Metals, content, feedstocks

Petroleos Mexicanos (PEMEX) licensed the process and built an LC-Fining unit at their Salamanca, Mexico refinery. This unit was designed to process 18,500 BPD of petroleum residua. The LC-Finer was started-up in September of 1973 and a successful performance test was completed in November of 1974. The PEMEX unit has been used to process very high metal content feedstocks (more than 300 ppm V and Ni) which are not feasible in competing technology such as fixed bed catalytic reactors. 

Residues containing high levels of heavy metals are not suitable for catalytic cracking units. These feedstocks may be subjected to a demetallization process to reduce their metal contents. For example, the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane, which separates the residue into an oil (with a low metal and asphaltene content) and asphalt (with high metal content). Demetallized oils could be processed by direct hydrocatalysis. 

The asphaltenes are selectively converted with a low hydrogen consumption decreasing significantly the metal content in the product. Catalyst was tested during a six-month period, processing various heavy feedstocks and showing a stable performance. The yields and product quality reported indicated almost complete conversion of the feed and total metal removal. The net effect of the ABC pretreatment was found to be an increase in catalyst life, higher metal quality of the product oil, and increase distillate yields. 

Reported residue conversion is significantly high for the five types of included reactors and largest for the slurry type of reactor. Besides, the slurry reactor together with the ebullated bed reactor can handle heaviest feedstocks and highest metal contents. Resid conversion requires higher temperatures, and pressure drop is essentially zero in these two reactors. However, product quality is better for the fixed and moving bed processes. 

RCC process catalysts with metals contents as high as 12,300 ppm nickel plus vanadium, plus 6,000 ppm of iron, have operated in the 200 B/D demonstration unit on feedstocks containing up to 84 ppm nickel plus vanadium.(4,5) Presently in our refinery, when metals levels are at still higher levels, the reduced crude is first processed in the Ashland ART unit, where some 85-95% of the metals and 75% of the Ramsbottom Carbon are removed.(6)... 

In the present context, heavy oils and residua can also be assessed in terms of sulfur content, carbon residue, nitrogen content, and metals content. Properties such as the API gravity and viscosity also help the refinery operator to gain an understanding of the nature of the material that is to be processed. The products from high-sulfur feedstocks often require extensive treatment to remove (or change) the corrosive sulfur compounds. Nitrogen compounds and the various metals that occur in crude oils will cause serious loss of catalyst life. The carbon residue presents an indication of the amount of thermal coke that may be formed to the detriment of the liquid products. 

Residua and heavy oils contain impurities other than sulfur, nitrogen, and oxygen, and the most troublesome of these impurities are the organometallic compounds of nickel and vanadium. The metal content of a residuum or heavy oil can vary from several parts per million (ppm) to more than 1000 parts per million (Table 6-15), and there does seem to be more than a chance relationship between the metals content of a feedstock and its physical properties (Reynolds, 1997 Speight, 1999). In the hydrodesulfurization of the heavier feedstocks the metals (nickel plus vanadium) are an important factor since large amounts (over 150 ppm) will cause rapid deterioration of the catalyst. The free metals, or the sulfides, deposit on the surface of the catalyst and within the pores of the catalyst, thereby... 

The Demex process is a solvent extraction demetallizing process that separates high metal vacuum residuum into demetallized oil of relatively low metal content and asphaltene of high metal content (Table 8-5) (Houde, 1997). The asphaltene and condensed aromatic contents of the demetallized oil are very low. The demetallized oil is a desirable feedstock for fixed-bed hydrodesulfurization and, in cases where the metals and carbon residues are sufficiently low, is a desirable feedstock for fluid catalytic cracking and hydrocracking units. 

Residua from various processes are the preferred feedstocks for the production of hydrogen-rich gases. Such fractions with high sulfur and/or high heavy metal contents are difficult to handle in upgrading processes such as hydrogenation or coking and, for environmental reasons, are not usually used as fuels without extensive gas clean up. 

The physical properties of a certain feedstock that determine the yields and product qualities include gravity, characterization factor, carbon residue, sulfur content and metals content. The last three properties are of specific importance. 

Metals Content. When producing coke for electrode or anode use, feedstock metals content must be reviewed relative to coke product specifications. As in the case of sulfur, metals tend to concentrate in the coke. 

The noble metal component may be either palladium or platinum the effect of the concentration of both metals on methylpentane as well as on dimethylbutane selectivity in C6 hydroisomerization on lanthanum and ammonium Y-zeolite with Si/Al of 2.5 has been studied by M.A. Lanewala et al. (5). They found an optimum of metal content for that reaction between 0.1 and 0.4 wt.-%. The noble metal has several functions (i) to increase the isomerization activity of the zeolite (ii) to support the saturation of the coke precursors and hence prevent deactivation, as was shown by H.W. Kouvenhoven et al. (6) for platinum on hydrogen mordenite (iii) to support the hydrodesulfurization activity of the catalysts in sulfur containing feedstocks. 

Through a series of round robin tests conducted by participating laboratories, ASTM Committee D-32 on Catalysts has characterized a variety of catalyst materials using standard test methods. Materials include fluid cracking catalysts, zeolites, silicas, aluminas, supported metals, and a gas oil feedstock. Properties characterized include surface area, crush strength, catalytic microactivity, particle size, unit cell dimensions and metal content. These materials are available from the National Institute of Standards and Technology as reference materials. 

The enhanced fouling rates and metal contamination (from the crude oil) generally makes atmospheric residua unsuitable as a cracker feedstock. However, some crude oils produce a waxy residual of low metal content (often referred to as low sulphur waxy residua, LSWR). Although more expensive than fuel oil, LSWR is considerably cheaper than gas oil and is an attractive feedstock for some gas oil cracker operations. 

The feedstock composition shows a large variety of products resulting from a great variety of treatments more or less toxic. The heavy metals content of our samples was determined (table 1). 

With wood waste, the feedstock characteristics (disposition in bulk, thick particles, low bulk density), lead to a very bulky bed. These conditions favour the rate of the pyrolysis process through a enhanced heat transfer and evacuation of the pyrolysis products. The loss of weight has been followed during the experiments. There are not much differences between the loss of weight for pyrolysis temperatures of 5S0 °C or 750 °C. In the fiiture, it would be interesting to perform such experiments with pyrolysis temperatures from 500 °C to 800 °C, in order to find the best appropriateness between the pyrolysis products quality and their heavy metals contents. 

Feedstock Characteristics. Several important feed characteristics considered in H-Oil desulfurization are (1) the character of the residuum, i.e., whether vacuum, atmospheric, deasphalter bottoms, cracked tars, or blends (2) the asphaltene and metal content (3) the sulfur level and degree of desulfurization required. These feed characteristics ultimately infiuence the selection of operating temperature, hydrogen partial pressure, space velocity, and catalyst type and usage. 

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