Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX
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A New Method for Quantifying Phosphorus of Various Occurrence Forms in Solid Fuels Xujun Chen, Sui Boon Liaw, and Hongwei Wu*
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Discipline of Chemical Engineering, Western Australian School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia ABSTRACT: Quantification of phosphorus (P) and determination of the occurrence forms of P in solid fuels are important to thermochemical processing of P-containing solid fuels. This study has developed a new three-step method for separating and quantifying the total P in a solid fuel into five major P-containing fractions. These consist of three organic P-containing fractions (i.e., acid-soluble organic P, two acid-insoluble organic P including P in lipids and P in nucleic acids and other acid-insoluble organic structures) and two inorganic P-containing fractions (i.e., acid-soluble inorganic P and acid-insoluble inorganic P). The first step of this new method uses cold 0.6 M HClO4 to extract the acid-soluble P species. The extracted solution is then neutralized, followed by selectively converting the acid-soluble organic P in the solution into orthophosphate (PO43−), pyrophosphate (P2O74−), and tripolyphosphate (P3O105−) by UV irradiation in the presence of H2O2. The second step of this new method uses an ethanol/chloroform mixture to extract the residue from the first step to yield a solution for quantifying the contents of P in acid-insoluble phospholipids using an inductively coupled plasma optical emission spectrometer (ICP-OES). The third step of this new method uses buffered NaCl solution at 100 °C to extract P in nucleic acids and other acid-insoluble organic structures from the residue of the second step into a solution for subsequent quantification using ICP-OES. The acidinsoluble inorganic P in the residue is then quantified using ICP-OES after HF/HNO3/H2O2 acid digestion. The new method is validated with a comprehensive set of standard samples loaded with known amounts of single or mixed P-containing species with known occurrence forms. Compared to the large errors of the conventional Standards, Measurements and Testing method, complete P recovery is achieved with minimal errors. Further applications of the new method to seven different solid fuels also achieve close to 100% mass balance of P. The results demonstrate that the new method is suitable for quantifying various forms of P in solid fuels. physicochemical fractionation,19,22−27 enzyme hydrolysis,28−30 and sequential extraction.9,12,31−42 Particularly, the Standards, Measurements and Testing (SMT) method12,31,32 based on sequential extraction is most commonly used to quantify organic and inorganic P in solid fuels. Unfortunately, as detailed in Section 3.2, none of those methods can be successfully applied to quantify phosphorus of various occurrence forms in solid fuels. Consequently, this study aims to develop a new method for quantifying different forms of P in solid fuels via chemical extraction and acid digestion techniques, in combination with the analysis of phosphorus using ion chromatography (IC) and inductively coupled plasma optical emission spectrometry (ICP-OES). The new method has been validated using a series of P standards with known contents and forms. It has also been successfully applied for analyzing the contents and forms of P in a wide range of seven solid fuels (i.e., biosolid, meat and bone meal, chicken litter, rice bran, algae, mallee leaf, and biosolid char), with far better accuracies than those determined using the conventional SMT method.
