem may be illustrated by the fact that the amount of the clay consumed yearly in USA is about 50 thousand tons. It is proposed that the clays consumed in the processes of contact purification of food and technical oils will undergo thermal treatment and the carburized hydrophobic adsorbent obtained in this way will be used as the protection screens in slime reservoirs [39] or as ion-exchangers [40]. The method of utilization of fuller’s earths consumed in the process of purification of food oils is patented also [41]. These

materials can be used, after appropriate thermal treatment, as carbon-mineral adsorbents in the processes of adsorption of dyes and surface-active agents. The important potential starting materials for production of carbon-mineral adsorbents are hydrolysed lignins [42], kerosene asphaltenes [43] or the wastes formed during the working of farm products. Adsorbents for laboratory purposes One of the first trials of preparation of carbonsilica adsorbents was described in the papers [4547]. On the surface of hydroxylated silica gel were chemisorbed aliphatic and aromatic alcohols, which were then carburized and complex carbonsilica adsorbents containing a few percent of carbon bonded stably with the surface were obtained. Such adsorbents were called carbosils [48]. In the papers of Bebris et al. [49, 501, and Colin and Guiochon [51, 521, other ways of preparation of such adsorbents have been proposed. Benzene vapors were passed over a stationary layer of thermally resistant silica at a temperature of 850-900 “C. Owing to decomposition of benzene pyrocarbon was formed on the surface of the inorganic matrix. The surface concentration of this pyrocarbon was 1.3-6.7 mg m-*. According to the adsorption characteristics of the surface unit, carbon-silica adsorbent prepared in this way and containing about 7 mg m-* has the characteristics similar to those of thermally graphitized carbon black, and in respect of geometrical and energetic homogenity of the surface has poorer properties than carbon black. Poor adhesion of carbon sprayed in the above way on the silica surface makes impossible the formation of a uniform modifying film. The surface of the carbosil is in fact a mosaic and has intermediate properties between these of silica gel and carbon adsorbents. From the investigations of Rudenko and coworkers [53] it results that perceptible deposition of a carboneous substance on the silica surface during the pyrolysis of benzene is observed at temperature ca. 700 “C, whereas in the conditions used by Bebris et al. [49] about 20% of benzene transforms into carbon. The already mentioned collection of papers [53] represents a rich source of data relating to the mechanism of formation of carbon deposits on the surface of adsorbents and catalysts owing to decomposition of substances of ditIerent chemical nature. The method proposed by Bebris et al. was used but without success for hardening mechanically unstable graphitized carbon blacks used in high performance liquid chromatography [54, 551.

250

The intermediate products formed before the pyrolysis of a given substance play an important role in the creation of the properties of carbosils. These products can be formed in different ways e.g.: a) by the chemisorption of chemical compounds sprayed on the surface of modified silica before their pyrolysis; b) by the formation of substances of greater molecular weight by mutual chemical reaction of the molecules of the substances sprayed physically on the solid surface (usually the mixtures of different compounds having functional groups or substances capable of polymerization). For example, alcohols react with silanol groups or siloxane bridges [56] of the silica surface, which leads to the formation of surface esters. The alcohols (or surface esters) dehydrated at elevated temperature form olefins, which form next, according to scheme 1, more complex compounds. The effect of pyrolysis of different alcohols on the properties of obtained carbosils [4547, 57-601 has been investigated. The reactions were made statically (in an autoclave) [45-47, 57-631 and in dynamic conditions, using a rotary reactor constructed specially for this purpose [59, 69, 701. In each case adsorbents of relatively low content of carbon deposit (few % w/w), not covering completely the silica surface, were obtained. In this connection other substances which would give, in the moderate conditions of the process, relatively great amounts of carbon deposited on modified silica surface with simultaneous avoidance of strong sintering of the skeleton of the modified adsorbents, have been looked at. In the papers [67, 681 has been described the carburization of the mixture of a-phenylethyl alcohol and p-chlorotoluene, which form initially intermediate products (alcoxytoluene with simultaneous evolvation of gaseous HCl) and finally the carbosils containing above 13% w/w of carbon are obtained. The products of pyrolysis of aromatic alcohols give in the same conditions a greater amount of carbon deposited on the silica surface than aliphatic alcohols having in their molecules the same number of carbon atoms. Carbosils prepared by carburization of mixtures of such alcohols have intermediate properties [57-60]. Chemisorption of alcohols on the surface silanol (=Si-OH) and siloxane (=Si-0-Si=) groups may occur at low temperatures [56]. With increase of temperature the olefines are evolved. These compounds may then condense with the aromatic compounds which leads to the formation of the coke. This phenomenon takes place in the case of pyrolysis of mixtures of aliphatic and aromatic

