High Carbon Deposition Research Articles

Mechanism of High-Carbon Paraffin Deposition and Preventing Methods

The high-carbon paraffin in crude oil will deposit at a very high temperature, which disturbs oil production seriously, so the prevention and control of high-carbon paraffin becomes an important task. Because of the characteristic of high-carbon paraffin, the conventional wax removal and inhibition only plays a small part. Components and structure of the crude oil from Shengli, Tuha, and Kazakhstan PKKR are analyzed by methods of GC, 1H-NMR and so on; It is proved that the main reasons why high-carbon paraffin deposition is serious are low content of asphaltene and resin, high gas to oil ratio, and high-carbon paraffin contained in the crude. The paraffin inhibition mechanism is researched by microscope and contact angle instrument. It is found that the paraffin inhibitor can prevent paraffin crystal from forming 3D network structure by modifying its structure, and mitigate paraffin deposition by changing the wettability of paraffin deposition surface. At last, both paraffin inhibition effect and evaluation method are referred. The paraffin inhibiting rate for the crude oil with high-carbon paraffin is above 60%.

Molybdenum substitution by copper or zinc in H-ZSM-5 zeolite for catalyzing the direct conversion of natural gas to petrochemicals under non-oxidative conditions

This work aims to investigate the influence of substituting half the Mo content in a standard 6%Mo/H-ZSM-5 catalyst with either Cu or Zn in H-ZSM-5 support, on the direct conversion of methane in a flow-type fixed-bed reactor atmospherically at 700 °C at a gas hourly space velocity 1500 cm 3 h −1 g −1 and times-on stream (TOS) up to 240 min. The most active was 6%Mo/H-ZSM-5 catalyst while Mo–Zn/H-ZSM-5 was more active than Mo–Cu/H-ZSM-5. The XRD data showed that the crystallite (particle) sizes were found compatible with the catalytic activities. At the initial TOS (5 min), methane splitting selectivity to C and H 2 approached 100%. Higher carbon deposition on Mo–Cu catalyst caused more inhibition of ethylene further conversion to larger hydrocarbons thus leading to ethylene accumulation. TPR showed an almost complete reduction of Cu oxides at relatively lower temperatures such that the Mo–Cu catalyst acquired the highest dehydrogenation activity that enhanced markedly ethylene formation. An outstanding accomplishment is obtaining the highest benzene yield and selectivity using Mo–Zn/H-ZSM-5 catalyst, which is a prosperous challenge against the standard monometallic one. The large size of naphthalene molecule caused significant diffusion restriction on its formation in catalytic pores. The exceptional enhancement of naphthalene yield and selectivity at longer TOS using the Mo–Cu/H-ZSM-5 catalyst can be indicative that naphthalene was mostly formed on external zeolitic surface.

Effect of Exhaust Gas Recirculation (EGR) on performance, emissions, deposits and durability of a constant speed compression ignition engine

To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post-treatment techniques have been employed in modern engines. Exhaust Gas Recirculation (EGR) is a pre-treatment technique, which is being used widely to reduce and control the oxides of nitrogen (NOx) emission from diesel engines. EGR controls the NOx because it lowers oxygen concentration and flame temperature of the working fluid in the combustion chamber. However, the use of EGR leads to a trade-off in terms of soot emissions. Higher soot generated by EGR leads to long-term usage problems inside the engines such as higher carbon deposits, lubricating oil degradation and enhanced engine wear. Present experimental study has been carried out to investigate the effect of EGR on soot deposits, and wear of vital engine parts, especially piston rings, apart from performance and emissions in a two cylinder, air cooled, constant speed direct injection diesel engine, which is typically used in agricultural farm machinery and decentralized captive power generation. Such engines are normally not operated with EGR. The experiments were carried out to experimentally evaluate the performance and emissions for different EGR rates of the engine. Emissions of hydrocarbons (HC), NOx, carbon monoxide (CO), exhaust gas temperature, and smoke opacity of the exhaust gas etc. were measured. Performance parameters such as thermal efficiency, brake specific fuel consumption (BSFC) were calculated. Reduction in NOx and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to have increased with usage of EGR. The engine was operated for 96h in normal running conditions and the deposits on vital engine parts were assessed. The engine was again operated for 96h with EGR and similar observations were recorded. Higher carbon deposits were observed on the engine parts operating with EGR. Higher wear of piston rings was also observed for engine operated with EGR.

