Non-catalytic Process Research Articles

Kinetic Aspects of Catalytic Interactions Involving Pentyl Acetate and Ethanolamine

A conversion scheme for pentyl acetate, ethanolamine, and the products resulting from their interaction through aminolysis, transesterification, and O-N-acyl migration reactions catalyzed by homogeneous and heterogeneous Brønsted-Lowry bases and acids is proposed. It has been determined that acid and base catalysts significantly enhance the aminolysis reaction of esters with amino alcohols when compared to the non-catalytic process. The impact of the catalyst on each reaction has been assessed.

Study on the differences between non-catalytic and catalytic oxidation of soot based on catalyst CeO2

Exploring the differences between soot non-catalytic and catalytic oxidation process is beneficial to enhance the catalyst performance and soot removal efficiency of catalytic diesel particulate filters. In this paper, the soot samples are pretreated under high temperature conditions at both non-catalytic and catalytic oxidation atmosphere to obtain target pretreated soot samples with different mass loss. Five typical oxidation stages are analyzed with corresponding soot mass loss rate of 15 %, 25 %, 50 %, 70 %, 85 %. The soot physicochemical properties including oxidation activity, porous structure, particle layer, nanostructure, graphitization and functional groups are explored; further, the correlations among these physicochemical properties are analyzed, and three levels of catalytic effect mechanism are proposed based on CeO2 catalyst. This paper helps in understanding the differences of the mechanisms between non-catalytic and catalytic oxidation of soot.

Understanding of the effect of oxygen on soot formation during non-catalytic partial oxidation process

Non-catalytic partial oxidation (NC-POX) process is a promising technology for hydrogen and syngas production, but the generation of soot hinders its development. In this study, the yields of soot and its precursors under different working conditions are quantified by experiments. When the O2/CH4 ratio is more than 0.6, the soot yield can be controlled below 1.07% from 2.53%. The soot precursor evolution mechanism in NC-POX is analyzed through the quantification of polycyclic aromatic hydrocarbon (PAH) compounds. It is found that hydrogen abstraction vinyl radical addition (HAVA*) and methyl addition cyclization (MAC) are the main growth pathways of PAHs. The concentrations of H2O, CO2, and oxygenated hydrocarbons increase with O2/CH4, which further inhibit the soot generation reactions and reduce the degree of graphitization of soot particles through surface reactions. A soot formation mechanism is proposed. This study provides a quantified reference for soot modeling and the elimination of soot in industry.

WAYS TO REDUCE CO<sub>2</sub> EMISSIONS AT THE CONVERSION OF NATURAL GAS INTO CHEMICAL PRODUCTS

One of the most realistic possibilities for reducing anthropogenic carbon dioxide emissions is its involvement as a feedstock in various processes for producing gas chemical products. First of all, it is advisable in the production of the largest-tonnage products, such as syngas, hydrogen and methanol. The paper considers the possibility of involving carbon dioxide in non-catalytic autothermal processes of the production of these products. A combined process for the production of methanol and hydrogen without CO2 emission based on the matrix conversion of natural gas into syngas is presented.

Enhancing CO2 desorption rate in rich MEA solutions by metal-modified attapulgite catalyst

To overcome the high energy consumption of the CO2-rich monoethanolamine (MEA) solution regeneration process, this study proposes to catalytically promote CO2 desorption using transition metal-modified attapulgite (ATP) composite catalysts (M/ATP, M = Ni, Zr) in a 5 M CO2-loaded MEA solution at 90 °C. The catalysts were characterized by XRD, FT-IR, BET, and Py-IR. The influences of different metals and metal salts on the activity of CO2 desorption for the ATP-based composite catalyst were studied. The findings proved that the introduction of metal oxide enhanced the activity of catalytic CO2 desorption for the ATP catalyst and reduced the relative energy requirement. Ni/ATP presented the superior catalytic activity, with an increase of 195 % and 144 % in the rate of CO2 desorption and desorption amount, respectively, compared with the noncatalytic desorption process. The excellent catalytic performance of metal-modified ATP composite catalysts was mainly due to the enhanced Brønsted acid sites. After 8 cycles of CO2 absorption–desorption experiment, the Ni/ATP catalyst still showed excellent stability. The introduction of the Ni/ATP catalyst had no adverse impact on the CO2 absorption in the MEA solution. Moreover, a possible catalytic MEA solution regeneration pathway over Ni/ATP was suggested based on FT-IR and 13C NMR measurements.

