JP2006061852A - Method for recovering useful hydrocarbon from sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering a useful hydrocarbon from sludge, by which the useful hydrocarbon such as acetone can be recovered efficiently from various kinds of sludge including digested sludge discharged from a sewage plant or the like by using a Zr-deposited iron oxide-based catalyst. <P>SOLUTION: This method comprises the steps of solubilizing various kinds of sludge including the digested sludge, cracking the solubilized sludge catalytically by the Zr-deposited iron oxide-based catalyst and recovering acetone-based ketones. The sludge is preferably solubilized in a water-saturated condition at 280-300°C. The iron oxide-based catalyst preferably contains Al (it is preferably a Zr-Fe-Al catalyst). When the Zr-Fe-Al catalyst is used, the sludge can continuously be cracked catalytically by a flow reactor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses an iron oxide-based catalyst supporting Zr, from sludge capable of efficiently recovering useful hydrocarbons such as acetone from various sludges including digested sludge from sewage treatment plants. The present invention relates to a method for recovering useful hydrocarbons.

  At present, there is a large amount of sludge from sewage treatment plants, and the amount is expected to increase more and more in the future due to the spread of sewerage. This sludge is usually incinerated in large cities and mainly buried in rural areas. However, incinerating or burying sludge requires a lot of energy, processing equipment, labor costs, and the like, and thus has a problem that it is very expensive.

On the other hand, recently in Japan, where resources are scarce, there is an increasing need to recycle and use biomass waste such as sludge as a resource, not just purification. This is because conventional treatment methods have environmental problems such as air pollution due to combustion gas, global warming due to CO ₂ generation, and energy problems accompanying depletion of fossil fuels. Accordingly, various sludges, which are a kind of biomass, are required to be recycled as useful chemicals such as alcohol by treating them with an appropriate method. For example, Patent Document 1 discloses that organic waste is converted to iron oxide. A method of decomposing with a system catalyst and recovering useful waste such as acetone has been proposed. However, the method of Patent Document 1 has many problems in practical use such as a low yield of useful waste and a short catalyst life.
JP 2001-129405 A

  The present invention solves the above problems and aims to recycle various types of sludge including digested sludge which is a kind of biomass, and to use useful hydrocarbons such as acetone from sludge from sewage treatment plants. It is an object of the present invention to provide a method for recovering useful hydrocarbons from digested sludge that can be efficiently recovered. Another object of the present invention is to provide a method for recovering useful hydrocarbons from sludge having a long service life and excellent practicality.

The method for recovering useful hydrocarbons from the sludge of the present invention made in order to solve the above problems is to solubilize various sludges including digested sludge, and then catalytically decompose them with an iron oxide catalyst supporting Zr. It is characterized by recovering ketones mainly composed of acetone.
Moreover, various sludges including digested sludge can be solubilized under a water saturation condition of 280 to 300 ° C., and this is the invention according to claim 2. Moreover, what contains Al as an iron oxide catalyst is preferable, and this is the invention according to claim 3. Furthermore, when an iron oxide catalyst containing Al is used, catalytic cracking can be carried out continuously using a flow reactor, and this is the invention according to claim 4.

  In the method for recovering useful hydrocarbons from the sludge of the present invention, soluble organic matter solubilized various sludges including digested sludge is dissolved by catalytic cracking using an iron oxide catalyst supporting Zr. It accelerates the oxidative decomposition of organic matter to generate ketones mainly composed of acetone, and is inert to acetone and can recover a large amount of acetone. In particular, if an iron oxide catalyst containing Al is used, the catalyst life can be extended.

Below, the preferable form of this invention is shown.
In the method for recovering useful hydrocarbons from sludge according to the present invention, various sludges such as digested sludge are solubilized, and then catalytically decomposed with an iron oxide catalyst supporting Zr to make ketones mainly composed of acetone. Recover.
The various sludges such as digested sludge as used in the present invention refers to various sludges such as waste sludge derived from household garbage, raw garbage, etc., and agricultural, forestry and fisheries sludge such as livestock dung, dumped fish and food processing residues.
The reason why the sludge is solubilized here is to efficiently perform catalytic cracking with an iron oxide-based catalyst described later as a soluble organic substance. Normally, the sewage sludge has a very high water content of 98% or more. Therefore, the solid content obtained by adding the polymer flocculant to the sludge is mechanically pressurized with a dehydrator to reduce the water content, and the water content is 80%. % Dehydrated cake, and this dehydrated cake is oxidatively decomposed with a hydrogen peroxide solution or the like to form a soluble organic substance.

