EP2164628A1

EP2164628A1 - Process for the regeneration of non-polar adsorbing zeolites used for the treatment of contaminated water

Info

Publication number: EP2164628A1
Application number: EP08773402A
Authority: EP
Inventors: Rodolfo Vignola; Umberto Cova; Fabio Fabiani; Rosa Sbardellati; Raffaello Sisto
Original assignee: Eni SpA
Current assignee: Eni SpA
Priority date: 2007-06-22
Filing date: 2008-06-10
Publication date: 2010-03-24
Also published as: ITMI20071264A1; WO2009000429A1; WO2009000429A8

Abstract

The invention relates to a process for the regeneration of non-polar, adsorbing zeolites used for the treatment of contaminated water, characterized in that the regeneration is carried out at temperatures ranging from 250 to 350°C, for a time ranging from 0.5 to 1.5 hours, in the presence of an air flow ranging from 150 to 250 m3/hr.

Description

PROCESS FOR THE REGENERATION OF NON-POLAR ADSORBING ZEOLITES USED FOR THE TREATMENT OF CONTAMINATED WATER

The present invention relates to a process for the re- generation of synthetic zeolites used in the treatment of water contaminated by non-polar compounds .

More specifically, the invention relates to a process for the regeneration of synthetic, non-polar zeolites characterized by structural channels having specific dimen- sions, based on a thermal treatment carried out under particularly mild conditions.

Non-polar zeolites characterized by a silica/alumina ratio > 50, are known as adsorbing materials for the treatment of water contaminated by non-polar compounds (WO 2003/002461} .

It is known, for example, that non-polar zeolites having structural channels with dimensions similar to those of the molecules of the contaminants to be eliminated, can be used for the treatment of water contaminated by halogenated solvents, aliphatic compounds, aromatic compounds or mix- tures thereof .

It is also known that the effectiveness of the treatment processes which normally use zeolites increases considerably when water is circulated thorough a system in- eluding at least two types of zeolites positioned in succession, characterized by a different dimension of the structural channels (WO2005/0636318) .

The use of zeolites and zeolite materials is also mentioned in literature as base components for the preparation of catalysts which can be used in numerous reactions of industrial interest .

Zeolites can be used, for example, as catalysts in oxidation processes (US 4,410,501; US 4,794,198), in catalytic transposition reactions of oximes to amides [Catalysis Let- ters 17 (1993), 139-140; Catalysis Today 38 (1997), 249- 253] , in ammoximation processes (EP 958,861) .

The exhausted zeolite-based catalysts are normally subjected to a regeneration process to eliminate the molecules involved in the chemical reactions contained in the struc- tural channels.

The regeneration is carried out under drastic conditions due to the strong bonds which are formed between the molecules and zeolite.

The regeneration is normally effected at high tempera- tures, ranging from 600 to 700⁰C, for 4-5 hours, in an at- mosphere containing oxygen at concentrations ranging from 0.1 to 4%. (Hu, A. Y. Controlled FCC catalyst regeneration using a distributed air system, US Patent 5,827,793; Nenoff, T. M. Enhanced selectivity of zeolites by controlled carbon deposition, US patent 7,041,616; Lacombe, S. Process for regeneration of a catalyst that contains an EUO- structural-type zeolite, US 2006046924; Grosch, G. Method for regenerating a zeolite catalyst, US Pat. Nr. 6,380,119).

The application of the conditions described for the re- generation of exhausted catalysts based on zeolites to the regeneration processes of the adsorbing zeolites can cause these materials to undergo structural modifications and a consequent change in the adsorbing properties.

It has been found that these zeolites can be effica- ciously regenerated by operating under particularly mild conditions. In practice, it is sufficient to provide a low amount of energy and a carrying gas to obtain the complete regeneration of the material.

This allows the structural integrity of the zeolite to be maintained, so that the latter can be regenerated an incredible number of times without substantially modifying their adsorbing properties.

