WO1989010189A1

WO1989010189A1 - A method of regenerating an adsorbent

Info

Publication number: WO1989010189A1
Application number: PCT/SE1989/000214
Authority: WO
Inventors: Mats Hassander; Anders Löfqvist
Original assignee: Munters Zeol Ab
Priority date: 1988-04-19
Filing date: 1989-04-18
Publication date: 1989-11-02
Also published as: SE467999B; AU3426189A; SE8801435L; SE8801435D0

Abstract

There is described a method of regenerating an adsorbant on which organic compounds have been adsorbed in a cleansing plant, for the purpose of reducing the emission of organic compounds in air and water. When carrying out the method, the adsorbent is heated to a temperature at which adsorb organic material is combusted, either totally or partially.

Description

1

A METHOD OF REGENERATING AN ADSORBENT

The present invention relates to a method of generating an adsorbent used in a purification plant for the adsorption of organic compounds for the purpose of reducing the emission of organic compound to air and water.

Organic substances are released into air and water from various different industries. These emissions contribute to the soiling of the environment, and consequently it is desirable to reduce such emissions to a minimum.

The most common method used hitherto for the reduction of emissions into air and water recipients is based on adsorption, with activated carbon as the adsorbent. The contaminated liquid or gas is caused to flow through a filter in which the activated carbon is either present in the form of a bed or is provided on a carrier sub- strate. The activated carbon may also be used in a fluidized bed system, with the contaminated liquid or gas flow constituting the fluidizing medium.

In recent years, adsorbents have been developed which are based on polymers and which can be used in the same manner as activated carbon. In some cases, these poly¬ meric adsorbents exhibit improved adsorption properties, especially when the organic contaminants are present in low concentrations.

When the adsorbent becomes saturated with organic sub¬ stances, it is necessary to regenerate the adsorbent, the organic substances being therewith desorbed and destructed, or processed in some other way. Conventional adsorbents are regenerated by blowing steam, air or nitrogen gas through the adsorbents, at temperatures beneath 150°C. Organic substances having high-boiling points are very difficult to desorb and destroy in practice, often because the adsorbent is blocked.

High-boiling organic substances are present in many industrial emissions, for instance in the smoke genera¬ ted by polyethylene extrusion plants, or are formed on the adsorbent by polymerization of reactive organic substances, e.g. styrene.

When the emissions released to air contain organic substances having high boiling points, catalytic combus¬ tion can be employed when the total concentration of hydrocarbons is in excess of 3 g/m 3 air. The hydrocarbon concentration of many industrial emissions is much lower, beneath 1 g/m 3, and consequently it is necessary to supply fuel in order to enable catalytic combustion processes to be used.

The present invention provides a practical and economic method of regenerating an adsorbent on which organic compounds have been adsorbed in a purification plant for the purpose of reducing industrial emissions, where known methods cannot be used or are uneconomical.

The present invention includes the use of a filter bed comprising an inorganic adsorbent. The contaminated liquid or gas to be cleansed is passed through the filter bed, and the adsorbent is regenerated when satu¬ rated with organic contaminants.

Regeneration is effected in accordance with the inven¬ tion by blowing hot air or some other hot gas through the filter bed, while adding oxygen. The temperature is increased successively to 300-1000°C, depending on the nature of the substances adsorbed, therewith totally or partially combusting the adsorbed organic substances.

The combustion rate and the bed temperature are con¬ trolled partly by the temperature of the gas blown through the bed and partly by the oxygen content of said gas. The adsorbent is completely cleansed of organic substances in this way, and the adsorbent capacity of the adsorbent is returned to its original level.

The adsorbent may comprise any inorganic material what¬ soever which is capable of withstanding those temper¬ atures at which regeneration of the adsorbent takes place in accordance With the invention. Suitable mate¬ rials in this respect include hydrofobic or hydrophilic zeolites in pellet or powder form.

The invention will now be described in more detail with reference to non-limiting examples and also with refe¬ rence to the accompanying drawings, in which

Figure 1 illustrates a plant for cleansing ventilation air emanating from a polyethylene extruder; Figure 2 illustrates the hydrocarbon content of the adsorbent used in the cleansing plant of Figure 1, as a function of time; and

Figure 3 illustrates the hydrocarbon content of the adsorbent used in the plant of Figure 1, as a function of time in another experiment.

EXAMPLE 1

Smoke present in ventilation air deriving from a poly¬ ethylene extruder was cleansed in a cleansing plant according to Figure 1. The adsorbent was a hydrophobic Y zeolite and the ventilation air had a total hydrocarbon ccoonncceennttrraattiioonn ooff 00..11 gg//mm 3 3.. TThhee hhyyddrrcocarbon content of the adsorbent was then 8% by weight.

The adsorbent was regenerated in accordance with three different methods: a) Nitrogen gas was blown through the adsorbent and the adsorbent heated to 150"C. b) Nitrogen gas was blown through the adsorbent and the adsorbent heated to 500^βC. c) Nitrogen gas was blown through the adsorbent and the oxygen content of the bed was raised successively by introducing air. The temperature was raised to 500°C.

As will be seen from the diagram shown in Figure 2, the hydrocarbon content of the adsorbent was lowered in all three cases.

EXAMPLE 2 Styrene was extracted from ventilation air in a clean¬ sing plant according to Figure 1. The adsorbent used was a hydrophobic Y zeolite and the total nitrogen concen- tration in the ventilation air was 0.3 g/m 3. Adsorptioi was interrupted when the hydrocarbon concentration of

₃ the cleansed ventilation air had reached 0.03 g/m . Tht hydrocarbon content of the adsorbent was then 11%.

The adsorbent was regenerated in accordance with three different methods: a) Nitrogen gas was blown through the adsorbent and the adsorbent heated to 150°C. b) Nitrogen gas was blown through the adsorbent and the adsorbent heated to 500°C. c) Nitrogen gas was blown through the adsorbent and the oxygen content of the bed was raised successively, by introducing air.

The temperature was raised to 500°C.

As will be seen from the diagram shown in Figure 3, the hydrocarbon content of the absorbent was lowered in all three cases.

Claims

1. A method of regenerating an adsorbent on which organic compounds had been adsorbed in a cleansing plant, for the purpose of reducing the emission of organic compounds to air and water, characterized by heating the adsorbent to a temperature at which adsorbed organic material is combusted either totally or par- tially.

2. A method according to Claim 1, characterized by heating the adsorbent to a temperature of 300-1000°C.

3. A method according to Claim 1 or 2, characterized by heating the adsorbent in the presence of oxygen.

4. A method according to one or more of the preceding claims, characterized in that the adsorbent is an inorganic material.

5. A method according to one or more of the preceding claims, characterized in that the adsorbent is zeolite.