Article pubs.acs.org/EF
Preparing, Characterizing, and Evaluating Ammoniated Lignin Diesel from Papermaking Black Liquor Xiaoli Sun, Xiuhua Zhao, Yuangang Zu,* Wengang Li, and Yunlong Ge Key Laboratory of Forest Plant Ecology, Ministry of Education, Northeast Forestry University, Harbin, Heilongjiang 150040, People’s Republic of China ABSTRACT: Managing papermaking black liquor has always been a problem in the papermaking industry. Alkali lignin is biologically difficult to treat and is the main factor that affects the treatment of papermaking black liquor. In this study, we used ammonization to process lignin from papermaking black liquor into ammoniated lignin and then added the ammoniated lignin into diesel oil by applying microemulsion technology. We investigated the influences of several process parameters on the diesel separation rate using an orthogonal array design. The ranges of hydrophilic−lipophilic balance (HLB), emulsifier, and coemulsifier were from 8.3 to 9.3%, from 4 to 6%, and from 0.8 to 1.6%, respectively. When range analysis and analysis of variation (ANOVA) were conducted, the order of affecting ammoniated lignin diesel production was determined as follows: HLB > emulsifier > co-emulsifier. Meanwhile, optimum microemulsion process conditions were found as follows: HLB (9.3%), emulsifier (6%), and co-emulsifier (1.6%). The physicochemical characterizations of ammoniated lignin diesel were determined to evaluate its feasibility as an engine oil. Engine capacity load velocity characteristic trial was conducted, and the engine emission of ammoniated lignin diesel was determined. Results show that ammoniated lignin diesel can save pure diesel by nearly 10% compared to traditional diesel; consequently, ammoniated lignin diesel can be used directly as a suitable fuel. compounds25 (35−40 kJ/cm3) in a unit volume, which contains carbon, hydrogen, and oxygen. The energy density of lignin26 is basically the same as that of diesel (36−38.3 kJ/ cm3). In addition, its complete combustion chemical oxygen demand in a unit volume is also close to that of diesel (2.8− 2.85 g/mL). The spontaneous combustion point27 of lignin is 350 °C, whereas that of diesel ranges from 300 to 380 °C.28,29 The main objective of this study is to conserve diesel resources and reuse black liquor by developing a new kind of biodiesel. Microemulsion technology was used to add lignin (or its derivatives) to diesel. Lignin does not dissolve in water, thus affecting the stability of microemulsion. Moreover, alkali lignin that contains Na+ may produce carbon deposits when it is added into diesel. Ammoniated lignin is a water-soluble lignin derivative that produces combustion products in the form of gases. Hence, ammoniated lignin is the best choice for a diesel fuel additive. In this study, we used ammonization to process lignin from papermaking black liquor into ammoniated lignin and then added the ammoniated lignin into diesel oil by applying microemulsion technology. We investigated the influences of several process parameters on the diesel separation rate using an orthogonal array design. The physicochemical characterizations of ammoniated lignin diesel were determined to evaluate its feasibility as an engine oil. Engine capacity load velocity characteristic trial was conducted, and the engine emission of ammoniated lignin diesel was determined.
1. INTRODUCTION Economic development is based on fossil energy;1−3 however, the supply of this carrier of economic resources has nearly dried up4,5 during the 21st century. Natural polymer, which is renewable and biodegradable,6,7 is receiving increasing attention as the human understanding of the energy crisis8,9 develops extensively. Plants and animal fats are currently the main sources of biodiesel production,10 which results in high cost issues and threatens the food supply.11 Lignin12 is a complex phenolic polymer13 that consists of three alcohol monomers14 (i.e., p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol).15−17 Lignin is a plant cell wall18 ingredient that links cells. Lignin19,20 is classified into three types based on different monomers: (1) syringyl lignin, which polymerizes from syringyl propane monomer, (2) guajacyl lignin, which polymerizes from guaiacyl propane monomer polymerization, and (3) hydroxyphenyl lignin, which polymerizes from phydroxyphenyl propane monomer polymerization.20 Lignin is widely distributed in nature; it exists extensively in plants as an amorphous molecular aromatic polymer.12,13 In terms of abundance in nature, lignin ranks second to cellulose21 and can regenerate at a rate of 50 billion tons every year.16,22 Alkali lignin in papermaking black liquor23 is frequently burned or discharged directly with liquid waste, thus resulting in waste resources and serious environmental pollution. Comprehensively using industrial alkali lignin has always been the focus of solving waste liquid pollution from papermaking and improving resource use of natural materials. Thus, adding lignin from papermaking black liquor into diesel can be a good solution to all of the aforementioned problems; moreover, this solution does not threaten the food supply. Lignin24 has an inherent advantage as a diesel substitute because lignin and diesel have similar energy densities. Lignin has the highest energy density among natural polymer © 2014 American Chemical Society
Received: April 12, 2014 Revised: June 3, 2014 Published: June 3, 2014 3957
dx.doi.org/10.1021/ef5008165 | Energy Fuels 2014, 28, 3957−3963
