Paraffinic feeds

UOP Inc. is the key source of technology in this area, having numerous patents and over 70 units operating worldwide (12). The dehydrogenation catalyst is usually a noble metal such as platinum. Eor a typical conversion, the operating temperature is 300—500°C at 100 kPa (1 atm) (13) hydrogen-to-paraffin feed mole ratio is 5 1. 

Patents cover a new reforming catalyst based on L-zeoHte which gives a significantly higher yield of BTX, especially benzene, from light paraffinic feeds (11). Other new zeoHtes (12) may also offer advantages over the traditional reforming catalyst supports. 

These metals permanently poison the FCC catalyst by lowering the catalyst activity, thereby reducing its ability to produce the desiretl products. Virtually all the metals in the FCC feed are deposited on the cracking catalyst. Paraffinic feeds tend to contain more nickel than vanadium. Each metal has negative effects. 

The K factor is a very useful indication of feed crackability. The K factor relates to the hydrogen content of the feed. It is normally calculated using feed distillation and gravity data, and measures aromaticity relative to paraffinicity. Higher K values indicate increased paraffinicity and more crackability. A K value above 12.0 indicates a paraffinic feed a K value below 11.0, aromatic. 

Hold the main column shed tray s liquid temperature under 700°F and minimize the level and residence time of the hot liquid. Ensure adequate wash to shed decks to minimize coking in the bottom of the main column. Some paraffinic feeds may require a lower temperature. 

Table III A. Pilot Plant Results at 72 vol% Conversion Paraffinic Feed, "P"...

Figure 5.3 shows light olefin yields of DCC process in four refineries with different feedstocks at reaction temperatures of 545-565°C. The propylene yield can reach 23 wt% with paraffinic feed, and about 18-19 wt% with intermediate-based feed. The propylene/ethylene ratio is about 3.5-6.2, much higher than that of steam cracking. The DCC operation can be modified to further increase the yield of propylene. For example, recycling a part of DCC cracked naphtha to the reactor resulted in a propylene yield increment of 3.5 wt % in Jinan Refinery [16]. 

The conditions favoring cracking by the monomolecular path are high temperature and low olefin concentrations, i.e. low paraffin partial pressure and/or low conversion. The proposed reaction intermediate is formed by protonation of the paraffin feed by a Brdnsted acid site of the catalyst. We may compare this with similar paraffin protonation by CH5 in chemical ionizations occurring in an ion cyclotron resonance mass spectrometer [10], The C0H15 ion produced collapses to the same products as we have observed with zeolites HZ as the proton source (Fig.1). This is surprising, since the... 

The duality of cracking mechanisms is summarized in Fig. 5, where RH paraffin feed, R -C=C = olefinic product, Kq = equilibrium constant of olefin chemisorption. Free Bronsted acid sites HZ interact directly with the paraffin feed by protonation, producing monomolecular cracking. When the acid sites are covered with adsorbed olefins to form... 

Olefins are formed by dehydrogenation of the n-paraffin feed over the metallic hydrogenation-dehydrogenation function and are adsorbed on the acidic surface of the catalyst as carbonium ions by proton addition. After skeletal isomerization they are desorbed as isoolefins and subsequently hydrogenated to the corresponding isoparaffins. The net result (i.e., the formation of carbonium ions) of the action of metal and acid in dual function catalysis is, on pure Friedel-Crafts type catalysts, described by the scheme ... 

Description DCC is a fluidized process to selectively crack a wide variety of feedstocks into light olefins. Propylene yields over 24 wt% are achievable with paraffinic feeds. A traditional reactor/regenerator unit design uses a catalyst with physical properties similar to traditional FCC catalyst. The DCC unit may be operated in two operational modes maximum propylene (Type I) or maximum iso-olefins (Type II). Each operational mode utilizes unique catalyst as well as reaction conditions. DCC maximum propylene uses both riser and bed cracking at severe reactor conditions, while Type II utilizes only riser cracking like a modern FCC unit at milder conditions. 

Description DCC is a fluidized process to selectively crack a wide variety of feedstocks into light olefins. Propylene yields over 24 wt% are achievable with paraffinic feeds. A traditional reactor/regenerator unit design uses a catalyst with physical properties similar to tra-... 

Catalyst. The catalyst studied in this work was a platinum (0.205% wt) supported on an amorphous mesoporous silica-alumina, MSA (Si02/Al203=100) extrud with 50% wt alumina. The synthesis of the catalyst and the metal deposition procedure were described in detail [9]. A used catalyst, prepared as the former and containing 0.186% wt of Pt, was studied after the hydroisomerization of an n-paraffin feed containing 10 ppm S. 

Examples of the application of the process to naphthenic and paraffinic feeds are given in Table 9.8 and Table 9.9, respectively.3839 Even for the naphthenic... 

In the case of paraffinic feeds, very low pour point products were most economically obtained by using partially solvent dewaxed feedstocks (Table 9.9). It can be seen as well that these are all relatively light lubes. The advantage cited for this approach is that this can debottleneck the solvent dewaxing unit, where throughput becomes very limited when attempting to produce very low pour products. 

The variation in predicted weight percentage of various products as a function of overall conversion agreed well with the published experimental data. The reactor model developed was also able to predict that for an overall conversion of 10% then over 80% of the surface of the catalyst would be covered with adsorbed Cf, olefin carbenium ion). However, once sufficiently high quantities of product olefins had been formed, the model predicted that the surface would become dominated by product olefins because of their relatively high adsorption equilibrium constants compared to that of the paraffinic feed. 

The reaction temperature in DCC is higher than that of conventional FCC but much lower than that of steam cracking. Propylene yields over 20 wt% are achievable with paraffinic feeds. Ethylene yield is much higher than the conventional FCC process. The DCC-mixed C s stream also contains increased amounts of butylenes and iso-C s as compared to an FCC. The high olefin yields are achieved by deeper cracking into the aliphatic components of the naphtha and ECO. The dry gas produced from the DCC process contains approximately 50% ethylene. The cracking reactions are endothermic, and compared to FCC, a higher coke make is required to satisfy the heat balance. Table 1 summarizes typical olefins yields for DCC with FCC. 

Over the past twenty-five years the development of efficient catalysts for selective oxidation resulted in a new generation of commercial processes which utilize inexpensive olefinic and paraffinic feeds, replacing more reactive and costly raw materials. The catalysts are complex solid metal oxide systems which selectively activate hydrocarbons. Olefins, in particular, are activated via an allylie intermediate formation. The catalysts contain facile solid state redox couples which allow for efficient electron and lattice oxygen transport between reactant, adsorption and surface active site, and the surface reoxidation site which is then reconstituted by gaseous oxygen. 

Lower olefins are today produced by steam cracking of naphtha, LSR or other paraffinic feeds. Hie actual methanol price does not allow the methanol to olefins process to compete economically. However, if methanol will become more available firom natural gas transforming routes, then there is a great chance for that process to become commercial. 

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