WO1990006176A1 - Synthetic, porous solid body - Google Patents

Abstract

A synthetic, porous solid body in the form of a granular, pourable material, useful in particular as a carrier for microorganisms, has a density which varies from the interior to the exterior and the local apparent density varies by at least 20 % between the core region (centre) and the outer surface of the solid body.

Description

 Description

Synthetic, porous solid bodies

The invention relates to synthetic, porous solid bodies in the form of a granular, pourable material.

Such solid bodies can be used primarily as carrier bodies in biochemical and chemical reactions. For this purpose, any bio- or chemical catalyst, the type and application of which is not the subject of the invention, can be bound to the porous solid body, so that a composite of support body and catalyst results.

Such solid bodies can, however, also be used in a different way, in particular as a fluidizable medium, for example as an adsorbent in purely physical processes. The following description of the invention relates essentially to the use of the solid body as a support for catalysts. However, this description is only to be understood as an example.

Known carrier bodies can be present as organic substances (e.g. polymer foams, synthetic fiber knits, ion exchange resins) or as an inorganic substance (e.g. sand, aluminum oxide, activated carbon). A wide field of application of the known and the solid support bodies according to the invention is in particular in the field of biotechnology, including biological wastewater treatment. The fixation of a catalyst (in the case of biocatalysts one speaks of an “immobilization”) on solid support bodies is always of procedural and economic advantage if the catalyst is washed out after a short time during continuous operation or when flowing through a reactor containing no support bodies threatens. The recovery of the catalyst from the effluent stream, which usually contains by-products and unreacted feedstocks in addition to the desired product, is generally complex and therefore more expensive than constantly using new, otherwise obtained or commercially available catalysts. Flushing occurs particularly in the case of finely dispersed catalysts, since these, as easily suspendable particles, easily follow a flow around them. In catalytic processes, the use of finely dispersed substances is the rule because, owing to the favorable ratio of catalyst surface to catalyst quantity, higher activities and yields are achieved than with coarser particles. The retention of the catalyst by fixing it to support bodies ensures that the catalyst can be used over a longer period of time and has to be regenerated less frequently.

If the catalyst has a density similar to that of the surrounding medium (carrier body), what has been said above applies to an increased degree. The presence of a small density difference applies in particular to reactions in which the catalyst is of biological origin and is used in the form of free cells, in the form of cell fragments, cell extracts or as a pure enzyme. A biocatalyst must be finely distributed in a mostly aqueous liquid phase that contains the substrate to be treated. The accessibility of the catalyst to the substrate must not be significantly impaired by immobilization. In addition, the resulting reaction products must be easy to remove. Since a focus of the use of the solid body according to the invention is in the field of biotechnology, the following description mainly relates to the use of such solid bodies in biological reactions and, in turn, to the main focus, namely the immobilization of intact, viable cells on such a body Solid support body. Suitable viable cells here are those of microorganisms (bacteria, yeasts, fungi) and those of animal or vegetable origin. With regard to the fixing of catalysts to the solid bodies, the following explanations also apply in principle to the use of conventional chemical catalysts.

The immobilization (or fixation) of a catalyst on a carrier body ideally brings about a complete retention of the catalyst, so that regular regeneration of the catalyst becomes superfluous. Regeneration can be completely dispensed with when working with living cells. In this case, the loss of washed-out cells during continuous operation (for example a fluidized bed reactor) is continuously compensated for by the cell propagation after reaching a steady operating state. A state of equilibrium is established between adsorption (colonization) and desorption (detachment): dead or only loosely adsorbed cells are carried out of the system and make room for fresh, active cells. At the same time, there is also a selection in favor of the species with a higher willingness to adsorb.

By restraining the cells and the associated decoupling of the residence time of the substance to be converted from that of the catalyst, an enrichment of the catalyst and a correspondingly increased productivity are obtained. In many cases, improved selectivity can also be achieved implementation and increased process stability. Contamination with undesired foreign germs is less likely due to the shorter dwell times, which may now be less than the generation time of the microorganism used.