Effect of NiO content in mesoporous NiO–Al 2O 3 catalysts for high pressure partial oxidation of methane to syngas

The effect of NiO content in mesoporous NiO–Al 2O 3 catalysts on stability of the catalytic activity was investigated for partial oxidation of methane to syngas under the reaction conditions at 650 °C and 1 MPa over the contact time range from 0.1 to 5 ms. Mesoporous/porous NiO–Al 2O 3 catalysts with a high BET surface area were prepared with NiO content of 3.7–75 wt%. From XRD patterns and TPR profiles observed in these catalysts before H 2 pretreatment, the presence of strong interactions between NiO and Al 2O 3 was indicated, which gave relatively small NiO particles in the catalysts. As results of activity tests conducted by changing the contact time from 5 ms to lower until the catalyst lost its oxidation activity, the order of the catalyst tolerance against oxidation of nickel active species on them was: NiO(75)–Al 2O 3 > NiO(40)–Al 2O 3 > NiO(90)–Al 2O 3 > NiO(11)–Al 2O 3. As results of long runs and TG–DTA analysis, NiO(40)–Al 2O 3 showed the stable activity without any carbon deposition after 24 h reaction. This is because the Ni particle size and dispersion are 5.9–7.1 nm and 10.8%, respectively, which are considered to be suitable to prevent both carbon deposition and oxidation of nickel species during reaction, while NiO(75)–Al 2O 3 with Ni particle size of 11.7–15.9 nm gave high carbon deposition after a long run. The Ni particle size of 10 nm was a borderline for carbon deposition under reaction conditions at 1 MPa.

High organic carbon deposition in the northern margin of the Aleutian Basin (Bering Sea) before the last deglaciation

High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bolling-Allerod[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO3 contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High Corg/N ratios and low δ13C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ15N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ15N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high Corg/N ratios and low δ13C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ15N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition.

H2-rich synthesis gas production over Co/Al2O3 catalyst via glycerol steam reforming

Alumina-supported cobalt catalyst has been employed in a fixed bed reactor for the direct production of synthesis gas from glycerol steam reforming. Physicochemical properties of the Co/Al2O3 catalyst were determined from N2 physisorption, H2 chemisorption, CO2 and NH3-temperature-programmed desorption measurements as well as X-ray diffraction analysis. Both weak and strong acid sites are present on the catalyst surface. The acidic:basic site ratio is about 6. Glycerol steam reforming gave relatively large H2:CO ratio (6 to 12) and near-stoichiometric values of H2:CO2 ratio (2 to 2.30) were obtained depending on feed composition (30 to 60 wt.% glycerol mixture). The glycerol consumption rate appeared to be a weak function of glycerol (0.1) and has 0.4 order with respect to the steam partial pressure. Increased glycerol partial pressure led to high carbon deposition (total organic carbon values of 20 to 24%). However, removal of the deposited carbon was essentially complete following a temperature-programmed oxidation (air)–temperature-programmed reduction (H2) scheme.

A comparative study between Co and Rh for steam reforming of ethanol

Rh and Co-based catalyst performance was compared for steam reforming of ethanol under conditions suitable for industrial hydrogen production. The reaction conditions were varied to elucidate the differences in reaction pathways on both catalysts. On Co/ZnO, CH4 is a secondary product formed through the methanation reaction, while it is produced directly by ethanol decomposition on Rh. The difference in the reaction pathway is shown to favor Co-based catalysts for selective hydrogen production under elevated system pressures (up to 15bar) of industrial importance. The carbon deposition rate was also studied, and we show that Co is more prone to coking and catalyst failure. However, the Co/ZnO catalyst can be regenerated, by mild oxidation, despite the high carbon deposition rate. We conclude that Co/ZnO is a more suitable catalyst system for steam reforming of ethanol due to the low methane selectivity, low cost and the possibility of regeneration with mild oxidation.

