Hydrotreating reactions

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

Hydrotreating is carried out by charging the feed to the reactor together with hydrogen at 300—345°C the hydrogen pressures are about 3450—6900 kPa (500—1000 psi). The reaction generally takes place ia the vapor phase but, depending on the appHcation, can also be a mixed-phase reaction. 

The breadth of reactions catalyzed by cobalt compounds is large. Some types of reactions are hydrotreating petroleum (qv), hydrogenation, dehydrogenation, hydrodenitrification, hydrodesulfurization, selective oxidations, ammonoxidations, complete oxidations, hydroformylations, polymerizations, selective decompositions, ammonia (qv) synthesis, and fluorocarbon synthesis (see Fluorine compounds, organic). 

The primary reactions occurring during hydrotreating are (43) desulfurization of sulfides, polysulftdes, mercaptans, and thiophene as exemplified by... 

Effect of HjS, Carbon Oxides, Etc. Hydrogen sulfide in the treat gas has an inhibiting effect on the kinetics of hydrotreating. Being a product of the desulfurization reactions, HjS must diffuse from the catalyst surface into the bulk gas stream. Any HjS present beyond that formed, further slows down the rate of diffusion with a consequent decrease in the amount of desulfurization for a given amount of catalyst. Therefore, additional catalyst would be required. 

Hydrotreating Technology for Pollution Control Catalysts, Catalysis, and Processes, edited by Mario L. Occelli and Russell Chianelli Catalysis of Organic Reactions, edited by Russell E. Malz, Jr. 

Hydrotreating was carried out at 3.1 MPa (450 psig) and 613 K (340 °C) in a three-phase upflow fixed-bed reactor (Figure 1). The feed liquid was prepared by combining different quantities of 1.0 wt% tetralin (Aldrich, 99%), 0.02 wt% N as quinoline (Aldrich, 99%), 0.05 wt% S as 4,6-dimethyldibenzothiophene (4,6-DMDBT, Fisher, 95%), 0.3 wt% S as dimethyldisulfide (DMDS, Aldrich, 99%), n-octane (Aldrich, 99%), and balance n-tridecane (Alfa Aesar, 99%). Liquid product compositions were determined with a Hewlett-Packard 5890A chromatograph equipped with a 50 m dimethylsiloxane colunm (Chrompack, CPSil 5B) of 0.32 mm i.d. Reaction products were identified by matching retention times with commercially available standards. 

Sulfided Mo and Co-Mo catalysts, used in hydrotreating reactions, contain Mo as M0S2. This compound has a layer structure consisting of sandwiches, each of a Mo layer between two S layers. The chemical activity of M0S2 is associated with the edges of the sandwich where the Mo is exposed to the gas phase the basal plane of the anions is... 

Hydrotreating has been proposed by Arbokem Inc. in Canada as a means of converting Grade Tall Oil into biofuels and fuel additives. However, this process is a hydrogenation process which produces hydrocarbons rather than biodiesel. Recently a process for making biodiesel from crude tall oil has been proposed. It relies on the use of an acid catalysts or of an acyl halide for the esterification reaction, but no information is given on the properties of this fuel, particularly concerning the oxidative stability. 

The aromatic hydrogenation reactions are reversible and at normal hydrotreating conditions, the equilibrium limits to achieve complete conversion. Low temperatures and higher pressures favor the aromatic saturation. The carbon atoms of a multi-ring system are hydrogenated in sequential steps, each one being equilibrium limited, as well. 

The increasing interest for HDN reaction is due to environmental push and business pull. The degradation of nitrogen compounds to ammonia and hydrocarbons consumes more hydrogen than any other hydrotreating reaction, and therefore any improvement in the efficiency of HDN catalysis would produce an immediate business advantage. 

Trickle-bed reactors are used in catalytic hydrotreating (reaction with H2) of petroleum fractions to remove sulfur (hydrodesulfurization), nitrogen (hydrodenitrogena-tion), and metals (hydrodemetallization), as well as in catalytic hydrocracking of petroleum fractions, and other catalytic hydrogenation and oxidation processes. An example of the first is the reaction in which a sulfur compound is represented by diben-zothiophene (Ring and Missen, 1989), and a molybdate catalyst, based, for example, on cobalt molybdate, is used ... 

If reaction (2-13) follows reaction (2-12) instantaneously, the effect will not be noticeable in the H2 signal [12]. In spite of these limitations, we conclude that TPS with mass spectrometric detection is a highly useful technique for studying the sulfidation of hydrotreating catalysts. We shall return to the sulfidation of molybdenum oxides in the chapters on photoemission (Chapter 3), ion spectroscopy (Chapter 4), and in a case study on hydrodesulfurization catalysts in Chapter 9. 

Before the molybdenum catalysts can be used in hydrotreating reactions, they have to be sulfided. Raman spectroscopy sensitively reveals this transition. The characteristic Mo-S frequencies of MoS2 are at 389 and 411 cm-1 [45,46], much lower... 

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

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