Functionalized Zn-based desulfurizer with ordered mesoporous structure based on insights into sulfur-release mechanism during hot coal gas desulfurization

Sulfur-release effect impedes the engineering application of hot coal gas desulfurization. However, the related mechanism is not clear. This study aims to clarify the aforementioned effects and directionally design/fabricate ordered mesoporous Zn-based sorbents with function of inhibiting sulfur-release behavior. The results reveal that COS is mainly formed via R-1 (reaction between CO and H2S) before the reaction gas contacts Zn-based sorbents. R-2 (reaction between CO2 and H2S) catalyzed by ZnS is more kinetically favorable than its non-catalytic process. Furthermore, R-1 and R-2 contribute almost equally to the overall amount of released COS during desulfurization process. Then, considering the composition of coal gas, the strategy of promoter (with function of catalytic hydrogenolysis of COS) modification was proposed to inhibit sulfur-release behavior. A series of functionalized sorbents with four Zn/Me (Me: Mo, Ni) molar ratios (88:12–97:3) were constructed. The sorbents exhibit ordered pore-arrangement structure. Compared to unmodified sorbents, Mo- and Ni-doping both result in significant decline (by 98 %−99 %) in the amount of released COS before H2S-breakthrough. Moreover, the doping of Mo/Ni into ZnO generally produces positive effects on H2S-uptake activity. However, regeneration leads to notable deterioration of performance for Mo-doped sorbents. It is ascribed to the inadequate conversion of ZnS and structure destruction of sorbents. On the contrast, Ni-doped sorbents with Zn/Ni molar ratio of 90:10 could not only greatly suppress the sulfur-release effect and but also maintain 92 %−95 % of initial sulfur capacity during five sulfidation-regeneration cycles.

Research on dynamic modeling and carbon load estimation of diesel particulate filter

ABSTRACT Accurate estimation of carbon load in diesel particulate filters is an important basis for efficient and safe operation of active regeneration. Currently, model-based carbon load prediction has the advantages of high accuracy and low influence by working conditions. In this paper, a dynamic model of diesel particulate filters was developed based on the deep bed and cake layer trapping mechanism and regeneration mechanism. The trapping process was described using the spherical trapping mechanism, while the regeneration process was based on the non-catalytic oxidation process of the trapped particles. A pressure drop correction based on the extended Kalman filter was developed to correct the errors accumulated in the carbon load prediction during the integration. The maximum error of carbon load prediction was 0.3 g/L, and the average error was less than 0.17 g/L, the maximum error of pressure drop was 0.7 kPa, and the average error was less than 0.33 kPa. The carbon load prediction algorithm was proved to have good accuracy and can be used for start-stop judgment of DPF active regeneration, and the pressure drop and temperature calculated by the DPF model can be used for DPF status monitoring during regeneration to ensure safety and reliability.

In-situ catalytic pyrolysis of pine powder by ZnCl2 to bio-oil under mild conditions and application of biochar

Fast pyrolysis of biomass is an effective way for biomass conversion and utilization. However, the pyrolysis temperature is usually high because it is a non-catalytic process, resulting in the complicated composition of bio-oil and difficulty to control. Aiming to explore in-situ catalysis in this paper, the fast pyrolysis of lignin, cellulose, corncob and pine wood powder was studied using ZnCl2 as the catalyst. The activation energies of non-catalytic pyrolysis and catalytic pyrolysis were obtained based on kinetic fitting of their thermal gravimetric curves. The variation in pyrolysis oil composition was analyzed. It was found that ZnCl2in situ catalysis could not only significantly reduce the pyrolysis temperature, but also simplify the resultant bio-oil composition. Even under pyrolysis temperature as low as 350 °C, fast pyrolysis of pine wood powder could achieve a yield of 47% of bio-oil, which was predominantly composed of the derivatives of cellulose and hemicellulose. ZnCl2in situ catalysis could significantly decrease the activation energy of cellulose cracking from 304.78 to 112.46 kJ/mol, but has little effect on that of lignin. The carbon residue from ZnCl2-catalyzed pyrolysis was further carbonized at 600 °C, affording activated carbon with adsorption capacity of phenol up to 165 mg/g. The research work provides guidance and reference for the development of in-situ catalytic pyrolysis technology with high efficiency.