Energy & Fuels
Article
the dispersed phase, and oil is the external phase). We added the emulsifier and co-emulsifier into the diesel and stirred until all substances were mixed evenly. We slowly poured ammoniated lignin into the mixed diesel liquor. The solution was mixed at high speed and sheared using an emulsion pump. The entire reaction system was kept at 25 kg, with lignin accounting for 10% of the total volume. These data were obtained from the preliminary experiment. A schematic of the preparation of ammoniated lignin diesel is shown in Figure 1. A
2. MATERIALS AND METHODS 2.1. Materials. Papermaking black liquor, which was prepared by alkaline pulping from poplar, was obtained from Harbin City Zhenxing Paper Mill (Heilongjiang, China). Ammonium hydroxide was purchased from Sigma-Aldrich Corporation (St. Louis, MO). The emulsifier (Span-80, CTAB) was purchased from Bodi Chemical Reagents Co. (Tianjin, China). The co-emulsifier (n-butanol) was purchased from Ruijinte Chemical Reagents Co. (Tianjin, China). Diesel 35 was obtained from a gas station of the China National Petroleum Corporation. Distilled water was purified using a Milli-Q water purification system from Millipore Corporation (Bedford, MA). Acetic acid and H2O2 were both from Fuguang Chemical Reagents Co. (Tianjin, China). 2.2. Lignin Preparation. We slowly added acetic acid into papermaking black liquor and stirred the reaction mixture until pH was less than 3. Then, we filtered the mixture to obtain the precipitate, i.e., solid lignin. 2.3. Ammoniated Lignin Preparation. Lignin is a poorly soluble biomass in water. To obtain water-soluble lignin, we prepared lignin in the ammoniation reaction. The main reaction mechanism30,31 is that lignin ammoniation produces nitrogenated compounds that mainly belong to ammonium carboxylate salts and amides (e.g., formamide, acetamide, and benzamide). The moiety of the aromatic rings, ether, and alcohol groups decreased as C−O, C−N, and C−N−H bonds increased.32 Then, 1 kg of lignin and 10 kg of distilled water were placed into a three-necked flask. The lignin suspension liquid was evenly heated while mixing. A water bath was set to 65 °C. The amounts of ammonia and H2O2 were 1.8 and 0.15 times that of lignin, respectively. We first mixed ammonia and H2O2 and then added the liquor mixture into the lignin suspension every 5 min. We added all of the mixed liquor 4 times until the desired temperature was reached. Finally, we obtained ammoniated lignin. We placed the ammoniated lignin solution into a tank and used air exhaustion and heat processes to obtain ammonia gas, which was used for recycling in the ammoniation reaction and to disintegrate extra H2O2. 2.4. Lignin and Derivative Characterization. To study ammoniated lignin, we compared lignin and alkali lignin to determine which one is more suitable as a diesel substitute in our experiment. We characterized each sample through the following detection processes. 2.4.1. Sodium Content. An AA800 atomic absorption spectrophotometer (PerkinElmer, Inc., Waltham, MA) was used for detection. The test conditions were as follows: lamp current of 1.0 mA, wavelengths of 589.3 and 0.2 nm slit, negative high voltage of 350 V, air flow rate of 6.7 L/min, and acetylene flow rate of 1.0 L/min. The alkali lignin sample was diluted 5000 times from 0.2 to 1.6 mg/L. The ammoniated lignin and lignin samples did not need to be diluted. 2.4.2. Thermogravimetric Analysis (TGA). TGA of ammoniated lignin was conducted using a Pyris 1 TGA instrument (PerkinElmer, Inc., Waltham, MA). The experiment was performed with a heating rate of 10 °C min−1 using nitrogen flow (50 mL min−1). Samples were weighed (approximately 5 mg) in open aluminum pans, and the percentage weight loss of the samples was monitored between 50 and 400 °C. 2.4.3. Differential Scanning Calorimetry (DSC) Analysis. DSC measurements were performed on a DSC 131 instrument (Setaram Instrumentation, Caluire, France). Samples (15 mg) were placed on aluminum pans and sealed in the sample pan press. The probes were heated from 40 to 250 °C at a rate of 10 °C min−1 under a nitrogen atmosphere. 2.4.4. Fourier Transform Infrared Spectroscopy (FTIR). FTIR was performed on ammoniated lignin and lignin. The FTIR spectra of the samples were obtained from an Avatar 360 FTIR (Thermo Fisher Scientific, Waltham, MA). Both samples were dried at 120 °C to remove any physically adsorbed water before FTIR analysis. The samples were mixed with potassium bromide (KBr) using an agate mortar and compressed into a thin disc. The scanning range was from 400 to 4000 cm−1, whereas the resolution was 4 cm−1. 2.5. Optimization Experiment of Microemulsion Diesel. Microemulsion diesel is a water-in-oil (W/O) system (i.e., water is
Figure 1. Preparation of the schematic diagram of ammoniated lignin diesel. L9(34) orthogonal design was adopted to select the most effective combinational measurement to optimize the microemulsion of ammoniated lignin diesel. Each row of the orthogonal experiment represented a run, which was a specific set of factor levels that should be tested. The basic range of the level of each factor was based on preliminary experiments. An extra column was assigned to each factor to avoid any personal or subjective bias. This extra column was used to record errors and show the reliability of the entire test. The factors obtained from the levels of the orthogonal test based on preliminary experiments are listed in Table 1.
