Active zeolite

Efficient contacting of the feed and catalyst is critical for achieving the desired cracking reactions. Steam is commonly used to atomize the feed. Smaller oil droplets increase the availability of feed at the reactive acid sites on the catalyst. With high-activity zeolite catalyst, virtually all of the cracking reactions take place in three seconds or less. 

When NOj levels are measured electrochemicaUy, NO and NO2 can lead to opposing signals because NO is oxidized and NO2 tends to be reduced. Moreover, it is preferred to obtain a total NO, measurement instead of only one of the constituents. The latter can be achieved by catalytically equilibrating the feed with oxygen before contact with the sensor by coating an active zeolite layer on top or placing a active catalyst bed in front of the sensor. Both approaches have been demonstrated successfully with a Pt-Y zeohte as active catalyst [74, 75]. The additional advantage of the filter bed is a reduction in the cross-sensitivity with CO due to CO oxidation above 673 K. 

Loading was accomplished by exposing the activated zeolites to benzene-de vapors. The extent of vapor adsorption was determined by the increase in weight of the zeolite. The samples were found to be extremely hydroscopic and thus kept in a vacuum desiccator until their use. After two or three temperature runs the samples began to adsorb water vapor. Therefore, only the data obtained for the first two variable temperature cycles are presented here. The samples studied are listed in Table I. 

Figure 2. FTIR spectra of water vapor adsorption under increased pressures (a) 2.25 kPa, (b) 4.20 kPa and (c) 7.55 kPa at 100°C on H-ZSM-5 zeolite and spectrum of the activated zeolite at 450°C (d).

Keywords acidity, activity, zeolites, hexane conversion... 

In the 1970s more-active zeolite catalysts were developed so that the cracking reaction could be conducted in the transport riser. Recently, heavier crude feedstocks have resulted in higher coke production in the cracker. The extra coke causes higher temperatures in the regenerator than are desired. This has resulted in the addition of catalyst cooling to the regeneration step, as shown in Fig. 17-25. 

Organic molecules spontaneously form corresponding cation-radicals on inclusion within activated zeolites (Yoon and Kochi 1988, Yoon 1993, Pitchumani et al. 1997). Zeolites are crystalline alu-mosilicate minerals that are widely used as sorbents, ion exchangers, catalysts, and catalyst supports. As zeolites act as electron acceptors due to the presence of Lewis- or Broensted-acid sites, confined organic compounds occur to be electron donors. Frequently, the interaction of electron donor with electron acceptor centers spontaneously generates cation-radicals and traps the ejected electrons. 

Despite the fact that many zeolites have been synthesized in the last 20 years, zeolite Y remains the active zeolitic component in most commercial cracking catalysts. 

Catalyst Preparation. For most of the experiments conducted in this study, nickel or vanadium impregnated non-zeolitic particles were blended with metals-free high activity cracking component. This allowed us to examine the effects of the metals on the non-zeolitic component. The high activity zeolitic particles were prepared by in-situ zeolite synthesis on kaolin-based microspheres... 

Catalysts were contaminated with nickel and vanadium according to the method of Mitchell ( ), using metal naphthenates. Prior to blending, all contaminated materials were steamed (1450 F, 4 hrs, 90% steam, 10% air) to age the metals. The selectivity effects of the metals on the non-zeolitic component were determined by blending impregnated non-zeolitic components with 20% of the steamed, uncontaminated high activity zeolitic component such that the overall blend yielded 70% conversion. 

Different results are obtained when NH4Y is activated at higher temperatures (600°C). Vedrine et al. (266) showed that y irradiation in vacuo of such an activated zeolite leads to two types of signals. The signal with g = 2.0125, g = 2.0030, and a 12-line hyperfine structure with A aiso = 10.0 G was attributed to a positive hole (V center) trapped on an oxygen bridging two aluminum atoms ... 

The application of lipases in synthetic biotransformations encompasses a wide range of solvolytic reactions of the carboxyl group, such as esterification, transesterification (alcoholysis), perhydrolysis, and aminolysis (amide synthesis) [103]. Transesterification and amide synthesis are preferably performed in an anhydrous medium, often in the presence of activated zeolite, to suppress unwanted hydrolytic side reactions. CaLB (which readily tolerates such conditions [104,105]), PsL, and PcL are often used as the biocatalyst [106]. 

By characterizing various zeolite catalysts under the same reaction conditions, the authors found weaker MAS NMR signals of alkoxy species for the less active zeolites HY and HZSM-5 than for the more active zeolite H-beta (250). This observation suggests that the alkoxy species observed under steady-state conditions act as reactive surface species in the MTBE synthesis from isobutylene and methanol on acidic zeolite catalysts. 

