Addition Of Chelating Agent Research Articles

Enhanced removal of 1,2-dichloroethane by nanoscale calcium peroxide activation with Fe(III) coupled with different iron sulfides.

Fe(II) is of great importance in iron-based advanced oxidation processes. However, traditional methods to maintain Fe(II) concentration, such as the addition of chelating agents or reducing agents, may lead to an increase in chemical oxygen demand of secondary pollution. Therefore, in this study, iron sulfides, namely ferrous sulfide (FeS), pyrite (FeS2), and sulfidated nanoscale zero-valent iron (S-nZVI), were applied for not only the regeneration of Fe(II) but also the direct dissolution of Fe(II). Nanoscale calcium peroxide (nCaO2) was synthesized and used as the oxidant. The removal of 1,2-dichloroethane (1,2-DCA) were significantly promoted from 8.8 to 98.2, 79.2, and 80.8% with the aid of FeS, FeS2, and S-nZVI within 180 min, respectively. The dominant reactive oxygen species were demonstrated and their steady-state concentrations were quantified. Besides, the dechlorination of 1,2-DCA reached 90.4, 69.5, and 83.9% in nCaO2/Fe(III) systems coupled with FeS, FeS2, and S-nZVI, respectively. All three systems had high tolerance to the complex water conditions, of which FeS-enhanced nCaO2/Fe(III) system displayed the best performance, which could be recommended to put into practice for the remediation of 1,2-DCA contaminated groundwater.

Amorphous iron oxyhydroxides nano precursors used for Reactive Yellow 84 removal from aqueous solutions

In this research, we investigated the potential use of amorphous iron oxyhydroxides, ferrihydrite (FHY), for the removal of persistent pollutants from aqueous solutions. Ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N, N′-disuccinic acid (EDDS) were used as complexing agents during synthesis aiming to enhance the FHY properties. Synthesized materials were characterized by X-ray diffraction, SEM and TEM Microscopy, N2 sorption/desorption, and FT-IR Spectroscopy for their mineralogy, crystallinity, morphology and size, surface properties, and the organic content in their structure. The addition of chelating agents led to differences in nanoparticles morphology, amorphic degree, and surface properties. Reactive Yellow 84 dye was chosen as a representative refractory pollutant and laboratory-scale adsorption studies were conducted at varying dye concentrations. Ca. 100 % RY 84 dye removal efficiency was achieved within one hour at dye concentrations of 5–10 mg/L for an adsorbent dosage of 1 mg/L FHY. Adsorption kinetics and isothermal studies were considered, the uptake capacity was calculated for each nanomaterial and empiric mechanistic information was derived. The results showed that ferrihydrite exhibits the best performance, with a maximum uptake capacity of 40.73 mg Reactive Yellow 84 dye per gram adsorbent followed by FHY_EDTA and FHY_EDDS (up to 35.86 mg/g). Coupling the adsorption with photodegradation processes led to a significant increase in removal efficiencies of persistent RY 84 from polluted aqueous solution, in good timing, suggesting a feasible alternative at sites where dye concentration in effluents is elevated.

One-step processing of waste dredged slurry into planting soil by targeted pretreatment and vacuum filtration

A novel method, targeted pretreatment and vacuum filtration (TP-VF), is introduced and validated in this study. TP-VF offers a one-step solution for efficiently dewatering dredged slurry (DS) characterized by heavy metal contamination, high salinity, and excessive moisture content. This innovative approach combines targeted pretreatment (TP) and vacuum filtration (VF) to transform DS into the viable planting soil. TP encompasses a dual optimization strategy that enhances both slurry dewatering efficiency and the quality of the resultant planting soil (cake). By employing flocculation pretreatment, TP increases the size of flocs and enlarges cake pores, leading to improvements in dewatering efficiency and infiltration rates. Additionally, targeted pretreatment results in the discharge of approximately 90% of heavy metal ions and most salts with the filtrate. Remarkably, the addition of chelating agents and freshwater as part of the pretreatment process positively impacts soil quality without compromising floc size or dewatering efficiency. Comparatively, TP-VF demonstrates a substantial reduction of 35.81% in operational costs when contrasted with the traditional two-step process, concurrently diminishing the potential for secondary environmental pollution. This study highlights TP-VF as a promising advancement in sustainable slurry management, addressing pressing environmental challenges while optimizing resource utilization.

