Absorption of volatile organic compounds derived from organic matter

(54) Title: USE OF ZSM-5-HYDROGEN Doped with Palladium in order to adsorb volatile organic compounds derived from organic matter (51) Int.CI .: B01J 20/18; B01J 20/32; B01J 20/34; A23B 7/148 (30) Unionist Priority: 02/07/2009 GB 0911478.6 (73) Holder (s): ANGLO PLATINUM MARKETING LIMITED (72) Inventor (s): ELISABETH ROWSELL; ANDREW WILLIAM JOHN SMITH; STEPHEN POULSTON

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USE OF ZSM-5-HYDROGEN Doped with Palladium in order to adsorb volatile organic compounds derived from matter

ORGANIC

This invention relates to the adsorption of volatile organic compounds (VOCs) derived from organic matter in an environment that contains little or no oxygen. More particularly, organic matter can be perishable organics, such as food.

The controlled atmosphere storage of fresh products uses high levels of CO2 and reduced oxygen in order to increase the product's shelf life. The modified atmosphere packaging is used to improve the shelf life and / or quality of the food, reducing the amount of oxygen (to zero) in the atmosphere compared to air. Fresh products tend to be packaged in a modified equilibrium atmosphere that uses high levels of CO2 and reduced levels of oxygen and allows for a reduced respiration rate.

VOCs include a range of compounds that are derived from organic matter. An example of a VOC derived from organic matter is ethylene, a plant hormone that causes ripening, while another example is trimethylamine, a gas commonly released by a fish upon decomposition.

The removal of VOCs derived from organic matter is of interest for a variety of applications. The adsorption of ethylene can prevent the occurrence of unwanted ripening and softening, loss of color, loss of leaves and seed germination in fruits and vegetables, and is also known to prevent other food products and the

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2/11 horticulture perish prematurely, and can assist in the elimination of unpleasant odors.

Several methods have been used for the oxidation or combustion of VOCs using Pt in AfoCc or KMnO4. However, although these systems are efficient for removing volatile organic compounds, they have disadvantages associated with their use. Pt on Al2O3 works by catalytic combustion of ethylene at high temperatures, therefore Pt on Al2O3 needs to be used in a separate unit heated from the source of volatile organic compounds (see for example GB

163 637 A and US 4,331,693). KMnO4 does not appear to remove

VOCs efficiently from humid environments. Since organic matter, such as food, cannot be heated without being altered and inherently exudes moisture, such systems are not suitable for use in removing volatile organic compounds derived from organic matter.

Other methods used to remove volatile organic compounds are suitable for use at lower temperatures; these include the use of supports with a high surface area, usually in conjunction with a promoter, for the adsorption of VOCs. For example, JP 2-261341 refers to ethylene adsorption from refrigerated storage compartments, JP 2-233381 refers to ethylene film adsorption and JP 2000-004783 refers to a product ethylene adsorber, deodorant and anti-bacterial combined for use in a refrigerator. Specific support materials are not disclosed in any of these publications, instead

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In addition, carbon and metal oxides are shown to be generally suitable for use as supports. GB 2 252 968 A refers to an adsorbent comprising a sepiolite in combination with a zeolite, and, optionally, a metal selected from the metals of the platinum group, the metals of the iron group, metals of group I, metals of the group VII and rare earth metals. The most preferred zeolites for use in the invention described in GB '968, are silicalites because their alumina content is almost zero.

WO2007 / 052074 refers to the use of palladium-doped ZSM-5 in order to adsorb VOCs derived from organic matter. WO2007 / 052074, however, does not describe the use of palladium doped ZSM-5 in an environment comprising little or no gaseous oxygen.

According to a first aspect of the present invention, the use of palladium-doped ZSM-5 is provided in order to adsorb volatile organic compounds (VOCs) derived from organic matter, in which the Si: Al ratio of ZSM20 5 is less than 5 or equal to 100: 1, and where the palladium doped ZSM-5 is used in an environment comprising less than 10% by volume of oxygen. Optionally, the reason

Si: Al of the ZSM-5 is from 22: 1 to 28: 1.

At least part of the adsorbed VOCs can be converted into secondary compounds after adsorption on the doped ZSM-5.

In one embodiment, organic matter consists of organic perishables, such as items to produce food and vegetables. Food items may comprise fruits and / or vegetables. The vegetable product can

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4/11 understand cut plants and / or flowers.

In another modality, organic matter comprises refuse. Such refuse can include kitchen scraps such as food scraps, which produce unpleasant odors during decomposition.