Table 1. Levels and Factors of the Orthogonal Array Design of the Microemulsion Diesel factors level
HLB A
emulsifier B (wt %)
co-emulsifier C (wt %)
1 2 3
8.3 8.8 9.3
4 5 6
0.8 1.2 1.6
A scoring method based on the diesel separation rate (diesel separation rate = volume of separation diesel/volume of total diesel) was applied to evaluate the stability of the obtained microemulsion diesel. The relationship between the score and separation rate of diesel is shown in Table 2. Range analysis and analysis of variation (ANOVA) were performed to obtain optimal reaction conditions.
Table 2. Relationship between the Score and Separation Rate of Microemulsion Diesel
3958
level
separation rate of diesel (%)
score
1 2 3 4 5
40
9 7 5 3 1
dx.doi.org/10.1021/ef5008165 | Energy Fuels 2014, 28, 3957−3963
Energy & Fuels
Article
SPSS software was employed to analyze the statistical experimental design. Finally, optimal reaction conditions were reproduced to ensure accuracy. 2.6. Physicochemical Characterization. As a diesel substitute, ammoniated lignin diesel should satisfy the standard of diesel. Therefore, the properties of ammoniated lignin diesel, which are similar to those of diesel, can be evaluated to determine if ammoniated lignin diesel can be used as a diesel substitute. The physicochemical characterizations (total of 14) of ammoniated lignin diesel and diesel were investigated in this study, including cetane value, cold filter, plugging point chrominance, oxidation stability, and sulfur content. ASTM D975-2010c,33 Standard Specification for Diesel Fuel Oils of the USA, was used in detection. By comparing ammoniated lignin diesel to diesel, we observed the performance of ammoniated lignin diesel. 2.7. Stability Test. Color and layering are two of the most important indices for emulsion systems. Karimi and Mohammadifar34 used a picture to prove the stability of an emulsion system. Hence, the prepared ammoniated lignin diesel and equivalent diesel were placed into a 10 mL tube at room temperature (20−25 °C). We observed the layering condition and took pictures once every 3 months. 2.8. Power Performance and Emission Performance of Ammoniated Lignin Diesel. 2.8.1. Engine Capacity Load Velocity Characteristic Trial. We conducted performance tests to reciprocate internal combustion engines in this experiment. We used a 485QB diesel engine with RSM/RPM at 32.3 kW/2600 rpm. All equipment, temperature, and pressure sensors were connected to the data acquisition and control system. The system collected engine data, whereas equipment measurements controlled the test. The parameters specified by the cycle were imposed. All tests were based on the ISO 15550:200235 standard. 2.8.2. Emission Performance of Ammoniated Lignin Diesel. A ZJY-1 autofilter-type smoke meter (Bei en Co., China) was used to test the emission performances of ammoniated lignin diesel and diesel.
