Supercritical water gasification of glycerol: Intermediates and kinetics

In this paper, the liquid products from supercritical water gasification (SCWG) of glycerol were analyzed and some intermediates were identified. A simplified reaction pathway for gases production from SCWG of glycerol was proposed. The first quantitative kinetics model for describing the gaseous products (H₂, CO, CH₄ and CO₂) of SCWG of glycerol was developed. The model comprises seven reactions to describe the typical reactions in SCWG, and the reaction rate constant of each reaction was obtained by using the nonlinear least-square fitting method. The reaction rate analysis showed that the main sources of hydrogen yield were glycerol pyrolysis and steam reforming of intermediates, while the hydrogen yield from water–gas shift reaction (WGSR) was very small. The temperature estimated by the kinetics model for completely SCWG of glycerol solution was given. In addition, the sensitivity analysis of rate constant of WGSR was done based on the model.     

超临界水在降解废弃物及资源化中的应用

综述了超临界水的特性及其在降解废旧塑料、橡胶、纤维素等废弃物及资源化中的应用现状。与传统热分解方法相比,超临界水可实现对高分子废弃物的快速、有效分解,通过分解反应条件的控制,可以控制产物组成,是一种很有前途的废弃物资源化技术。     

Char and Coke Formation as Unwanted Side Reaction of the Hydrothermal Biomass Gasification

The hydrothermal biomass gasification is a promising technology to produce hydrogen and/or methane from wet biomass with a water content of ≥ 80 % (g/g). In the process, the coke formation usually is very low, but already low amounts may cause problems like, e.g., fouling in the heat exchanger. To learn more about the product formation, the results of the hydrothermal treatment (at 400, 500, 600 °C and 1 h) of different biomass feedstocks (artichoke stalk, pinecone, sawdust, and cellulose as model biomass) in a microreactor are compared. The gas composition and the total organic carbon content of the aqueous phase were determined after reaction. The gas formation rises with increasing temperature. The formation of carbon deposits and their characterization has been investigated by scanning electron microscopy (SEM). The variation of the solid morphology during the hydrothermal conversion is discussed based on chemical pathways occurring during hydrothermal biomass degradation.     

Hydrothermal gasification of olive mill wastewater as a biomass source in supercritical water

In this study, the hydrothermal gasification of biomass in supercritical water is investigated. The work is of peculiar value since a real biomass, olive mill wastewater (OMW), is used instead of model biomass compounds. OMW is a by-product obtained during olive oil production, which has a complex nature characterized by a high content of organic compounds and polyphenols. The high content of organics makes OMW a desirable biomass candidate as an energy source. The hydrothermal gasification experiments for OMW were conducted with five different reaction temperatures (400, 450, 500, 550 and 600 °C) and five different reaction times (30, 60, 90, 120 and 150 s), under a pressure of 25 MPa. The gaseous products are mainly composed of hydrogen, carbon dioxide, carbon monoxide and C₁-C₄ hydrocarbons, such as methane, ethane, propane and propylene. Maximum amount of the gas product obtained is 7.71 mL per mL OMW at a reaction temperature of 550 °C, with a reaction time of 30 s. The gas product composition is 9.23% for hydrogen, 34.84% for methane, 4.04% for ethane, 0.84% for propane, 0.83% for propylene, 49.34% for carbon dioxide, and 0.88% for minor components such as n-butane, i-butane, 1-butene, i-butene, t-2-butene, 1,3-butadiene and nitrogen at this reaction conditions.     

