DE102006022866A1 - Carbon granules, process for their preparation and their use - Google Patents

Abstract

The invention relates to a carbon granulate which is formed pyrolytically from microcrystalline cellulose. Furthermore, the invention relates to a method for producing this granulate. The granulate according to the invention is used in particular as a carrier structure for solid catalysts.

Description

The The invention relates to a carbon granulate consisting of microcrystalline Cellulose is formed pyrolytically. Furthermore, the invention relates a process for producing these granules. Use finds that Granules according to the invention in particular as a carrier structure for solid catalysts.

The capacity of solid catalysts is essentially characterized by two properties determines: the activity and the selectivity. The activity the catalyst is characterized by the catalytically active surface and the accessibility the active surface certainly. The selectivity the catalyst defines how strong the reaction to be catalyzed across from dominated by competing side reactions. Although the properties the catalytically active surface the selectivity Determining a catalyst can also increase the accessibility of the catalyst active surface crucial for the selectivity be. Thus, the residence time of the educts of the catalyzed Reaction as well as the intermediates within the catalyst body the Catalysis products and so greatly affect the selectivity.

In a solid catalyst is the catalytically active material usually finely dispersed to a sufficiently large active surface to achieve the catalyst. High activity of the solid catalyst requires that the catalytically active substance does not sinter to larger particles because it involves less surface area. The stability of solid catalysts is through the resilience the small catalytically active particles against sintering during the Use as a catalyst.

As well it is important to be porous Structure and mechanical strength of the catalyst body too check. The porous one Structure determines the transport properties of the catalyst. The mechanical strength is important because fragments of the catalyst body too a reinforced one Pressure drop of the gas flow through the fixed bed can lead. In terms of in one liquid suspended catalyst body The mechanical strength is important because abrasion to the emergence of fines that leads heavy from the reaction products by filtration or centrifugation to be separated.

There it is not possible in general is, all you want Properties related to the catalytically active material at the same time to accomplish these different characteristics of solid catalysts usually by using carrier structures achieved together with the catalytically active substances. The support structure determines the shape, size and mechanical strength the catalyst body as well as the porous one Structure of the surface of the catalyst. In general, the support structure is catalytically inactive, but provides a surface ready, on which the catalytically active substance finely dispersed is.

The most widely used catalyst support structures are based on γ-alumina, which is prepared by dehydrogenation of bayerite or gibbsite (Al (OH) ₃ ) or boehmite (AlOOH). Carrier structures of this type, however, share the common drawback that the recovery of the catalytically active substances from the catalyst is cumbersome. The dissolution of the catalyst body and subsequent separation of the dissolved material is difficult and requires much caustic. Another technique relies on melting the catalyst in a vacuum oven at very high temperatures. However, in view of the expensive equipment required for this purpose and the high energy consumption, this is only economically feasible for noble metal catalysts.

Farther are from the prior art carrier structures of activated carbon known. these can very easy from the catalytically active substances by simple Combustion of carbon are removed. Since activated carbon itself does not dissolve in an alkaline or acidic environment, activated carbon provides the support structure the choice for Noble metal catalysts in catalytic reactions in the liquid phase When burning the activated carbon remains only the catalytic active substance, e.g. then the precious metal, back.

So is out of the US 6,906,000 a carbon catalyst having a carbon content in the range of 2 to 25 wt .-% known. Here, the carbonaceous support material is mixed with catalytically active metals or metal oxides, resulting in a lower carbon content. However, this is associated with a reduced compressive strength of these catalysts, which can only be improved by an additional coating with a carbon layer.

From the US 4,052,336 is a support structure of activated carbon with a particle size between 1 and 60 microns known. This small particle size has the disadvantage that in a fixed bed reactor, a high pressure drop is the result and therefore the use of the catalysts described herein is severely limited.

The US 3,576,767 describes a carbon-based catalyst containing a catalytic amount of platinum. The carbon is obtained here from residues of organic materials recovered from cellulose liquid.

