Hydrotreatment effects

Catalysts used in hydrotreatment (hydrodesulfurization, HDS) processes are the same as those developed in Germany for coal hydrogenation during World War II. The catalysts should be sulfur-resistant. The cobalt-molybdenum system supported on alumina was found to be an effective catalyst. 

In the reverse flow type, the hydrotreater reactor is fed with fresh and recycled feeds, and is operated to accomplish partial conversion of that combined feed in the first stage. A graded HDT-HCK bed or a multi-functional catalyst can be used in the first stage. A very effective H2 separation is used for the first-stage effluent gas. A bottoms fractionator or an adsorption unit is used for removal of heavy PAHs. Carbon adsorption extends the catalyst life. The liquid product of the first reactor is mixed with a mixture of fresh and recycled H2. The whole second stage effluent is hydrotreated in the first stage. 

The desulfurization process reported by the authors was a hybrid process, with a biooxidation step followed by a FCC step. The desulfurization apparently occurs in the second step. Thus, the process seems of no value, since it does not remove sulfur prior to the FCC step, but only oxidizes it to sulfoxides, sulfones, or sulfonic acids. The benefit of such an approach is not clearly outlined. The benefit of sulfur conversion can be realized only after its removal, and not via a partial oxidation. Most of the hydrotreatment is carried out prior to the FCC units, partially due to the detrimental effect that sulfur compounds exert on the cracking catalyst. It is widely accepted that the presence of sulfur, during the regeneration stage of the FCC units, causes catalyst deactivation associated with zeolite decay. In general terms, the subject matter of this document has apparent drawbacks. 

Consent decrees may specify hardware or additive solutions for individual applications. When a refiner agrees to implement a hardware solution, emissions limits are typically specified in the Consent Decree. This requires the refiner to design and implement an appropriately sized unit to meet these limits. With FCC additive solutions or hybrid solutions combining hardware and additives (such as a hydrotreater and SOj reduction additive), final emissions limits are not generally defined in the Consent Decree. Instead, a testing and demonstration program is defined to determine the performance of the additive(s) in the FCC unit at optimized concentrations. This may also be the case for some hardware solutions. The process to determine the optimized additive rate and process conditions is also identified. A baseline period and model is often used to determine additive effectiveness. A series of kick-out factors based upon additive performance are evaluated to determine the optimized level... 

Flue gas scrubbing also has high capital and operating costs associated with it, but also offers PM control. An additive-only solution is almost always the least expensive option when including both capital and operating expenses for SO, reduction depending on the feed sulfur. SO, reduction additives can also be effectively used in conjunction with one of the other solution options. For example, several refiners with FCC feed hydrotreaters use a SO, reduction additive to trim the SO, emissions to the required 25 ppm level rather than to hydrotreat the FCC feed more severely or to install a flue gas scrubber. The optimum choice for a given unit is often site specific. 

Two-Stage Hydrotreatment of Asphaltene in Australian Brown Coal Liquid Effects of Two-Stage Concept on Catalyst Deactivation (Changes of Catalyst Activations and Weight in the Repeated Runs")... 

Fig. 14. Effect of decationizing pretreatment on the liquefaction, (a I) First-stage noncata-lytic hydrogen-transferred Morwell coal in the two-stage hydrotreatment (4(X)°C-10 min, 20 atm N>, tube bomb and molten tin bath, rapid heating) 4HFI/coal = 3.0g/3.()g. (a2) Second-stage catalytic hydrotreated Morewell coal in the two-stage hydrotreatment (400°C-20 min, 50 cc autoclave, slow heating).

Figure 2. Effect of oil concentration in supercritical hydrotreatment of arabian topped crude.

Figure 3. Space velocity effects on supercritical hydrotreatment of shale oil.

Catalysts with a high loading of impregnated metals, such as Ni-Mo and Co-Mo on alumina hydrotreatment catalysts, necessarily suffer from matrix modifications with variations in metal content. As wc are not limited in this instance by the need to analyse trace elements, the solid phase dilution method can be used to attenuate the matrix effects. 

Several researchers have experimentally demonstrated the inhibiting influence of hydrogen sulfide (H2S) on HDS. This inhibiting influence is expected from simple and kinetic and equilibrium considerations. Refiners take great care to keep H2S in commercial hydrotreaters at an optimum level. For example, hydrogen—used in excess in a hydrotreater—is recirculated after scrubbing out the H2S by-product carefully. The recycle stream needs to contain an optimum level of H2S to keep the catalyst as a sulfide and thus maintain its activity and selectivity. Sie has described other process options to minimize inhibition effects by H2S, e.g., countercurrent flow reactors and monolithic catalyst systems. ... 

Wax isomerisation In principle, any of the existing processes for upgrading crude oil fractions such as hydrocracking, hydrotreatment and isomerisation can be used to convert the waxy hydrocarbons into useful base oils. Mild hydrotreatment can be useful for converting any olefins and alcohols but the preferred process makes use of isomerisation as hydrocracking tends to be used to produce GTL diesel fuel. The iso-de-waxing process described previously in Section 1.5.5 is particularly effective as is also the Shell Middle Distillate Synthesis process that combines hydrocracking and isomerisation over a dual-function catalyst. Typical conditions use a platinum catalyst on an alumina-silica support with a pressure of 30 bar and temperature of 350°C [35]. 

A schematic of the process developed for this program is shown in Figure 1. The crude shale oil is initially allowed to settle batchwise at above ambient temperature. This has been found to be effective in breaking the water/oil emulsion, thereby precipitating suspended water and ash to the bottom of the tank. The shale oil is also pumped through a 20 micron filter enroute to the hydrotreater to remove any entrained debris left in the tank. 

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