Co-pyrolysis of biomass and soapstock in a downdraft reactor using a novel ZSM-5/SiC composite catalyst

A ZSM-5/SiC composite catalyst was synthesized and characterized by Brunauer-Emmett-Teller analysis, X-ray diffraction, and scanning electron microscopy in this study. The composite catalyst had the characteristics of ZSM-5 and SiC, and the surface of SiC grew evenly with a layer of ZSM-5. The effect of the composite catalyst on the product distribution and chemical composition in a co-pyrolysis downdraft system was investigated. In a down system with a catalytic temperature of 450 °C, a feed-to-catalyst ratio of 2:1, and a soybean-soapstock-to-straw ratio of 1:1, the proportions of alkanes, olefins, aromatics, and phenoxy compounds were 6.82%, 4.5%, 73.56% and 11.11%, respectively. The composite catalyst combined the catalytic performance of ZSM-5 and SiC, increasing the proportion of aromatics and decreasing the proportion of oxygen-containing compound in the bio-oil. Moreover, the composite catalyst maintained its activity after reusing several times.

Cultivation of Chlorella vulgaris in sludge extracts: Nutrient removal and algal utilization

In order to utilize the excess sludge and reduce the cost of algal cultivation, Chlorella vulgaris was cultivated in increasing proportions of sludge extracts for simultaneous nutrients removal and algal utilization. Results showed that C. vulgaris cultivated in the 100% sludge extract gained the highest total biomass (33.98 ± 0.30 × 10⁶ cells/mL) and showed good results in TOC (absolute value 175 mg/L) and nutrients (TN: 77.1%; TP: 95.0%) removals. According to the Excitation-emission matrix spectra (EEMs) analysis, the 8th day was suggested as the optimal time for biomass harvesting. Although the lipid contents showed a negative correlation with the proportion of sludge extract, the FAME analysis showed that the saturated fatty acids (SFA) contents decreased and the unsaturated fatty acids (UFA) content increased as the concentration of sludge extract increased. The 100% sludge extract could be a desirable alternative medium for the algae cultivation.

Renewable jet-fuel range hydrocarbons production from co-pyrolysis of lignin and soapstock with the activated carbon catalyst

The current study aims to investigate the effects of agricultural waste-derived activated carbon catalyst on the jet-fuel range hydrocarbons distribution from raw biomass pyrolysis under the hydrogen donor condition provided by a solid waste. Ex-situ catalytic fast co-pyrolysis of lignin with and without soapstock was carried out using the corn stover-derived activated carbon catalyst in a facile fixed bed reactor. Results showed that the soapstock, as the hydrogen donor, exhibited a positive synergistic effect with lignin on enhancing the production of valuable aromatics in the obtained bio-oil. Additionally, biomass-derived activated carbon catalyst has the robust catalytic ability to convert pyrolysis vapors into high-density jet fuel-ranged aromatic hydrocarbons rather than phenols with the assistance of soapstock solid waste. Results indicated that the proportions of jet-fuel range aromatics increased monotonically with elevating pyrolytic temperatures from 400 to 550 °C, and the optimal lignin/soapstock ratio was 1:2 with regarding the yield of attained bio-oils. The maximum proportion of jet-fuel ranged aromatics (87.8%) and H₂ concentration (76.4 vol%) could be achieved with the pyrolytic temperature, lignin/soapstock ratio, and catalyst/feedstock ratio of 550 °C, 2:1, and 1:1, respectively. The current study may provide a novel route of converting solid wastes into value-added jet fuels and hydrogen-enriched fuel gases, which will advance the utilization of renewable biomass.

Comparative study on characteristics of the bio-oil from microwave-assisted pyrolysis of lignocellulose and triacylglycerol

Microwave-assisted pyrolysis of Camellia oleifera shell (COS) and stillingia oil (SO) was performed in the temperature range of 400-600 °C. The effects of feedstock and pyrolysis temperatures on product yield and bio-oil composition were discussed in detail. The bio-oil yield from COS pyrolysis varied from 37.30 wt% to 40.27 wt%, which was 11.32 wt% to 21.62 wt% lower than that from SO pyrolysis. Gas chromatography-mass spectrometry analysis indicated that SO bio-oil was rich in hydrocarbons, whereas COS pyrolysis produced mainly oxygen-containing compounds predominantly comprising phenols and acids. Fourier transform infrared and ¹H-nuclear magnetic resonance spectra showed significant differences in the chemical structure of bio-oils from COS and SO pyrolysis. Elemental-composition and physical-property analyses further revealed that SO bio-oils were similar to gasoline and heavy fuel oil.

Catalytic co-pyrolysis of Alternanthera philoxeroides and peanut soapstock via a new continuous fast microwave pyrolysis system

Continuous fast microwave catalytic co-pyrolysis of Alternanthera philoxeroides and peanut soapstock was studied using HZSM-5 as catalyst. The effects of catalyst temperature, feedstock-to-catalyst ratio, and A. philoxeroides-to-peanut soapstock ratio on the yield and composition of bio-oil were studied. Experimental results showed that the optimum catalyst temperature was 400 °C. The catalyst increased the proportion of aromatics but reduced the bio-oil yield. The optimum feedstock-to-catalyst ratio was 2:1. A. philoxeroides presented a significant synergistic effect with peanut soapstock, which facilitated the production of aromatics in the bio-oil. The optimum A. philoxeroides-to-peanut soapstock ratio was 1:2.