The WO 03/55599 A1 describes a catalyst composition comprising contains extruded carbon material. The carbon particles can from products such as lignite or wood. The shape takes place here with the carbon particles, causing significant disadvantages in terms of mechanical strength brings.

at the carbon-containing hitherto known from the prior art support structures There are several disadvantages. Since activated carbon from natural Materials such as e.g. Peat, wood or Koosnussschalen, won it is difficult, consistent and consistent quality of the starting material sure. Furthermore is the mechanical strength of carrier structures made of activated carbon usually problematic. Also, the abrasion of activated carbon provides a previously unresolved problem, which is when used as catalysts causes that the catalytically active material with the reaction products mixed. Because of the difficulties of separating the precious metals Of the reaction products, this is a significant drawback the use of activated carbon as a carrier structure. Another important Disadvantage is based on the fact that activated carbon is difficult to form bodies can be, which have a sufficient mechanical strength. Consequently is the use of those previously known from the prior art support structures from activated carbon in fixed bed reactors only conditionally possible.

outgoing This was the object of the present invention, the disadvantages eliminate the materials known in the art and novel, as a carrier structure to provide suitable materials that have a high mechanical Have strength, but at the same time have a porosity, which use as carrier structures for e.g. Enable catalysts.

These The object is achieved by the process for producing a carbon granulate with the features of claim 1, the carbon granules with the features of claim 12 and the catalyst having the features of claim 31 solved. In claim 21, the use of such carbon granulators for the preparation of a catalyst. The further dependent claims show advantageous Weiterbildun conditions.

According to the invention is a Carbon granules providing 50 to 99.9 wt .-% carbon contains. Furthermore, 0.1 to 50 wt .-% minerals and / or non-charred Contain additives. At least 20% by weight of the carbon becomes of granulated microcrystallised cellulose (MCC) as well as optionally further binders and / or additives pyrolytically formed. In this case, the individual grains of carbon granules a porosity in the core, the bigger than the porosity on the surface the grains is.

There the surface has a lower porosity, is the surface the individual grains smooth, what a high mechanical strength as well as a low abrasion of the granules according to the invention entails.

Especially the properties regarding the abrasion resistance are clarified in that the granules in the drum abrasion test according to ASTM D4058 preferably has an abrasion in the range of 0.2 to 5 wt .-%. Particularly preferably, the abrasion is in a range of 0.2 to 1.5% by weight.

In principle, the specific surface area of the carbon granulate can be adjusted as desired, it being possible to control the specific surface area by the proportion by weight of MCC in relation to binders and other additives. The specific surface is preferably in a range from 60 to 1200 m ² / g.

It is further preferred that the carbon granules have a compressive strength in accordance with D 7084-4 in Range of 2 to 20 wt .-%, wherein the compressive strength on the Weight fraction of MCC is controllable.

The Carbon granules can be in any geometric form available. Particularly preferred here is the spherical shape, since this is a lesser Abrasion was detected. This brings in particular for the production of catalysts benefits with it. The present in spherical form granules should preferably be uniform in size, when reactions are carried out using catalyst bodies suspended in solutions. Here, however, variations of up to 20% in terms of the diameter of the in spherical Form present grains quite acceptable. Another advantage, which results from a uniform size of the grains, is the easier to perform Loading and unloading of the catalyst body. Preferably, the carbon granules in spherical Form a length-to-width ratio of a maximum of 3: 1, preferably a maximum of 2: 1 and most preferably a maximum 1.5: 1 up. A variant according to the invention further provides that the porosity of the granules of the carbon granules of Core to the surface decreases.

• i) Mischen eines Pulvers bestehend aus mindestens 20 Gew.-% mikrokristalliner Cellulose (MCC) und ggf. weiteren Bindemitteln oder Zusatzstoffen mit Wasser,
• ii) Agglomeration des Gemisches zu einem MCC-Granulat mit anschließender Trocknung des MCC-Granulats und
• iii) thermische Behandlung bei Temperaturen größer oder gleich der Zersetzungstemperatur des MCC-Granulats in einer sauerstoffarmen Atmosphäre unter Bildung des Kohlenstoff-Granulats.

According to the invention, a method is also provided for producing a carbon granulate comprising the following steps:

• i) mixing a powder consisting of at least 20 wt .-% of microcrystalline cellulose (MCC) and optionally other binders or additives with water,
• ii) agglomeration of the mixture into an MCC granulate with subsequent drying of the MCC granules and
• iii) thermal treatment at temperatures greater than or equal to the decomposition temperature of the MCC granules in a low-oxygen atmosphere to form the carbon granules.