alcohols. Alcoxytoluene formed during some stage of this process (pyrolysis of the mixture of (Yphenylethyl alcohol and p-chlorotoluene) is bonded with the silica surface more strongly that the strarting components, due to the increase of molecular weight. This stage, consisting in strong adsorption, plays a very important role in the creation of greater amounts of the coke on the solid catalyst [71] and is one of the reasons for good adhesion of the carbon deposit to the surface of the mineral matrix. Very fashionable from the viewpoint of reaction mechanism and the consequences resulting from this mechanism are described in the paper [72]. This paper describes the carburization of acenaphthene on a silica surface. The course of the pyrolysis reaction is presented in Fig. 3. A characteristic feature of this process is the fact that already at low temperature (about 200 “C) this substance (i.e. acenaphthene) undergoes polymerization and forms products of high molecular weight. Then the formed macromolecule of polyacenaphthylene (III in Fig. 3) interacts strongly with the silica surface. This macromolecule is less mobile and therefore a greater amount of carbonized substance deposits on the surface (in comparison to the gas phase) during the establishment of the equilibrium. For this reason it obtains a great degree of conversion of acenaphthene to carboneous substance. This degree may attain 90%, whereas pyrolysis of alcohols may attain from few [57-581 to ten to twenty percent only [67, 68, 731 depending on the type of alcohol and on the conditions of its carburization. Benzene and hexane show still lower conversion degrees. Figure 4 shows the dependence of the amount of carbon deposit contained in the complex adsorbent on the amount of carburized acenaphthene. Depending on the temperature of the reaction, different products may form. At temperatures near 500 “C (or higher) the pyrolysis process leads only to the formation of one product i.e. a polycyclic aromatic hydrocarbon. This is very important from the viewpoint of surface properties of the complex adsorbent because the energetic properties of such an adsorbent will depend on the chemical structure of the carbon deposit. The more homogeneous the products of the reaction the more homogenous energetically the surface of the adsorbent. The products of pyrolysis of naphthalene and anthracene give similar (although less clear) reactions to those presented in Fig. 3 [75]. Another noteworthy type of reaction consists in the decomposition of methylene chloride on the surface of mineral adsorbents [2, 59, 691:

251

I :urther corldensation

Fig. 3. Pyrolysis of acenaphthene: I - acenaphthene; II - acenaphthylene; III - polyacenaphthylene; diacenaphthylene; VI - fluorocyclene; VII - decacyclene; VIII - zethrene.

Fig. 4. Dependence of carbon content in Carbosil on the amount of acenaphthene pyrolysed on the silica gel surface.

CH,Cl, Temp. C + 2HCl This reaction was utilized occasionally by Grobb [81] and Zoccolillo and Liberti [82]. Comprehensive experimental material is contained in Gierak’s dissertation [83]. The ease of formation of carboneous substance in the above reaction results from the stoichiometry of this reaction as well as the high energy of formation of HCl. This does not mean however that all halogen-derivatives of organic compounds in which the C:halogen atomic ratio is 1:l (as in the case of CH,Cl,) will form carbon deposits easily. For example trials of decomposition of C6H3C13 at 900 “C on silica did not give satisfactory results. Reaction (3) performed on the surface of a solid adsorbent permits us to obtain practically any amount of carbon [78]. This last article relates to the studies of the effect of parameters of the process of carbonization of methylene chloride in dynamic conditions on the properties of carbosils.

