Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Sulfur or sulfur containing component
Patent
1994-11-22
1997-03-11
Lewis, Michael
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Sulfur or sulfur containing component
42324401, 95136, 95902, 502 64, 502 68, B01J 800
Patent
active
056098421
DESCRIPTION:
BRIEF SUMMARY
The invention relates to processes for desulfurization of hydrocarbon gases and to zeolitic adsorbents that can be used in these processes. The invention may be applied in the oil, gas, and petrochemical industries and in petroleum refining.
Widespread use is made of adsorbents belonging to the category of type A and X molecular sieves, in order to purify gases containing sulfurated compounds. As described, for example, in Soviet Patent No. SU 753449, they have the advantage of possessing a good dynamic sulfur capacity and to lead to high purification rates. Nevertheless, when they are used in conjunction with crude, natural, or structurally similar gases having the composition: hydrocarbons of 1-4 carbon atoms catalyze the reaction: which is not retained on the adsorbent and is found in the purified gases.
More precisely, in the case of gases containing more than 1% by volume of CO.sub.2, e.g., 2%, and 0.1% of H.sub.2 S, a 5A sieve exchanged at 65-70% and granulated by means of a kaolinite binding agent generates some 140 to 220 mg/m.sup.3 of COS (see French Patent No. 2,618,085). To express this phenomenon in practical terms, the standard allowed on Russian soil is 35 to 40 mg/m.sup.3.
The present invention is intended to solve these problems and to supply adsorbents for desulfurization of high capacity gases, which at the same time are effective in removing H.sub.2 S from the gases and have very limited COS-formation catalytic activity; and, more specifically, adsorbents endowed with a high dynamic adsorption capacity of approximately 2% by weight, but with which the level of COS formation remains limited to a maximum of 35 mg/m.sup.3.
According to the invention, this result is achieved by using CaA zeolite whose microcrystals have sizes ranging between approximately 1 and 2 .mu.m, whose rate of Ca.sup.2+ ion exchange is between 76 and 90% , and preferably between 78 and 88% , and which is granulated using a natural mineral binding agent, e.g., bentonite, kaolinite, montmorillonite, attapulgite, etc., this binding agent being required to contain less than 0.5% iron (expressed in Fe.sub.2 O.sub.3) and a phosphate content of 0 to 3 4% , expressed in added alumina phosphate, and to have an acidity (expressed in terms of adsorption of NH.sub.3 at 150.degree. C.) of less than 0.1 mmole/g, as well as a basicity (expressed n terms of adsorption of SO.sub.2 adsorbable at 150.degree. C.) of less than 0.15 mmole/gram.
Secondary porosity of the adsorbent is an important characteristic of the adsorbents according to the invention. To date, only diffusion in the zeolite microcrystals had been taken into account. The inventors revealed the substantial advantage to be gained by considering permeability as an additive property, defined by the equation 1/D.sub.gr =1/D.sub.z +1/D.sub.por.sec, where D.sub.gr, D.sub.z, and D.sub.por.sec are the coefficients of diffusion in the granulate, the microcrystals, and the secondary pores, respectively. They verified that, by increasing the volume of these secondary pores, and thus the total permeability of the granulates to the adsorbate, the contact time between the adsorbate and the adsorbent was reduced while improving the adsorption capacity. This is a new result, which is confirmed by example 7 below. This secondary porosity of the agglomerate is estimated based on the adsorption of hexane at 20.degree. C. from 0.18.degree. to 0.95.degree. P/Ps), and is chosen so as to range preferably between 0.42 and 0.55 cm.sup.3 /g for pore radii of between 10 and 500 Angstrom units (10.10.sup.-10 m to 500.10.sup.-10 m). This secondary porosity is governed by the judicious choice of the conditions under which the agglomerated products are fabricated, i.e., parameters well known to the specialist, such as the choice of the binding agent, the moisture of the paste, the vis pressure of the mixer shaft, the cooking rate, the use of gas-forming additives by thermal decomposition during cooking, e.g., molasses, methylene blue, or surfactants, such as nonylphenol oxyethylenated at 40 OE, in quan
REFERENCES:
patent: 5001098 (1991-03-01), Pacaud et al.
Kirk-Othmer Encyclopedia of Chemical Technology, 1979 (no month) vol. 6 pp. 195-196.
Hawley The Condensed Chemical Dictionary 1981 (no month) p. 777.
Mayolet Francis
Mourine Vladimir I.
Plee Dominique
Tsybulevski Albert M.
Dunn Jr. Thomas G.
Lewis Michael
Vniigaz
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