The Binder is preferably selected from the group consisting from carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, Methyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, Glucose or mixtures thereof.

Regarding the other additives are in particular those from the group consisting of water glass, carbon powder colloidal silica, colloidal alumina, colloidal titania, colloidal zirconia and mixtures thereof are preferred.

Regarding the agglomeration different process variants are possible. A first, that first the powder is mixed with the water in a weight ratio, so that gives a doughy consistency. This dough is then followed extruded and processed to a MCC granules with a cylindrical shape. As well but are also tri-, quadro- or multilobal forms or ring forms possible. Another variant provides that agglomeration by tabletting the microcrystalline cellulose takes place. A third preferred Variant provides that the agglomeration in a fluidized bed reactor to form a substantially spherical MCC granules. Another variant of the invention relates to the agglomeration in a Rondierer, where it is to form a substantially spherical one MCC granules are coming.

The Thermal treatment is preferably carried out at a temperature of at least 400 ° C. Generally However, the temperature is dependent on the composition of the MCC granules, since by this the decomposition temperature can be determined. In Another preferred variant is in the thermal treatment the temperature in stepped steps up to the decomposition temperature of the MCC granules increased.

The Thermal treatment is preferably carried out in an inert gas, wherein Nitrogen and / or carbon dioxide are particularly preferably used here becomes.

According to the invention as well the use of the previously described carbon granules and at least one catalytically active substance for the preparation of a Catalyst provided. With regard to the catalyst material there are basically no restrictions. Preferably, the catalytically active substance is selected from Group VIII of the Periodic Table of the Elements or the Group the transition metals. Which includes for example, platinum, ruthenium, palladium, rhodium, rhenium, silver, Gold, lead, tin, copper, nickel, cobalt, vanadium, zinc, iron, Chromium, molybdenum, Tungsten and mixtures thereof.

Regarding There are basically two process variants of the preparation of the catalyst. The first method variant is based on that in the above-described Step i) the catalytically active substance or a precursor thereof is added to the mixture of water and microcellulose. As well it is natural also possible, the catalytically active substance or a precursor thereof first in To suspend water and this suspension then the microcrystalline Add cellulose. A second variant provides that the carbon granules with a solution or a suspension of the catalytically active substance or a Precursor thereof is brought into contact. Especially preferred the contacting with the catalytically active substance takes place here by spraying of carbon granules with the solution or suspension.

A Another preferred variant provides that the previously described Catalyst additionally provided with at least one further final coating is preferably formed as an oxygen-protecting layer is. This coating preferably consists of a wax and / or a fat ingredient with a melting point greater than 50 ° C.

Based the following figures and examples, the subject invention be explained in more detail, without this on the specific embodiments shown here restrict to want.

1 shows an electron micrograph of the carbon granules according to the invention in spherical form.

2 shows an electron micrograph of the surface of the carbon granules of the invention.

3 shows an electron micrograph (SEM) of the core of the carbon granules according to the invention.

4 shows an electron micrograph (TEM) of a catalyst according to the invention with nickel as the catalytically active substance at a magnification of a factor of 135,000.

5 shows an electron microscope Aufnah me (TEM) of the catalyst according to the invention with nickel as the catalytically active substance at a magnification by a factor of 500,000.

In 1 An electron micrograph (SEM) with a magnification factor of 200 shows the different porosity in the core and on the surface of the granule grain. It can be seen here that there is a significantly higher porosity in the core than at the surface of the granule grain. It can be seen a smooth surface of the granule grain, which can explain the good properties in terms of mechanical strength and abrasion.

In 2 An electron micrograph (SEM) of the surface of the granule grain at a magnification of a factor of 5,000 is shown. Here is the small number of pores in the surface.

3 shows for comparison an electron micrograph of the core at a magnification by a factor of 500. Here, a significantly higher porosity compared to the surface becomes apparent.