Thermodynamic analysis of biodiesel production with catalyst and non-catalyst process: incase energy analysis

Biodiesel production from renewable resources needs a certain amount of energy Input. The effectiveness of biodiesel production depends on the energy ratio, i.e. the ratio of energy contained in the biodiesel to the energy input during production, including energy content in the feedstock. The objective of the study is aimed to evaluate the energy ratio in biodiesel production. The input and output energy were analyzed for each process (catalyst and analysist). Materials required in biodiesel production was evaluated in term of their energy content. The equipment used to obtain data on the non-catalytic biodiesel production process was a prototype bubble column reactor designed by the Department of Global Agricultural Sciences at The University of Tokyo, Japan and data on the catalytic biodiesel production process was obtained from the Center for Design and Technology System Engineering, BPPT Serpong,by the design of the equipment owned by the institution. The results showed that the energy ratio and the energy needed to produce per kilogram of biodiesel using the non-catalytic production method with a modified process were 1.00 and 39.63 MJ/kg while using the catalytic method were 0.98 and 41.05 MJ/kg, respectively. The non-catalytic production method with a modified process is better than the catalytic method in energy ratio. The energy needed to produce per kilogram of biodiesel due to the heat exchanger is critical for the performance improvement of the modified non-catalytic process.

Two-Stage Selective Non-Catalytic Process for Nitrogen Oxide Removal from Thermal Generating Unit Flue Gases

Two-Stage Selective Non-Catalytic Process for Nitrogen Oxide Removal from Thermal Generating Unit Flue Gases

Hydrochar derived from Liquorice root pulp utilizing catalytic/non-catalytic hydrothermal carbonization: RSM optimization and cationic dye adsorption assessment

The present study targeted producing hydrochar from Liquorice root pulp employing the catalytic/non-catalytic hydrothermal carbonization (HTC) method and evaluating its performance in methylene blue adsorption from an aqueous solution. The response surface methodology (RSM) was utilized to assess the impact of operational variables such as temperature, time, and water/ solid ratio on the yield of hydrochar production and MB adsorption capacity. The maximum yield of hydrochar production and dye adsorption capacity was achieved at 168 °C, 2.016 h, and a water/solid ratio of 9.215. The assessment of the catalytic HTC process at different concentrations of ZnCl2 demonstrated the 0.25 M solution had the most positive effect on MB adsorption capacity. The physicochemical characteristics of hydrochars were evaluated utilizing techniques such as CHN, FTIR, BET, XRD, TGA, and SEM. Also, the peak fitting method presented a semi-quantitative assessment of the impact of the catalytic/ non-catalytic HTC process on the oxygenated functional groups of hydrochars. The methylene blue adsorption process was evaluated by conducting the experiments at different values of effective parameters such as pH, contact time, initial dye concentration, and dose of adsorbent as temperature. Furthermore, the kinetic and isotherm models were studied to describe the dominant mechanisms in the MB adsorption process. The maximum MB adsorption capacity was achieved at 290.65 and 314.62 mg/g for hydrochar and modified hydrochar at pH of 9, initial dye concentration of 400 mg/L, 45 min of contact time, 1 g/L of adsorbent dose, and temperature of 25 °C. Finally, studying the thermodynamic parameters of the adsorption process demonstrated MB adsorption's spontaneity and exothermic nature.

Density functional theory study of acid-catalyzed conversion of glucose to hydrochar precursors under hydrothermal conditions