Figure 2. TG curves of ammoniated lignin, lignin, and alkali lignin.
ammoniated lignin was 5% more than that of lignin from 700 to 800 °C. The weight loss rate of ammoniated lignin was 40% from 600 to 800 °C, which was the smallest value. Given that the temperature of the engine cylinder could reach 600−800 °C, ammoniated lignin exhibited considerable weight loss at this temperature range. The residual quantity of ammoniated lignin was observed to be the smallest value, thus implying that ammoniated lignin could not cause carbon deposition on the engine. Therefore, ammoniated lignin is the most suitable diesel substitute. 3.1.3. DSC Analysis. DSC analysis is a technique used to measure temperature and energy variations involved in phase transitions, which are related to the endothermic and exothermic changes in samples during the heating process.37 As shown in Figure 3, ammoniated lignin has high thermal
3. RESULTS AND DISCUSSION 3.1. Characterization of Lignin and Derivative. 3.1.1. Sodium Content. The sodium contents36 of lignin, ammoniated lignin, and alkali lignin are shown in Table 3. The Table 3. Content of Sodium in Three Kinds of Lignin sample
sodium content (%)
alkali lignin lignin ammoniated lignin
2.52
Figure 3. DSC curves of ammoniated lignin, lignin, and alkali lignin.
stability. It only exhibited a small amplitude exothermic peak at 169.25 °C and a small endothermic peak at 344.35 °C. However, the curve of ammoniated lignin tends to stabilize. Lignin exhibited an absorption phenomenon from 354.27 °C, and thermal stability was gradually reduced after 354.27 °C. Alkali lignin exhibited the lowest thermal stability, with two large endothermic peaks at 289.81 and 457.31 °C, whereas ammoniated lignin exhibited the highest. Consequently, ammoniated lignin is the most suitable diesel substitute in this experiment. 3.1.4. FTIR Analysis. Ammoniated lignin was chosen for this experiment. The chemical properties of ammoniated lignin should remain unchanged to use similar energy densities. FTIR was conducted for both lignin and ammoniated lignin (Figure 4). The FTIR spectrum of ammoniated lignin showed typical features of the lignin classification system. All lignin characteristic peaks between 1250 and 1120 cm−1 (band 6) diaryl-ether bond were minimally modified. The unique aromatic functional peaks between 843 and 734 cm−1 (band 1), the corresponding methoxyl group from 1221 to 1270 cm−1 (band 5), and the
sodium content of alkali lignin was relatively high at 2.52%, whereas those of ammoniated lignin and lignin were below the atomic absorption spectrometry detection limit. A high sodium content easily causes the formation of carbon deposits on the diesel engine. Given that the sodium contents of lignin and ammoniated lignin are extremely low, carbon deposits are not easily formed. Such deposits, which are needed in diesel substitutes, are added to diesel via microemulsion technology. 3.1.2. TGA. TGA is commonly employed to determine sample characteristics (e.g., degradation temperatures and solvent residues). The qualities of the three kinds of samples were gradually reduced as the temperature increased, as shown in Figure 2. The thermogravimetry (TG) curve of ammoniated lignin was basically the same as that of lignin when the temperature was below 600 °C. No obvious change was observed, thus implying that weight losses in both samples were similar. However, the weight loss rate of alkali lignin was smaller than those of lignin and ammoniated lignin after 200 °C. The weight loss rate of 3959
dx.doi.org/10.1021/ef5008165 | Energy Fuels 2014, 28, 3957−3963
Energy & Fuels
Article
is the range for each factor. This range shows the difference between maximum and minimum values. A high mean value R indicates that the level has a significant effect on the score.41 Therefore, the best level for each factor is determined according to the highest mean value of the experimental condition. In Table 4, the highest score of ammoniated lignin diesel for each level was clearly distinguished [hydrophilic−lipophilic balance (HLB) was 9.3; emulsifier dosage was 6%; and co-emulsifier dosage was 1.6%]. The range value Rj (j = A, B, and C) indicates the significance of the effect of the factor. A large Rj value indicates a significant factor effect on the experimental result. Therefore, comparing the range values of different factors (Rj) shows the following levels of significance of the factors: HLB (4.67) > emulsifier (3.33) > co-emulsifier (0.66). The range value of HLB was the largest, thus indicating that a slight change in HLB produces a significant change in the score. The mean values of each factor are shown in Figure 5. These graphs were only used to show the trends of each factor and not to predict other values that were not tested experimentally. On the basis of the change in the mean value of each factor (panels a−c of Figure 5), we observed that scores increased sharply from 3 