In accordance with the above, an object of the present invention relates to a process for the regeneration of non- polar adsorbing zeolites used for the treatment of contami- nated water, characterized in that the regeneration is effected at a temperature ranging from 250 to 350⁰C, for a time ranging from 0.5 to 1.5 hours, in the presence of an air flow ranging from 150 to 250 m³/hr. The regeneration is preferably effected within the temperature range of from 330 to 350⁰C, for a time ranging from 0.5 to 1 hr, in the presence of an air flow of 200 m³/hr.

The regeneration conditions have been found in a 7 Ii- tre oven (figure 1) and verified in a rotating oven of 50 kg under an air flow (figure 2) . The oven can be filled with different quantities of zeolites so as to occupy from 20 to 60% of its volume, preferably from 40 to 50%.

The heating of the oven can be effected at a heating rates ranging from 10 to 140 °C/min, preferably ranging from 50 to 100°C/min.

The treatment processes of water contaminated by non- polar organic compounds envisage the circulation of the contaminated water through the zeolite system. The zeolite system has proved to be particularly effective with waters contaminated by toxic organic compounds coming from the petrochemical industry and from oil refining (organic solvents such as alkanes and chlorinated al- kenes, aromatic hydrocarbons such as BTEX) . Zeolites have also proved to be effective in the removal of compounds frequently associated in the underground water layers of the industrial sites considered, with the above-mentioned compounds, i.e. linear, branched or cyclic, oxygenated or non-oxygenated, aliphatic hydrocarbons, alkanes, alkenes, with concentrations ranging from 1,000 to 30,000 ppb.

Even if the latter organic compounds, called GROs (Gasoline Range Organics - hydrocarbons from C₆ to C₉) and DROs (Diesel Range Organics - hydrocarbons from Ci₀ to C₂e) , are not individually subject to regulation limits due to the low toxicity, they should not on the whole exceed 350 ppb (DLgs 152/2006, Sole Environmental Text, Italy) .

These compounds are co-adsorbed in the structural channels, which represent the adsorption sites of the contaminants, contributing to the accumulation and immobilization within these structures of true organic contaminants.

When the water concentration at the outlet of the treatment system exceeds the target concentration, normally established within the legal limit allowed, the zeolite is considered exhausted and subjected to regeneration accord- ing to the process object of the patent.

The efficacy of the regeneration of the invention process is evaluated by determining the organic carbon (Total Hydrocarbons Carbon, THC) eliminated by the zeolite during the treatment and, at the same time, by comparing the ad- sorbing capacity of the fresh adsorbing material and regen- erated material .

Zeolites which can be suitably subjected to the regeneration process of the present invention are non-polar zeolites having a silica/alumina ratio > 50, characterized by structural channels having dimensions similar to those of the molecules of the contaminant compounds. Generally the channel dimension ranges from 4.5 to 10 A.

Typical examples of these zeolites are silicalites, ZSM-5 zeolite, Mordenite, Beta Zeolite, Y Zeolite, MSA zeo- lites, ERS-8 and MCM-41.

Zeolites which can be subjected to the process of the invention are zeolites obtained by synthesis (Carati, A., Bellussi, G., Mantegazza, M., and Guido Petrini . Process for preparing zeolites, EP 1614658 (A2) 2006-01-11) which can be in the form of microcrystals having dimensions ranging from 1 to 10 μm, as they appear after the preparation of the crystalline phase, or they can already be subjected to mixing and forming processes with suitable materials .