4 shows a catalyst according to the invention by means of a transmission electron micrograph at a magnification of a factor of 135,000. Here, the dense coverage of the carbon structure with nickel particles becomes clear. The same result is out 6 to recognize the same shot at a magnification of a factor of 500,000. Here are nickel particles with a size of about 5 nm can be seen. The difference in the contrast of the individual nickel particles is due to the fact that some Ni ckel particles appear under Bragg reflection conditions.

example 1

Synthesis of a Carbon granules according to the invention

15.1 g of granules of microcrystalline cellulose (MCC granules) of spheres of microcrystalline cellulose were placed in a fluidized bed reactor brought in. The fluidized bed reactor consisted of a vertical quartz tube with a diameter of 3 cm. The temperature of the fluidized bed reactor could through a the quartz tube surrounding furnace to be set to temperatures of 57 ° C. Bulk density of the MCC granules was 15.1 g / ml. The minimum linear velocity of the gas flow of Nitrogen to achieve turbulence was 4 cm / sec. at 70 ° C.

The MCC granules were filled with a gas flow at a linear speed of 5.4 cm / sec. swirled. Previously, the granules were dried at 100 ° C for 1 hour and 14 minutes. The temperature was increased according to the following temperature scheme:

following the granules were cooled to room temperature.

It resulted in 3.9 g of carbon granules with a bulk density of 0.6 g / ml, which means a remaining weight of 26%. It It is very important that the carbon granules produced according to the invention be placed in a fluidized bed reactor without friction loss can. The mechanical strength and the smooth surface of the Lead balls to the high stability in a fluidized bed reactor.

The Results achieved were by a trial in the thermobalance approved. The granules according to the invention was kept in a nitrogen flow while the temperature was around 5 ° C per minute elevated has been. The weight loss began at about 250 ° C and at 315 ° C was a maximum weight loss observed. At 360 ° C, the weight loss fell noticeably However, a weight loss up to temperatures of 700 ° C was observed become. The remaining weight was 21 of the original one Weight.

Example 2

Synthesis of a Carbon granules according to the invention

MCC powder was mixed with water to a dispersion having a solids content of about 30%. This dispersion was agglomerated in a fluidized bed rotor agglomerator and dried. The spherical agglomerates of the MCC powder formed had a particle size D50 of 300 μm. They were placed in an oven and preheated at 250 ° C for 1 hour, with the exclusion of oxygen, and then thermally treated for 2 hours at 450 ° C (also under reducing conditions) to initiate decomposition into carbon and gas components and a spherical carbon substance granules to form. The carbon granules had a carbon content of more than 98% by weight. The grain size D50 of the carbon granules was reduced to a value of 150 μm by the decomposition process. The coefficient of friction of the carbonaceous spheres was determined by a modified drum abrasion test according to ASTM D4058 with a Heubach tester. The result was an abrasion value of 1.7 wt .-%.

Example 3

Synthesis of a carbon granulate according to the invention with a particle size D50> 200 μm

To another variant of the invention The MCC powder was mixed with water to form a dough with a Moisture content between 30 and 40% mixed. This dough was with a basket extruder Fuji-Paudall) extruded. The extruded particles were placed in a spheronizer (Smooth) given to spherical To form spheres, which were dried in a fluidized bed dryer (Smooth). It resulted spherical Granules with a diameter of 800 microns (D50). This granule was prepared in the same manner as in Example 2 under exclusion of oxygen preheated for 1 h at 250 ° C and then for 2 h long at 450 ° C thermally treated. The friction value here was 1.4 wt .-% and the compressive strength here was 11 wt .-%.

Example 4

Synthesis of a catalyst according to the invention with nickel

130.4 g of the MCC granules with a diameter of 1000 to 1400 μm were stored in a solution of 51.7 g of Ni (NO ₃ ) ₂ .6H ₂ O in 118.6 ml of water for 16 hours. Subsequently, the granules were separated from the liquid by decantation. The granules had taken up about 40 ml of the liquid, which corresponds to about 63 g of the solution. The impregnated granules were predried at a low pressure in a Rota Vapor at a pressure of 14 mbar.

5.02 g of the pre-dried granules were kept in a nitrogen flow, raising the temperature up to 450 ° C. The granules showed a weight loss of about 65% during the thermal treatment. A sample of the catalyst was ground for testing in a mortar, dispersed in ethanol and sonicated. A small volume of the suspension was placed on a holey carbon film on a copper grid, which is commonly used for studies in a TEM electron microscope. The recording of the electron microscope, as in 4 and 5 to see showed that the surface of the catalyst is homogeneously covered with nickel particles with a diameter of about 4 nm. The BET surface area of the passivated catalyst was measured from the adsorption capacity to nitrogen at 77K. The nickel surface area was calculated from the adsorption capacity to water, resulting in a surface area of 40 m ₂ / g nickel. Before the hydrogen adsorption measurement, the catalyst in the adsorption apparatus was reduced at 400 ° C.

