Hydrocarbon Partial Pressure Research Articles

A Review on Production of Light Olefins via Fluid Catalytic Cracking

The fluid catalytic cracking (FCC) process is an alternative olefin production technology, with lower CO2 emission and higher energy-saving. This process is used for olefin production by almost 60% of the global feedstocks. Different parameters including the operating conditions, feedstock properties, and type of catalyst can strongly affect the catalytic activity and product distribution. FCC catalysts contain zeolite as an active component, and a matrix, a binder, and a filler to provide the physical strength of the catalyst. Along with the catalyst properties, the FCC unit’s performance also depends on the operating conditions, including the feed composition, hydrocarbon partial pressure, temperature, residence time, and the catalyst-to-oil ratio (CTO). This paper provides a summary of the light olefins production via the FCC process and reviews the influences of the catalyst composition and operating conditions on the yield of light olefins.

Initiation of Carbon Nanofiber Growth on Polycrystalline Nickel Foam under Low Ethylene Pressure

AbstractThe initiation of carbon nanofiber (CNF) growth on polycrystalline Ni foam was investigated by using a combination of ex situ and in situ methods, which include SEM, XRD, and Raman spectroscopy. Experiments were performed at a low hydrocarbon partial pressure to slow down the initiation process. Very little to no CNFs were observed on reduced samples, which is caused by diffusion of C to the bulk of the Ni foam. This prevents the formation of Ni3C as a precursor of Ni nanoparticles at a low hydrocarbon partial pressure from acting as active particles for CNF formation. CNF growth was significant on oxidized samples and the initiation was slowed down by using an extremely low ethylene pressure. Ni nanoparticles are able to catalyze CNF growth, provided these are isolated from the Ni bulk by unreduced NiO, which results from the incomplete reduction of the NiO layer.

Understanding zeolite-catalyzed benzene methylation reactions by methanol and dimethyl ether at operating conditions from first principle microkinetic modeling and experiments

In methanol-to-hydrocarbon chemistry, methanol and dimethyl ether (DME) can act as methylating agents. Therefore, we focus on the different reactivity of methanol and DME towards benzene methylation in H-ZSM-5 at operating conditions by combining first principles microkinetic modeling and experiments. Methylation reactions are known to follow either a concerted reaction path or a stepwise mechanism going through a framework-bound methoxide. By constructing a DFT based microkinetic model including the concerted and stepwise reactions, product formation rates can be calculated at conditions that closely mimic the experimentally applied conditions. Trends in measured rates are relatively well reproduced by our DFT based microkinetic model. We find that benzene methylation with DME is faster than with methanol but the difference decreases with increasing temperature. At low temperatures, the concerted mechanism dominates, however at higher temperatures and low pressures the mechanism shifts to the stepwise pathway. This transition occurs at lower temperatures for methanol than for DME, resulting in smaller reactivity differences between methanol and DME at high temperature. Our theory-experiment approach shows that the widely assumed rate law with zeroth and first order in oxygenate and hydrocarbon partial pressure is not generally applicable and depends on the applied temperature, pressure and feed composition.

Dual Role of Hydrogen in Low Temperature Plasma Enhanced Carbon Nanotube Growth

The gas composition during carbon nanotube (CNT) growth has received much attention because it largely determines the properties of the nanotubes and the yield of the growth. Here, we investigated the influence of hydrogen to hydrocarbon ratio on the CNT growth at low temperatures (<500 °C) using plasma-enhanced chemical vapor deposition (PECVD). Hydrogen was found to have a dual role during the growth process on TiN using catalytic nickel or cobalt nanoparticles. On the one hand, when the ratio of hydrogen to hydrocarbon partial pressure was low, CNT growth terminated well before the total process duration. As a result, no CNT growth was observed without hydrogen added to the gas mixture. The growth process could not be prolonged or reactivated upon performing in situ reducing or oxidizing cycles. On the other hand, when [H2]/[C2Hx] was high, catalyst dependent etching of the CNT forest occurred. For nickel catalyzed CNT growth, the high relative hydrogen content resulted in etching of the CNT forest, wh...