Restraint of the catalyst in immobilized form is of course only possible if the support body itself, to which the catalyst is fixed, remains in the system (reactor) or is prevented from leaving the reactor by suitable measures. However, this is much easier than retaining the catalyst itself.

The advantages of immobilization become relevant in transition states and especially in start-up processes. In particular anaerobic microorganisms multiply very slowly and are therefore not immediately and everywhere in large numbers, e.g. B. available in a bioreactor. Living cell organisms are also subject to special readout and adaptation processes, which can be very time-consuming and therefore run very slowly.

It is therefore important that the biocatalysts can be fixed right from the start, because this helps to shorten the start-up phase in terms of discharge losses. On the other hand, the adhesion of the cells to the carrier body enables them to face the biological selection pressure more successfully and to establish themselves more quickly. This in turn has a positive effect in the form of faster product sales and a higher yield.

In processes in which gas is formed in the course of the reaction, which is the case with most biological reactions, the solid body according to the invention is advantageously used in the form of fluidizable particles (carrier particles). A

REPLACEMENT B _L ATT Another possible application is to introduce the solid bodies in the form of a bed into a fixed bed reactor. However, this can cause procedural difficulties in gas-forming reactions (“gas embolism”, channel formation, constipation). The carrier bodies suspended in a liquid phase can be retained, for example, by sieves with a mesh size adapted to the respective grain size. As a rule, in order to avoid the risk of clogging of screens or membrane foils, the retention of the carrier bodies will be based on the principle of "gravity sedimentation" or "buoyancy sedimentation".

With regard to the immobilization of in particular microorganisms, especially with regard to aerobic and anaerobic wastewater treatment, reference is made, for example, to the following previously published patents or patent applications: DE 29.05 391, EP 0 021 378, EP 0 024 758, EP 0 058 247, EP 0 075 298, EP 0 119 430, EP 0 161 469 and EP 0 241 999.

The synthetic, porous solid bodies used as carrier materials according to the invention should be inert and stable over a longer period of time. This includes sufficient chemical and mechanical resistance. Porous carrier materials also have further advantages owing to their large usable surface area for colonization with microorganisms. Special carrier bodies are known, for example, from the patents and patent applications mentioned below: DE 28 39 580, DE 33 23 078, DE 34 02 697, DE 36 11 582, DE 36 13 575, DE 36 15 103, DE 37 35 680, EP 0 046 901, EP 0 112 597, EP 0 131 251, EP 0 155 669, EP 0 158 909, EP 0 186 125, EP 0 200 486, EP 0 216 272 and EP 0 245 088.

The known methods for connecting a catalyst to a support can be divided into several groups. in the

REPLACEMENT LEAF In the simplest case, spontaneous adsorption occurs as soon as the catalyst comes into contact with the support surface. However, this does not lead to a sufficiently strong bond in all cases, so that sufficient stability of the adsorption is often only achieved by coating the support with coupling agents which have suitable functional groups. In some cases, cross-linking of the catalyst with glutar (di) aldehyde brings about better catalyst stability. However, it must be taken into account that such measures can at least partially block active centers of the catalyst, so that natural adsorption should always be given preference if possible. Surface treatments of substrates are described, for example, in patent applications EP 0 131 251, EP 0 158 909 and EP 0245 088.

Another known method consists in embedding the catalyst in a polymer matrix which is permeable to the liquid phase. This can also be done by soaking a porous substance with a polymer that contains whole cells or enzymes and then allowing the polymer to harden to a gel. This is described in patent application DE 36 13 575.