IV - biacenaphthylene;

V - l,l’-

In spite of the simplicity of reaction (3) the process of carbonization on the silica surface is complex. Its course depends on the temperature of pyrolysis, the concentration of pyrolyzate, the rate of pyrolyzate and the rate of removal of hydrochloride from the reaction medium. The mass exchange of the substrates and products of the reaction occuring on the solid surface in dynamic conditions plays a very important role in this case. Hydrochloride evolved during this reaction may block the active surface of silica and make the deposition of carbon difficult. For this reason the simple relations are not stated between the parameters of dynamic process and such quantities as specific surface area and thermodynamic characteristics of adsorption of different substances. Adsorbents of the type of graphitized carbon blacks are very attractive for chromatographic and other analytical purposes. They are characterized by strictly defined and homogenous topography of adsorption centers [84]. Unfortunately these adsorbents are brittle, which makes their practical application difficult and moreover the graphitization process is made at very high temperature (-3000 “C) and in oxygen free or reducing atmosphere. It is evident that no carbon-mineral adsorbent will stand treatment in such conditions. However, Gierak et aE. [85-871 have shown that even in moderate conditions (350-700 “C) complex carbon-silica adsorbents of highly ordered structure of carbon deposit can be obtained. This type of adsorbent was prepared by catalytic decomposition of n-butane on the surface of nickel catalyst (which was removed after the carburization process) sprayed on the surface of silica gel. In this way

252

can be deposited even 90% w/w of carbon characterized by graphite-like structure. The mechanical properties of such carbon deposits depend on the mechanism of the carbonization process. The investigations described in [85] have permitted to obtain carbon deposits of poor mechanical properties but the next article from this series [86] describes carbosils of good mechanical resistance. Deposition of pyrocarbon on residual active centers of the supports of liquid stationary phases was utilized for reduction of the adsorption and catalytic activity of these centers [88]. The diatomite support Celite 545 was treated preliminarily with phenol-formaldehyde solution and then, after the removal of the solvent, the organic substance remaining on the surface underwent pyrolysis in inert atmosphere at a temperature of 1200 “C. In this way a support of increased mechanical resistance and inert in the adsorption process was obtained. The authors of the paper referred to in this chapter were guided by a purpose of elaboration of the methods of preparation of complex adsorbents (which can be used in exchange for carbon adsorbents) not containing micropores, having hydrophobic and energetically homogenous surfaces and characterized by high mechanical resistance (in contrast to carbon adsorbents). Such a type of adsorbent is not described in any of these publications. In the introduction to this article the feedback referred to can be now presented in that the investigations described above have resulted in a new type of sorbent not used earlier in chromatography. In further parts of this article we will show that they may be used successfully in analytical and investigative practice [89]. Carburization of catalysts and adsorbents

During the catalytical processing or purification of hydrocarbons and other carbon-containing substances, the catalysts or adsorbents undergo carburization and lose in a significant degree their initial properties. This is an undesirable phenomenon because the restoration of initial activity and selectivity of the catalyst is not always possible. Although in many cases the sorbents and catalysts are subjected to regeneration and then used again in the technological processes, however after several cycles adsorption/catalysis regeneration, the activity of the regenerated material decreases to such a degree, that its further exploitation becomes inexpedient and the consumed carburized material is removed to waste dumps. Such materials however, as we will shown in a further part of this

article, may be utilized successfully as carbonmineral sorbents in different processes of purification or separation of different mixtures of substances. The literature relating to carburization of catalysts and adsorbents is very extensive (e.g. [4, 53, 90-953) but its detailed discussion in this paper appears to be inexpedient. A more important question consists in indicating the sources of starting materials for preparation of complex adsorbents or their utilization. The most important conclusion resulting from the literature review is the statement of existence of differentiated forms of carbon deposits and different ways of their formation depending on the external conditions as well as on the type of cataiyst and starting material. This betokens the possibility of existence of differentiated forms of complex adsorbents characterized by different chemical and physical properties. In this connection not all adsorbents will possess carbon deposits of useful morphology. In the case of metal oxide materials the tendency to conversion to cokes is observed mainly for unsaturated hydrocarbons [96]. The method of isolation of aromatic hydrocarbons from unsaturated substances is based on the exceptionally high chemical resistance of these hydrocarbons [96-991. The essence of this method consists in the fact that aromatic hydrocarbons separated by extraction from reforming catalysts and containing small amounts (-0.35%) of unsaturated substances are passed through a layer of granulated aluminosilicate (prepared on the basis of specially activated natural clays). Unsaturated hydrocarbons undergo polymerization on the acidic centers of the adsorbent surface and then condense which leads to the formation of the coke, whereas the aromatic compounds mainly benzene, toluene and xylenes remain after previous percolation purification practically unchanged. Similarly during the purification of aromatic hydrocarbons obtained in catalytical processes of reforming and hydrocracking-hydroalkylation, the working life of adsorbents prepared on the basis of natural palygorskite-montmorillonite clay may be equal e.g. to one year [loo]. In this period of time about S-10% w/w of coke deposits on the adsorbent surface [21, 1011 which leads to strong deactivation of the adsorbent. Although there exist the methods of self-oxidative regeneration of such types of sorbents [102], in practice however the consumed material is removed to a waste dump and the adsorber is filled with a new charge of fresh sorbent. The above examples show on the one side what materials should be selected for carburization and on the other side