Forming processes envisage the use of binders such as alumina, silica, clay for obtaining calibrated particles having a dimension ranging from 0.2 to 14 mm, therefore capable of ensuring a high permeability for functioning in a treatment system based on the adsorption of contaminants . The binder normally consists of 20/60% of the zeolite used. Typical examples of non-polar organic contaminants present in water treated with zeolites are: styrene, p- xylene, benzoanthracene, benzopyrene, benzofluoroanthrene, benzoperylene, chrysene, pyrene; halogenated solvents such as carbon tetrachloride, tetrachloroethylene, trichloro- ethylene, 1, 2-cis-dichloroethylene, 1,2-trans- dichloroethylene, 1, 1-dichloroethane, 1, 2-dichloroethane, hexachloroethane, hexachlorobutadiene , vinyl chloride, chloromethane, trichloromethane, 1, 1-dichloroethylene, 1,2- dichloropropane, 1, 1, 2-trichloroethane, 1,2,3- trichloropropane, 1 , 1 , 2 , 2-tetrachloroethane, monochloroben- zene, 1, 2-dichlorobenzene, 1, 4-dichlorobenzene, 1,2,4- trichlorobenzene, 1, 2 , 4-5-tetrachlorobenzene, pentachloro- benzene, hexachlorobenzene, 2-chlorophenol, 2,4- dichlorophenol , 2,4,6-trichlorophenol , pentachlorophenol , methyl tert-butylether (MTBE) , ethyl-tert-butylether, tert- amyl-methyl-ether, BTEX (benzene, toluene, ethylbenzene, xylenes) , naphthalene, 2-methylnaphthalene, acenaphthene , phenanthrene .

Some illustrated examples are provided for a better un- derstanding of the present invention which however should in no way be considered as limiting the scope of the invention itself. Examples Determination of the Adsorbing Capacity 20-150 mg of pulverized zeolites (100-150 μm) were in- cubated for 24 hours in a completely filled tube so that there is no space at the head and closed with a teflon stopper. 120 ml tubes containing an aqueous solution with 1-2 mg/L of contaminants to be subjected to adsorption with the zeolites, were used. At the end of the incubation, 5 ml aliquots were taken and the non-adsorbed contaminant, remained in solution, was determined with a gas-chromatograph using the "headspace" method. The concentration of the contaminant adsorbed in the zeolite was determined by differ- ence with respect to the initial concentration. Analysis method

The organic compounds taken into consideration were mainly MtBE and BTEX, which were quantitatively determined by means of headspace analysis according to the method EPA 5021.

MtBE and BTEX analysis

An aliquot of exactly 10.0 mL of water to be analyzed was incubated in a suitable 20 ml phial, in the presence of 6.0 g of anhydrous Sodium Sulfate. The phial is hermeti- cally closed and immersed in boiling water for 2' controlling that there is no development of bubbles (the presence of bubbles indicates a loss of product and the sample must be prepared again) . The phial is transferred to an automatic headspace sampler (Method EPA 3810) and the volatile fraction is transferred directly to the gas-chromatograph for quantitative analysis (Method EPA 8015B-1996) . The following instruments were used:

Headspace Sampler Agilent mod. 7693; Gas-chromatgraph

Agilent mod. 6890 equipped with a FID detector (flame ioni- zation) and introduction system with an automatic syringe

Agilent mod. 7683; Data integration and processing system of Hewlett Packard "HP ChemStation" used according to the method EPA 8015b. High concentration (50-100-200-500-700-

1000 ppb w/v) and low concentration (10-20-50-70-100 ppb w/v) calibration curves were used.

"Headspace" Sampler conditions :

Sample incubation temperature: 86°C

Valve temperature: 105⁰C

GC transfer line temperature: 150⁰C Sample equilibrating time: 50,0'

Phial shaking : high

Quantity of sample injected: 1.0 ml

Gas-chromatograph conditions :

Column: DB-WAXETR 15m x 320 urn df = 1,00 urn Injector temperature (Split r. 5:1): 85°C

FID detector temperature: 23O⁰C

Nominal column flow (carrier gas helium): 3,4 L/min

Average flow-rate: 59 cm/sec

Oven column thermal program: 50⁰C for 5 min, from 50⁰C to 180⁰C with an increase of 5.00°C/min, 180⁰C for 5 minutes. Description of the regeneration apparatus used.

