| 摘要 |
<p>#CMT# #/CMT# The adsorbent contains a small proportion of an inert binder and has cationic sites occupied by barium ions alone or barium and potassium ions. The zeolitization of the binder improves the adsorbency of the product. #CMT# : #/CMT# The agglomerated zeolite adsorbent comprises at least 90% of a zeolite X with a Si/Al ratio greater than 1.15 and less than or equal to 1.5. At least 90% of the cationic exchangeable sites are occupied either by Ba ions only or Ba and K ions. The sites occupied by K ions may represent up to 1/3 of the Ba + K sites (the possible complement being made up by alkali or alkaline earth ions other than Ba). The content of inert binder is no more than 10%. Independent claims are also included for the preparation of the adsorbent and its uses as an adsorbent or separating agent. #CMT#USE : #/CMT# The desorbents can be used for the separation of aromatic C8 isomers, particularly xylenes, and also in the separation of sugars, polyhydric alcohols and substituted toluene isomers such as nitrotoluene, diethyltoluene, toluenediamine and cresols. #CMT#ADVANTAGE : #/CMT# The preparation of the adsorbents is less laborious (requiring fewer stages than products of the prior art) and contain a smaller amount of binder material. The adsorbents have an improved adsorbent capacity. #CMT#ORGANIC CHEMISTRY : #/CMT# Preferred Recovery Process: The process for the recovery of para xylene from 0C aromatic cuts, in the liquid or gaseous phase, is affected using an adsorbent as defined above in the presence of a desorbent. The desorbent is toluene or paradiethylbenzene. The process is operated using a simulated mobile bed, counter-current or co-current. #CMT#INORGANIC CHEMISTRY : #/CMT# Preferred Adsorbent: The adsorbent preferably contains at least 95% of zeolite X and an exchange content of Ba or Ba + K ions greater or equal to 95%. The loss on firing at 900[deg]C. is 4-7.7%, more preferably 5.2-7.7%. The adsorbent is prepared by the following stages: (a) agglomeration of zeolite X powder with a binder containing at least 80% wt. of zeolitizable clay, forming, drying and calcining; (b) zeolitization of the binder by treatment with an alkaline solution; (c) replacement of at least 90% of the exchangeable sites of zeolite X with Ba, then washing and drying; (d) optional replacement of no more than 33% of the exchangeable sites with K, followed by washing and drying; and (e) activation. The optional exchange with K may be carried out before or after the Ba exchange. The activation stage (e) is a thermal treatment effected at 250-300[deg]C. The alkaline treatment (b) uses an alkaline solution of at least 0.5 M. #CMT#EXAMPLE : #/CMT# (Reference) An industrial NaX zeolite of ratio Si/Al = 1.25 and Na/Al = 1 was agglomerated by mixing intimately with 850 g of zeolite X, 150 g of Charente kaolin and 6 g of carboxymethylcellulose (water retention additive) and water sufficient for extrusion. The extrudate was dried, crushed to obtain 0.7 mm granules, then calcined in N 2 at 550[deg]C. for 2 hours. Its toluene adsorption capacity at 25[deg]C. and 0.5 partial pressure was 20.2%. The microporous volume was 20.2/0.86 = 0.235 cm 3>/g (where 0.86 is the density of the adsorbed toluene). The granulate was exchanged in 4 stages using a 0.5 M BaCl 2 solution at 95[deg]C. For each stage, the volume ratio of solution to solid was 20 ml/g with a 4 hour period for each and inter-stage washing. It was then activated at 250[deg]C. for 2 hours in N 2. The degree of exchange in Ba was 97% and the adsorption capacity for toluene was 14.8% at a microporous volume of 0.17 cm 3>/g. The loss on firing was 4.5%, and the microporous volume for N 2 adsorption at 77[deg]K was 0.22 cm 3>/g, corresponding to a zeolite content of 85%. The selectivity values for para xylene (PX) adsorptions were: PX/OX = 2.25; PX/MX = 2.12; PX/EB = 1.77; and PX/Tol = 1.52. The amount of PX adsorbed was 0.054 cm 3>/g. The selectivity test was carried out as follows: 17 g of the activated adsorbent was immersed in 80 g of an aromatic mixture dissolved in 2,2,4-trimethylpentane. The mixture was composed of 2% each of PX, MX, OX, EB and toluene (as desorbent), where MX = meta xylene, OX = ortho xylene and EB = ethylbenzene. The mixture was autoclaved at 150[deg]C to assure equilibration, then part of the liquid was sampled, condensed at -30[deg]C. and analyzed by GLC (Invention) An industrial NaX zeolite (as above) was agglomerated by mixing 800 g of zeolite X powder, 150 g of kaolin, 56 g of colloidal silica ( Cecasol 30, containing 30% SiO 2 and 0.5% Na 2O) and 6 g of carboxymethylcellulose with water sufficient for extrusion. The extrudate was treated as before to obtain granules. 200 g of the granules were placed in a glass reactor regulated at 100[deg]C.(plus or minus 1[deg]C.) then 1.5 l of aqueous NaOH (100 g/l) added and the mixture stirred for 3 hours. The granules were then washed to a final pH of 10-10.5. The toluene adsorption capacity was measured as before, giving a value of 22.5%, corresponding to a microporous volume of 0.26 cm 3>/g (a gain in crystallinity of 13% compared to the reference). A Ba exchange was then carried out in similar conditions except a concentration of 0.6 M BaCl 2, washing and drying at 80[deg]C. and activation at 250[deg]C. for 2 hours in N 2. The degree of Ba exchange for this adsorbent was 97.4%, the toluene adsorption capacity was 16.2% and loss on firing 5.2%. The microporous volume for N 2 adsorption at 77[deg]K was 0.244 cm >g corresponding to a zeolite content of 94%. The selectivity tests gave results similar to those for the reference. The amount of PX adsorbed was 0.06 cm 3>/g.</p> |
