Carbon-12 formation

In H2 production from methane, carbon formation usually takes place in the form of fibres or whiskers, with a small Ni particle at the top of a fibre.5,6 Carbon formation may lead to the breakdown of the catalyst, and carbon deposits and degraded catalyst may cause partial or complete blockage of the reformer tubes. Uneven flow distribution is responsible for localised overheating of the hot tubes. Accordingly, carbon formation must be avoided in tubular reformers. There are two major reactions responsible for carbon formation  

Nickel carbide is not stable under SMR conditions. As a consequence, carbon nucleates in the form of whiskers after an induction period (tc), after which the carbon whisker grows at a constant rate  

The growth mechanism appears to be the same, irrespective of the hydrocarbon. However, the resulting morphology depends not only on the metal 

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A considerable amount of carbon is formed in the reactor in an arc process, but this can be gready reduced by using an auxiUary gas as a heat carrier. Hydrogen is a most suitable vehicle because of its abiUty to dissociate into very mobile reactive atoms. This type of processing is referred to as a plasma process and it has been developed to industrial scale, eg, the Hoechst WLP process. A very important feature of a plasma process is its abiUty to produce acetylene from heavy feedstocks (even from cmde oil), without the excessive carbon formation of a straight arc process. The speed of mixing plasma and feedstock is critical (6). 

Carbon produced by these latter reactions is formed in the catalyst pores, making it much more difficult to remove, and potentially causing physical breakage. Operating steam to carbon ratios are chosen above the minimum required in order to make carbon formation by these reactions thermodynamically impossible (3). Steam is another potential source of contaminants. Chemicals from the boiler feedwater or the cooling system are poisons to the reformer catalyst, so steam quality must be carefully monitored. 

The formation of carbon black in a candle flame was the subject of a series of lectures in the 1860s by Michael Faraday at the Royal Institution in London (23). Faraday described the nature of the diffusion flame, the products of combustion, the decomposition of the paraffin wax to form hydrogen and carbon, the luminosity of the flame because of incandescent carbon particles, and the destmctive oxidation of the carbon by the air surrounding the flame. Since Faraday s time, many theories have been proposed to account for carbon formation in a diffusion flame, but controversy still exists regarding the mechanism (24). 

Carbon dioxide can cause product contamination through ammonium carbonate formation. Ammonium carbonate may also form by oxidation of carbon monoxide by cupric ion (eq. 27) ... 

Acrylamide—polymer/Ct(III)catboxylate gel technology has been developed and field tested in Wyoming s Big Horn Basin (211,212). These gels economically enhance oil recovery from wells that suffer fracture conformance problems. The Cr(III) gel technology was successful in both sandstone and carbonate formations, and was insensitive to H2S, high saline, and hard waters (212). 

Commercial potassium cyanide made by the neutralization or wet process contains 99% KCN the principal impurities are potassium carbonate, formate, and hydroxide. To prepare 99.5 + % KCN, high quahty hydrogen cyanide and KOH must be used. 

Steam reforming is the reaction of steam with hydrocarbons to make town gas or hydrogen. The first stage is at 700 to 830°C (1,292 to 1,532°F) and 15-40 atm (221 to 588 psih A representative catalyst composition contains 13 percent Ni supported on Ot-alumina with 0.3 percent potassium oxide to minimize carbon formation. The catalyst is poisoned by sulfur. A subsequent shift reaction converts CO to CO9 and more H2, at 190 to 260°C (374 to 500°F) with copper metal on a support of zinc oxide which protects the catalyst from poisoning by traces of sulfur. 

In the steam reforming reaction, /rC02/p C0 = 2.08 (hr = 5.64) at this temperamre, and at lOOOK the results are hr A = 0.55 for carbon formation, and the PCO2/p CO ratio is 0.155 (hr A = 1.16), and tlrus the tendency for carbon formation passes from zero to unity in tlris temperature range. The presence of CO2 is not indicated in this reaction as given above, but its partial pressure can be obtained from data for the concunent reaction... 

Alkyl 4-Ethoxy-l-naphthyl Carbonate Formation/Cleavage ... 

By the mid-1930s, catalytic technology entered into petroleum refining. To a greater extent than thermal cracking, catalysis permitted the close control of the rate and direction of reaction. It minimized the formation of unwanted side reactions, such as carbon formation, and overall improved the yield and quality of fuel output. 

Lu has demonstrated that cyclic carbonate formation can dominate over polymer formation at much lower C02 pressures when the (salen)Co-OTs catalyst 24 and... 

Ethers and alcohols (m/z 31. 45, and 59)t Primary straight-chain alcohols Primary alcohols bonded at the y-carbon Formates... 

Two other components, methanol and benzene, were included in this study. Methanol is important in processes using Rectisol Systems for C02 removal prior to methanation. Benzene was considered in order to determine the effect of aromatics on catalyst activity and potential carbon formation. 

The methanation of synthesis gas occurs by Reactions 1 and 2 in the absence of carbon formation. With the given hydrogen carbon monoxide... 

There is no separate shift conversion system and no recycle of product gas for temperature control (see Figure 1). Rather, this system is designed to operate adiabatically at elevated temperatures with sufficient steam addition to cause the shift reaction to occur over a nickel catalyst while avoiding carbon formation. The refractory lined reactors contain fixed catalyst beds and are of conventional design. The reactors can be of the minimum diameter for a given plant capacity since the process gas passes through once only with no recycle. Less steam is used than is conventional for shift conversion alone, and the catalyst is of standard ring size (% X %= in). 

Various design and operating problems have been experienced by most developers of methanation systems. Specifically, carbon formation and catalyst sintering are two of the more common problems in methanation processes. Carbon formation refers to the potential production of carbon from carbon oxides and methane by the following reactions. 

The conditions favorable for carbon formation from these sources can be predicted by straightforward thermodynamic calculations. However, because a number of other chemical reactions can occur simultaneously and... 

Figure 3. Carbon formation Equilibrium isotherms (°F) at 30 psia...

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