Fig. 6. An example showing the use of gas chromatography and mass spectrometry (GC-MS) for identifying reaction products on zeolites. Styrene was first reacted for ca. 30 min on activated zeolite HY at 298 K in a sealed glass tube the sample was extracted using toluene as solvent, and the extracts were then analyzed with GC-MS. The total ion chromatogram of the extracts (a) shows three major peaks eluting at 13.83, 13.93, and 14.31 min, respectively. The peak at 14.31 min was readily identified as the linear dimer. The peaks at 13.83 and 13.93 min show equal ion intensity and nearly identical mass spectra (the mass spectrum of the 13.93-min peak is shown in (b)), and these were assigned to the cis and trans isomers of the cyclic dimer.

Friedel-Crafts catalysts are more easy handling, fewer side reactions, and longer catalyst lifetime. Over the years numerous technologies applying different reactors have been developed.7 277 284-289 Because of their rapidly declining activity, zeolites have not reached commercial application in alkane-alkene alkylation.7... 

As a test reaction, we selected the bleaching of phenolphthalein at pH 10 with H2O2. Apart from the Mo-LDH, several redox-active zeolites were used, such as Mn2t-exchanged Y, or Y zeolites with entrapped Mn... 

Figure 1731. Fluidized bed reactor processes for the conversion of petroleum fractions, (a) Exxon Model IV fluid catalytic cracking (FCC) unit sketch and operating parameters. (Hetsroni, Handbook of Multiphase Systems, McGraw-Hill, New York, 1982). (b) A modem FCC unit utilizing active zeolite catalysts the reaction occurs primarily in the riser which can be as high as 45 m. (c) Fluidized bed hydroformer in which straight chain molecules are converted into branched ones in the presence of hydrogen at a pressure of 1500 atm. The process has been largely superseded by fixed bed units employing precious metal catalysts (Hetsroni, loc. cit.). (d) A fluidized bed coking process units have been built with capacities of 400-12,000 tons/day.

The most active zeolites are more active than pyridine, and less active than piperidine, showing basic sites with pKb<13.3. The selectivity to the desired condensation product when using zeolites is, at least, as high as in the case of the homogeneous catalyst. 

Prior to sorption measurements, zeolite samples were activated by evacuation at elevated temperatures. There is frequently some question as to how precisely one can establish the mass of a zeolite sample from which all zeolitic water, but no water arising from collapse of structural hydroxyl groups, has been removed (l f ). In order to establish that the (zeolitic-water-free) masses of the activated zeolite samples used here are well defined, the following stepwise activation procedure was used. Each sample was first heated in vacuo at 300°C. When the pressure had dropped to below about 10 torr, the balance was isolated from the pumps, the rate of pressure increase measured, and evacuation resumed. This process was repeated until the rate of pressure increase fell to below 5 X 10 torr min l, a duration of time which was from 15 to 30 minutes. This is a rate such that were the increase due to water vapor alone, and were the rate to remain constant, the weight loss would still be undetectable after 2h hrs., a duration seldom exceeded in activating zeolites. 

The static testing served primarily as a feasibility study to determine if the proposed dehydration could in fact be carried out as a practical process. Static tests were performed by putting preweighed amounts (0.1-5 gm) of freshly activated zeolite into sealed vessels containing approximately 50 ml of the test liquid. A vessel containing only the test liquid was also prepared for use as an experimental blank. 

The pore opening in ZSM-5 is smaller than for zeolite Y and access of the complex gas oil molecules into the pores will be restricted. As a result, ZSM-5 has little effect on the primary cracking of gas oil and, when allowance is made for the slight loss in conversion arising from dilution of the active zeolite Y concentration, there is no significant change in coke, bottoms, or light gas yields. 

Developments in the zeolite field in terms of non-framework alumina control, leading to super low delta coke zeolites and the advent of enhanced surface activity zeolites, seem promising for the resid cracking field (3). 

Adsorption experiments The method developed for the analysis of carbonaceous compounds formed and trapped within the zeolite micropores during catalytic reactions1581 can be adapted for determining the occupancy of micropores by reactant, solvent and product molecules. However, this method cannot be used with compounds sensitive to hydrolysis, such as AA, because of the step of dissolution of the zeolite in a hydrofluoric acid solution necessary for the complete recovery of the organic molecules located within the zeolite micropores.[58] This method was used to determine the composition of the organic compounds retained within the micropores of three different zeolites [H-BEA (zeolite Beta), H-FAU (zeolite Y), and H-MFI (zeolite ZSM-5)] after contact in a stirred batch reactor at 393 K for 4 min of a solution containing 20 mmol of 2-methoxynaphthalene (2-MN), 4 mmol of l-acetyl-2-methoxynaphthalene (1-AMN) and 1 ml of solvent (sulfolane or nitrobenzene) with 500 mg of activated zeolite.[59 61] From the comparison of... 

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