Role of Acetonitrile Additive in Enhanced Performances of Aqueous Zn Anodes

Zinc-ion batteries have been proposed as promising candidates to address ever-growing demands for energy storage and limited resources available for the currently used lithium-battery systems. Despite their promise, the apparent advantages of aqueous zinc-ion batteries (low cost and high energy density) are still overshadowed by uncontrolled water interactions at the zinc metal-electrolyte interface, such as the hydrogen evolution reaction and electrode corrosion. A number of different strategies – e.g., water-in-salt, addition of chelating agents and/or co-solvents – have been proposed to overcome the aforementioned interfacial problems. Among them, the addition of acetonitrile to aqueous ZnSO4-based electrolytes has shown great promise, with reports of improved Coulombic efficiencies and increased cycle life. However, the actual role of this additive remains unclear. In this work, we determine the mechanistic principles behind the participation of acetonitrile in enhancing the performance of aqueous Zn batteries. For this purpose, we utilized a combination of X-ray absorption and Raman spectroscopies, cyclic voltammetry, and galvanostatic coin cell cycling. Our results indicate that the addition of acetonitrile perturbs the interfacial solvation structure, rather than the bulk. Specifically, acetonitrile does not penetrate the first solvation shell of the Zn2+ ion, but does modify interfacial solvation behavior, likely by physisorption to the electrode surface. The Coulombic efficiency of half cells was found to depend on electrode material, employed current density and capacity, and only moderately on acetonitrile concentration. Overall, this works points strongly to the need for systematic evaluation of battery performance in co-solvent systems, and provides a new framework for future efforts to optimize ion transport and performance in zinc-ion batteries._______________________The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. http://energy.gov/downloads/doe-public-access-plan

Effect of the heating rate on crystallization and densification of TiO2 films prepared from alkoxide solutions containing various organic additives

ABSTRACT The effect of the heating rate on crystallization and densification of sol–gel-derived TiO2 films has been investigated. The TiO2 gel films were prepared from Ti(OC3H7 i )4 solutions containing alcohols (2-butanol and 2-methoxyethanol), glycols (propylene glycol, diethylene glycol and dipropylene glycol) and chelating agents (acetylacetone and benzoylacetone) as organic additives, followed by heat treatment to 800°C at various heating rates. In the cases without organic additives and with alcohols, anatase films were obtained irrespective of the heating rate, where the refractive indexes of the films were higher for slower heating rate. Conversely, for the films prepared with glycols and chelating agents, rapid heating activated crystallization and densification. In particular, addition of chelating agents led to the formation of rutile films with much higher refractive indexes than those of the anatase films.

Comparative study of phytoremediation of chromium contaminated soil by Amaranthus viridis in the presence of different chelating agents

Chromium is a harmful heavy metal to the environment due to the toxicity induced by it to plants and other living organisms. High concentration of Cr in soil poses severe toxicological problems ecosystem. Phytoremediation using different plants is an economical and environment-friendly method for removing Cr from soil. The addition of chelating agents augments the phytoextraction using plants.The present study aimed to augment the Cr phytoremediation capacity of Amaranthus virdis, a predominant plant species in the Cr-contaminated open dumpsites of Bangalore. . Phytoextraction of Cr by Amaranthus viridis was studied in the presence of different chelating agents viz. ethylenediaminetetraacetic acid (EDTA), citric acid (CA), growth promoting hormone- indoleacetic acid (IAA) and NPK fertiliser. A. viridis grown under different concentrations (5, 10 and 20 mg/Kg) of Cr were treated with 0.5g EDTA/Kg of soil, 0.5g CA/Kg of soil, 1mg IAA/Kg of soil and NPK (125 mg of nitrogen, 45 mg of phosphorous and 156 mg of potassium per Kg of soil). Results indicated that CA, at 10 mg/kg Cr supply, induced the highest uptake (up to 29.25 µg/plant). Furthermore, the study revealed that CA amendment induced maximum Cr uptake in A. viridis at all levels of Cr supply as compared to other amendments. This was due to the increased solubility of Cr in the presence of citric acid and the amelioration of oxidative stress due to Cr to plants by citric acid. This study inferred that the non-hyperaccumulating plant, A. virdis could be used as a phytoremediator for Cr in the presence of citric acid in the places where it is grown abundantly.