Maximizing propylene production via FCC technology

This review looks at the main processes available for the production of light olefins with a focus on maximizing the production of propylene. Maximization of propylene production has become the focus of most refineries because it is in high demand and there is a supply shortage from modern steam crackers, which now produce relatively less propylene. The flexibility of the fluid catalytic cracking (FCC) to various reaction conditions makes it possible as one of the means to close the gap between supply and demand. The appropriate modification of the FCC process is accomplished by the synergistic integration of the catalyst, temperature, reaction-residence time, coke make, and hydrocarbon partial pressure. The main constraints for maximum propylene yield are based on having a suitable catalyst, suitable reactor configuration and reaction conditions.

MFI and FAU-Type Zeolites as Trapping Materials for Light Hydrocarbons Emission Control at Low Partial Pressure and High Temperature

The adsorption of light hydrocarbons (C2–C5 olefins and paraffins, toluene) on HZSM-5, silicalite, and HY was studied for application in treatment of exhaust streams of the petrochemical industry and of vehicles under cold start conditions. At this aim the trapping capability was evaluated on hydrated zeolites by breakthrough curves at low hydrocarbon partial pressure (0-1 kPa), in the temperature range 298–523 K and at space velocity of 30000 h−1. The basic adsorption properties of materials were also verified for three selected hydrocarbons (ethylene, isobutene, and toluene) by equilibrium isotherms on dehydrated zeolites at 298 K. The role of physicochemical characteristics of adsorbent materials was discussed in relation with their trapping capability of different types of hydrocarbons.

Influence of partial pressure on base-growth of single carbon nanotube

Influence of hydrocarbon partial pressure on single carbon nanotube (CNT) growth in chemical vapor deposition is investigated by a new theoretical model based on kinetic theory of gases and, phonon vibrations of carbon nanotube on catalyst. Results show that CNTs with larger diameter grow lesser owing to higher damping factors and CNT inertia. In addition, an optimum temperature for the growth is obtained for a CNT with a specific diameter and catalyst. Also it is shown that the optimum temperature is changed by using different catalysts. Finally effect of the partial pressure on the growth is also discussed. It is demonstrated that increasing partial pressure leads to the longest CNTs and also, influence of partial pressure on CNTs with smaller diameters is stronger. All results of the presented mechanism are in good agreement with reported experimental results.

Adsorption of Light Hydrocarbons on LTA and FER Zeolites

This paper reports the results of an experimental study on adsorption of light hydrocarbons on small pore microporous materials. The choice of hydrocarbons studied was affected taking into consideration the application of adsorption processes in removal of light hydrocarbons from exhaust streams of the petrochemical industry and of light-duty gasoline vehicles under cold start conditions (C4-C5 paraffins and olefins). The materials investigated were 5A and Ferrierite zeolites, characterized by different pore opening and Si/Al ratio. Equilibrium isotherm curves at room temperature were determined by a gravimetric method on dehydrated zeolites, while breakthrough curves in dynamic tests were used to evaluate the adsorption properties of hydrated zeolites at low hydrocarbon partial pressure (0-1 kPa) and in experimental conditions close to those of a HC trap at the engine exhaust. The experimental results regarding the adsorption capacities were discussed with the aim to understand how the physico-chemical characteristics of the adsorbent material could affect its trapping capability in adsorbing different types of hydrocarbons.