253

a source of potential carbon-mineral adsorbents. Regarding the above observation the research group from Novosibirsk [103] has elaborated the method of preparation of complex adsorbents consisting in carburization of the surface of aluminium oxide by the products of pyrolysis of divinyl. It has stated [104] that the coke deposits mainly in the form of particles of 3 nm dimensions on the whole of the kinetically available surface of aluminium oxide. In general the percentage of the coke deposited on this surface is l&22% w/w. In the macropores of size above 10 pm there deposits 25-30% of the total amount of the coke, in the pores of size 20-200 nm. 15%, and in the pores of size 20 nm, 45-50% of the total amount of the coke [ 1051. Great attention was paid [106-1081 either to the ways of realization of catalytic cracking or to regeneration of catalysts (especially these containing costly zeolites) in such way that the catalyst will not loss its activity during a lot of cycles. For this purpose it uses short cycle operations of the catalyst introducing to it the different admixtures capable of bonding sulphur, and uses ion exchange resins in order to demetalise the catalyst etc. This permits us to obtain stable working of the zeolite containing catalysts during many cycles. However, poor mechanical resistance causes, in the circulating stream of the catalyst, chips of their granules of relatively great cross-section i.e. 2 mm. Stable working of technological devices is possible even in these conditions when the content of the chips does not exceed 1.5%. For this reason some part of the carburized catalyst is directed to the separator in which the chips of the catalyst of size of 1.5-2 mm are removed from the system [106], and then a new, fresh portion of the catalyst is introduced to the system. In the USA the consumption of such catalysts is 400 tons per day [loo]. In industrial practice instead of costly zeolite containing catalysts (for the cracking of some fractions of crude oil) less costly semi-synthetic sorbents prepared on the basis of natural silicates are often utilised. Owing to this, more frequent exchange of consumed catalyst becomes profitable from an economical viewpoint [lOS] because the consumed catalyst can be utilized as a carbonmineral adsorbent. We have indicated here the several sources of obtaining carburized sorbents and catalysts. Consumed catalysts used in such processes as vapor reforming of hydrocarbons, hydrogenation and dehydrogenation of hydrocarbons [90], dehydrogenolysis [93], methan~ation [94], Fischer-Tropsch

synthesis [94, 951, adso~tion-catalytic separation of saturated hydrocarbons from nonsaturated impurities [loo], and deep adsorption drying of propylene gas [llO-1141 can be potentially the starting materials for the production of carbon-mineral adsorbents. In this last case 11141 the heavy fractions of condensate adsorb on the surface of aluminosilicates, bauxites or natural zeolites and then undergo the transformation which leads to the fo~ation of the coke. This process is observed especially in this case when the natural gas contains unsaturated compounds as impurities. There is evidence that the process of carburization of adsorbents/catalysts can be utilized purposely for production of complex carbon-mineral adsorbents which can be used for defined purposes (see e.g. [SS-871). Discussion The title of this article contains the question mark. This is connected with the fact that it results from the references that the materials which can be considered as carbon-mineral adsorbents were described (although occasionally) in the literature long ago. Although the phenomena of carburization of adsorbents and catalysts is known also long ago, the product of such processes were not called ‘carbon-mineral adsorbents’. (Searching the first paper relating to this phenomenon, Buyanov [4] comes to the conclusion that this phenomenon was known already before the introduction by Berzelius in 1835 of the term ‘catalysis’.) It is known however, that such materials may be only the starting materials for production of carbonmineral adsorbents. Although only some sources of such materials have been shown, it is supposed however that the number of these sources is significantly greater. The demands made for complex adsorbents used for laboratory purposes are different from those made for ‘technical’ sorbents. Tarasevich [1] supposes, however, that the conclusions resulting from the preparation of the former adsorbents can be utilized successfully in prediction of the conditions of preparation of the sorbents used for technical purposes. This relates mainly to the sorbents used for purification of water and other substances because the effectiveness of functioning of such materials is determined among others, by proper selection of the mineral adsorbent and the carbonized substance. The main purpose of formation of carbon-mineral adsorbents consists not at all in preparation of the sorbents as simple exchange for active carbons or more general carbon-adsorbents, which has taken place in investigations related to chromatography. Technical carbon-min-