For example, sludge can be solubilized by a subcritical process to form a soluble organic substance. Specifically, it is solubilized under a moisture saturation condition of 250 to 300 ° C. When the temperature is lower than 250 ° C., it is difficult to sufficiently solubilize, and the treatment at a temperature higher than 300 ° C. is expensive because the apparatus becomes large and the cost becomes high.
By such hydrothermal solubilization, the following production solution (solubilization solution) is obtained.
Total carbon: 1.082 mol / L
Total nitrogen: 0.370 mol / L
Ca: 0.0012 mol / L
P: 0.0027 mol / L

Next, the thus obtained soluble organic substance is catalytically decomposed with an iron oxide catalyst supporting Zr to recover ketones mainly composed of acetone.
The iron oxide based catalyst carrying Zr, Zr / Fe catalysts and carrying ZrO ₂ by impregnation method FeO _X, then co-precipitated Fe and Al salts, carrying ZrO ₂ by impregnation Zr / An Fe—Al catalyst can be used. Furthermore, a Zr—Fe catalyst or a Zr—Fe—Al catalyst obtained by co-precipitation with highly dispersed ZrO ₂ can also be used. The present inventor has found that such an iron oxide catalyst supporting Zr is different from a simple Fe catalyst and exhibits sufficient water resolution even in a liquid phase reaction temperature region, and the active oxygen species generated from water is Fe. Since the oxidative decomposition of the solubilized organic substance is promoted on the catalyst, the present invention has been completed based on the knowledge that it becomes a catalyst suitable for the catalytic decomposition of the soluble organic substance under hydrothermal conditions.

Further, the reason why the ketones mainly composed of acetone can be finally recovered is considered as follows.
When active oxygen species generated on ZrO ₂ move to the FeO _X surface (main reaction field) and accelerate oxidative decomposition, soluble organic substances are oxidized and decomposed to produce alcohols and organic acids. For example, in the case of an ester, an alcohol or an organic acid is produced by hydrolysis.
According to the inventor's research, it has been found that FeO _X has the activity of de-CO ₂ , so that the organic acid becomes an organic substance (hydrocarbon) having one less carbon number by de-CO ₂ . That is, it becomes alcohol first by oxidative decomposition. In addition, alcohol oxidizes to aldehyde, and molecules with a large number of carbons undergo oxidative degradation at other sites and become low molecular as needed. For example, those having 3 carbon atoms are sequentially oxidized with propion alcohol → propionaldehyde.
On the other hand, when Gibbs free energy is calculated, since aldehyde and ketone are in an equilibrium relationship, propionaldehyde → acetone is in an equilibrium relationship. The equilibrium is 300 ° C., the equilibrium constant is approximately 60, and it is biased toward acetone. That is, once propionaldehyde is formed, it is converted to acetone. Further, some propionaldehyde is further oxidized to an organic acid, undergoes de-CO ₂ to lower the molecular weight, and changes to ethyl alcohol.
Since acetone is less susceptible to oxidation, the ZrO ₂ / FeO _X catalyst becomes inactive with respect to acetone. For the above reasons, acetone can be recovered in a high yield using an iron oxide catalyst supporting Zr.
The total yield from the inlet (digested sludge) to the outlet (acetone) is shown as follows, where digested sludge is 100.
Digested sludge (100) → Hydrothermal solubilization outlet (82) → Concentration outlet (72) → Ketonization outlet (61)

In order to investigate the stability of the catalyst, the result of steam cracking of heavy oil as an accelerated deterioration test is shown in FIG. As is apparent from FIG. 1, when the reaction → regeneration operation is repeated, the activity of the Zr / Fe catalyst decreases, but the activity of the Zr / Fe—Al catalyst into which Al is introduced is improved by repeating the reaction → regeneration operation. It was seen. However, the activity decreased when the reaction was continued without performing the regeneration operation. On the other hand, it was confirmed that the Zr—Fe—Al catalyst in which Zr was highly dispersed and Al was introduced maintained the initial activity even if the reaction was continued without performing the regeneration operation.
Therefore, it was found that the Zr—Fe catalyst and the Zr—Fe—Al catalyst prepared by the coprecipitation method are suitable for catalytic cracking of digested sludge with respect to activity and stability.

Next, FIG. 2 shows the results of a digestion sludge decomposition test performed in a batch reactor using a Zr—Fe catalyst. It was confirmed that ketones mainly composed of a large amount of acetone were produced as compared with the case where the Fe catalyst was used. That is, it was found that digested sludge was decomposed into ketones by the water resolution of Zr.
Moreover, the result of having performed the decomposition | disassembly test of digested sludge with the flow-type reactor using the Zr-Fe-Al catalyst whose heat stability was improved more is shown in FIG. Also in this case, it was confirmed that ketones mainly composed of a large amount of acetone were produced, and it was found that acetone can be continuously recovered from digested sludge by using a Zr-Fe-Al catalyst. .

  As is clear from the above explanation, the present invention solubilizes various sludges including digested sludge, and then catalytically decomposes them with an iron oxide catalyst supporting Zr, whereby ketones mainly composed of acetone are obtained. Recovering sludge, which is a kind of biomass, is possible, and useful hydrocarbons such as acetone can be efficiently recovered from sludge from a sewage treatment plant.

It is a graph which shows a time-dependent change of heavy oil decomposition reaction. It is a graph which shows the product yield in biomass waste liquid decomposition | disassembly.

Claims (4)

  Recover useful hydrocarbons from sludge, characterized by solubilizing various sludges including digested sludge and then catalytically decomposing them with an iron oxide catalyst supporting Zr to recover ketones mainly composed of acetone how to.   The method for recovering useful hydrocarbons from sludge according to claim 1, wherein various sludges including digested sludge are solubilized under a water saturation condition of 280 to 300 ° C.   The method for recovering useful hydrocarbons from sludge according to claim 1 or 2, wherein the iron oxide catalyst contains Al. The method for recovering useful hydrocarbons from sludge according to claim 3, wherein the catalytic cracking is continuously carried out by a flow reactor.

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