Boron-impregnated zeolites

AIBN = a,a -azobisisobutyronitrile. - DTBP=di-f-butyl peroxide. - DBP = dibenzoyl peroxide. - HMBG = heptamethyl biguanide. - Z 1 = boron silicate zeolite impregnated with Cr(N03)3. - Z 2 = boron silicate zeolite. 

Zeolites have also proven applicable for removal of nitrogen oxides (NO ) from wet nitric acid plant tail gas (59) by the UOP PURASIV N process (54). The removal of NO from flue gases can also be accomplished by adsorption. The Unitaka process utilizes activated carbon with a catalyst for reaction of NO, with ammonia, and activated carbon has been used to convert NO to N02, which is removed by scrubbing (58). Mercury is another pollutant that can be removed and recovered by TSA. Activated carbon impregnated with elemental sulfur is effective for removing Hg vapor from air and other gas streams the Hg can be recovered by ex situ thermal oxidation in a retort (60). The UOP PURASIV Hg process recovers Hg from clilor-alkali plant vent streams using more conventional TSA regeneration (54). Mordenite and clinoptilolite zeolites are used to remove HQ from Q2, clilorinated hydrocarbons, and reformer catalyst gas streams (61). Activated aluminas are also used for such applications, and for the adsorption of fluorine and boron—fluorine compounds from alkylation (qv) processes (50). 

This research was carried out on BP-US-69 sample (1) obtained by treatment of start US-69 by vapors of ethyl ethers of boron and phosphoric acids with following hydrolysis, and on BP-US-69 sample (2), prepared by impregnation US-69 by aqueous solution of equimolecular mixture of boron and phosphoric acids. Various Ce hydrocarbons were used as adsorbates. In conditions of experiment only the initial sites of isotherms, when p/ps ratio did not exceed 0.015 were obtained. The results for starting and modified zeolites are represented in a fig. 3. It was necessary to expect, that the adsorption values of n-hexene measured at identical p/ps values should increase under decrease of kinetic diameter of adsorbate molecules. Actually, adsorption isotherms of n-hexene lay above, than for other hydrocarbons for all samples. 

The shape selectivity of ZSM-5 is modified significantly by treatment with a variety of chemical reagents. For example, modification with phosphorus or boron was made by impregnating the zeolite crystals with aqueous phosphoric acid or orthoboric acid, followed by calcination in air to convert the acid into the oxides. Selected results are summarized in Table 4.3. Though the selectivity iorpara isomer in alkylation with ordinary ZSM-5 is close to that expected from the thermal equilibrium, selectivity as high as 97% is achieved with the modified ZSM-5. 

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