Example 5

Synthesis of a catalyst according to the invention

The Carbon granules prepared in Example 2 were placed in a rotor agglomerator. 1 kg of a suspension of 15% by weight per kg of carbon granules MCC and 20 wt .-% iron (III) citrate on the carbon granules sprayed. That sprayed Carbon granules was in the absence of oxygen, as described in Example 2, heated and the activated catalyst was directly under a nitrogen atmosphere placed in a cylinder of molten candle wax. The lower Part of the cylinder containing more than 80% of the activated catalyst was in a granulator (Glatt VG) for preparing a free-flowing granules in the wax-encapsulated activated catalyst.

Example 6

Synthesis of a catalyst according to the invention

The carbon granules prepared in Example 2 were placed in a rotor agglomerator, with 1 kg of a suspension of 5 wt .-% MCC (Avicel PH 102, FMC Corp.) and 15 wt .-% NiNO ₃ per kg of carbon granules and 10 wt% ground coconut carbon powder (Pica G202X). This suspension was sprayed on the carbon granules in a rotor (Smooth) to obtain a grain size D50 of about 200 μm. As in Example 2, the carbon granules were thermally treated in the absence of oxygen and the activated catalyst was transferred immediately under a nitrogen atmosphere in a cylinder of molten candle wax and pressed down with a sieve plate. The lower portion of the candle wax cylinder, containing more than 80% of the activated catalyst, was placed in a granulator (Smooth VG) to form a free flowing granule of the activated catalyst encapsulated in the wax. This resulted in a spherical catalyst, with at least 50% of the HG porosity value in pores having a diameter greater than 1500 Angstroms occurs.

Claims (41)