Hydrothermal carbonization is a thermochemical technology to convert sludge into hydrochar through the use of Lewis and Brønsted acids. However, the mechanisms by which Lewis and Brønsted acids catalyze the conversion of small-molecule carbohydrates into hydrochar remain unclear. In this study, we used glucose as a small-molecule modulo, and Lewis (CuCl2) and Brønsted (NH4+) acids as catalysts to investigate the reaction mechanisms in the sludge hydrothermal process using density functional theory. Glucose was isomerized to fructose catalyzed by CuCl2 and Cl−, followed by three consecutive dehydrations of fructose to produce 5-hydroxymethylfurfural catalyzed by NH4+. 5-Hydroxymethylfurfural proceeded through multiple NH4+-catalyzed hydration and dehydration reactions to produce small organic molecules, polymerization of which generated hydrochar precursor polymers. The addition of CuCl2 and NH4+ reduced reaction energy barriers during this process. The NH4+-catalyzed polymerization reaction energy barrier between two 5-hydroxymethylfurfural was decreased by 28.0 kcal/mol, whereas that between 5-hydroxymethylfurfural and 1,2,4-benzenetriol was decreased by only 0.72 kcal/mol. Compared to the noncatalytic process, the intermolecular hydrogen transfer in the NH4+-catalyzed conversion of 5- hydroxymethylfurfural to levulinic acid was the best catalytic effect throughout the catalytic process. In this study, using quantum chemical theory, we investigated the conversion mechanism of the CuCl2-and NH4+-catalyzed hydrothermal formation of hydrochar precursor polymers from glucose at the atomic level, thus contributing to the design of catalysts for sludge hydrothermal carbonization and providing theoretical support for this technology.

Thermo-catalytic pyrolysis of marine debris: A waste to wealth conversion study for energy recovery

The rapid increase in marine waste has resulted in the accumulation of plastic marine debris (PMD), which is of concern to the scientific community due to the need for its safe disposal worldwide. PMD primarily consists of non-degradable polymeric waste, namely thermoplastics, which contain a substantial amount of energy as they are made from petroleum-based sources. Proper disposal and energy reclamation of this waste have become pressing topics. This study aimed to investigate PMD through thermogravimetric analysis followed by pyrolysis in the temperature range of 450–600 °C. Additionally, two catalysts, 10% nickel impregnated activated alumina (10% Ni/Al2O3) and sodium aluminosilicate (AlNaO6Si2), were incorporated (non-contacting method) to evaluate their effect on product yield and quality. During the non-catalytic process, the highest yield (∼78%) was achieved at a temperature of 550 °C while the presence of a catalyst had a minimal effect on oil density (0.74–0.76), and the percentage yield decreased to ∼ 58 and ∼ 62% using AlNaO6Si2 and 10% Ni/Al2O3 at 550 °C. The catalyst had a significant effect on the fraction of oxygenated compounds in the oil, reducing it by ∼ 18% from the non-catalytic process. AlNaO6Si2 resulted in a higher fraction of gasoline-range compounds, while 10% Ni/Al2O3 showed a higher similarity towards diesel fractions. Gas chromatography-mass spectrometry (GC–MS) analysis identified the presence of alkanes, alkenes, aromatics, alcohols, and other compounds in the oil product, with variations observed depending on the catalyst used. The results showed that among all hydrocarbons, propane had the maximum fraction, followed by ethane, methane, and butane in the gaseous compounds. Based on the degradation mechanism, yield distribution, and component evolution, the dissociation mechanism for both processes was explained.

A comprehensive review of the production methods and effect of parameters for glycerol-free biodiesel production

This review appraises the latest scientific progress and the accomplishments of interesterification technology as an alternative to conventional transesterification reaction. The merits and limitations of various types of catalytic techniques as well as non-catalytic supercritical glycerol-free processes have been elucidated with a comprehensive comparison. Contrary to the cheap price of glycerol, the higher-revenue by-products, triacetin and glycerol carbonate, will boost the gross profit margin of biodiesel production. The influences of reaction parameters such as reactant ratio, catalyst loading, reaction time, temperature, and co-solvent addition are also addressed. According to the latest research, the alkali-catalyzed and non-catalytic supercritical interesterifications are preferable due to higher yield. Methyl acetate, ethyl acetate and dimethyl carbonate do not inhibit lipase activity, unlike typical alcohols. Acidic catalysis may be the way forward to resolve the extreme operating conditions of non-catalytic supercritical interesterification, high cost of enzymes and manage waste feedstocks with high free fatty acid and water contents under moderate conditions. Currently, the majority of interesterification reactions were undertaken on laboratory size, whereas just a handful was evaluated on a pilot scale. A continuous research in interesterification technology is necessary by conducting a thorough investigation of the feasibility of state-of-the-art technology to engage a wide array of feedstocks. Future study should also concentrate on microbes and agricultural waste as a sustainable route for energy recovery from renewable feedstocks.