If the carrier bodies are not to be used as a bed or packing in a fixed bed reactor, they have to be fluidized. This can be accomplished by means of a stationary or rotating fluidized bed. In the first case, the fluidized bed can be formed in a fluidized bed reactor (sometimes also referred to as a fluidized bed or fluidized bed reactor), in the second case a loop reactor with internal or external loop flow is to be used. The design of such reactors which are also suitable for the solid bodies according to the invention and in which further functions, such as calming sections, separators, heat exchangers and

REPLACEMENT LEAF The like are integrated, can be done in different ways and is already described in part of the above-mentioned documents.

Knowing the speed of movement W _{p of} the carrier particle (sinking or ascending speed) is important for the design of fluidized bed reactors. It can be calculated approximately as follows:

"= V ^{, g} . ⁽ ? _s - $ _L > Eq. 1

18.1.

This means: d _p the diameter of the carrier particle, g the acceleration due to gravity, _s the material diameter of the carrier particle, ^~ _L the density of the fluid medium of the fluidized bed and j _L the dynamic viscosity of this medium.

und der dynamischen Viskosität ff _L infolge der Schwerkraft oder Auftriebskraft eine Bewegung ausführen. Die Reynoldszahl ist hier definiert als:Depending on the density difference, there is a positive (carrier particle decreases) or negative (carrier particle increases) speed. Equation 1 applies in the strict sense only to spherical particles with the diameter d _p , which for Reynolds numbers Re _p __ = - 0.5 in an infinitely extended, dormant medium with the density

and the dynamic viscosity ff _L due to gravity or buoyancy. The Reynolds number is defined here as:

In the case of porous supports, the bulk density is to be used instead of the pure density g of the solid. The bulk density ^{~ of} the carrier, formerly also called the density, represents the density of the

REPLACEMENT LEAF porous carrier body including its air-filled pores. It is calculated by neglecting the density of the air from the pure density of the material forming the framework σ _s and the porosity6 _p according to the equation:

For ceramic goods, the bulk density is determined according to DIN 51065, the porosity according to DIN 51056. If the bulk density of a solid body varies from the inside to the outside, one also speaks of the local bulk density.

The following applies:

g _ Volume of all pores of the carrier body Eq. 4

P Volume of the carrier body including its pores

For the submerged particle, completely saturated with the liquid with a density of ⁵ ^, the bulk density is to be used for porous bodies in equations 1 and 2 instead of p g:

= j ⁽¹ -V ⁺ Λ.- ^ζ ? Gl,

Since the density of microorganisms generally hardly differs from the density of the (aqueous) solutions used, the density according to equation 5 is at the same time also approximately disregarded for the density of an overgrown carrier body (gas inclusions).

REPLACEMENT LEAF For suspensions with solids _{contents τ} > 0.05, the sinking rate of the particles in the swarm collective can be calculated as a first approximation according to the equation:

_m = W. n

P ^{* (1} - * w> with n = 4.65 Eq. 6

Knowledge of the swarm sink rate W _τ is of great importance, since it is to be equated to the liquid empty space speed with which the reactor must be flowed through in order to keep the particles in suspension as a fluidized bed. The solids content of the suspension or fluidized bed is defined as:

- _ Volume of all carrier bodies in the suspension Eq. 7 '' W ^~ volume of suspension

For a Reynolds number Re _p > 0.5, various calculation sets are given in the literature. They are usually much more complicated than the relationship according to Eq. 1. The same applies to refinements of Eq. 6. The following example calculations were carried out on the basis of the information provided by P. Zehner (Chem. Eng. Process. 19 (1985) 57-65).

If the bulk density of the carrier body is greater than the density of the medium, the reactor must be flowed through from bottom to top in order to fluidize the carrier. Examples of such reactors are the patent applications EP 0 090 450 and EP 0 168 283.

Is the bulk density less than the density of the medium

ERS _A TZBLÄTT if the material is floating, a reverse flow guidance is required, as described for example in patent application EP 0 025 309.

Reactors with circulating fluidized beds or reactors which are suitable both for sedimenting and for floating support bodies are a special case. Reference is made in this connection to patent applications DE 34 29 355, EP 0 072 093 and EP 0 268 225.

