Feedstock impurities

Beta zeolite catalyst can be optimized to nearly eliminate all undesirable side reactions in the production of cumene. The improvement in beta zeolite catalyst quality has occurred to the point that any significant impurities in the cumene product are governed largely by trace impurities in the feeds. The selectivity of the catalyst typically reduces by-products to a level resulting in production of ultrahigh cumene product purities up to 99.97 wt%. At this level, the only significant byproduct is n-propylbenzene with the catalyst producing essentially no EB, butylbenzene, or cymene beyond precursors in the feed. Fig. 7 shows the reactions of some common feedstock impurities that produce these cumene impurities. 

The historical development of beta zeolite showed that early versions of beta catalyst demonstrated less than optimum performance when compared to today s state-of-the-art formulation. Fig. 8 is a plot of the relative stability of beta zeolite as a function of the Si/Al2 ratio of the beta zeolite structure in which the dominating influence of this parameter is evident. Uop has learned to stabilize the zeolite structure through careful process and chemical means. This has resulted in a catalyst system that is extremely robust, highly regenerable, and tolerant of most common feedstock impurities. 

Feedstock impurities are often a source of reactor waste. In different cases, impurities can cause these problems ... 

Unreacted feedstock Impurities in the feedstocks Undesirable by-products Startup and shutdown losses Gas purges Reactor washings Catalyst usage and losses... 

The debenzylation reaction was found to be very sensitive to feedstock impurities. Eigure 8 illustrates the hydrogen uptake of debenzylation reaction of 4-(benzyloxy) phenol from two different feedstock lots. As shown in Figure 8 that the hydrogen uptake was completed in 6000 seconds on a pure feed stock how-... 

Figure 8 Effects of the feedstock impurity on the reaction rate for debenzylation of 4-(benzyloxy) phenol. Reaction conditions methanol solvent, 35°C, 1.1 bar hydrogen, 2000 rpm, 3% catalyst loading (5%Pd/CPS3).

Feedstock impurities, or chemicals left over in the system from a previous operation, are often the cause of undesirable reactions in columns. Should an undesirable reaction be suspected, it may pay to look into the nature and effects of feedstock impurities, and to attempt deriving plant feedstock from an alternative source for a trial period. If the impurity is chemically unstable, or reacts with the column chemicals explosively, a detonation may result some examples were reported (96, 275). In absorber-regenerator systems, contamination of the solvent charge can lead to imdesirable reactions or poor stripping one example has been reported (14a). 

When it finally comes to continuous processing of transition metal catalysis in ionic liquid-organic biphasic reaction mode, some additional aspects have to be taken into account. First is the ease of phase separation that will determine the size of the separator unit and thus indirectly the ionic hquid hold-up required. Another very important aspect is the build-up of side-products or feedstock impurities in the ionic catalyst phase. Side-products and impurities that are likely to build up in the ionic liquid are relatively polar in nature and this brings along a significant risk of unfavorable interactions with the transition metal catalyst complex. Apart from this, all build-up of undesired components in the ionic hquid vnU also affect the ionic liquid s physicochemical properties. Therefore, a continuous build-up of components in the ionic catalyst phase that is not restricted by thermodynamic limits (e.g. solubility limits) will always require an extensive purge of the ionic catalyst solution. 

Even slight differences in temperature, feedstock, impurities, or cooling water source make the data less relaible. However, corrosion data from a similar process provide information to improve the accuracy of a test program. 

Recent examples of contamination of electrochemical reactors include the production of (1) adiponitrile and (2) glyoxylic acid." In (1) the source of the problem is the anode and polymer formation in (2) the anode, process hardware, and feedstock impurities contribute. Operation in both suffers from a gradual decrease in current efficiency due to increasing hydrogen evolution which accompanies the cathodic reaction. 

Table 6.10.1 Influence of feedstock impurities on sulfuric acid consumption in a refinery alkylation unit (Corma and Martinez, 1993 and Albright, 2003).

The quahty of naphthalene required for phthaUc anhydride manufacture is generally 95% minimum purity. The fixed plants do not require the high (>98%) purity naphthalene product and low (<50 ppm) sulfur. The typical commercial coal-tar naphthalene having a purity ca 95% (freezing point, 77.5°C), a sulfur content of ca 0.5%, and other miscellaneous impurities, is acceptable feedstock for the fixed-bed catalyst process based on naphthalene. 

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

Both processes also use up-graded ilmenite (slags). About 30% of the world s titanium feedstocks are suppHed by titanium slag producers in Canada, South Africa, and Norway. Slags are formed by the high temperature reduction of ilmenites in electric furnaces. Much of the iron oxide content is reduced to metallic iron and separated as a saleable by-product. Magnesium and other impurities may also be incorporated in the following equations. 

Under typical chlorination conditions, most elements are chlorinated. Therefore, for every metric ton of titanium tetrachloride produced, lower grade feedstocks requite more chlorine. Minor impurities such as alkaline-earths, where the chlorides are relatively involatile, may either inhibit bed-fluidization or cause blockages in the equipment and requite particular consideration regarding feedstock specification. 

The carbon monoxide product is removed from the top of the column and warmed against recycled high pressure product. The warm low pressure stream is compressed, and the bulk of it is recycled to the system for process use as a reboder medium and as the reflux to the carbon monoxide column the balance is removed as product. The main impurity in the stream is nitrogen from the feed gas. Carbon monoxide purities of 99.8% are commonly obtained from nitrogen-free feedstocks. 

The quaHty of the feedstock is important since it affects not only the product quaHty but the rate of hydrogenation. Some of the impurities that affect the rate are sulfur, phosphoms, haHdes, polyethylene, and moisture. Impurities are usually removed by clay treatment or by distillation (30). 

The hterature consists of patents, books, journals, and trade Hterature. The examples in patents may be especially valuable. The primary Hterature provides much catalyst performance data, but there is a lack of quantitative results characterizing the performance of industrial catalysts under industrially reaHstic conditions. Characterizations of industrial catalysts are often restricted to physical characterizations and perhaps activity measurements with pure component feeds, but it is extremely rare to find data characterizing long-term catalyst performance with impure, multicomponent industrial feedstocks. Catalyst regeneration procedures are scarcely reported. Those who have proprietary technology are normally reluctant to make it known. Readers should be critical in assessing published work that claims a relevance to technology. 

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