Application Of Molecular Sieves

Molecular sieves is a term synonymous in this context to aluminosilicate hydrate also called zeolite. The zeolite is applied to deodorization, gas separation and some other processes. Since this material is, unlike activated carbon, non-combustible, it has increasingly been applied to concentrate volatile organic compounds, VOC. The concentration process discussed here applies to the "VOC concentrator" developed by Seibu Giken Co. Ltd. Japan.2 The element referred to here as the VOC concentrator is non-combustible and has a honeycomb structure. The key features are summarized below.

Key features of honeycomb rotor concentrator

  • Hydrophobic zeolite is embedded into a calcinated ceramic honeycomb substrate with an inorganic binder and recalcinated at high temperature to improve the compatibility of zeolite with the ceramic substrate.
  • Various types of VOCs can be efficiently purified and concentrated.
  • The most suitable zeolite and composition are selected for application.
  • Absorption medium is non-combustible
  • Heat resistance up to 500°C
  • Desorption temperature: 150 - 220°C

Functions of the VOC concentrator

  • 1) Purification - The VOC laden exhaust air stream is purified by zeolite or other adsorbent while passing through the rotor, and the purified air stream is vented into the atmosphere.
  • 2) Concentration - The VOC laden exhaust air stream is adsorbed in the process zone and desorbed in the desorption zone into a heated desorption air stream with much less air volume than that of process air stream. The VOC is concentrated nearly equal to the air volume ratio (5-15) of the process and desorption (QP/QD).

Basic design of VOC concentrator

VOC concentrator consists of a VOC rotor, a rotor driving device, a rotor casing with a set of seals, a pair of chambers (front/rear) with a zone partition wall, and a desorption heater as shown in Figure 22.2.2.

Dfsorpbou

Dfsorpbou

Concentrator Voc

Figure 22.2.2. VOC concentrator.

Advantages

VOC concentrators, outstanding in their purifying and concentrating efficiency, have been used worldwide as a high-quality and safe product owing to material engineering expertise. By being combined with oxidizers, and other recovery equipment, the initial investment and running cost of the total system can be drastically diminished. Even for such VOCs as cyclohexane/MEK/ammonia/methyl alcohol/ethyl alcohol/styrene/formalde-hyde/isophorone/phenol, which have been found unsuitable for the existing technology using activated carbon, due to economic or safety concerns, the VOC concentrator is cost-effective and safe.

  • Non-combustible components - The development of non-flammable rotors has been achieved by engineering the appropriate materials for the honeycomb substrate, the adsorbent, and the binder and by application of special material processing technique.
  • Treatment of VOCs which have high boiling point - Taking advantages of zeolite rotors, non-combustible component, and high heat resistance, concentrators can use adsorption air at high temperatures. Accordingly, VOCs that could not be treated by carbon material due to its desorption temperature limit have turned out to be easily treated.
  • Inertness - VOCs that can easily polymerize, such as, styrene, cyclohexanone, etc., can be effectively treated by hydrophobic zeolite.
  • Cleaning and reactivation - Zeolite rotors can be calcinated under high temperature, due to their all inorganic content (including binder). The rotors can be easily washed. Zeolite rotors can be reactivated by heat treatment.

Table 22.2.2 shows the typical applications of the VOC concentrator.

Table 22.2.2. Typical applications of the VOC concentrator

Industry

Facilities

Treated VOCs

Automobile, Steel structure manufacturing

Painting booth

Toluene, xylene, esters, alcohols

Steel furniture

Painting booth, oven

Toluene, xylene, esters, alcohols

Printing

Dryer

Toluene, xylene, esters, alcohols

Adhesive tape Hook and loop fastener

Coating process Cleaning unit

Ketones (MEK, cyclohexanone, methyl isobutyl ketone, etc.)

Chemicals

Oil refinery, reactors

Aromatic hydrocarbons, organic acids, aldehydes, alcohols

Synthetic resin adhesive

Plastics

Plywood manufacturing process

Styrene, aldehydes, esters

Semiconductor

Cleaning unit

Alcohols, ketones, amines

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Responses

  • Vappu
    Can molecular sieves remove xylenes?
    8 years ago

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