In these methods, the aim is to use cell organisms capable of reproduction and these by their natural adhesive properties, ie. H. to be fixed on supports as far as possible without the use of further aids. Thus, it is often only through the use of entire cell organisms that it is ensured that all the necessary cofactors are present in order to achieve a rapid, selective implementation. When using a pure enzyme, these factors may be missing. In some cases, the adhesion can be supported by a change in the composition of the medium to be treated compared to the fermentation with unfixed cells or by a different pH value.

When operating the aforementioned systems (reactors), undesirable impairments can occur, the most important of which are mentioned below. These undesirable side effects are at least to be reduced by means of special solid support bodies according to the invention.

Possible impairments when operating a system with immobilized microorganisms can consist of the following:

a. Low natural adhesive power of the microorganisms.

b. Abrasion on the solid surface or mechanical Destruction of this carrier body by too frequent and too violent collisions of the bodies during fluidization.

c. Inadequate diffusion, that is to say diffusion limitations, due to too narrow and deep pores or due to excessive colonization of the pores, which in the borderline case can be completely filled with microorganisms.

d. Insufficient retention of the carrier particles in the reactor, the carrier particles floating, although they should decrease due to their bulk density.

e. The carrier material is not reusable if you want to switch to another process or the material has to be regenerated because contamination with foreign germs has occurred.

f. Contamination from turbid substances or other solids, which are introduced by the incoming medium, accumulate in the reactor.

G. Restarting from suspended suspension after an accident is difficult.

In principle, the following possible solutions can be considered to remedy these difficulties.

a. Porous, rigid solid support bodies with a large surface / volume ratio are used, since mechanical forces (abrasion) or hydraulic forces (relative speed of the particles to the fluid) can act less strongly on the cell organisms. The porosity enables the cells to settle in protected cavities; by choosing a rigid body that becomes Avoid squeezing cells, as z. B. occurs with foams. If this does not yet sufficiently secure the settlement, there is the possibility, already mentioned, of using adhesion promoters. The porosity of the carrier body must not be chosen too high, since otherwise the carrier body cannot be mechanically loaded.

b. Small carrier particles with a low mass are used. Moderate fluidization conditions are sufficient to suspend small, light particles. Assuming that the speed at which the particles move in a suspension and collide with one another depends on their relative speed according to Equations 1 and

6 is proportional, the same volumetric content of carrier bodies results in an increased number of impacts per unit of time for the individual particle in the order of about 1 / d _p , but this is caused by a reduction in the momentum in the particle collision on the order of magnitude of about d _p overcompensated.

c. It is advantageous to use large, interconnected, permeable pores. The pore diameter for optimal colonization can be, for example, 5 times the diameter of the cells. However, maximum population density does not necessarily mean maximum activity of the organisms and maximum yield. For this, a free exchange of liquid and gas in the pores is just as important, so that larger pores or a juxtaposition of micro and macro pores should be sought.

d. The density difference in the numerator of equation 1 is increased.

Since the pure density of organic substances is generally above 2000 kg m, inorganic materials are preferred. Any gas evolution can cause porous

ERS _A T _ZB LATT Particles fill with gas and float, so that a larger density difference offers more security here.

e. A carrier material is used which can be annealed or leached chemically in order to remove unwanted growth and to sterilize the material.

f. The density difference is increased (corresponding to letter d.), So that solid, non-degradable constituents and impurities which have been introduced can be more easily passed through the reactor by increasing the flow rate.

G. A colonization enveloping the carrier particle is prevented, so that after an accident the biofilms of neighboring carrier particles do not grow together in the bed immediately. The layer thickness of the biofilm on the outer contour of the particles as well as the abrasion of the carrier body itself, which, however, only starts with far higher forces, can be determined by using a fluidized bed in a narrower range by the selected space velocity, which however influences the expansion of the fluidized bed, control in a larger area by the selected particle diameter. Also for other reasons, such. B. diffusion limits, it may be necessary to limit the growth of microorganisms to a certain level.