Influence of in Situ Steam Formation by Radio Frequency Heating on Thermodesorption of Hydrocarbons from Contaminated Soil

Thermal desorption of a wide spectrum of organic contaminants, initiated by radio frequency (RF) heating, was studied at laboratory and pilot-plant scales for an artificially contaminated soil and for an originally contaminated soil from an industrial site. Up to 100 °C, moderate desorption rates were observed for light aromatics such as toluene, chlorobenzene, and ethylbenzene. Desorption of the less volatile contaminants was greatly enhanced above 100 °C, when fast evaporation of soil-water produced steam for hydrocarbon stripping (steam-distillation, desorption rates increased by more than 1 order of magnitude). For hydrocarbons with low water solubility (e.g., aliphatic hydrocarbons), the temperature increase above 100 °C after desiccation of soil again led to a significant increase of the removal rates, thus showing the impact of hydrocarbon partial pressure. RF heating was shown to be an appropriate option for thermally enhanced soil vapor extraction, leading to efficient cleaning of contaminated soils.

Study on the technology of thermal cracking of paraffin to alpha olefins

Alpha olefins are mainly produced from paraffin cracking in China, but their quality is not good because of bad quality of cracking feed and outdated technology. The technology of paraffin once-through cracking, paraffin recycle cracking of removing the heavy fraction after wax vaporizing and that of removing the heavy fraction before wax vaporizing were investigated in this paper. It was found that the technology of paraffin recycle cracking of removing the heavy fraction before wax vaporizing is new and better under the same operating conditions. Using hard paraffin (mp 54–56 °C) as feed, the high-quality alpha olefins products (C 5–C 21) containing more than 97 wt% of olefins and more than 88 wt% of alpha olefins are produced under optimum process conditions, which are a steam to paraffin ratio of 15 wt%, process temperature of 600 °C, low hydrocarbon partial pressure and residence time of 2 s. In addition, with the technology of the second injecting steam in ethylene cracking used in paraffin cracking, producing coke in paraffin cracking furnace has been markedly reduced.

Formation of Carbon and Hydrogen from Lower Hydrocarbons in a Packed Bed of Nickel-plated Alumina Balls.

This study is a starting point for creating a new plastic recycling process. The process consists of two spouted bed reactors. In the first reactor, plastic chips are fed and instantaneously thermally decomposed into lower hydrocarbons (gas or vapor). In the second reactor, the hydrocarbons are further decomposed into carbon and hydrogen. Carbon can be utilized as carbon black, activated carbon and so forth. Hydrogen is a useful and clean fuel (no carbon dioxide evolution) and a raw chemical material. In this study, the decomposition of hydrocarbons (methane, ethane, propane, ethene and propene) was investigated to obtain basic data for the second reactor of the process. The hydrocarbons were decomposed in a fixed bed flow reactor packed with 1-mm-diameter α-alumina balls or 1-mm-diameter nickel-plated α-alumina balls, which were used as a decomposition catalyst. Carbon and hydrogen were the main products. The nickel-plated α-alumina balls gave a higher hydrogen production rate than the unplated α-alumina balls. This is caused by the dehydrogenation activity of nickel. For alkanes, the higher the carbon number, the greater the hydrogen production rate. For alkenes, a similar tendency was observed. The hydrogen production rate showed positive temperature dependency and positive hydrocarbon partial pressure dependency. The results obtained in this study showed that production of hydrogen and carbon is possible using the second reactor of the process we proposed.

Selective catalytic reduction of NO under lean conditions by methane and propane over indium/cerium-promoted zeolites

The potential of zeolites MFI and MOR promoted by In and Ce as catalysts for the SCR of NOx by methane and propane was studied, particularly considering their stability in the presence of water vapour. A preparation route for a zeolite-based Ce/In composite catalyst was developed and the influence of several reaction conditions was studied to optimise the catalyst performance. TPR and FTIRS were used to check the preparation steps and to investigate the catalyst structure. These data were used together with results from characterisation by X-ray-based techniques to describe the generation and catalytic function of different indium species ((InO)+, In2O3 cluster) and their co-operation with ceria in the composite catalyst. The primary role of the CeOx promoter is to catalyse the oxidation of NO to NO2. Probably, NO2 reacts with methane on Lewis-acidic and redoxactive (InO)+ species, but the further reaction of the intermediate formed needs the presence of residual Brønsted-acid sites. SCR of NOx by methane or propane is still partially inhibited by adsorption competition between water and the hydrocarbons on the (InO)+ species. Higher SCR activity could be achieved by increased hydrocarbon partial pressure in the feed, shifting presumably the competitive adsorption to enhanced adsorption of methane and propane, respectively. Furthermore, combining of methane and propane as reductants opens an opportunity to broaden the ‘temperature window’ for the SCR of NOx. Different influence of hydrothermal ageing was obtained with methane and propane, respectively, as reducing agent.