Study of Chelating Agent—Surfactant Interactions on the Interphase as Possibly Useful for the Well Stimulation

Chelating agents’ application for EOR and well stimulation is fast growing nowadays. However, reagents of this class have some drawbacks, with high values of interfacial tension (IFT) being among them. IFT may be lowered with the addition of surfactants; however, the simultaneous application of chelating agents and surfactants has not yet been widely studied. This paper focuses on the experimental and theoretical investigation of the interaction between chelating agent (ethylenediaminetetraacetic acid, EDTA) and surfactants of anionic and cationic types (sodium dodecyl sulfate, SDS, and dodecyl trimethynlammonium bromide, DTAB). IFT measurement was performed at ambient conditions, with normal octane being as the reference hydrocarbon to eliminate the temperature and salinity effects and compare surfactant-containing systems. The experimental results show that chelating agents’ addition to the solutions of surfactants leads to a decrease in IFT value. Moreover, surfactants’ critical micelle concentration is lowered, whereas their effectiveness and efficiency are increased, which points to the salting-out nature of chelating agents. Molecular dynamics reveal that chelating agent addition causes closer packing of surfactant layer, the decrease in head groups’ hydration, and, at least in the case of SDS, specific surfactant–chelating agent attractive interaction. These molecular-level insights, experimental dependencies, and the combined methodology may be useful for the proper selection of fluids for real-field operations.

Review on Phytoremediation Potential of Floating Aquatic Plants for Heavy Metals: A Promising Approach

Water pollution due to heavy metals has become a serious environmental concern due to their hazardous properties. Since conventional water remediation techniques are generally ineffective and non-environmentally friendly, phytoremediation has gained increasing attention from worldwide researchers and scientists due to its cost-effectiveness and environmental friendliness. Hence, this review first discussed soil and water remediations. Phytoremediation can be divided into five techniques to remove heavy metals from the polluted environment, namely, phytostabilization (phytosequestration), phytodegradation (phytotransformation), phytofiltration (rhizofiltration), phytoextraction (phytoaccumulation), and phytovolatilization. Four common floating aquatic plants (accumulator plants), such as duckweed (Lemna minor), water lettuce (Pistia stratiotes), water hyacinth (Eichhornia crassipes), and watermoss (Salvinia) were discussed in detail due to their great capability in absorbing the metal ions by their roots and further translocating the metal ions to the aerial parts. Furthermore, the parameter studies, such as optimum pH and temperature of the water, exposure duration, initial metal concentration, water salinity, and the addition of chelating agents, were evaluated. The absorption kinetics of the plants was discussed in detail. In short, phytoremediation is a promising green and sustainable water remediation approach. However, further research is necessary to enhance its practicability and performance at large-scale implementation.

Reprint of : Recent strategies for synthesis of metallosilicate zeolites

Incorporation of catalytically active metallic sites into the framework of silica-based zeolites is highly efficient for design of active, selective, and stable heterogeneous catalysts, but there are still many challenges for this kind of preparation such as the presence of aggregated metallic sites due to the alkaline media in the synthesis, relatively low concentration of these metallic sites in the zeolite frameworks, and difficulty for morphological control of metallosilicate zeolites. To overcome these issues, it has been developed new strategies for synthesis of metallosilicate zeolites such as introduction of additives to adjust crystallization rate, addition of chelating agents to form heteroatom complexes, growth of zeolite crystals along with targeted directions, zeolite transformation, and heteroatom replacements. In this review, the recent progresses for syntheses of metallosilicate zeolites are concisely summarized. In addition, the fundamental principles are briefly discussed for the formation of the metallosilicate zeolites. This review should be helpful for design and preparation of the heteroatom-substituted silica-based zeolites as highly efficient heterogeneous catalysts.