To solve the problems mentioned above, the invention proposes synthetic, porous solid bodies in the form of a granular, pourable material which are distinguished by the fact that they have a bulk density which varies from the inside out, and the local one

E _R SET BLADE The bulk density between the core area (center point) and the outer surface of the solid body varies by at least 20%.

Percentage changes in the local bulk density are related to the local bulk density in the core area (center). The local bulk density can in principle increase or decrease from the inside to the outside.

It is advantageous to produce carrier bodies with a relatively large volume fraction of pores for which no significant diffusion limitations are to be expected, the core of the carrier particle being used at the same time to set a desired overall bulk density in order to achieve precisely that To make sedimentation properties favorable. This can take place in particular through a multilayer structure of the solid body, in which the local bulk density and / or preferably the local porosity changes abruptly from the inside to the outside. The carrier bodies can also be constructed in such a way that the local bulk density and / or possibly the local porosity changes continuously from the inside to the outside. As a rule, it is expedient to design the outer, porous layer of the carrier body from the point of view of optimal colonization capacity and to design the core of the body in accordance with the desired sedimentation properties (sinking or floating).

The invention can also be understood as consisting in the method according to which, starting from a porosity which is favorable for the application in question, the bulk density of the solid bodies with regard to the reaction system to be operated is adjusted in accordance with the above-mentioned values such that give the best sedimentation properties of the solid body for the application.

ER _S ATZBLATT The invention is explained in more detail below on the basis of a number of exemplary embodiments in conjunction with the accompanying drawing. Show on the drawing:

FIG. 1 shows a porous solid body with a continuously decreasing solid density from the inside to the outside;

FIG. 2 shows a solid body with a continuously increasing porosity from the inside out;

FIG. 3 shows a multilayer structure of a porous solid body;

Figure 4 shows a solid body similar to Figure 3 with an internal cavity and

5 shows a solid body similar to FIG. 4 with an intermediate layer surrounding the inner cavity.

Figures 1 to 5 each consist of three superimposed partial representations. The solid body is realistically depicted on the left side of the representations in the top row, while it is more or less schematized on the right side of this representation. The solid which forms the framework of the solid body is in each case denoted by the reference symbol 1, and the pores contained in it are identified by the reference symbol 2. In FIG. 3, the reference number 3 denotes the material from which the core of the body is made, in FIGS. 4 and 5, an inner cavity of the solid body is designated with the reference number 4, and in FIG. 5, finally, an intermediate layer closing the cavity 4

REPLACEMENT LEAF provided with the reference number 5.

bzw. äer Porosität- (£_p)» Mit $ g ist die mittlere Dichte des Stoffes angenommen, aus dem der insoweit einheitliche Feststoffkörper als Ganzes besteht, bzw. die mitt¬ lere Dichte bestimmter Abschnitte des Feststoffkörpers (z. B. Kern 3) bezeichnet. Der Radius des jeweiligen Feststoffkörpers ist mit R angenommen.The graphic representations in the middle and lower row of FIGS. 1 to 5 show the dependence of the relative bulk density measured in the radial direction (r) of the respective solid body

or porosity- (£ _p ) »With $ g the average density of the substance from which the solid body is made up as a whole is assumed, or the average density of certain sections of the solid body (e.g. core 3) designated. The radius of the respective solid body is assumed to be R.

The solid support bodies shown in FIGS. 1 to 5 are the most important limit cases of the invention. In the illustration, the pores are considered empty ( _p = 0). The pores in the solid body are at least partially connected to one another and the fluid flows through them for the most part and can therefore be populated.

In FIG. 1, the solid body consisting of material 1 has a bulk density that decreases continuously from the inside to the outside (cf. the middle representation in FIG. 1). The porosity (lower representation in FIG. 1) is constant or uniform. It could also vary (as assumed in Figure 2); H. have a gradient.

