I PRODUCTION CotTii^sitibriMrenweranjre^Kresswre A r e Keys to Synthetic Zeolites
Sodium I hydroxide I Typical Composition;^ Si0 2 /A! 2 O 3 = 1.5 to 3.0 Water
N a 2 0 / S i 0 2 = 0 . 9 t o 1.5 j H 2 0 / N a 2 0 = 3 5 t o 200 j W \
troni silk a geSL silicic acid, or s o d i u m silicate. A l u m i n u m sources include a l u iniiia, a l u m i n a tribydrate, or sodium aluminate. S o d i u m hydroxide supplies sodium ion a n d helps control t h e r e action's p H . T l i e p r e f e r r e d way to m a k e t h e m a terials react is t o first rttake^a water solution of sodiuizi aluminate a n d sodiiun hydroxide- T i i i s solution is then a d d e d to sodium silicate dissolved in w a t e r . T h e system is stirred until it is h o m o g e neous, or at least until all the gels AT^ broken. T h e first s t e p c a n b e d u n e a t room tempera.ture. Zeolites can form at this t e m p e r a t u r e , but heat speeds u p die process. H e a t i n g is d o n e in steel jacketed vessels. Zeolite .-i forms in six days at 2 1 " O . in about 45 m i n u t e s at 1 0 0 ' C . a n d even faster a t 150 C . Zeolite X takes longer: S S h o u r s a t 5 0 " C , six hours or less at 10O~ C a n d about 9 0 m i n u t e s at 120 3 C. O n c e t h e crystals form, they keep tiieir structure. Keeping t h e m at t h e r e a c t i o n t e m p e r a t u r e longer than necessary' doesn't h a r m the crystals as long a s the t e m p e r a t u r e is 100 C. or less. Above 1O0C C , some c h a n g e s take place. W h e n the reaction is completed, t h e zeolite c r y s t a l s are filtered and w a s h e d w i t h water u n t i l w a s h w a t e r p H is b e tween 9 a n d 12. Drying is done in a vented oven ast 25 ~ t o 1 5 0 ' C. • Cubic C r y s t a l s . Zeolite A crystals are cubic j»»"»cf most o£ t h e m a r e a b o u t 0.1 to 1 0 m i c r o n s . Zeolite X crystals ". si. . :. 'v-:jS'^v2&i£^^
Linde Unmasks Zeolite Process
Composition of starting materials plays most important role in making molecular sieves J L I X D E is planning a six-fold hike in i t s zeolite process is relatively simple. Difmolecular sieve capacity a t T o n a w a n d a , ferent t v p e s are m a d e b y varying reacN . Y., as t h e company makes public i t s tion time, temperature, a n d starting maprocess for making t w o classes of d i e terials. Zeolite A a n d zeolite X a r e the synthetic zeolites ( U . S. patents 2.882,- t w o major classes of sodium aluminum silicate sieves covered b y t h e patents. 2 4 3 a n d 2,882,244). Molecular sieves a r e crystals of d e - Oifference between the t w o is the oxide h y d r a t e d aluminum silicate w h i c h con- ratio. Typical analysis for each t y p e is: tain billions of molecular-sized holes. • Z e o l i t e A-O.dQNa-Oil.OAl-Qs:T h e s e holes, or cages, separate sub- l.SoSiOv.o-lH^O. stances by trapping larger molecules • Z e o l i t e X - 0 . 9 N a _ . 0 . A l 2 O s . 2.5from a mixture of c o m p o u n d s ; for e x SiO,:6.1HUO. ample, some sieves separate o c t a n e The process uses a variety of raw m a from isooctane. • Simple Process. T h e s y n t h e t i c terials- F o r example, silicon can coine
• Monovalent ions—lithium, sium, a n d arrunoniurii.
potas-
• Divalent ions— magnesium, t i u m , ami b a r i u m .
stron-
• Trivalent
ions—cerium.
L i n d e first synthesized sieves during the Lite 194^)*s. started making t h e m commercially in 1934. In 1957, t h e company tripled its capacity. Linde now has three* types of molecular sieves: Types 4 A a n d 5A a r e used to dry refrigerants a n d natural g a s . purify a n d separate h y d r o c a r b o n mixtures, a n d clean argon. Type 13X is a high capacity a i r d r i e r ; it is a chemically loaded sieve t o c o r e r u b b e r and plastics sO&EX. M a y 26. 19-5S. page 6 2 : a n d I&ECT ApriL. p a g e 5 3 1 ) . • MAY
II.
1959
C&EN
45