Cloud point extraction and Flame Atomic Absorption Spectrometry in the determination of Cu (II), Cr (III), Cd(II), Fe(III) and Mn(II) using Glycerin and PO/EO-block polymer as a surfactant

A simple cloud point extraction (CPE) method has been proposed for the separation & preconcentration for determination of Cr3+, Cu2+, Cd2+, Fe3+ and Mn2+ ions by complexation with ammonium pyrrollidine dithiocarbamate (APDC) in the presence of Glycerin and PO/EO-block polymer. The phase separation occurred when micellar solution was heated at 60◦C. A complete separation of the metal ions with and without addition of chelating agent could be achieved at PH= 3-10 the efficiency of separation is 85-100%. Glycerin showed 75-100% separation for Cr3+, Cu2 and Mn2+ while PO/EO-block polymer showed 60-99% for Cd2+and Fe3+. Other factors also tested include surfactant and metal ions concentration, temperature, time and foreign ions. One gram of surfactant is an enough amount for separation of 20 ppm of each metal ion solution. The analysis of metal ions were carried out using flame atomic absorption spectrometer with deuterium lamp background correction and calibration curve method.

A Review on Unknown Repercussions Associated with Metallic Nanoparticles and their Rectification Techniques

Background:The wide use of metallic nanoparticles (MNPs) has toxic effects on the human body affecting vital organs such as brain, liver and kidney. Therefore it is necessary to develop approaches to eradicate such health issues without compromising plus the potential benefits of the respective metallic nanoparticles including silver, gold, zinc, copper, etc.Objective:This study aimed to assess methods which can mutually reduce the nanotoxicity while retaining the therapeutic benefits of metal-based nanocarriers.Methods:The implementation of certain methods, such as the addition of chelating agents, providing protective coatings and surface modification during the synthesis of metallic nanoparticles can subsequently minimize metallic toxicity.Results:Through extensive and exhaustive literature survey it was proved that the above strategies are effective in reducing nanotoxic effects which can be further assessed by toxicity assessment tools as biochemistry, histopathology, etc.Conclusion:Metallic nanoparticles have emerged as a beneficial tool for treating various diseases such as cancer, hepatitis, etc. Scientists are also preserving their efficacy by escorting novel techniques for limiting its toxicity in the world of nanotechnology.

Insight into chelating agent stimulated in-situ growth of MgAl-LDH films on magnesium alloy AZ31: The effect of initial cationic concentrations

A strategy based on chelating agent addition was used to assist the in-situ growth of MgAl-layered double hydroxides (LDHs) films on magnesium alloy AZ31 in a relatively mild condition. The growth behavior of MgAl-LDH films was studied on the magnesium alloy AZ31 substrate as the sole source of Al3+ and/or adding aluminum compounds as a supplementary source of respective ions. The composition, structure, corrosion resistance, and formation mechanism of LDH films were investigated and discussed. Results showed that the LDH-coated samples could effectively retard the corrosion of magnesium alloy. A thicker Mg (OH)2/MgAl-LDH composite film with larger flake size was formed without additional aluminum source. MgAl-LDH film fabricated with moderate additional Al3+ concentrations showed better corrosion resistance and an interesting stable network structure on a flat surface both covered/consisting of very fine LDH flakes.

Phytoremediation of cadmium-contaminated soils by Solanum nigrum L. enhanced with biodegradable chelating agents.

The application of biodegradable chelating agents to enhance phytoremediation is a low-cost and promising method to improve the remediation efficiency of heavy metal-contaminated soil. The effects of N, N-bis glutamic acid (GLDA) on the growth and heavy metal absorption of Solanum nigrum were studied by pot experiment. The addition of chelate on the 20th day after sowing can improve the bioavailability of cadmium (Cd) in the soil. The results showed that the addition of chelating agents effectively improved the migration rate of the target heavy metal Cd in the soil, and significantly increased the accumulation of heavy metal in the roots, stems, and leaves of plants. The results showed that compared with the control group, the chelating agent could increase the extraction rate of total Cd by 28.65-68.74%. The application of GLDA significantly increased the accumulation of Cd (20mgkg-1 and 40mgkg-1), reaching 24.28-40.30 and 25.71-33.16μg of pot-1 DW, respectively. At the same time, GLDA increased Cd stress by decreasing plant biomass, inhibiting photosynthetic pigment synthesis and increasing MDA levels. These results indicated that GLDA could improve the absorption of Cd by S. nigrum, which provided a new idea for its practical application in the remediation of Cd-contaminated soil.