A porous solid support body according to FIG. 1 can be produced in the following way: in a pellet mixer or by means of a build-up granulation, the bodies can be produced by time-dependent addition of different raw materials with different densities in such a way that a density gradient is established within the body . Depending on whether first the speci¬ fisch heavier material or first a material with a smaller one

ERS _A TZ _B LATT If the density is added, the bulk density of the resulting carrier body will decrease from the inside out or increase from the inside out. A porosity that is constant over the cross-section (in the direction r) can be achieved either by an equal particle size distribution of the various raw materials added or - more advantageously - by the addition of pore formers of known size distribution during the entire production process, the pore formers subsequently being removed, e.g. B. be drained or burned out.

FIG. 2 shows a solid body with a continuously increasing porosity from the inside out, in such a way that either the number of pores or the pore size increases locally from the inside out. With such a structure of the body, a variation or a gradient of the local bulk density is obtained at the same time. The core can be non-porous, while the outer layer exposed to the medium to be treated can have a maximum porosity, which is only limited by the desired mechanical stability of the solid body. In this case too, as in all other cases, the pores are advantageously connected to one another and open to the outside (pores through which they can flow).

FIG. 3 shows a multi-layer structure of a solid support body, the inner or core area of the body, provided that it is made of the same material as the outer area of the body, has a relatively low or no porosity compared to the outer area or, if the inner area differs materially from the material of the outer area, has at least a significantly higher bulk density than the outer area. The outer area, which is exposed to the medium to be treated, can have a maximum porosity, which in turn only by

REPLACEMENT BLADE the desired mechanical stability is limited, which is conveyed in particular by the inner or core area.

The example according to FIG. 4 corresponds to that according to FIG. 3, but the core area is designed as a cavity (porosity = 1) and thus has a lower bulk density than the outer area.

The embodiment according to FIG. 5 corresponds to that according to FIG. 4, but the cavity of the carrier body is additionally encased by a non-porous, impermeable intermediate layer made of the same or a different material as the material of the outer region.

When producing the solid bodies according to the invention from inorganic material for fixing microorganisms, in particular according to FIGS. 1 to 5, the density gradient within a particle and thus the effective porosity can be varied within wide limits by corresponding process parameters during production. For example, the size (as well as the internal and external density) can be adjusted according to the fluid dynamic requirements of the reactor via the method of manufacture (e.g. mixing duration, speed of rotation of a mixing drum for solid bodies to be produced from several starting materials). It is also possible to use appropriate raw material compositions or mixture recipes, e.g. B. by the order of addition of the individual components, the density gradient or a different porosity depending on the particle diameter. When using a raw material with a uniform solid density over the entire diameter range of the particle, __. B. by adding pore formers, the porosity can be specifically changed so that the difference in bulk density is at least 20%.

REPLACEMENT LEAF In the cases in which porous carrier materials with a sharp density gradient (gradual density variation) in the interior of the material are involved, this requirement can be met, for example. B. the following production methods lead to the goal:

a. The core of the solid body has a higher density than the bulk density of the porous outer layer (s).

In this case, it is advantageous to use dense, round and readily available, spherical base materials, for example quartz sand (density = 2200 kg / m), aluminum oxide (corundum; density% = 4000 kg / m), silicon carbide (density ^ = 3200 kg / m ³ ), silicon dioxide (glass; density? = 2400 kg / m ³ ), mullite (density J? = 3160 kg / m ³ ) or in extreme cases - taking into account the high firing temperatures - also cores Metal (density j 7000 kg / m).

b. The core has a lower density than the bulk density of the porous outer layer (s).

These applications can be realized, for example, by using organic cores such as wooden or plastic spheres (eg polystyrene) as appropriate supports for the porous, ceramic mass to be applied. In the subsequent high-temperature fire above 1000 ° C., the material of the base is burned, so that a corresponding cavity is created. In this case, of course, the penetration of liquids into the core cannot be prevented easily. This can be remedied if a closed hollow sphere, e.g. B. Kugelko¬ round, is used.