Alternative concept for SOFC with direct internal reforming operation: Benefits from inserting catalyst rod

AbstractMathematical models of direct internal reforming solid oxide fuel cell (DIR‐SOFC) fueled by methane are developed using COMSOL® software. The benefits of inserting Ni‐catalyst rod in the middle of tubular‐SOFC are simulated and compared to conventional DIR‐SOFC. It reveals that DIR‐SOFC with inserted catalyst provides smoother temperature gradient along the system and gains higher power density and electrochemical efficiency with less carbon deposition. Sensitivity analyses are performed. By increasing inlet fuel flow rate, the temperature gradient and power density improve, but less electrical efficiency with higher carbon deposition is predicted. The feed with low inlet steam/carbon ratio enhances good system performances but also results in high potential for carbon formation; this gains great benefit of DIR‐SOFC with inserted catalyst because the rate of carbon deposition is remarkably low. Compared between counter‐ and co‐flow patterns, the latter provides smoother temperature distribution with higher efficiency; thus, it is the better option for practical applications. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Bimetallic mesoporous materials for high yield synthesis of carbon nanotubes by chemical vapour deposition techniques

Mesoporous Fe-MCM-41, Zn-MCM-41 and Fe–Zn-MCM-41 molecular sieves were synthesized in various Si/metal ratios by the hydrothermal method. The synthesized materials were characterized by various physicochemical techniques such as XRD, N 2 adsorption–desorption isotherm, TGA, DRS-UV spectroscopy, SEM and TEM. The catalytic activity of monometallic Fe-MCM-41, Zn-MCM-41 and bimetallic Fe–Zn-MCM-41 molecular sieves was tested and optimized for the maximum yield of carbon nanotubes (CNTs) by decomposition of acetylene (C 2H 2) at 700–900 °C. The deposited carbon materials were purified and characterized by XRD, SEM, TEM and Raman spectroscopy techniques. The purified samples show the presence of well-graphitized SWNTs over the bimetallic Fe–Zn-MCM-41 (3:1) molecular sieve. It was found that Fe–Zn-MCM-41 in the ratio of 3:1 (Fe:Zn) contains an optimum amount of metal to form metallic clusters, which in turn leads to the formation of CNTs with higher carbon deposition. The diameters of the carbon nanotubes are in the range of 1.2–2.5 nm, which was revealed by the Raman spectroscopy. This study shows that the bimetallic Fe–Zn-MCM-41 mesoporous molecular sieve as a promising catalytic template with good thermal stability and high productivity for the synthesis of CNTs.

Effect of Ni content on hydrogen production via steam reforming of methane over Ni/GDC catalysts

Steam reforming of methane was studied over gadolinia-doped ceria (GDC) supported Ni catalysts. The Ni content was varied from 1 to 10 wt% and the molar ratio of H2O to CH4 in the feed was 2. A Ni content of about 5 wt% leads to the highest formation rates of both hydrogen and CO2. Over 1 wt% Ni/GDC catalyst at 700°C, the hydrogen yield equals almost 4 for complete CO2 formation. Increasing the Ni content leads to decreasing hydrogen yield. A Ni content of about 5 wt% or lower is beneficial for high CO2 selectivity and low carbon deposition associated with high methane conversion. Increased Ni content results in larger Ni particle size and increased carbon deposition.

Experimental investigations of heavy metal addition in lubricating oil and soot deposition in an EGR operated engine

Exhaust gas recirculation (EGR) is a technique, which is being used widely to reduce and control the NO x emissions from diesel engines. However, the use of EGR leads to rise in soot emission because of soot–NO x trade-off. This EGR generated soot leads to several other problems inside the engine like degradation of lubricating oil, enhanced engine wear etc. In the present study, an experimental investigation has been carried out to evaluate the effect of EGR on characteristics of lubricating oil with time of its usage. A two cylinder, air cooled, constant speed direct injection diesel engine of 9 kW rating was used for conducting the experiments. The experiments were conducted in two phases for a comparative study on the normally operated engine (i.e. without EGR) and the engine operated with EGR for 96 h in each phase. Lubricating oil samples were collected after every 24 h interval and were analysed for soot loading (total carbon content) and various metal addition due to wear of the engine. Higher metal contents were found in the lubricating oil drawn from the engine using EGR. Higher carbon deposits were also observed on vital parts of the engine operating with EGR.