254

era1 adsorbents should be remunerative, lower cost than the active carbons, and should be characterized by increased mechanical resistance and very differentiated adsorption properties. In this connection great attention is paid to utilization of aluminium oxides, aluminosilicates and natural silicates as the mineral matrices of complex adsorbents. In this case the application of narrowpore mineral adsorbents of predominating pore radius less than 3 nm is inexpedient because low molecular substances e.g. n-propyl alcohol [61] are used as carbonized substances and then such pores are eliminated from the adsorption process owing to deposition of carbon (these pores are easily penetrated by small molecules) and on the other side when larger organic molecules e.g. furfurol are pyrolyzed the carbon does not deposit in these pores [116]. From a chromatographic viewpoint the blocking or micropores is usually useful. In order to increase the affinity of the carbon layer towards the surface of the mineral matrix and to decrease the temperature of the pyrolysis process (which is very important from economical and energetic viewpoints) it is advantageous to carry out the reaction in conditions permitting the chemisorption of the carbonized substance at the catalytic centers of the inorganic sorbent, because in this case there is a good adhesion of the carbon deposit to the surface of the inorganic sorbent. Some investigations related to preparation of complex adsorbents for chromatography were realized just in this way. References 1 Yu. I. Tarasevich, Khim& i tiechnol. wody, (1989) 699. 2 R. Leboda, Complex carbon-silica adsorbems -preparation and properties (Habilitation Thesis) (in polish), UMCS, Lublin, 1980. 3 E. Fitzer, K. Mueller and W. Schaefer, in P. L. Walker, Jr. (ed.), Chembbyand Physics of Carbons, Vol. 7, Marcel Dekker, New York, p. 237. 4 R. A. Buyanov, Zakoksowanje katalizatorov, Izd. Nauka, Novosibirsk, 1983. 5 Z. Plzak, F. P. DouSek and J. Jansta, J. Chromatogr., 147 (1978) 137. 6 H. Kinle and E. Bader, Aktiwnyje ugli i ich promeshelloe primienienie, Leningrad, Khimija, 1984, p. 216. 7 Pat. No 229 3963, France, B 01D 53/02. 09.07.1976 8 Pat. No 51-35.558 Japan, 14E 331 /CO1 B31/10; 02.10.1976 9 Pat. No 49-37035 Japan, 13/9/F2/BOl d 15/00/, 04.10.1974. 10 N. A. Shilov, M. M. Dubinin and S. A. Toporov, Zhurn. Russ. Khim. 0-va, 61 (1929) 1765. 11 I. E. Nejmark Sintietitcheskiye minerabryje aa!sorbienty i nositieli katalizutotov, Izd. Naukowa Dumka, Kiev, 1982. 12 H. A. Fells and J. B. Firth. Chem. Ind., 46 (1927) 39. 13 N, W. Polyakov, I. E. Nejmark and I. M. Malkin, Zhurn. fiz. khimii, 5 (1934) 1079.