REPLACEMENT LEAF In the case of the material according to the invention, it is therefore always assumed that the outer layers completely surround the inner core area, that is to say, in the case of spherical solid bodies, they are designed as a self-contained sphere. Coatings which are not closed, that is to say, for example, only layers applied to one core on one side, are not taken into account. In contrast, shapes of solid bodies deviating from the spherical shape, in particular also ring shapes, are definitely within the scope of the invention.

In the examples below, solid bodies according to the invention, similar to FIG. 3, are compared with a comparative solid body of a known type, the comparative solid body being uniformly porous throughout and also having a constant density from the inside to the outside.

The aim of the calculation examples below is to demonstrate that a solid body according to the invention, with an improved range of usable pores, has the same good sedimentation properties as conventional comparative material with uniform porosity and density.

The following assumptions are made for the calculation:

a. The solid according to the invention and the comparative solid are spherical.

b. The heavy core of the solid body according to the invention is spherical and lies concentrically in the interior of the particle.

c. The heavy core of the solid body according to the invention is non-porous, but consists of the same substance as

REPLACEMENT LEAF the outside area (envelope).

d. The porosity of the coating layer of the solid body according to the invention is uniform, i. H. it has no local gradient. The same applies to the comparative solid body as a whole.

e. The outer surface of both the inventive and the comparison carrier body and an underlying, spherical shell-shaped layer with a thickness of 6 _D are open-pore. Diffusion no longer takes place in radially underlying layers (infinitely large diffusion limitation). The comparative solid body thus comprises an external, effective spherical shell with the thickness c _{Q /} in which diffusion processes and thus reactions take place between the medium to be treated and the microorganisms located in the pores. The above assumption applies to the conditions in practice: no appreciable diffusion takes place in the porous core located within the spherical shell. The cells that settle there are undersupplied and not very productive. The core, which is ineffective in this regard, is usefully used in the case of the carrier body according to the invention to set a desired overall bulk density.

f. The outer spherical shell layer (cladding layer) of the solid body according to the invention, which in turn encloses a solid core, is selected in its layer thickness _H so that this value corresponds to the above-mentioned value _D.

G. The porosity, _{p of} the spherical shell-shaped outer area of the solid body according to the invention and the Comparative solid bodies agree overall.

H. The solid volume fraction _{w of} the fluidized beds is specified as a fixed value.

x. The swarm sinking rates of the suspensions of inventive and comparative solids are the same.

example 1

Given:

Diameter of the comparative solid body

Layer thickness without diffusion limitation

porosity

Density of the solid

Density of the medium

Viscosity of the medium

Solids content of the fluidized beds

Result:

HE ^SAT ZBLATT Swarm sink rate of both solid body suspensions ^ _p = 0.013 ms

Diameter of the solid support body according to the invention, subject to the conditions a. to i. _p = 750.10 m

Gross density of the solid body according to the invention p - 1811 kg.m ^"3

Volume increase with regard to the effective, diffusion-unlimited layers through the

Use of the invention

Solid body f = 30%

Example 2

In contrast to example 1, assumption c does not apply here: the core consists of a different solid than the porous coating layer.

Given:

Diameter of the comparison

Solid body cj _p = 2000.10 ^{~ 6} m

Layer without diffusion imitation <^ D ⁼ 142.10 ^"6 m

Porosity £ ^" _p = 0.50 m ³ .m ^-3

REPLACEMENT LEAF

Result :

Swarm sink rate of both solid body suspensions W 0.028 m.s -1

Density of the solid in the core area of the solid body according to the invention? Κ = 4000 kg.m -3

Diameter of the solid body according to the invention with the validity of the requirements a. to i. d "= 1000.10 ^{" 6}

Bulk density of the solid body according to the invention 5 ^J P - 2418 kg.m -3

Volume increase with regard to the effective, diffusion-unlimited layers through the use of the solid body according to the invention f = 72%

REPLACEMENT BLA Example 3

In contrast to example 1, assumption c does not apply here: the core consists of a different solid than the porous coating layer.