Turgor, solute import and growth in maize roots treated with galactose

It has been observed that extension growth in maize roots is almost stopped by exposure to 5 mm d-galactose in the root medium, while the import of recent photoassimilate into the entire root system is temporarily promoted by the same treatment. The aim of this study was to reconcile these two apparently incompatible observations. We examined events near the root tip before and after galactose treatment since the tip region is the site of elongation and of high carbon deposition in the root. The treatment rapidly decreased root extension along the whole growing zone. In contrast, turgor pressure, measured directly with the pressure probe in the cortical cells of the growing zone, rapidly increased by 0.15 MPa within the first hour following treatment, and the increase was maintained over the following 24 h. Both tensiometric measurements and a comparison of turgor pressure with local growth rate demonstrated that a rapid tightening of the cell wall caused the reduction in growth. Single cell sampling showed cell osmotic pressure increased by 0.3 MPa owing to accumulation of both organic and inorganic solutes. The corresponding change in cell water potential was a rise from -0.18 MPa to approximately zero. More mature cells at 14 mm from the root tip (just outside the growing region) showed a qualitatively similar response.

A Model for Early Diagenetic Processes in Sediments of the Continental Shelf of the Black Sea

A numerical model for early diagenetic processes in the sediments of the north-western continental shelf of the Black Sea is presented. The north-western shelf area is influenced by nutrient, organic matter and reactive iron inputs from major rivers such as the Danube, Dnieper and Dniester. Low oxygen concentrations in the bottom water and high carbon deposition rates have resulted in a dominance of anoxic mineralization processes including manganese, iron and sulphate reduction. The model includes six solid phase variables (labile and less labile organic carbon, iron-and manganese oxides, iron monosulphide and pyrite) and eight solutes (oxygen, nitrate, ammonium, manganese, ferrous iron sulphate, hydrogen sulphide and methane). The cycling of iron and sulphur is explicitly incorporated in the model since these elements play an important role in the mineralization of organic matter on the continental shelf. The model is capable of performing both steady state and dynamic simulations and can be coupled to biogeochemical models for water-column processes. The output of the model is composed of depth profiles of the state variables and their biogeochemical reaction rates and fluxes of the solute substances across the sediment–water interface. The model has been applied to solid-phase and porewater data from a station near the Danube delta. A steady state stimulation reasonably reproduced the main features, but not the distribution of iron and the concentrations of oxygen and total organic carbon in the first 2 cm. A dynamic simulation revealed that a pulse flux of organic matter resulting from the spring bloom could be responsible for the deviation from steady state in the near-surface distribution of total organic carbon and oxygen. The effect of carbon loading on organic matter degradation pathways has been investigated. There is a gradual increase in the relative importance of anoxic mineralization pathways as carbon loadings increase, but the transitions from manganese-based respiration to iron-based respiration and from iron-based respiration to sulphate reduction are rather abrupt. The first jump is due to the positive feedback between manganese reduction coupled to ferrous iron oxidation and iron oxide reduction. The second swap is due to the formation of iron sulphides. This will consume part of the reduced iron, which is consequently not available for re-oxidation to iron oxide, and the iron-reducing bacteria become iron-oxide limited. The cycling efficiency of iron changes abruptly, and a larger part of the iron will be fixed as iron sulphides.

Organic carbon deposition on the North Carolina continental slope off Cape Hatteras (USA)

Abstract The continental slope off Cape Hatteras, NC is a region of high sediment accumulation and organic matter deposition. Sediment accumulation rates range from 3 to 151 cm kyr−1. Organic carbon deposition rates are 5–13 moles C m−2 yr−1, the highest reported for the slope off the eastern US. Burial efficiencies are 3–40%. The organic matter deposited is marine in origin and a mix of old and young particles. High organic carbon deposition rates support remineralization throughout the upper 2–3 m of sediment. Deep bioirrigation to depths of 60–100 cm within the seabed affects the biogeochemistry of the sediments by extending the zone of sulfate reduction and by steepening DIC porewater gradients through the non-local exchange of porewater. Stable and radiocarbon isotope mixing curves for porewater dissolved inorganic carbon (DIC) indicate that the dominant source of DIC accumulating in the upper 2–3 m of the seabed is of nearly uniform δ13C (−21.10‰) and Δ14C (−546‰).