Deposition characteristics of diesel and bio-diesel fuels

The aim of this study is to investigate the deposition characteristics of different types of fuels by using the hot surface deposition test (HSDT) as a substitute procedure for real engine deposit tests. Deposit development, deposit compositions and deposit surface temperature fluctuation for diesel fuels and bio-diesel fuels (palm oil based and coconut oil based) are discussed. Deposit development depended on hot surface temperature, overlapping conditions, fuels, deposit properties, initial stage of deposition and competition phenomena during deposit formation. Results show DFP having 1% B100C in composition, showed a greater deposit development rate compared to DF, which resulted in a relatively large amount of deposits for DFP. However, for bio-diesel fuels, B100C obtained a slower deposit development rate compared to B100 although the test conditions were changed. Due to the lower value of MEP and shorter droplet lifetime before MEP, utilization of B100C had a greater potential in reducing deposit formation compared to B100.     

High energy syngas production by waste tyres steam gasification in a rotary kiln pilot plant. Experimental and numerical investigations

This paper presents experimental and numerical results on steam gasification of waste tyres in a rotary kiln pilot plant. Both the process performance and the gas features have been evaluated varying the feeding ratio (FR), defined as the steam/tyres mass ratio. First, several experimental tests have been performed. Then, the obtained experimental results have been used to verify the consistency of a numerical model developed with the aid of the commercial code ChemCAD®. Once done, the effect of increasing the FR on the gas energy content has been evaluated.Numerical results showed that the gas energy content increases as the FR increases as well, achieving a maximum value for FR = 0.33 that produced a gas which composition N₂ free is (H₂ = 52.7%_vol, CO = 18.1%_vol, CO₂ = 7.0%_vol, CH₄ = 22.2%_vol) in correspondence of which the lower heating value (LHV) is equal to 29.5 MJ kg_gas⁻¹. Higher FR values do not produce a further increase of the gas energy content, rather require a greater amount of input energy for heating the steam from the atmospheric to the process temperature.     

Production and fuel properties of fast pyrolysis oil/bio-diesel blends

This paper describes the production and fuel properties of fast pyrolysis oil/bio-diesel blends. The bio-oils used in this study were produced from the fast pyrolysis of woody biomasses, oil mallee and pine. The bio-diesel employed was derived from canola vegetable oil. The conditions used to prepare the bio-oil/bio-diesel blends, as well as some of the fuel properties of the resulting bio-diesel rich phase, are reported. The experimental results show that the solubility of fast pyrolysis oils in bio-diesel is not as high as was previously reported for decanted oils obtained by Auger pyrolysis. The carboxylic acids, mono-phenols, furans and lignin derived oligomers were the compounds most soluble in bio-diesel, while the sugars, on the other hand, showed poor solubility. Although the presence of phenols enhances the oxidation stability of the bio-diesel rich phases, other fuel properties deteriorate. For example, the content of solid residues increased primarily because of the solubilisation of lignin derived oligomers, which were quantified by UV-fluorescence. Concentrations as high as 3.5 mass % of these compounds were observed in the bio-diesel rich phase. The solubility of bio-oil in bio-diesel was enhanced by using ethyl acetate/bio-diesel blends. Some fuel properties of the bio-diesel rich phase, after the removal of ethyl acetate, are reported.     

Biomass gasification in supercritical water: Part 1. Effect of the nature of biomass

In this study, biomass feedstocks, including lignocellulosic materials and the tannery wastes, were gasified in supercritical water. Gasification experiments were performed in a batch autoclave at 500 °C. The amount of gases, the gas compositions and the amount of water soluble compounds from gasification were determined. The hydrogen yields ranging between 4.05 and 4.65 mol H₂/kg biomass have been obtained. The results showed that the yields and composition of gases depend also on the organic materials other than cellulose and lignin in lignocellulosic material. In addition to this, it was concluded that the kind of lignin may also have an effect on gasification products. In the case of tannery wastes, the type of tannen agent used in leather production considerably effected the gasification results.     