Supramolecular Polysulfide Polymers with Metal‐Ligand Interactions

AbstractWe report the first preparation of a supramolecular polysulfide polymer using metal‐ligand interactions. The supramolecular polysulfide polymer was prepared by introducing 2,2’‐bipyridine (bpy) at both ends of linear sulfur and linking the bpy with Cu2+. The molecular weight of the supramolecular polysulfide polymer was higher than polysulfide polymer obtained via conventional polymerization. Disassembly and re‐assembly of the supramolecular polysulfide polymers were controlled by de‐metalation of Cu2+ from the complex between bpy and Cu2+ and re‐formation of the complex with the addition of chelating agents and Cu2+, respectively.

Recent strategies for synthesis of metallosilicate zeolites

Incorporation of catalytically active metallic sites into the framework of silica-based zeolites is highly efficient for design of active, selective, and stable heterogeneous catalysts, but there are still many challenges for this kind of preparation such as the presence of aggregated metallic sites due to the alkaline media in the synthesis, relatively low concentration of these metallic sites in the zeolite frameworks, and difficulty for morphological control of metallosilicate zeolites. To overcome these issues, it has been developed new strategies for synthesis of metallosilicate zeolites such as introduction of additives to adjust crystallization rate, addition of chelating agents to form heteroatom complexes, growth of zeolite crystals along with targeted directions, zeolite transformation, and heteroatom replacements. In this review, the recent progresses for syntheses of metallosilicate zeolites are concisely summarized. In addition, the fundamental principles are briefly discussed for the formation of the metallosilicate zeolites. This review should be helpful for design and preparation of the heteroatom-substituted silica-based zeolites as highly efficient heterogeneous catalysts.

The effect of chelating agents on iron plaques and arsenic accumulation in duckweed (Lemna minor)

Iron plaques have been found to limit the phytoremediation efficiency by reducing iron solubility, while chelating agents can increase the bioavailability of iron from Fe plaques to numerous terrestrial plants. However, the effects of chelating agents on Fe plaques along the As accumulation in aquatic plants remain unknown. In this study, the effects of five chelating agents (EDTA, DTPA, NTA, GLDA, and CA) on the As (As(III) or As(V)), phosphate, and iron uptake by iron plaques and duckweed (Lemna minor) were examined. The results showed that the chelating agents increased the As accumulation in L. minor plants by desorbing and mobilizing As from Fe plaques. The desorption rates of As(V) (As(III)) from the Fe plaques by the chelating agents were 5.26–8.77% (8.70–15.02%), and the plants/DCB extract ratios of As(V) (As(III)) increased from 2.63 ± 0.13 (1.97 ± 0.06) to the peak value of 3.38 ± 0.21 (2.70 ± 0.14) upon adding chelating agents. Besides, the addition of chelating agents increased the uptake of P and Fe by L. minor plants. This work provides a theoretical basis for the remediation of As-contaminated waters by duckweed with the help of chelating agents.

Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review

Persistent organic contaminants affecting soil and groundwater pose a significant threat to ecosystems and human health. Fenton oxidation is an efficient treatment for removing these pollutants in the aqueous phase at acidic pH. However, the in-situ application of this technology for soil remediation (where pHs around neutrality are required) presents important limitations, such as catalyst (iron) availability and oxidant (H2O2) stability. The addition of chelating agents (CAs), forming complexes with Fe and enabling Fenton reactions under these conditions, so-called chelate-modified Fenton process (MF), tries to overcome the challenges identified in conventional Fenton. Despite the growing interest in this technology, there is not yet a critical review compiling the information needed for its real application. The advantages and drawbacks of MF must be clarified, and the recent achievements should be shared with the scientific community. This review provides a general overview of the application of CAs to enhance the Fenton process for the remediation of soils polluted with the most common organic contaminants, especially for a deep understanding of the activation mechanisms and influential factors. The existing shortcomings and research needs have been highlighted. Finally, future research perspectives on the use of CAs in MF and recommendations have been provided.