The organic matter from which VOCs are derived may be contained within a container or storage package, such that the doped ZSM-5 has a closed or semi-closed environment in which to adsorb the

VOCs. In the case of organic perishables in the container or storage package it is likely to be the container or packaging in which the goods are contained, for example, boxes used to store the goods when in transit or the packaging in which the goods are kept when on display before purchase. In another embodiment, the doped ZSM-5 is incorporated into, or part of, the storage container or the packaging itself. In an additional embodiment, the palladium-doped ZSM-5 is incorporated into a label comprising a substrate for insertion and retention within a storage container or packaging.

If perishable organic products comprise food items, the doped ZSM-5 can be packaged in order to avoid direct contact with food, for example, behind a gas-permeable barrier layer. The gas permeable barrier layer can form part of a powder doped ZSM-5 sachet or label or the gas permeable layer can be affixed on top of a paint layer comprising the doped ZSM-5. The paint can be attached to an inner surface of the container or

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5/11 storage package by printing, molding, roller application, brushing, spraying or similar techniques. In addition, since the adsorption capacity of the doped ZSM-5 is moderately sensitive to the presence of water, the doped ZSM-5 can be packaged with a water adsorption material, such as silica gel.

If, however, the source of VOCs is waste, the storage container or package can be a waste receptacle.

The commonly doped ZSM-5 will be particulate and can be freely packaged, just like in a sachet (see above). Alternatively, the particulate can be associated with another object, such as incorporation into a storage container, incorporation into a packaging material (for example, a plastic such as PET), incorporation into an ink (see above), or simply to coat in or on another object, for example, a ceramic or metal monolith, such as those used as catalyst carriers. Other forms of low pressure drop substrates, such as those commonly used as catalyst carriers, can also be used. In another modality, the doped ZSM-5 is in the form of extrudates, pellets (pellets), tablets, grains or granules. ZSM-5 can be doped before or after being formed in such extrudates, pellets, tablets, grains or granules.

Other methods of using the present invention can be used in appropriate circumstances.

An advantage associated with the present invention is that volatile organic compounds can be adsorbed to

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6/11 relatively low temperatures, such as in the range of 10 ° C to 50 ° C, more generally 0 ° C to 40 ° C. For example, the temperature range can be about 0 ° C to about 35 ° C or about 0 ° C to about 30 ° C. This allows the doped ZSM-5 to be used in the environment where organic matter is commonly found, for example, refrigerators or at room temperature, without the need for complex heating and gas recirculation equipment to be used. However, when a particular application allows heating and gas recirculation of the equipment to be used (for example, a gas conditioning system), the doped ZSM-5 can also be operated at an elevated temperature, for example, above 60 ° C.

In one embodiment, volatile organic compounds comprise ethylene. Ethylene is a gaseous hormone released by plants that can cause plants to wilt and fruit to ripen. Removing VOCs produced by plants can delay these processes, allowing food and vegetables to be kept in transit and / or in storage for longer without accelerating perishing. Therefore, a particular application of the present invention is for industries that produce, ship (transport), export and purchase food and vegetables. Initial tests suggested that, contrary to prior art methods, the use of an adsorber according to the present invention may allow the post-climacteric fruit shelf life to be extended (Terry L, llkenhans T, Poulston S, Rowsell E and

Smith AWJ, Postharvest Biology and Technology 45 (2007)

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214-220). That is, even after the climacteric respiratory appearance is initiated, the fruit can be prevented from maturing (or at least having a delayed maturation rate) using palladium-doped ZSM-5 in order to adsorb ethylene.

In another embodiment, VOCs comprise formaldehyde and / or acetic acid. Acetic acid and formaldehyde are the smelly chemicals that are usually found at home. Formaldehyde can be released from glued pressed wood products, such as plywood, but it is also found in paints, textiles, plastics, paper products, fertilizers and cosmetics. Acetic acid can be released from kitchen waste and animal waste. Therefore, a potential application of the present invention is for removing foul odors from the home environment.

Another point of interest is that, although there is some loss of activity in the palladium-doped ZSM-5, after being exposed to water, they are still able to function efficiently when wet. Since food and vegetables are normally stored in humid environments, this resource is also advantageous for interested industries.