Corrosion control methods in supercritical water oxidation and gasification processes

Use of supercritical water (SCW) as a medium for oxidation reactions, conversion of organic materials to gaseous or liquid products, and for organic and inorganic synthesis processes, has been the subject of extensive research, development, and some commercial activity for over 25 years. A key aspect of the technology concerns the identification of materials, component designs, and operating techniques suitable for handling the moderately high temperatures and pressures and aggressive environments present in many SCW processes. Depending upon the particular application, or upon the particular location within a single process, the SCW process environment may be oxidizing, reducing, acidic, basic, nonionic, or highly ionic. Thus, it is difficult to find any one material or design that can withstand the effects of all feed types under all conditions. Nevertheless, several approaches have been developed to allow successful continuous processing with sufficient corrosion resistance for an acceptable period of time. The present paper reviews the experience to date for methods of corrosion control in the two most prevalent SCW processing applications: supercritical water oxidation (SCWO) and supercritical water gasification (SCWG).     

Hydrogen production by biomass gasification in supercritical water: A systematic experimental and analytical study

Hydrogen production from biomass gasification in supercritical water is a new technology, which was developed in last two decades. Biomass energy of low quality can be converted to hydrogen energy of high quality by supercritical water gasification. Particularly, supercritical water gasification is an elegant way of wet biomass utilization. Up to now, many important progresses have been made in supercritical water gasification technology by the studies of researchers around the world. Since 1997, supercritical water gasification, which include reaction system, rule of biomass gasification and theory, have been studied in State Key Laboratory of Multiphase Flow in Power Engineering of Xi’an Jiaotong University. In this paper, we summarize the results from systematic experimental and analytical study on biomass gasification in supercritical water in our laboratory. Also, the development status and future prospect on supercritical water gasification is evaluated.     

焦化废水处理工艺升级改造的实践

对邯钢焦化厂的废水处理工艺进行技术升级改造,改造主要针对预处理系统和生化系统,将A—A／O法工艺改造成A／O法工艺后,废水处理达到了国家一级排放标准。同时对改造前后工艺的优缺点及生产过程中的影响因素进行了分析。     

超临界方法在塑料分解回收中的应用研究

综述了超临界水在废旧塑料如聚对苯二甲酸乙二醇酯,聚碳酸酯,聚乙烯等回收利用中的研究进展。对比于传统的废旧塑料处理方法,利用超临界水所具有的特殊的化学,物理性能对上述废旧塑料的处理,同时可达到效率,原材料回收比例高且后处理工序简便,无公害等多优点,为废旧塑料的回收利用开辟了新的途径。     

Reforming of methanol and glycerol in supercritical water

Reforming of pure glycerol, crude glycerin, and methanol (pure and in the presence of Na₂CO₃) in supercritical water was investigated. Continuous experiments were carried out at temperatures between 450 and 650 °C, residence times between 6 and 173 s, and feed concentrations of 3-20 wt%. For methanol the gas products are mainly H₂, CO₂, and CO. The carbon-to-gas efficiency and the observed activation energy for pure methanol are higher than for methanol with Na₂CO₃. This can be explained by assuming different decomposition mechanisms for pure methanol and methanol with Na₂CO₃. For glycerol, H₂, CO, CO₂, CH₄, and higher hydrocarbons are produced. The carbon-to-gas efficiencies of crude glycerin and pure glycerol are comparable. Overall, 2 of the 3 carbon atoms present in glycerol end up in carbon oxides, while 1 carbon atom becomes C_xH_y. The overall mechanism of glycerol decomposition involves the dehydration of 1 mole of H₂O/mole glycerol. For both, methanol and glycerol at carbon-to-gas efficiencies below 70%, the gas yields (mole/mole feed) and carbon-to-gas efficiency correlate well.     