14 N. F. Yermolenko and M. M. Rozova, Trudy A. N. Bssr, 4 (1939)45. 15 N. F. Yermolenko and M. I. Yacewskaya, Koll. zhum., 34 (1972) 604. 16 Z. Z. Wysockiy, I. E. Nejmark, Dokl. A.N. SSSR, 92 (1953) 357. 17 H. F. Yermokenko and M. I. Yacewskaya, Zhum. jiz. Khimii, 44 (1970) 189. 18 N. G. Taran, Adsorbienty i jonity wpishtchievojpromyshlennosti, Moscow, Legk. i pishtch. prom., CT6, 1983, p. 248. 19 M. A. Kerdivarenko, Moldavskiye prirodnye sorbienty i tiechnologtya ich primienientja, Kishiniev, Kartija Moldavienskaya, 1975, p. 192. 20 N. I. Shtangeeva, L. S. Danchuk, T. A. Ped’ko and Yu. I. Tarasevich, Puhchev. prom. 2 (1985), 38. 21 Yu. I. Tarasevich, W. M. Rudenko, Z. G. Ivanova, W. E. Doroshenko and K. W. Kulik, Khimija i tiechn. wody, 6 (1987) 510. 22 B. Bilitewski, Korrespod. Abwaser, 2 (1981) 75. 23 W. P. Cvitiel’skiy, B. F. Omieshchanskiy and Yu. I. Tarasevich, Khimtja i tiechn. wody, 4 (1981) 374. 24 Cho Byung Rin and Suzuki Motoyuki, J. Chem. Eng. Jap., 6 (1980) 463. 25 Pat. No. 785233, USSR, M. Ki3C02 F 11/12; 07.12.1980. 26 M. I. Bogdanovich and L. N. Kuzniecova, Zzw. qvzsh. ucheb. zawiedienij, Lesn. Zhum., 6 (1986) 86. 27 W. D. Gwozdev and B. S. Ksenofonton, Ochistka proizwodstwiennyh stochnyh wod i utihzacija osadkov, Moskow, Khimija, 1988, p. 122. 28 L. A. Stiecenko and Yu. I. Tarasevich, Khimija i tiechn. wody, 2 (1989) 175. 29 R. D. Schwartz and C. J. McCoy, J. Water Pollut. Contr. Fed., 2 (1976) 274. 30 B. K. Theng, 7’he chembtty of clay-organic reactions. AHalsted Press Book, Bristol, 1974, p. 343. 31 A. Krzyzanowski and M. ZyIa, Chemiu Stosowana, 3 (1986) 341. 32 Z. Klapyta and M. Zyla, Miner. Pal., 8(2) (1977) 49. 33 W. M. Rudenko, Yu. I. Tarasevich and Z. G. Ivanova, Khinr@ i tiechn. wody, 6 (1983) 499. 34 G. F. Kalapusha and Yu. I. Tarasevich, Ukr. /&in. zhurn., 2 (1982) 584. 35 R. H. Loeppert, M. M. Mortland and T. I. Pinnavaia, Clay and CZuy Miner., 3 (1979) 201. 36 Pat. No. 53-9285, Japan, 13/9/F29/wOl, D 15/00; 27.01.1978. 37 D. U. Pirs and I. Walter (eds.), Issledowanije wtorichnyh produktov. Ekonomicheskije aspiek& Moskow, Ekonomika, 1981, p. 289. 38 Ya. A. Karelin, I. A. Popov, L. A. Evseeva and 0. Ya. Evseeva, Ochistka sfochnyh wod niefiepierembatywayushchih zawodow, Moskow, Ctpajizdat, 1982, p. 185. 39 F. F. Mazheyko, W. S. Komarov, N. M. Aleksandrovich and T. G. Rudakovskaya, Dokl. A.N.BSSR, 2 (1974) 141. 40 New type collection agent for heavy metal ions, Technocrat, 8 (1975) 85. 41 M. Korczak and J. Kurwiel, Pat No. 107835, Poland, 1983. 42 E. I. Ahmina, Uglerodnyje adsorb&@ i ich primienienie w promyshlennosti, Moskow, Nauka, 1983, p. 48. 43 I. W. Pokopova, M. S. Oleynik and L. S. Ivanova, Sir&z i j?.ziko-khimicheskiye swojstwa nieotganicheskih i ugherodnyh adsorbientov, Kijev, Naukowaja Dumka, 1986, p. 114. 44 F. G. Lupashka, W. W. Strielko and W. M. Raport,A&orbienfy i a&orbcjonnye ptocieqv w resheni problemy ochnmy prim& Kishinev, Shtinica, 1986, p. 38. 45 R. Leboda, Ph. Thesis, Maria Curie-Sklodowska University, Lublin, 1974.