Ce/Pumice and Ni/Pumice as heterogeneous catalysts for syngas production from biomass gasification

This work presents a study of synthesis and characterization of catalysts-based cerium and nickel supported on the pumice stone (Ce/Pumice and Ni/Pumice) to be used in the gasification process of an invasive species present in the Canary Islands, such as Pennisetum setaceum to obtain syngas. Specifically, the effect of the metal impregnated on the pumice, and the effect of catalyst on the gasification process was studied. For this purpose, the composition of the gas was determined and the results obtained were compared with those obtained in non-catalytic thermochemical processes. Gasification tests were performed using a simultaneous thermal analyzer coupled with a mass spectrometer, providing a detailed analysis of the gases released during the process. The results showed that during the catalytic gasification process of the Pennisetum setaceum, the gases produced appear at lower temperatures in the catalytic process that in the non-catalytic process. Specifically, H2 appears at 640.42 °C and 641.84 °C when Ce/pumice and Ni/pumice were used as catalyst, respectively, compared to 697.41 °C for the non-catalytic process. Moreover, the reactivity at 50 % of char conversion for the catalytic process (0.34 and 0.38 min−1 for Ce/pumice and Ni/pumice, respectively) was higher than for the non-catalytic process (0.28 min−1), indicating that the incorporation of Ce and Ni on the pumitic material increases the gasification rate of the char compared to the pumitic support. Catalytic biomass gasification is an innovative technology that can provide new opportunities for research and development of renewable energy technologies, as well as for the creation of green jobs.

Ex Situ Catalytic Pyrolysis of Invasive Pennisetum purpureum Grass with Activated Carbon for Upgrading Bio-Oil

Energy demands keep increasing in this modern world as the world population increases, which leads to a reduction in fossil fuels. To resolve these challenges, Pennisetum purpureum, an invasive grass in Brunei Darussalam, was examined as the feedstock for renewable energy through a catalytic pyrolysis process. The activated carbon was applied as the catalyst for a simple and economical solution. The catalytic pyrolysis was executed at 500 °C (the temperature for the highest biofuel yield) for both reactors to produce the highest amount of upgraded biofuels. The biochar produced from the non-catalytic and catalytic pyrolysis processes showed a consistent yield due to stable operating conditions, from which the activated carbon was generated and used as the catalyst in this work. A significant amount of improvement was found in the production of biofuels, especially bio-oil. It was found that for catalysts, the number of phenolic, alcohol, furans, and ketones was increased by reducing the amount of acidic, aldehyde, miscellaneous oxygenated, and nitrogenous composites in bio-oils. The highest amount of phenolic compounds was produced due to a number of functional groups (-C=O and -OH) in activated carbon. The regenerated activated carbons also showed promising outcomes as catalysts for upgrading the bio-oils. The overall performance of synthesized and regenerated activated carbon as a catalyst in catalytic pyrolysis was highly promising for improving the quality and stability of bio-oil.

Numerical Simulation of Selective Non-Catalytic Reduction Denitrification Process in Precalciner and the Effect of Natural Gas Injection on Denitrification

Cement production is the third largest source of nitrogen oxides (NOx), an air pollutant that poses a serious threat to the natural environment and human health. Reducing NOx emissions from cement production has become an urgent issue. This paper aims to explore and investigate more efficient denitrification processes to be applied in NOx reduction from precalciner. In this study, firstly, the flow field, temperature field, and component fraction in the precalciner are studied and analyzed using numerical simulation methods. Based on this, the influence of the reductant injection height and amount on the SNCR was studied by simulating the selective non-catalytic reduction (SNCR) process in the precalciner. The effect of natural gas on the NOx emissions from the precalciner was also investigated. The simulation results showed that, with the increase in height, the NOx concentration in the precalciner decreased, then increased, then decreased, and then increased again. The final NOx concentration at the exit position was 531.33 ppm. In the SNCR denitrification process, the reductant should be injected in the area where the precalciner height is 26–30 m so that the reductant can fully react with NOx and avoid the increase of ammonia escape. The NSR represents the ratio of reductant to NOx, and the results show that the larger the NSR is, the higher the denitrification rate is. However, as the NSR approaches 2, the denitrification rate slows down and the ammonia escape starts to increase. Therefore, according to the simulation results, the NSR should be kept between 1 and 1.6. The denitrification rate reached the maximum value of 42.62% at the optimal condition of 26 m of reductant injection height and 1.6 of NSR. Co-firing of natural gas with pulverized coal can effectively reduce the NOx generation in the furnace. The denitrification rate reached the maximum value of 32.15% when the natural gas injection amount was 10%. The simulation results of natural gas co-combustion and SNCR combined denitrification showed that combined denitrification was better than natural gas co-combustion or SNCR denitrification. Under the condition of NSR of 1 and natural gas injection of 10%, the denitrification rate increased by 29.83% and 31.64% compared to SNCR-only or co-combustion-only denitrification, reaching 61.98%, respectively. Moreover, less reductant is used in co-denitrification, so the problem of excessive ammonia emissions can be avoided. The results of this study provide useful guidance for denitrification process development and NOx reduction in cement production.

