FIELD OF THE INVENTION

The present invention relates to cost-effective processes and apparatus for the treatment of fumigation waste/exhaust gas, and, more particularly, to the recovery of alkyl halide from an air stream containing same and the concomitant conversion of the recovered alkyl halide into useful compounds.

BACKGROUND OF THE INVENTION

Fumigants are used to treat agricultural products, such as fruits, grains or logs, in enclosures before these products are allowed to be exported overseas, imported or distributed locally. After fumigation, sufficient time elapses for the fumigant to be absorbed by the products. Subsequently, the enclosures are aerated, causing the release of residual fumigant, which can be as high as 50% of the original amount applied, into the atmosphere. Alkyl halides, especially methyl bromide (MeBr), are commonly used fumigants.

Due to its toxicity, methyl bromide is considered to be an effective quarantine/phyto-sanitary fumigant in the control of insects and other pests. However, studies in humans have confirmed acute and chronic health effects associated with methyl bromide, and the EPA has classified methyl bromide as a Group D compound. In addition to its toxicity, another serious concern about the use of methyl bromide is the damage it causes to the stratospheric ozone layer. In fact, methyl bromide is considered an ozone-depleting chemical and thus it has been classified as a Class I ozone-depleting substance by the Montreal protocol, while also falling under the Clean Air Act with an ozone depletion potential of 0.2%. As a result, international, federal and state regulations require strict control of methyl bromide emissions because of their hazardous effect on the environment.

Due to the lack of effective alternatives, the use of methyl bromide as a fumigant has not been completely discontinued, but such usage is only permitted if its emissions can be sufficiently reduced. This has an adverse economic impact on, for example, logging companies, which are limited by federal and state regulations on how much of the fumigant they can release into the atmosphere, thus limiting their operations.

Currently, there are methods being implemented on a large scale for capturing fumigants; however, they typically destroy the fumigants, creating by-products and attendant disposal problems. Moreover, they are also expensive. Most of the current methods rely on the use of activated carbon beds, and the absorbing solution is not recoverable. Other shortcomings associated with these current technologies include the following, for example. They involve complicated systems comprising multiple stages, thus requiring high capital investment and operating expense. These technologies often require the modification of existing fumigation processes which may affect the effectiveness and reliability of the processes by, for example, requiring longer processing time per container. The existing emission control methods/processes mainly focus on the capture of the halogenated fumigants using different adsorbents/absorbents, whereby a further treatment process is usually required for the safe disposal of the halogen-containing agents/absorbents, which adds extra costs to the process and makes it less economically favorable. Current treatment systems are typically large which makes their transportation for onsite gas treatment difficult. Existing processes also typically involve extreme treatment conditions of high temperature or energy input.

SUMMARY OF THE INVENTION

The present invention relates to processes and apparatus for capturing and converting fumigants using a reactive absorber/scrubber, which is equipped to circulate an aqueous buffer solution of alcohol and metal hydroxide. Air containing alkyl halide fumigant (i.e., fumigant/air mixture) is then passed through the absorber/scrubber apparatus such that the fumigant/air mixture and the buffer solution come into contact, causing the fumigant to be absorbed by the alcohol and thereby cleaning the air of the fumigant. The captured alkyl halide then reacts with the metal hydroxide to yield a metal halide. A purge stream containing concentrated metal halide solution, or metal halide slurry, is continuously discharged to avoid buildup of solids and contaminants in the system. Upon discharge from the absorber/scrubber apparatus, the solid metal halide will be precipitated and separated from the aqueous alcohol and metal hydroxide solution that remains. After the salt (e.g., metal halide) recovery process, the solution is fed back to the absorber as absorbing solution. In an embodiment, the fumigant/air mixture is processed in continuous mode and the buffer solution is processed in continuous mode but recirculating mode. In an embodiment, the fumigant/air mixture is processed in continuous mode and the buffer solution is processed in batch mode.