Process for the preparation of carbon granules with the following steps: i) mixing a powder consisting of at least 20 % By weight of microcrystalline cellulose (MCC) and optionally other binders or additives with water, ii) agglomeration of the mixture to a MCC granulate with following Drying of the MCC granules and iii) thermal treatment at temperatures greater than or equal to equal to the decomposition temperature of the MCC granules in an oxygen-poor the atmosphere forming the carbon granules. Method according to claim 1, characterized in that that the binder is selected is selected from the group consisting of carboxymethylcellulose, hydroxyethylcellulose, Hydroxypropylcellulose, methylcellulose, polyvinylalcohol, polyvinylpyrolidone, Polyethylene glycol, glucose or mixtures thereof. Method according to one of the preceding claims 1 or 2, characterized in that the further additives are selected from the group consisting of water glass, carbon powder, colloidal Silica, colloidal alumina, colloidal titania, colloidal zirconia and mixtures thereof. Method according to one of the preceding claims, characterized characterized in that the agglomeration to form a dough done by subsequent Extrusion to an MCC granulate with cylindrical tri-, quadro- or multilobal shape or ring shape. Method according to one of claims 1 to 3, characterized that the agglomeration is done by tableting. Method according to one of claims 1 to 3, characterized that the agglomeration in a fluidized bed reactor with formation a substantially spherical one MCC granules takes place. Method according to one of claims 1 to 3, characterized that the agglomeration in a ringer to form an im Essentially spherical MCC granules takes place. Method according to one of the preceding claims, characterized characterized in that the thermal treatment at a temperature of at least 400 ° C he follows. Method according to one of the preceding claims, characterized characterized in that during the thermal treatment the temperature in stepped steps up to the decomposition temperature of the MCC granules elevated becomes. Method according to one of the preceding claims, characterized characterized in that the thermal treatment in an inert gas is carried out. Method according to the preceding claim, characterized characterized in that nitrogen and / or carbon dioxide as the inert gas is used. Carbon granules containing at least 50% by weight of granulated microcrystalline cellulose (MCC) and optionally other binders and / or additives pyrolytically formed Carbon. Carbon granules according to claim 12, characterized in that that the carbon granules In the drum abrasion test according to ASTM D4058, abrasion in the range of 0.2 wt .-% to 5 wt .-%. Carbon granules according to claim 13, characterized in that that the carbon granules In the drum abrasion test according to ASTM D4058, abrasion in the range of 0.2 wt .-% to 1.55 wt .-%. Carbon granules according to any one of claims 12 to 14, characterized in that the carbon granules have a specific surface area in the range of 60 to 1200 m ² / g, the specific surface area being controllable via the proportion by weight of MCC. Carbon granules according to any one of claims 12 to 15, characterized in that the carbon granules a compressive strength, determined according to Has ASTM D 7084-4, in the range of 2 to 20 wt .-%, wherein the Pressure resistance over the weight fraction of MCC is controllable. Carbon granules according to any one of claims 12 to 16, characterized in that the porosity of the grains of the carbon granules from the core to the surface decreases. Carbon granules according to any one of claims 12 to 17, characterized in that the carbon granules are in spherical form. Carbon granules according to any one of claims 12 to 18, characterized in that the carbon granules in spherical form a length-to-width ratio of a maximum of 3: 1, preferably a maximum of 2: 1 and most preferably a maximum 1.5: 1. Carbon granules according to any one of claims 12 to 19, characterized in that the carbon granules according to one of claims 1 to 11 can be produced. Use of the carbon granules after a the claims 12 to 20 and at least one catalytically active substance for Preparation of a catalyst. Use according to claim 21, characterized that the catalytically active substance is selected from the group consisting platinum, ruthenium, palladium, rhodium, rhenium, silver, gold, Lead, tin, copper, nickel, cobalt, vanadium, zinc, iron, chromium, Molybdenum, Tungsten and mixtures thereof. Use according to one of claims 21 or 22, characterized in step i) the catalytically active substance is added to the mixture becomes. Use according to one of claims 21 or 22, characterized that the carbon granules with a solution or a suspension of the catalytically active substance or a Precursor thereof is brought into contact. Use according to claim 24, characterized that the carbon granules with the solution or sprayed suspension becomes. Use according to one of Claims 21 to 25, characterized that the carbon granules finally is coated. Use according to claim 26, characterized that the coating with a melt, dispersion or emulsion he follows. Use according to claim 26 or 27, characterized a coating protecting the carbon granules from oxygen is used. Use according to one of Claims 26 to 28, characterized that the coating of a wax, a fat and / or a fat component having a melting point of more than 50 ° C. Use according to claim 28, characterized that the coating is selected is from the group consisting of paraffins, stearic acid, palmitic acid, their De rivaten and mixtures thereof. Catalyst containing a carbon granules according to one of the claims 12 to 20 and at least one catalytically active substance. Catalyst according to claim 31, characterized in that that the catalytically active substance is selected from the group consisting platinum, ruthenium, palladium, rhodium, rhenium, silver, gold, Lead, tin, copper, nickel, cobalt, vanadium, zinc, iron, chromium, Molybdenum, Tungsten and mixtures thereof. Catalyst according to one of claims 31 or 32, characterized in that that the carbon granules is provided with at least one coating. Catalyst according to claim 33, characterized in that the coating is a coating that protects the catalyst from oxygen is. Catalyst according to Claim 33 or 34, characterized that the coating is a wax, a fat and / or a fat component having a melting point of more than 50 ° C. Catalyst according to the preceding claim, characterized characterized in that the coating is selected from the group consisting from paraffin, stearic acid, palmitic acid, their derivatives and mixtures thereof. Catalyst according to one of Claims 33 to 36, characterized that the proportion by weight of the coating based on the total weight of carbon granules, catalytically active substance and coating in the range of 10 to 60 wt .-%, preferably 10 to 40 wt .-% and particularly preferably 10 to 25 wt .-% is. Catalyst according to one of Claims 33 to 37, characterized that the content of the at least one catalytic active substance in the catalyst in the range of 20 to 30 wt .-% is. Use of the catalyst according to any one of claims 33 to 38 in the hydrogenation of fats or aromatics and the Fischer-Tropsch synthesis. Use of the carbon granules after a the claims 12 to 20 as adsorbent, in particular for the adsorption of substances from gaseous Media, e.g. in air conditioners, or from liquid media, e.g. Drinking water. Use of the carbon granules after a the claims 12 to 20 as a carrier for drugs.