Biodiesel fuel. Part III. Quantum chemical research and simulation of the process

THE PURPOSE. The purpose of this work was to use the associated paradigm for a correct quantum-chemical description of non-catalytic and catalytic supercritical fluid processes of transesterification of triglycerides with alcohols and hydrolysis of triglycerides and to model a one-stage process for obtaining biodiesel fuel, carried out under supercritical fluid conditions with its subsequent scaling to the commercial level.METHODS. The Gaussian09 software product was used to describe quantum chemical studies. The process modeling was carried out using the ASPEN Plus® v2006 software product. The behavior of thermodynamic systems at high temperatures and pressures is modeled using "RK ASPEN EOS". For modeling processes carried out at low pressures, mathematical models UNIQUAC and UNIFAC-LL were used. The scaling of the process was carried out in the VMGSim program.RESULTS. The third part of the review focuses on the quantum-chemical modeling of the transesterification reaction carried out under supercritical fluid conditions. It is shown that taking into account the associative paradigm makes it possible to obtain calculated reaction rate constants that agree in order with the experimental values. And also an analysis was carried out and the results of modeling the process of obtaining biodiesel fuel and scaling it to a commercial level, with a capacity of up to 9000 tons / year, were presented.CONCLUSION. The conducted analysis showed that biodiesel fuel can be a competitive fuel in our and the world market.

Supercritical Water Gasification of Coconut Shell Impregnated with a Nickel Nanocatalyst: Box–Behnken Design and Process Evaluation

The energy conversion of nickel-impregnated coconut shells using supercritical water has not yet been explored. The impregnation process was conducted at room temperature and a pH of 5.80 for 72 h. Characterization of the prepared sample confirmed the presence of nickel nanoparticles with an average size of 7.15 nm. The gasification of control and impregnated samples was performed at 400–500 °C, biomass loading from 20 to 30 wt% and residence time from 20 to 60 min. The response surface methodology (RSM) approach, with a Box–Behnken method, was used to design the experiments. The optimization model showed that the non-catalytic process at 500 °C, 60 min and 20 wt% of biomass loading could promote an H2 yield of 8.8 mol% and gasification efficiency of 47.6%. The gasification of nickel-impregnated coconut shells showed significantly higher gasification efficiency (58.6%) and hydrogen yield (17.2 mol%) with greater carbon and hydrogen efficiencies (109.4 and 116.9%) when compared to the non-catalytic process. The presence of nickel particles in the biomass matrix as nanocatalysts promoted higher hydrogen production and supercritical water gasification efficiency.

Non-Catalytic Partial Oxidation of Hydrocarbon Gases to Syngas and Hydrogen: A Systematic Review

The review contains a comparative analysis of studies on the production of hydrogen and syngas based on the processes of partial oxidation of natural gas and other types of gas feedstock. The results presented in the literature show the high potential of non-catalytic autothermal processes of partial oxidation of hydrocarbons for the development of gas chemistry and energetics. The partial oxidation of hydrocarbons makes it possible to overcome such serious shortcomings of traditional syngas production technologies as technological complexity and high energy and capital intensity. The features of non-catalytic partial oxidation of hydrocarbon gases, the obtained experimental results and the results of kinetic modeling of various options for the implementation of the process, which confirm the adequacy of the kinetic mechanisms used for the analysis, are considered in detail. Examples of industrial implementation of processes based on partial oxidation and proposed alternative options for its organization are considered. Designs of reactors used to ensure stable conversion of rich mixtures of hydrocarbons with an oxidizer are presented. The possibility of obtaining other chemical products by partial oxidation of hydrocarbons is discussed.