Given:

Diameter of the comparative solid body = 2000.10 -6 ^~ m

Layer without diffusion limitation

porosity

Density of the solid

Density of the medium

Viscosity of the medium

Solids content of the fluidized beds

Result:

Swarm sink rate of both solid body suspensions w. 0.041 ms -1

E ^RSAT ZBLAT Density of the solid in

Core area of the solid body according to the invention? _κ = 4000 kg.m -3

Diameter of the solid body according to the invention, with the validity of the conditions a. to i. d _p = 750.10 m

Bulk density of the solid body according to the invention - ^ p ⁼ 3142 kg.m

Volume increase with regard to the effective, diffusion-unlimited layers by the

Use of the invention

Solid body f = 150%

The above examples are based on simplifying calculations. The substance transition on the solid body surface and in the pores (pore diffusion) would have to be used for more detailed considerations. However, since in the selected examples both types of carrier bodies (inventive and comparative solid bodies), the same pores and the same material were assumed, at least in the outer region of the body, the calculation is justified as an estimate. The mass transfer on the solid body surface plays a much smaller role compared to pore diffusion.

The result of the three examples clearly shows that, with the same fluidized bed volume, considerably more usable pore volume can be provided if solid bodies according to the invention are used. From a different perspective

REPLACEMENT LEAF viewed this can also mean that the fluidized bed or reactor volume can be significantly smaller in order to achieve corresponding yields. This could not be achieved by using a finely dispersed fraction of particles with a smaller diameter alone, since the particles can only be reduced in size to a limited extent because of the risk of discharge.

ZBLATT

Claims

Patent claims 1. Synthetic, porous solids in the form of a granular, pourable material, characterized in that the solids have a bulk density which varies from the inside out and the local bulk density between the core area (center) and the outer surface of the solid body by at least 20 % varies. 2. Solid body according to claim 1, characterized in that its bulk density varies continuously from the inside to the outside. 3. Solid body according to claim 1, characterized in that its bulk density varies from inside to outside step by step. 4. Solid body according to claim 1, 2 or 3, characterized gekenn¬ characterized in that the variation in bulk density is achieved by varying the solid density. 5. solid body according to claim 1, 2 or 3, characterized gekenn¬ characterized in that the variation in bulk density is achieved by varying the porosity. 6. Solid body according to claim 1, 2 or 3, characterized gekenn¬ characterized in that their porosity varies from them to the outside. 7. solid material body according to claim 6, characterized in that REPLACEMENT LEAF that their porosity varies gradually. 8. Solid body according to one of claims 1 to 7, characterized in that they have a closed cavity in the inner core region. 9. Solid body according to one of claims 1 to 7, characterized in that they are non-porous in the inner core region. 10. Solid body according to one of the preceding claims, characterized in that it contains pores of different sizes. 11. Solid body according to one of the preceding claims, characterized in that they consist of several chemically different substances. 12. Solid body according to claim 8, characterized in that the inner cavity is enclosed by a metallic or ceramic interlayer. 13. Solid body according to one of the preceding claims, characterized in that they are of substantially spherical shape. 14. Solid body according to one of the preceding claims, characterized in that they consist of an inorganic substance. 15. Solid body according to claim 14, characterized in that at least its outer region consists of silicate. 16. Solid body according to one of the preceding claims, REPLACEMENT LEAF characterized in that the projection surface of a volume of the same volume has a diameter of 100 µm to 15 mm. 17. Solid body according to claim 16, characterized in that the projection surface of the same volume ball has a diameter of 200 microns to 3 mm. 18. Solid body according to one of the preceding claims, characterized in that at least its outer regions are porous. ER ^S A ^T ZBLATT