An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas

Today only a small percentage of methane is used as a chemical feedstock to produce syngas that is a valuable feedstock for the production of higher hydrocarbons or methanol. Currently, the process extensively used in industry for the production of syngas is the steam reforming of methane in large furnaces. The reaction is industrially operated under strong conditions resulting in several undesirable consequences: sintering of the catalyst, danger of explosion, very high carbon deposition and the use of high-temperature resisting materials. A potential alternative technique to steam reforming processes for producing syngas is the partial oxidation of methane with oxygen, having over steam reforming the disadvantage that pure oxygen is required. Utilisation of air instead of pure oxygen is beneficial only if it can be performed by using a membrane reactor in which the membrane is permselective to oxygen. Another route to produce syngas using the partial oxidation of methane is offered by membrane reactors, i.e. engineering systems that combine the separation properties of membrane with the typical characteristics of catalytic reactions. It is well known that the use of dense palladium as membrane enables hydrogen product to permeate out through the membrane, shifting thereby conversions towards the values higher than thermodynamic equilibrium ones and providing pure hydrogen product. In fact, only hydrogen is allowed to permeate through dense palladium membranes. In this work five reactors are investigated with respect to the partial oxidation of methane. In particular, the performance of a traditional reactor (TR), three composite ceramic palladium membrane reactors (MRa, MRb and MRc), and a dense palladium membrane Reactor (PMR), all having the same geometrical dimensions and using the same Ni-based catalyst, are evaluated in terms of experimental results of methane conversion to syngas and in terms of hydrogen selectivity. A comparison between methane conversion at various temperatures and data in literature is also presented.

Cyclohexane oxidation and carbon deposition over metal oxide catalysts

Catalytic activity of V, Mn, Ni, Cu, Zn, Mo, Zr and Ce oxides over an α-alumina support was evaluated for cyclohexane oxidation under oxygen deficient conditions in order to understand the relation between carbon deposition and catalytic activity/selectivity. Carbon formation over the catalysts during the oxidation reaction was measured by means of Fourier transformed infrared spectroscopy (FTIR). Catalysts Mn/Al 2O 3 and Ce/Al 2O 3, which are selective for deep oxidation of cyclohexane, possessed relatively carbon free surfaces. The catalysts with relatively high carbon deposition (V, Ni, Cu, Zn, Mo and Zr) produced CO in addition to CO 2. Traces of formaldehyde were produced over the catalysts Mo and V.

High temperature corrosion and carbon deposition phenomena on stainless steels

Depending on their history and composition, stainless steels can develop two types of protective oxide scale, comprising either a thin layer of chromium oxide or a more complex layer with the spinel structure. Both these types of scale are found in the heat exchangers of nuclear reactors cooled by carbon dioxide. Moreover, the type of scale has been found to correlate with deposition of carbon. The reason for these variations and the means by which equilibrium thermochemistry can be applied to a system that is very far from equilibrium are considered in the present paper.MST/2019

Studies of pelagic-benthic coupling extended onto the Soviet continental shelf in the northern Bering and Chukchi seas

Studies of pelagic-benthic coupling and benthic carbon cycling in the northern Bering and Chukchi seas were extended onto the Soviet continental shelf as part of the third U.S.A.-U.S.S.R. Oceanographic Expedition to the Bering and Chukchi seas in 1988. High sediment oxygen uptake rates (an indicator of food supply to the benthos) and benthic biomass were observed in the western shelf regions of the Gulf of Anadyr, Chirikov Basin and southern Chukchi Sea. Low sediment respiration and faunal biomass were observed in the central and slope areas of the Gulf of Anadyr and near the Alaska coastline. Both high sediment respiration and benthic biomass were related to regions of high carbon deposition to the benthos and sediment organic carbon content. Preliminary studies of sediment accumulation, measured using organic carbon content and atmospherically-derived 210Pb values in surface sediments, were low in the sandy regions of the northern Bering Sea, with higher sediment accumulation zones occurring in the silt and clay regions in the central Gulf of Anadyr and southern Chukchi Sea. Hydrodynamics have a major influence on organic carbon loading and sediment composition, which in turn influences benthic community structure, biomass and sediment respiration in this Arctic region.