Methods of making palladium doped ZSM-5 are known to the specialist chemist, and include the use of a variety of palladium salts, such as Pd (NO3) 2, Pd (OAc) 2, PdCl2, palladium oxalate, (palladium tetraamine hydrogen carbonate), palladium tetraamine hydroxide) and palladium tetraamine acetate). Commonly

ZSM-5 will be calcined after impregnation with at least one

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8/11 palladium salt, however, for some applications this may not be necessary. Samples of palladium doped ZSM-5 that are calcined will at least partially comprise oxidized palladium.

Palladium itself may comprise between 0.1% by weight at

10.0% by weight based on the total weight of the ZSM-5, optionally from 0.5% by weight to 5.0% by weight based on the total weight of the ZSM-5.

The doped ZSM-5 can be conveniently used in a controlled atmosphere or modified atmosphere environment. In one embodiment, the oxygen level in these environments is present in a range between> 0.5% by volume and <10% by volume. For example, the oxygen level can be about 1% by volume, about 2% by volume, about 3% by volume, about 4% by volume, about 5% by volume, about 6% by volume, about 7% by volume, about 8% by volume or about 9% by volume. In another embodiment, the oxygen level is substantially 0% by volume. The balance of the gas composition may comprise an inert gas (such as nitrogen), optionally carbon dioxide and / or optionally carbon monoxide.

In one embodiment, the doped ZSM-5 is effective for adsorbing VOCs to a level less than or equal to 0.10 ppm, optionally to a level less than or equal to 0.05 ppm. In another embodiment, the doped ZSM-5 is effective for adsorbing substantially all VOCs, that is, no detectable amount of VOCs remains.

Another advantage of the present invention is that the doped ZSM-5 can be used continuously for the removal of VOC for an extended period of time, for example, several days,

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9/11 (the effective time depending on the environment in which it is used). In addition, after use, the ZSM-5 can be heated to 250 ° C for 30 minutes in air in order to release the VOCs adsorbed on the palladium-doped ZSM-5 and any secondary compounds present, thus regenerating the ZSM-5 doped with palladium for later use. This allows the palladium doped ZSM-5 to be used for long periods of time, then removed from the VOC source, regenerated and reused. Since the regeneration process is neither long nor expensive, this means that the doped ZSM-5 is a cost effective product for removing VOCs. It is worth noting that, on the contrary, KMnO4 regeneration is not possible since the material decomposes on heating to K2O and manganese oxide (s).

In order to identify the time when the doped ZSM-5 reached its VOC adsorption capacity and therefore needs regeneration, a VOC indicator can be included for use with doped ZSM-5.

Suitable indicators include the palladium-based ethylene indicator disclosed in the JP patent application

60-201252.

In order that the invention may be more fully understood, the following non-limiting Examples are provided by way of illustration only and with reference to the accompanying drawings, in which:

<td>Figure 1</td><td>is</td><td>a chart that</td><td>show</td><td>adsorption</td><td>in</td>

<td>ethylene over</td><td>of</td><td>time by ZSM-5</td><td>doped</td><td>with palladium</td><td>in</td>

<td>an environment that</td><td colspan="2">comprises about</td><td>8.4%</td><td>in volume</td><td>in</td>

oxygen.

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EXAMPLE 1 Preparation of doped supports

The doped support, also known as an adsorber, was prepared using the incipient wet impregnation method. Normally, 20 g of the support (for example, in the form of zeolite hydrogen) was impregnated with the nitrate salt or palladium chloride salt and then dried at 110 ° C before being calcined in air at 500 ° C for 2 hours.

EXAMPLE 2

Ethylene adsorption measurements

The measurements were carried out in a piston flow reactor at 21 ° C with 0.1 g of doped support of particle size of 250-355 pm with a flow rate of 50 ml / min of gas comprising various concentrations of O2, 200 ppm of

C2H4, ~ 80% relative humidity and nitrogen balance. The results of this experiment are defined below:

<td>O2 concentration of /%</td><td>Adsorption capacity of</td>

<td>in volume</td><td>ethylene / pl.g^-1</td>

<td> 10</td><td> 3500</td>

<td> 4</td><td> 3600</td>

<td> 2</td><td> 3800</td>

<td> 1</td><td> 3700</td>

<td> 0</td><td> 6050</td>

EXAMPLE 3

Ethylene adsorption measurements

Measurements were performed at 21 ° C, with 0.1 g of doped support of particle size 250-355 pm. A 1 liter jar was partially evacuated and then filled with 500ppm of ethylene in nitrogen, which was mixed with the remaining air, so the initial concentration was 8.4%

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11/11 in O2 volume.

Figure 1 illustrates that the Pd-doped support substantially adsorbed all ethylene over a period of about 12 hours.

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