Dilution effect of the feed on yield of olefins during catalytic cracking of vacuum gas oil

A vacuum gas oil has been co-fed with nitrogen at different partial pressures in a microacitivity (MAT) unit. The cracking rate versus hydrocarbon partial pressure can be fitted to a first-order kinetic rate equation. On the other hand, hydrogen transfer reactions, which follow second-order kinetics, are more affected than conversion by the decrease in hydrocarbon partial pressure, resulting in an increase in the yield of propylene and in general of LPG olefins. The decrease in conversion, due to the lowering of hydrocarbon partial pressure, could be compensated by a mechanical mixing effect introduced by the dilution gas that improves feed vaporization and mixing. It will be shown that a MAT unit can be used to show both effects separately, i.e. feed dilution and feed dispersion.

Non-isothermal Modelling of Hydrocarbon Adsorption on A Granulated Active Carbon

The adsorption of n -butane on extruded cylindrical activated carbon grains is studied providing two kinds of information: the influence of the temperature and the hydrocarbon partial pressure on the adsorption dynamics (kinetic study) and on the adsorption capacities (thermodynamic study). The thermodynamic aspect could be interpreted by a Langmuir model. From a kinetic point of view, we have experimentally proved that strong temperature variations occur inside the particles during the adsorption. In this paper, a kinetic model including both mass and heat transfer phenomena is proposed. Good agreement is found between the kinetic model predictions and the experimental mass and temperature variations inside the grain during the hydrocarbon adsorption.

Synthesis of Multiwalled Carbon Nanotubes

ABSTRACTIn a recent publication we have described the synthesis of multiwalled carbon nanotubes (MWNTs) by the reaction of a hydrocarbon vapor over a dispersed iron catalyst that is deposited in situ on quartz substrates. Our system configuration involves entraining a mixture of xylene and ferrocene into an inert gas stream. Decomposition of the ferrocene at temperatures in the range 625-775 °C, and at atmospheric pressure, produces a coating of iron nanoparticles on the quartz surfaces, and these metal sites function as catalysts for the formation and growth of MWNTs. In this study, we report the influence of operating conditions on MWNT purity and yield. These parameters include the feed injection temperature, furnace temperature, hydrocarbon partial pressure, reaction time, space velocity, and iron to carbon ratio in the feed. We observed that the quality of the MWNTs dependc sensitively on the growth parameters and a window for the operating conditions is identified for the growth of high purity aligned MWNTs. Characterization of the MWNTs by electron microscopy has shown that there is a relationship between metal particle size and MWNT diameter.

Adsorption of n-Alkanes on Silicalite Crystals. A Temperature-Programmed Desorption Study

The adsorption mechanism of n-alkanes on silicalite has been studied by a modified temperature-programmed desorption (TPD) technique. These experiments are performed by thermogravimetry at constant hydrocarbon partial pressure and at slow heating rate. This work establishes the reversibility of the adsorption equilibrium, and it is demonstrated that TPD experiments occur under conditions that are very close to equilibrium. A quasi-chemical approach taking into account different adsorption sites provides a good modeling of the TPD curves. Sorption enthalpy and entropy variations of n-alkanes are obtained. The sorption data for n-butane to n-octane are in good agreement with adsorption literature data. Moreover, they provide relevant information on the adsorption mechanism and show that entropic effects are predominant.