255

46 R. Leboda, Z. Suprynowicz and M. Waksmundzka-Hajnos, Chem. Anal., (Warsaw), 21 (1976) 437. 47 R. Leboda and A. Waksmundzki, Chromatographia, 4 (1979) 207. 48 R. Leboda, A. Waksmundzki, A. Gierak and Z. Suprynowicz, Chem. Anal. (Warsaw), 22 (1977) 683. 49 K. K. Bebris, R. G. Vorobieva, A. V. Kiselev, Yu. S. Nikitin, L. V. Tarasova, I. I. Frolov and Ya. I. Yashin, J. Chromatogr., 117 (1976) 259. 50 K. K. Bebris, A. V. Kiselev, Yu. S. Nikitin, I. I. Frolov, L. V. Tarasova and Ya. I. Yashin, Chromatographia, 4 (1978) 206. 51 H. Cohn and G. Guiochon, J. Chromatogr., 126 (1976) 43. 52 G. Guiochon and H. Colin, Chromatography Review, Spectra Physics, Santa Clara, California, vol. 4, 1978, p. 2. 53 A. R. Rudenko, A. A. Ballandin and I. I. Grashchenko, in: A. A. Ballandin (ed.), Zzbrannye trudy, Izd. Nauka, Moscow, 1972, p. 302. 54 H. Colin, N. Ward and G. Guiochon, J. Chromatogr., 159 (1978) 169. 55 H. Colin, C. Eon and G. Guiochon, ibid., 122 (1976) 223. 56 P. K. Iler, Chemistry of Silica, Wiley, New York, Chichester, Binsbao, Toronto, 1979. 57 R. Leboda, Chromatographia, 9 (1980) 549. 58 R. Leboda, ibid., 11 (1980) 703. 59 R. Leboda, ibid., 9 (1981) 524. 60 R. Leboda, Chem. Anal., (Warsaw) 25 (1980) 783. 61 R. Leboda, ibid., 25 (1980) 979. 62 R. Leboda, ibid., 26 (1981) 19. 63 R. Leboda, J. Skubiszewska, E. Mendyk and A. N. Korol., ibid., 30 (1985) 30. 64 E. Tracz, J. Skubiszewska and R. Leboda, .I. Chromatogr., 287 (1984) 136. 65 E. Tracz, R. Leboda and ibid., 346 (1985) 346. 66 E. Tracz, R. Leboda and E. Mizera, ibid., 355 (1986) 412. 67 R. Leboda, J. Therm. Anal., 32 (1987) 1435. 68 R. Leboda and A. Lodyga, J. Anal. Appl. Pyrol., 14 (1988) 203. 69 R. Leboda, Znjnieria them. i proces., (Wroclaw) 3,2 (1982) 343. 70 R. Leboda, Chem. Anal., (Warsaw), 29 (1984) 61. 71 W. G. Appley, J. V. Gibson and G. M. Good, Znd. Eng. Chem., I (1962) 102. 72 R. Leboda, Chemia Stosowana, 2 (1988) 229. 73 R. Leboda, Chem. Anal., (Warsaw) 25 (1980) 69. 74 R. Leboda, Polish Z. Chem., 54 (1980) 2305. 75 R. Leboda, E. Mendyk and A. Lodyga, Che. Stosow.-3-4 (1988) 423. 76 R. Leboda and J. Skubiszewska, Chem. Anal., (Warsaw) 29 (1984) 61. 77 A. Gierak, R. Leboda and A. Lodyga, Folia Sot. Sci. Lublinensis, 28 (1986) 42. 78 A. Gierak and R. Leboda, Mater. Chem. Phys., 19 (1988) 503. 79 A. Gierak, R. Leboda and E. Tracz, J. Anal. Appt! Pvr., 13 (1988) 89. 80 A. Gierak and R. Leboda, L Th&n. Anal., 35 (1989) 2213. 81 K. Grobb, Helv. Chim. Actu, 48 (1965) 1362. 82 L. Zoccolillo and A. Liberti, J. Chromatogr., 77 (1973) 69. 83 A. Gierak, Ph.D. Thesis, UMCS, Lublin, 1985. 84 C. Vidal-Madjor, M. F. Gonor, G. Guiochon, in E. Grushka (ed.), Advances in Chromatography, Vol. 13, Marcel Dekker, 1975, p. 177.