Formation and stability of CoMoS nanoclusters by the addition of citric acid: A study by high resolution STEM-HAADF microscopy

In this work, we present atomic-scale images of Co promoted MoS2 slabs supported on γ-Al2O3 obtained by High Resolution Scanning Transmission Electron Microscopy equipped with High Angular Annular Dark Field detector (HR STEM-HAADF). These images allow to study the effect of citric acid (CA) addition during preparation, on the slab length and its stability during thiophene hydrodesulfurization (HDS) reaction. Thus, the observations, obtained for sulfide catalysts prepared without or with citric acid as chelating agent, evidenced strong decrease in size of the CoMoS nano-slabs as detected indirectly by the adsorption of CO followed by Infrared spectroscopy (IR/CO). Quantitative dispersion values were calculated from the images taking into account the true shape of the particles instead of the classical hexagonal shape hypothesis. Characterization of the used catalyst shows that these nanoclusters are stable under model thiophene HDS reaction. Such observations allow a better understanding of the effect of chelating agent addition on promoted MoS2 samples in order to explain their catalytic activity.

Assisted phytoremediation of lead contaminated soil using Atriplex halimus and its effect on some soil physical properties

Lead is one of the most harmful trace elements found in soils. Despite reductions in environmental lead exposure, an historical lead pollution continues affecting soils in many areas. To mitigate the impact of lead, phytoremediation assisted with addition of chelating agents can be a suitable option. In order to evaluate the phytostabilization and/or phytoextraction capacity of Atriplex halimus, a pot assay with six phytoremediation treatments was established using different combination of two chelating agents (citric acid and fulvic acids), a composted substrate as organic amendment and a soil highly contaminated with lead (2952 ± 280 mg Pb kg−1, pH 6.30 ± 0.13) collected in the Valparaiso Region, Central Chile. Chelating agents were applied to irrigation water considering a concentration of 4 g L−1, while the organic amendment was applied at the beginning of the assay (dose of 5% v/v). After 180 days, the addition of the chelating agents significantly increased the Pb concentrations in tissues, an effect that was enhanced by application of the organic amendment, reaching concentrations of 32, 42, and 360 mg Pb kg−1 in leaves, stems, and roots, respectively. The treatments considered the addition of fulvic acids showed higher total plant dry weight levels (16.4 and 18.2 g, respectively) compared to the rest, which ranged from 8.3 to 10.0 g. With respect to soil physical properties, chelating agents increased microaggregate stability, but fulvic acids addition significantly decreased the soil available water. In general, Atriplex halimus demonstrated good potential for the phytostabilization of lead contaminated soils and a limited phytoextraction capacity.

Effect of sulfidation pressure on the structure and activity of Ni(CyDTA)W/γ-Al2O3 hydrodesulfurization catalysts

In this paper NiW/γ-Al2O3catalysts were prepared by consecutive impregnation of a W/γ-Al2O3 catalyst with an aqueous solution of nickel salt. The structural control of the nickel ion precursor in the impregnation solution was achieved by the addition of 1, 2-cyclohexanediamine-N, N, N’, N’-tetraacetic acid (CyDTA) as a chelating agent at different pH. The influence of the sulfidation pressure (1 bar vs 40 bar) on the activity and structure of the NiW catalysts was investigated. The catalysts performances were tested in hydrodesulfurization (HDS) of thiophene after sulfidation at atmospheric or high pressure. The catalysts were characterized by X-Ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and infrared spectroscopy of adsorbed CO (IR/CO) to explain the modification in surface species composition due to the chelating agent CyDTA and sulfiding conditions.NiW catalysts prepared in presence of CydTA and sulfided under high pressure displayed the highest HDS activity. These two factors enhanced the sulfidation degree of W-based species as characterized by XPS. A linear correlation was found between the HDS activity and the sulfidation degree. In addition, chelating agent addition induced a decrease on metal-support interaction, as pointed out by TPR, and strongly favored the creation of CUS sites on the NiWS phase as seen by IR/CO. All these features favored a high catalytic activity. In addition, high pressure sulfidation not only leads to more active NiW catalysts but improved the butene-over-butane ratio.