The conditions in the rotating cylindrical oven having a total volume of 7 litres, shown in figure 1, are determined using quantities of zeolites ranging from 0.5 to 2 Kg; pilot experimentations of 50 Kg were effected in the rotating oven of figure 2. Example 1

Compounds immobilized in the zeolites used in the regeneration process . The underground water treatment was effected with the system based on two zeolites having different structures, in succession. The first, ZSM- 5, and the second, Mordenite, respectively specific for BTEX and MtBE, the former, and mainly for MtBE the latter. The time trend of the concen- tration of the compounds monitored [MtBE, BTEX, GROs (C₆ to C₉ hydrocarbons), and DROs (Ci₀ to C₂s hydrocarbons)], registered in the first six operating months indicated in the graphs in the subsequent figures, shows the type of compounds present in the water and removed from the zeolites. The figures indicate the concentration of the organic compounds measured at both the inlet of the treatment system with zeolites and at the outlet, removing ZSM-5 from the sample holder at the outlet of the filter 1, and also Mordenite at the outlet of the filter 3. By separately ex- amining the adsorption process of GROs (figure 3) and DROs (figure 4) on the two zeolites in succession, the greater effectiveness relating to ZSM-5 on the GROs and Mordenite on the DROs can also be revealed.

The average removal effectiveness of GROs (C₆ to C₉ hydrocarbons) is in fact 96% on the part of ZSM-5, and 78%, of the residual fraction enriched in heavy compounds, on the part of Mordenite.

For DROs (Cio to C₂β hydrocarbons) , the situation is inverted: the average removal effectiveness is 41% on the part of ZSM-5, and 71%, of the residual fraction, on the part of Mordenite.

This behaviour is in optimum compliance with the expected performances of the two zeolites, ZSM-5 being particularly suitable for the adsorption of small slightly po- lar molecules and Mordenite more suitable for the adsorption of hydrocarbons having greater dimensions (and also MtBE) . The specificity of ZSM-5 is more evident considering its action with respect to aromatic hydrocarbons having one ring (BTEX) , as indicated in the graph of figure 5. Even in the presence of an unstable feeding concentration, ZSM-5 effects the complete removal of BTEX aromatic hydrocarbons .

In order to demonstrate more clearly the effectiveness of the removal effected by ZSM-5, the trend of benzene alone is indicated in the subsequent figure 6. The specific action of Mordenite, on the other hand, can be clearly seen in the graph of figure 7 relating to the adsorption of MtBE.

Whereas ZSM-5 does in fact show a very rapid exhaus- tion of some of the adsorption sites with respect to MtBE,

Mordenite continues however to exert an effective finishing action, maintaining the concentration of MtBE at the plant outlet well below 10 μg/litre. Example 2 Regeneration activity of the zeolites

When the concentration of the water at the outlet of the treatment system has exceeded the target concentration, established within the legal limit allowed, the zeolites used in example 1 were considered exhausted and subjected to a regeneration process.

The 7 litre cylindrical oven (figure 1) was filled with 1 Kg of ZSM-5 and heated up to 500⁰C with a heating gradient of 10°C/min. The rotation rate of the oven was 2 rpm. The air was introduced at a flow-rate of 2 m³/h. The permanence time at the temperature of 500⁰C was 10 minutes. The total time of the treatment was 60 minutes. The entity of organic carbon expelled from the zeolite was determined by THC with the variation of the temperature of the oven. The data are indicated in figure 8. Example 3 As for example 1 with 3 kg of ZSM-5. The THC data are indicated in figure 9. The test was carried out under the following conditions.-

Temperature gradient: 10°C/min Oven rotation rate: 2 rpm;

Air flow-rate: 2 m³/hr

Max T : 500⁰C

Max Temperature permanence: 10 min.

Total test time: 1 hr Example 4

As for example 2 with a heating rate of 70°C/min. Permanence at 500⁰C of 43 minutes. The THC data are indicated in figure 10. The test was carried out under the following conditions: Quantity of material: 3 Kg ZSM- 5;

Temperature gradient: 70°C/min

Oven rotation rate: 2 rpm;

Air flow-rate: 2 m³/hr

Max T : 500⁰C Total test time: 1 hr

Example 5

As for example 2 with a maximum temperature of 400⁰C.