On the Transition State between the Oil−Water and Air−Water Interface

Insoluble monolayers at the air-water interface are exposed to a gas phase containing organic hydrocarbons. The hydrocarbons are partly incorporated within the monolayer which leads to changes in orientational order and the formation of new phases of different morphology. The transition state resembles features of the air-water and oil-water interface and the control of the hydrocarbon partial pressure allows continous tuning between both interfaces. The phospholipid D,L-α-dipalmitoylphosphatidylethanolamine, DPPE, and an esterdiol hexadecanoic acid, 2,3-dihydroxypropyl ester, ESD-16, are used as amphiphiles, and pentane, n-hexane, cyclohexane, 2,2-dimethylbutane, n-heptane, n-decane, and n-dodecane are used as hydrocarbons. Both amphiphiles differ in their headgroup size. In DPPE the aliphatic tail determines the packing within the monolayer, but in the case of ESD-16 it is the headgroups. The structural changes are monitiored by surface pressure-area (π,A) isotherms and imaging ellipsometry. The influence of the chemical nature of the hydrocarbon and the effect of the partial pressure of the hydrocarbon on the monolayer structure are assessed.

Effect of the reaction temperature and hydrocarbon partial pressure on the activity of carbon-modified MoO 3 for n-hexane isomerization

The isomerization of n-hexane on MoO 3 leads to the formation of a new catalytically active phase, molybdenum oxycarbide, that exhibits high and stable activity and isomer selectivity with time on stream under soft reaction conditions. The study as a function of the reaction temperature shows that too low a temperature prevents the MoO 3 transformation, while too high a temperature prevents the development of the MoO xC y phase to the benefit of a surface carbide phase. For variable n-hexane partial pressure the same trend is observed with the appearance of carbonaceous and carbide species with higher partial pressure, which are not active for the isomerization.

Nucleation and Void Formation Mechanisms in SiC Thin Film Growth on Si by Carbonization

The nucleation mechanisms for thin films on Si were investigated by interrupting the growth at very brief times (∼1 to 10 s) using rapid thermal chemical vapor deposition in conjunction with hydrocarbon carbonization. The resulting nuclei and films on Si have been studied by scanning electron microscopy and atomic force microscopy. The hydrocarbon partial pressure in the gas stream was found to determine the nucleation mode. Low precursor concentration results in initial three‐dimensional (island) growth which enables the study of trench and void formation. Voids were observed to initiate when two neighboring nuclei come in contact. Trenches in the Si substrate surround each isolated nucleus, with the trench depth increasing with the diameter of the island. films grown for a nominal reaction time of 1 s indicate that increasing the propane concentration results in decreases in grain size and surface roughness and an increase in the nuclei density. A model is proposed for the nucleation process of growth on Si by carbonization consisting of the following key steps (i) the initial nucleation density is determined by the precursor concentration; (ii) lateral and vertical growth of individual nuclei proceeds by consumption of Si atoms around their periphery, forming trenches in the substrate; (iii) Si voids are formed in the Si substrate near the interface when nuclei grow large enough to come in contact and, thus, restrict the supply of Si atoms.

Amorphous carbon antireflective coatings in the 10 to 50 μm region of the far-IR

The efficiency of far-IR germanium photoconductive detectors can be markedly improved by antireflective coatings. Recently, there has been an effort to develop several micrometer thick, low stress, amorphous carbon films for this purpose. To date, films of no more than 1 to 2 μm have been reported in the literature. In this paper we report the deposition of low stress carbon films which are over 5 μm thick and are effective antireflective coatings at wavelengths of up to Λ = 43 μm. Minimal stress, a requirement for good adhesion, was achieved with a chemical vapor deposition process (CVD) by controlling the hydrocarbon partial pressure (2.2 mTorr) and by doping the carbon film with nitrogen.