Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Faujasite type
Reexamination Certificate
2001-01-03
2004-10-19
Sample, David (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Faujasite type
C502S085000, C502S086000, C423S700000, C423SDIG002, C095S095000, C095S130000, C095S902000
Reexamination Certificate
active
06806219
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to zeolites of X type, to their preparation and to their use in the separation of gas mixtures and more particularly to zeolites of type exchanged with lithium and with trivalent and/or divalent ions which are selective for nitrogen and which have an improved thermal stability and an improved crystallinity, to their preparation and to their use in the separation of nitrogen from less strongly adsorbed gases.
BACKGROUND OF THE INVENTION
The separation of nitrogen from other gases, such as, for example, oxygen, argon and hydrogen, is of considerable industrial importance. When the separation is carried out on a large scale, fractional distillation is often used. However, distillation is very expensive because of the high initial costs for the plant and of the considerable energy demand which it involves. Other separation methods have recently been studied in efforts to reduce the overall cost of these separations.
An alternative to distillation which has thus been used to separate nitrogen from other gases is adsorption. For example, a sodium zeolite X, disclosed in U.S. Pat. No. 2,882,244, has been used with a degree of success for the separation by adsorption of nitrogen from oxygen. One disadvantage of the use of sodium zeolite X for the separation of nitrogen from oxygen is that it only has a low separating efficiency in the separation of nitrogen.
According to U.S. Pat. No. 3,140,933, an improvement in the adsorption of nitrogen is obtained when some of the base ions are replaced by lithium ions. This patent states that the zeolite of X type having base ions replaced by lithium ions can be efficiently used to separate nitrogen from oxygen at temperatures ranging up to 30° C. Because the exchange of ions is not total and because the zeolites X have been synthesised in a sodium medium, the adsorbent used is a mixed sodium/lithium zeolite.
U.S. Pat. No. 4,859,217 discloses that very good separation of nitrogen from oxygen can be obtained by absorption at temperatures of 15 to 70° C. using a zeolite of X type which has more than 88% of its ions in the form of lithium ions, in particular when a zeolite is used with a silicon/aluminium atomic ratio of between 1 and 1.25.
Unfortunately, the zeolite of X type highly exchanged with lithium has a very strong affinity for water and the presence of adsorbed water, even small amounts, seriously reduces the adsorption capacity of the zeolite. Consequently, in order to ensure optimum performance as regards adsorption, it is necessary to activate the zeolite by heating it to temperatures ranging up to 600 to 700° C. in order to drive off as much adsorbed water as possible. Because the zeolites of X type exchanged with lithium are not stable at temperatures greater than approximately 740° C., the activation of these adsorbents must be carefully controlled in order to prevent them from being damaged. Another disadvantage of zeolites of X type highly exchanged with lithium stems from the fact that they have a high production cost due to the price of the lithium compounds needed in their manufacture.
A need thus exists for adsorbents which have good thermal stability, good crystallinity and adsorbent properties for nitrogen at least equal to those of zeolites highly exchanged with lithium but which can be produced at more reasonable costs.
U.S. Pat. No. 5,179,979 maintains that lithium/alkaline earth metal zeolites of X type having lithium/alkaline earth metal molar ratios of the order of 95/5 to 50/50 approximately have a higher thermal stability than that of the corresponding zeolites with pure lithium and good adsorption selectivities and capacities.
U.S. Pat. No. 5,152,813 discloses the adsorption of nitrogen from gas mixtures which uses crystalline zeolites X having an Si/Al zeolite ratio≦1.5 in which the exchangeable sites are occupied by at least 2 ions: between 5 and 95% of lithium ion and between 5 and 95% of a second ion chosen from calcium, strontium and mixtures of these, the total (lithium and second exchangeable ion) being at least 60%.
U.S. Pat. No. 5,464,467 or EP 667 183 provide a zeolite of X type, the cations of which comprise, referred to as equivalents, from approximately 50 to approximately 95% of lithium, from approximately 4 to approximately 50% of trivalent ions chosen from aluminium, scandium, gallium, iron(III), chromium(III), indium, yttrium, lanthanides alone, mixtures of two lanthanides or more, and mixtures of these, and from 0 to approximately 15% of residual ions chosen from sodium, potassium, ammonium, hydronium, calcium, strontium, magnesium, barium, zinc, copper(II) and mixtures of these, which is prepared by exchange of the exchangeable cations of the zeolite, preagglomerated with a binder, first with lithium and then with the trivalent cation or cations.
U.S. Pat. No. 5,932,509 provides for the preparation of these same zeolites according to a process which consists first in exchanging the exchangeable cations of the powdered zeolite X with trivalent cations, in then agglomerating with a binder and finally in carrying out the lithium exchange on the agglomerated zeolite.
DETAILED DESCRIPTION OF THE INVENTION
The Applicants have found that the zeolites prepared according to the teaching of U.S. Pat. Nos. 5,179,979, 5,152,813, 5,464,467 or 5,932,509, although exhibiting good thermal stability and a good nitrogen adsorption capacity, have an insufficient crystallinity and exhibit a degree of heterogeneity in the distribution of the tri- and/or divalent cations.
The present invention provides zeolites of X type having an Si/Al atomic ratio of less than 1.5 and preferably of between 0.9 and 1.1, the exchangeable cations of which comprise, referred to as equivalents,
from approximately 50 to approximately 95% of lithium ions,
from approximately 4 to approximately 50% of trivalent ions chosen from aluminium, scandium, gallium, iron(III), chromium(III), indium, yttrium, lanthanides or rare earth metals, alone or as a mixture, and/or of divalent ions chosen from calcium, strontium, zinc, copper, chromium(II), iron(II), manganese, nickel or cobalt, alone or as a mixture,
0 to approximately 15% of residual ions chosen from sodium, potassium, ammonium or hydronium, alone or as a mixture,
Which are capable of being obtained according to a process which comprises the following stages:
a) suspension of the zeolite in water, then
b) exchange of the exchangeable cations of the suspended zeolite with one or more di- and/or trivalent ions by simultaneous and/or successive contact(s) in a rapid mixer of the said suspension with one or more solutions comprising compounds of the di- and/or trivalent ions,
c) exchange of the exchangeable cations of the zeolite resulting from stage b) with lithium,
which stages will be explained in detail below.
The zeolites of the present invention can be provided in various forms and the exact form which they assume can determine their usefulness in the industrial adsorption processes. When the zeolites of the present invention are used in industrial adsorbers, it may be preferred to agglomerate (for example, to convert into granules) the zeolite in order not to risk compacting the pulverulent zeolite in an adsorption column of industrial size, thus blocking or at the very least greatly reducing the flow through the column. These techniques generally involved mixing the zeolite with a binder, which is usually a clay, converting the mixture to an agglomerate, for example by extrusion or bead formation, and heating the zeolite/binder mixture formed to a temperature of 600-700° C. approximately in order to convert the “green” agglomerate to an agglomerate which is resistant to crushing. The binders used to agglomerate the zeolites can include clays, silicas, aluminas, metal oxides and their mixtures.
It is possible to prepare agglomerates comprising less than 10%, indeed even less than 5%, by weight of residual binder. A process for producing these agglomerates with a low level of binder consists in converting the binder of the agglomerates describe
Masini Jean-Jacques
Plee Dominique
Ceca S.A.
Sample David
Smith , Gambrell & Russell, LLP
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