1. INTRODUCTION Thermochemical utilization of P-containing solid fuels, such as biosolid, seed-originated biomass, and animal wastes has become increasingly important for combating climate change and reducing fossil fuel consumption.1−4 However, thermal utilization of P-rich solid fuels could face various process challenges such as fouling/slagging,5 corrosion,6 bed agglomeration, and deactivation of catalysts.7 The release of Pcontaining species during the conversion of these fuels also contributes to various environmental problems, such as particulate matter (PM) emission8 and eutrophication in water systems.9 The occurrence forms of P in solid fuels vary significantly and dictate P transformation during fuel thermochemical processing. For example, organic P is likely to be released into gaseous phase during combustion or gasification of solid fuels,10,11 while some inorganic P species can be transformed into refractory minerals and thus are retained in the ash.11 More importantly, different forms of P in the byproducts (i.e., char, ash, and fly ash) from thermochemical processing of these solid fuels have different mobilities and bioavailabilities once they are discharged into the environment.12 Therefore, a thorough understanding of the distribution and transformation of P is critical for optimizing the operation conditions during thermochemical utilization of P-rich solid fuels. Several methods have been developed to separate or analyze the forms of P in various solid fuels over the last several decades, including methods based on colorimetry,13−21 © XXXX American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Samples. The experimental program considers a broad range of seven solid fuels with various occurrence forms of P, including Received: February 2, 2019 Revised: March 5, 2019 Published: March 5, 2019 A
DOI: 10.1021/acs.energyfuels.9b00361 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels Table 1. Proximate and Ultimate Analyses of Solid Fuels Used in This Studya proximate (wt %, dbc) b
d
samples
moisture (wt %, ar )
ash
VM
BS RB MBM algae litter leaf BSC
4.2 3.5 2.6 3.9 4.6 7.8 1.8
19.5 9.2 21.6 4.3 31.2 3.9 56.2
67.4 35.9 12.9 39.4 26.9 74.8 4.2
ultimate (wt %, daff) e
FC
C
H
N
Og
13.1 54.9 65.5 56.3 41.9 21.3 39.6
53.78 46.82 42.37 48.92 40.87 56.21 94.10
8.15 7.90 6.28 6.90 3.42 7.29 0.22
9.98 2.35 9.04 9.02 17.28 1.49 4.68
28.09 42.93 42.31 35.16 38.43 35.01 1.00
a BS, biosolid; BSC, biosolid char; RB, rice bran; and MBM, meat and bone meal. bar, air dried. cdb, dry basis. dVM, volatile matter. eFC, fixed carbon. fdaf, dry ash-free. gBy difference.
Table 2. Contents (mg/kg_Solid Fuels, db) of Inorganic Species in Solid Fuelsa inorganic species Na K Ca Mg Cl S Fe P Si Al
BS 1346.2 2008.6 20652.3 4852.6 892.4 8548.9 3158.9 21887.6 19007.9 6708.9
± ± ± ± ± ± ± ± ± ±
RB 18.2 20.3 26.9 36.9 2.9 29.7 48.5 99.7 69.4 48.7
129.1 17563.9 426.6 8489.2 526.2 2026.9 87.5 11532.6 298.6 52.6
± ± ± ± ± ± ± ± ± ±
MBM 12.3 26.3 10.6 22.8 3.2 15.9 2.9 29.7 7.8 2.9
14761.3 7440.2 70191.5 1768.4 8182.5 4687.6 928.3 45532.5 5543.2 554.7
± ± ± ± ± ± ± ± ± ±
algae 22.1 32.9 99.8 37.8 21.1 36.9 55.8 23.6 32.4 5.6
780.7 9139.5 1332.2 2865.2 1970.2 4428.6 2.6 15282.9 127.7 109.7
± ± ± ± ± ± ± ± ± ±
litter 12.5 71.1 15.9 44.2 12.9 26.9 0.3 3.6 5.2 9.5
8849.9 17763.3 32293.1 5463.6 5569.1 2218.6 1492.6 18259.6 18793.1 3002.3
± ± ± ± ± ± ± ± ± ±
leaf 81.1 92.1 94.2 41.1 32.1 3.6 9.6 32.9 32.7 69.3
5537.5 3780.6 7633.0 1418.5 1852.6 1184.6 142.6 1613.3 504.7 198.7
± ± ± ± ± ± ± ± ± ±
BSC 4.9 6.7 9.6 2.4 12.3 12.3 0.4 2.6 8.2 5.7
4200.3 5302.1 70120.1 16052.6 15.6 5302.6 10625.6 60155.2 61425.2 28125.6
± ± ± ± ± ± ± ± ± ±
3.2 9.5 4.1 11.2 3.4 5.2 11.8 14.9 24.0 8.7
a
Descriptions of the sample labels are the same as those in Table 1. column. The recovered mallee wood and rice bran samples were dried at 80 °C to yield the acid-washed mallee wood and rice bran (hereafter termed as AWMW and AWRB, respectively). A double acid-washed biosolid was also prepared from biosolid through repeated acid washing using HF and HCl acid solution according to the procedure reported elsewhere.43 This sample is hereafter termed DAWB in this study. The contents of inorganic species in these acid-washed samples are presented in Table 3. Clearly, after acid washing, only a negligible amount of P (