to 8 when HLB increased from 8.3 to 9.3 and reached the highest point at 9.3. For the emulsifier, the score increased steadily and reached a maximum of 7 at 6%. Meanwhile, the co-emulsifier only had an effect on the score from 5 to 5.65 but had no effect before 1.2%. The score also reached a maximum of 5.65 at 1.6% co-emulsifier. Hence, the conditions for the optimum microemulsion technology process were determined as follows: HLB (9.3), emulsifier (6%), and co-emulsifier (1.6%). The optimizing experiment was repeated 3 times. The microemulsion system had no stratified condition and was extremely clear each time. The optimized condition exhibited excellent repetition capability. All testing samples were prepared under optimum conditions. 3.2.2. ANOVA of the Orthogonal Experiment. The ANOVA results for ammoniated lignin diesel are shown in Table 5 to identify the main factor in the microemulsion process. Vj (j = A, B, and C) was compared to VD before calculating Fj to increase the reliability of the F test. Co-emulsifier variance (VC = 0.44) was less than 2-fold of the experimental error (VD × 2 = 0.45 × 2 = 0.7) for the score of ammoniated lignin diesel, thus indicating that the effect of the co-emulsifier was minimal. Table 5 shows how the F value was calculated. The critical value for the inspection level (α = 0.10) was found in the F value distribution table: F0.10(2, 2) = 9.0. The F value obtained in ANOVA was clearly higher than the listed F0.10(2, 2) = 9.0 when Fj (j = A, B, and C) and Fα were compared. Table 5 clearly shows that FA > Fα and FB > Fα. Therefore, the significance of HLB and the emulsifier are the prominent factors that affect the score of ammoniated lignin biodiesel, thus proving that the best microemulsion condition is correct. 3.3. Physicochemical Characterization Analysis. Diesel fuel for internal combustion engines should possess physicochemical characterization to ensure autoignition of fuel and smooth unproblematic combustion. The physicochemical characterization of fuel depends upon the 14 items listed in Table 6.33 The standard specifications of diesel fuel are also shown in Table 6 as the objective satisfaction of the following properties. The main items of standard diesel engines are inflammable point and liquidity scale. The comparison of the indices of ammoniated lignin diesel and traditional diesel are shown in Table 6. The cetane value was the evaluation
Figure 4. FTIR absorbance spectrum of ammoniated lignin, lignin, and alkali lignin.
huge peak from 1430 to 1445 cm−1 (band 8) showed that ammoniated lignin and lignin have similar main functional structures38,39 (Figure 4). However, ammoniated lignin degraded the aromatic rings through the oxidative ring opening, thus deforming the intensities of the guaiacyl band at 1270 cm−1 (C−H band). The arom C−H out-of-plane deformation vibration bands at 858 and 820 cm−1 (band 2) were mostly reduced. These results are consistent with those by Varela et al.32 and Meier et al.40 The results of gas chromatography− mass spectrometry and nuclear magnetic resonance spectroscopy in the study by Varela et al.32 also showed that lignin and ammoniated lignin have similar spectra frames after the reaction. Hence, the functional structures of lignin and ammoniated lignin are similar. These results provide the foundation for the following research. 3.2. Optimization of the Microemulsion Process. 3.2.1. Range Analysis of the Orthogonal Experiment. The obtained ammoniated lignin diesel product was scored after the microemulsion process based on the rules presented in Table 2, which evaluate the stability of a microemulsion. Nine experiments were conducted according to the orthogonal experiment analysis. The score results are shown in Table 4. The blank column (D) was used as the experimental error to indicate the reliability of all experiments as a whole. This information was regarded as the original data and used in range analysis and ANOVA. The mean values of K for various factors at different levels for the range analysis are shown in Table 4. R Table 4. L9(34) Design and Experimental Results of the Orthogonal Array of the Microemulsion Diesel trial number
HLB A
emulsifier B (wt %)
co-emulsifier C (wt %)
1 2 3 4 5 6 7 8 9 K1 K2 K3 K̅ 1 K̅ 2 K̅ 3 R
8.3 8.3 8.3 8.8 8.8 8.8 9.3 9.3 9.3 3.00 5.00 7.67 1.00 1.67 2.56 4.67
4 5 6 4 5 6 4 5 6 3.66 5.00 7.00 1.22 1.67 2.33 3.33
0.8 1.2 1.6 1.2 1.6 0.8 1.6 0.8 1.2 5.00 5.00 5.67 1.67 1.67 1.89 0.66
blank D score 1 2 3 3 1 2 2 3 1 5.00 5.67 5.00 1.67 1.89 1.67 0.66
1 3 5 3 5 7 7 7 9
3960
dx.doi.org/10.1021/ef5008165 | Energy Fuels 2014, 28, 3957−3963
Energy & Fuels
Article
Figure 5. Effect of each factor on the score.
Table 5. Analysis of variance (ANOVA) parameters of the orthogonal test of the microemulsion process factor
SS
DF
V
F
F(0.10)(2, 2) = 9.0
A (HLB) B (emulsifier) C (co-emulsifier) D (blank)
32.89 16.88 0.88 0.89
2 2 2 2
16.45 8.44 0.44 0.45
36.99 18.99 1
> >