High-yield hydrogen production by supercritical water gasification of various feedstocks: Alcohols,glucose, glycerol and long-chain alkanes

Continuous supercritical water gasification (SCWG) of various feedstocks of C1–C16 was conducted to produce hydrogen-rich gas. These feedstocks represent model compounds of biomass such as methanol/ethanol (alcohol-type), glucose and glycerol (byproducts of biodiesel synthesis), and model compounds of petroleum fuels such as iso-octane/n-octane (gasoline), n-decane/n-dodecane (jet fuels) and n-hexadecane (diesel). Almost complete gasification of all the feedstocks was achieved at 25 MPa, 740 °C and 10 wt% with low total organic carbon values of their liquid effluents. The hydrogen gas yields of each feedstock were very similar to the theoretical equilibrium yields estimated by Gibbs free energy minimization. SCWG at different gasification temperatures (650 and 740 °C) and concentrations (10 and 20 wt%) revealed that methanol and ethanol (alcohols), the simple oxygenated hydrocarbons, were easier to be gasified, producing negligible amounts of liquid products, when compared with long-chain hydrocarbons (iso-octane and n-decane) under the identical conditions. When the feedstock concentration was increased from 10 to 20 wt%, the equilibrium hydrogen ratio from iso-octane gasification decreased from 1.02 to 0.79 while that of n-decane increased from 1.12 to 1.50, implying that a branched hydrocarbon may be more resistant to gasification in supercritical water.     

Conversion of waste cooking oil to biodiesel using ferric sulfate and supercritical methanol processes

In this comparative study, conversion of waste cooking oil to methyl esters was carried out using the ferric sulfate and the supercritical methanol processes. A two-step transesterification process was used to remove the high free fatty acid contents in the waste cooking oil (WCO). This process resulted in a feedstock to biodiesel conversion yield of about 85-96% using a ferric sulfate catalyst. In the supercritical methanol transesterification method, the yield of biodiesel was about 50-65% in only 15 min of reaction time. The test results revealed that supercritical process method is probably a promising alternative method to the traditional two-step transesterification process using a ferric sulfate catalyst for waste cooking oil conversion. The important variables affecting the methyl ester yield during the transesterification reaction are the molar ratio of alcohol to oil, the catalyst amount and the reaction temperature. The analysis of oil properties, fuel properties and process parameter optimization for the waste cooking oil conversion are also presented.     

Catalytic hydrogen production from 2-propanol in supercritical water: Comparison of some metal catalysts

The gasification of organics in supercritical water is a promising method for the direct production of hydrogen at high pressures, and in order to improve the hydrogen yield or selectivity, activities of various catalysts are evaluated. In this study, hydrogen production from 2-propanol over Ni/Al₂O₃ and Fe–Cr catalysts was investigated in supercritical water. The experiments were carried out in the temperature range of 400–600 °C and in the reaction time range of 10–30 s, under a pressure of 25 MPa. The hydrogen yields and selectivities of Ni/Al₂O₃ and Fe–Cr used in this study, and those of Pt/Al₂O₃ and Ru/Al₂O₃ used in our previous work were compared. The hydrogen contents of the gaseous products obtained by using Ni/Al₂O₃ and Fe–Cr were measured as 62 mol% and 70 mol%, respectively, at low temperatures and reaction times. However, the hydrogen yields remained in low levels when compared with that of Pt/Al₂O₃ used in previous study. Pt/Al₂O₃ was established to be the most effective and selective catalyst for hydrogen production. During the catalytic gasification of a 0.5 M solution of 2-propanol, hydrogen content up to 96 mol% and hydrogen yield of 1.05 mol/mol 2-propanol were obtained.     

The preparation and shock tube investigation of comparative ignition delays using blends of diesel fuel with bio-diesel of cottonseed oil

This paper describes an experimental effort for the production of cotton methyl ester (CME), cotton ethyl ester (CEE) and CEE-diesel blends from neat cottonseed oil (CSO) for use as a bio-diesel fuel and the investigation of the ignition delay times of these fuels using the shock tube. The transesterification of the neat CSO with methanol or ethanol has been performed to determine the optimum conditions for the preparation. The optimum parameters were cottonseed oil/alcohol molar ratio, 1:6; NaOH amount, 1% by the weight of the oil and reaction time, 75 min. The physical properties of all the tested fuels are measured. 89% of the neat CSO was converted into CME or CEE and the use of different alcohols (methanol or ethanol) presents few differences with regards to the kinetics of reaction but the final yield of esters remains almost unchanged. The ignition delay times were measured using a piezo-electric pressure transducer, charge amplifier, data acquisition card, IBM computer and LabVIEW program. Effects of equivalence ratio, initial charge temperature and initial charge pressure on the ignition delay times are discussed. The results show that the minimum ignition delay time was observed at an equivalence ratio of 1.05 for all the tested fuels. The ignition delay can be reduced considerably together with an increase of the initial charge temperatures and pressures. Also, the ignition delays of the tested fuels are compared with the diesel fuel.     