85 A. Gierak, R. Leboda and D. Nazimek, Chem. Anal., (Warsaw), 32 (1989) 957. 86 A. Gierak and R. Leboda, J. Chromatogr., 483 (1989) 197. 87 A. Gierak, R. Leboda and D. Nazimek, Patent No. 148716 (Poland), 28.02.1990. 88 D. H. Desty, J. High Resol. Chromatogr., and Chromatogr. Commun., 4 (1981) 381. 89 R. Leboda, Mater. Chem. Phys., - submitted (Part II). 90 G. A. Somorjai, Advances Catul., 26 (1977) 1. 91 R.T.K. Baker, Catal. Rev., Sci. Engn., 19 (1979) 161. 92 S. M. Davis and G. A. Somorjai, J. Catal., 65 (1980) 78. 93 R. K. Herz, W. D. Gillespie, E. E. Petersen and G. A. Somorjai, J. Catal., 67 (1981) 371. 94 V. Ponec, Catal. Rev. Sci. Eng., 18 (1978) 151. 95 G. T. Ott, T. Flecisch and W. N. Delgass, J. Catal., 65 (1980) 253. 96 R. A. Buyanov, Zakokrowanije i regeneracija katalizatorow dlja poZutchenija monomerov Sk Novosybirsk, Nauka, 1983, p. 65. 97 Z. A. Lityaeva, I. I. Marcin and Yu. I. Tarasevich, Ukr. khim. Zhum., 10 (1971) 1004. 98 Z. A. Lityaeva, M. M. Kuiralyeva, Yu. I. Tarasevich and I. I Marcin, Zssledovanije asorbcjonno-kataliticheskih svoistv gliniastyh mineralov w swiazi s razrabotkoj processa ochistki aromatichestkih uglewodorodow ot niepriedielnuch sojedinienq, in: Poluchenije i razdielenije prod&tow nieftiechimicheskovo sintieza, Krasnodar. Kn. Izd-two 1979, p. 121. 99 H. Hawakami, K. Teramoto and M. Soda, Sekito Gakkaisi, No 9 (1972) 763. 100 R. W. Alekseyeva, M. M. Kuvayeve and L. K. Haritonova, Adsotbienty na osnowie prirodnych glin dia ochistki uglewodorodow, M. CNIITE Nieftiekhimia, 1978, p. 48. 101 Yu. I. Tarasevich, Prirodnyje sorbienty w processach ochistki wody, Kiev, Naukowa Dumka, 1981, p. 207. 102 S. Oldrich and S. Frantishek, Pat. No 150 374, 129 l(O1) B 01 I l/100. (CSSR) 15.09.1973. 103 I.. N. Rachhovshaya, E. M. Morozov and W. F. Anufrienko, Zzw. SO AN SSSR, ser. khim. nauk., 5 (1982) 34. 104 W. Yu. Gavrilov, W. B. Fenalov and L. I. Rachkovskaya, fin. kut., 5 (1983) 1149. 105 W. Yu. Gavrilova, W. B. Fenalov and L. N. Rachkowskaya, ibid., 3 (1986) 683. 106 W. P. Suhanov, Kataliticheskijeprocessy w niefiiepiererabotkie, Moscow, Chimija, 1979, p. 344. 107 S. N. Chadiiewa (ed.), Kreking niejtisanych frakcji na cieolitsodietiuszczych katulizatorach, Moskow, Chimija, 1982, p. 280. 108 R. M. Masagutov, B. F. Morozov and B. I. Kutienov, Regenaracija katalizatorov w nieftiepiererabotkie i nieftiekhimii, Moscow, Kbimija, 1987, p. 144. 109 T. Tomas, Promyshlennoje kataliticheskijeprocessy i effektivnyje katalizatoty, Moskow, Mir, 1973, p. 386. 110 A. P. Ku1 and F. S. Risenfeld, Ochistka gazu, Moskow, Nedra, 1968, p. 392. 111 N. W. Kelcev, Osnowy adsotbcjonnoj tiechniki, Moskow, Khimija, 1976, p. 512. 112 D. H. Kembel, Ochistku i piererabotka prirodnych gazow, Moskow, Nedra, 1977, p. 350. 113 N. W. Zudanov and A. L. Haliv, Uslcsrka uglewodomych gazow, Moscow, Khimija, 1984, p, 190. 114 I. G. Kowzyn, Yu. I. Tarasevich, Ya. W. Mastyankevich and A. I. Zhukhova, Ukr. khim. zhum., 43 (1977) 247. 115 A. S. Russell, N. Jaret, H. I. Bruno and J. A. Remper, Pat. No 3 811916, USA, B44d l/02. 21.051974. 116 P. I. Carrot, K. S. Sing and J. H. Raistrick, Colloid SurfI, 21 (1986) 9.