The maximum temperature was maintained for 20 minutes. The

THC data are indicated in figure 11. Comparative isotherm between the material regenerated at 400⁰C and the raw mate- rial in figure 14. The test was carried out under the following conditions:

Quantity of material: 3 Kg ZSM-5; Temperature gradient: 10°C/min Oven rotation rate: 2 rpm; Air flow-rate: 2 m³/hr Total test time: 1 hr Example 6

As for example 2 with a maximum temperature of 300⁰C. The maximum temperature was maintained for 30 minutes. The THC data are indicated in figure 12. Comparative isotherm between the material regenerated at 300⁰C and the raw material in figure 15. The test was carried out under the following conditions: Quantity of material: 3 Kg ZSM-5; Temperature gradient: 10°C/min Oven rotation rate: 2 rpm; Air flow-rate: 2 m³/hr Total test time: 1 hr Example 7

As for example 2 with a heating rate of 140°C/min. Permanence at 500⁰C for 55 min. To show the effects of the thermal treatment on the zeolite, the material was cooled and heated for 10 minutes, two cycles. The THC data are in- dicated in figure 13. The test was carried out under the following conditions: Quantity of material: 3 Kg ZSM-5; Oven rotation rate: 2 rpm; Air flow-rate: 2 m³/hr Total test time: 1 hr Example 8

The rotating oven heated to 300⁰C was filled with 50 Kg of ZSM-5. The rotation rate of the oven was 2 rpm. The air was introduced in countercurrent to the flow direction of the material at a flow-rate of 300 m³/hr. The total time of the treatment was 60 minutes. The comparison between fresh ZSM-5 and that regenerated according to example 8 was based on the comparison of the adsorption capacity of the two adsorbents. The results are indicated in figure 16 and clearly show the effect of the regeneration. Example 9

250 g of ZSM-5, saturated with a mixture of MtBE and Benzene, were regenerated in a cylindrical oven at 500⁰C. The rotation rate of the oven was about 1 rpm. The air was introduced at a flow-rate of 2 m³/hr. At the end of each regeneration treatment, the retention capacity of the regenerated zeolite with respect to the raw zeolite was compared following the same operational procedures described above. This saturation and regeneration cycle was repeated 11 times. The results are indicated in figure 17. Example 10

The same as example 8 but using Mordenite. The saturation and regeneration cycle was repeated 20 times. The re- suits are indicated in figure 18.

Claims

1. A process for the regeneration of non-polar, adsorbing zeolites used for the treatment of contaminated water, characterized in that the regeneration of said material is carried out at a temperature ranging from 250 to 35O⁰C, for a time ranging from 0.5 to 1.5 hours, in the presence of an air flow ranging from 150 to 250 m³/hr.

2. The process according to claim 1, characterized in that the regeneration is carried out within a temperature range of from 330 to 35O⁰C, for a time ranging from 0.5 to 1 hr, in the presence of an air flow of 200 m³/hr.

3. The process according to claim 1, characterized in that the regeneration is carried out in a rotating oven in which the zeolite occupies from 20 to 60% of its volume and under an air flow.

4. The process according to claim 3, characterized in that the zeolite occupies from 40 to 50% of the volume of the rotating oven.

5. The process according to claim 3, characterized in that the oven is heated at a heating rate ranging from 10 to 140°C/min.

6. The process according to claim 5, characterized in that the heating rate ranges from 50 to 100°C/min.

7. The process according to claim 1, characterized in that the zeolites have been used for the treatment of water contaminated by organic compounds belonging to the chemical group of linear, branched or cyclic, oxygenated or non- oxygenated, aliphatic hydrocarbons, alkanes, alkenes, with concentrations ranging from 1,000 to 30,000 ppb.

8. The process according to claim 1, characterized in that the non-polar zeolites have a silica/alumina ratio > 50, and are characterized by structural channels having dimensions similar to those of the molecules of the contaminating compounds .

9. The process according to claim 8, characterized in that the non-polar zeolites are characterized by structural channels having dimensions ranging from 4.5 to 7.5 A.

10. The process according to claim 8, characterized in that the non-polar zeolites are selected from the group consisting of silicalites, ZSM-5 zeolite, Mordenite, Beta- Zeolite, Y Zeolite, MSA zeolites, ERS-8, MCM-41.

11. The process according to claim 1, characterized in that the adsorbing non-polar zeolites are in the form of microcrystals having dimensions ranging from 1 to 10 mi- crons or are obtained from mixing and forming processes with suitable materials.