Continuous salt precipitation and separation from supercritical water. Part 1: Type 1 salts

The precipitation and separation performance of various binary type 1 salt-water mixtures was systematically studied for the first time in a continuously operated laboratory plant. The aim was to find a field of operation for the salt separator where salts can be separated with high efficiency. Experiments with aqueous solutions of the salts NaNO₃, KNO₃, Ca(NO₃)₂, K₂CO₃, KHCO₃, (NH₄)₂CO₃, K₃PO₄, K₂HPO₄, KH₂PO₄, NaCl, KCl, NH₄Cl and (NH₄)₂SO₄ were carried out at 30 ± 0.5 MPa varying the salt separator temperature from sub-critical to supercritical. For most of these salts separation efficiencies ranging from 80 to 97% were obtained. For the nitrates the separation efficiency increased in the order NaNO₃ < KNO₃ < Ca(NO₃)₂, whereas for potassium salts the separation efficiency of the phosphates was significantly higher than that of KNO₃. Considerable hydrolysis of the phosphate and the hydrogen phosphate salts in supercritical water was found, although this had no negative influence on the phosphate separation efficiency. It was found that the ammonium salts decompose in supercritical water, probably to ammonia and the corresponding mineral acids, leading to reduced separation of the ammonia due to its high solubility in supercritical water.     

Hydrothermal flames in supercritical water oxidation: investigation in a pilot scale continuous reactor

Hydrothermal flames at 25 MPa supercritical water environment were investigated using a 4800 ml reaction tower, in which the sapphire windows were fitted for optical access. Down flowing hydrothermal flames were observed for oxidation of 2-propanol when the reactor was fed with inlet organic concentration higher than 2 vol% and air ratio higher than 1.8. Flame temperature, as high as 1100 °C, was measured by means of a thermocouple and the temperature was found to be strongly influenced by air ratio. Effective and stable oxidation of organics with TOC removal rate of 99.9% was achieved. Dioxins were also decomposed with a ratio higher than 99.9%, within 1 min reaction time in this reactor configuration.     

Hydrothermal gasification of glucose using Raney nickel and homogeneous organometallic catalysts

Catalytic gasification of biomass to fuel gaseous in sub and super critical water is a promising method for production of sustainable energy. In this paper, a microreactor has been utilized to study the hydrothermal gasification of glucose in the presence of transition metal chelates consisting of nickel(II) acetylacetonate (Ni(acac)₂), cobalt(II) acetylacetonate (Co(acac)₂), iron(III) acetylacetonate (Fe(acac)₃) and Raney-nickel particles. The reaction temperature and pressure were 310–350 °C and 100–210 bar, respectively. Effects of addition of catalysts, reaction temperature, reaction time, glucose concentration and liquid water volume fraction on the amount of the generated gas as well as its composition were investigated. Results indicated that the presence of the organometallic compounds can slightly facilitate the rate of decomposition of glucose. This enhancement in reaction rate was more pronounced at higher concentrations of the feed (~ 0.65 M) compared with lower concentrations (~ 0.06 M). In contrast to these homogeneous catalysts, Raney-nickel catalyst improved the gas yield by a factor of 3 to 5. It has been observed that the amount of the produced gas almost doubles when the batch time increased from 3 to 30 min, while no significant change was observed from 30 to 60 min. Finally, remarks on optimization of the amount of added water into the reaction vessel are provided.