Evaluation of Cronobacter sakazakii inactivation and physicochemical property changes of non-fat dry milk powder by cold atmospheric plasma

Cronobacter sakazakii can cause life-threatening infections in neonates. Exposure to contaminated powdered food, especially milk powder, is a major route for C. sakazakii infection. Cold atmospheric plasma (CAP) is well known as a non-thermal method for inactivating microbial pathogens. This study evaluates the effectiveness of CAP on C. sakazakii in non-fat dry milk (NFDM) powder using a fluidized reaction system. The CAP treatments for 20-120 s led to 1.17-3.27 log₁₀ reductions of C. sakazakii. C. sakazakii inactivation increased with increasing flow rate from 8 to 20 L/min. In terms of quality attributes of NFDM after the CAP treatments, no noticeable color changes (ΔE < 1.5) were observed. Moreover, no significant changes in crystallinity, amino acid composition, or phenolic content occurred following a 120s-CAP treatment. These results indicate that this fluidized reaction system combined with CAP can provide an effective antimicrobial activity with minimal effects on some physicochemical properties of NFDM powder.

Nutrient removal from digested swine wastewater by combining ammonia stripping with struvite precipitation

Typical biological processing is often challenging for removing ammonia nitrogen and phosphate from swine wastewater due to inhibition of high ammonia on activity of microorganisms, exhaustion of time, and low efficiency. In this study, a physicochemical process by combining ammonia stripping with struvite precipitation has been tested to simultaneously remove ammonia nitrogen, phosphate, and chemical oxygen demand (COD) from digested swine wastewater (DSW) with high efficiency, low cost, and environmental friendliness. The pH, temperature, and magnesium content of DSW are the key factors for ammonia removal and phosphate recovery through combining stripping with struvite precipitation. MgO was used as the struvite precipitant for NH₄⁺ and PO₄^3- and as the pH adjusted for air stripping of residual ammonia under the condition of 40 °C and 0.48 m³ h^-1 L^-1 aeration rate for 3 h. The results showed that the removal efficiency of ammonia, total phosphate, and COD from DSW significantly increased with increase of MgO dosage due to synergistic action of ammonia stripping and struvite precipitation. Considering the processing cost and national discharge standard for DSW, 0.75 g L^-1 MgO dosage was recommended using the combining technology for nutrient removal from DSW. In addition, 88.03% NH₄⁺-N and 96.07% TP could be recovered from DSW by adsorption of phosphoric acid and precipitation of magnesium ammonium phosphate (MAP). The combined technology could effectively remove and recover the nutrients from DSW to achieve environmental protection and sustainable and renewable resource of DSW. An economic analysis showed that the combining technology for nutrient removal from DSW was feasible.

Integrated process for anaerobically digested swine manure treatment

An integrated three-step process was proposed for the treatment of the anaerobically digested swine manure (ADSM). The flocculation and struvite precipitation were used as the pre-treatment to remove the particles and reduce phosphorus to balance the condition for the algae growth. In the biological step, the 40% group (2.5× dilution) represented the optimal cultivation condition for the A + B co-cultivation, with the highest biomass concentration of 2.325 ± 0.16 g/L and performed well with nutrients removal (COD: 9770 ± 184 mg/L; TN: 235 ± 5.4 mg/L; TP: 25.3 ± 0.8 mg/L). 94.8% of the biomass from the 40% group could naturally settle down in 30 min which is good for harvest. The activated carbon adsorption was applied as the advanced treatment to resolve the issues with the dark color and residual compounds. After these processes, the removal efficiencies of COD, TN, TP and NH₄-N reached 97.2%, 94.0%, 99.7% and 99.9%, respectively.

Cultivation of Chlorella vulgaris in manure-free piggery wastewater with high-strength ammonium for nutrients removal and biomass production: Effect of ammonium concentration, carbon/nitrogen ratio and pH

Ammonia toxicity is a major disadvantage of microalgal growth when high-strength ammonium wastewaters like manure-free piggery wastewater (MFPW) were used as microalgal growth medium. In the present study, the effect of ammonium concentration, carbon/nitrogen ratio, and pH on ammonia toxicity of Chlorella vulgaris cultivated in the MFPW and nutrients removal was investigated. The three important parameters affected ammonia toxicity of C. vulgaris and nutrients removal of the MFPW significantly. The ammonium concentration of the MFPW could be decreased by air stripping. Microalga grew best at a carbon/nitrogen ratio of 25:1 with the maximum biomass concentration of 3.83 g L^-1, the highest cell viability of 97%, and the removal of 100% ammonia, 95% of total phosphorus, and 99% of chemical oxygen demand. Ammonia toxicity was alleviated by pH control. The application of the established strategies can enhance nutrients removal of the MFPW while mitigating ammonia toxicity of C. vulgaris.

Conversion of woody oil into bio-oil in a downdraft reactor using a novel silicon carbide foam supported MCM41 composite catalyst

This study reports the synthesis of a SiC-MCM41 composite catalyst by a microwave-assisted hydrothermal process and the composite catalyst had the characteristics of MCM41 and SiC, and the surface of SiC grew evenly with a layer of MCM41 after characterization of the catalysts by various means (X-ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy). The catalyst was applied in the pyrolysis of waste oil to investigate how it influences the bio-oil component proportion compared with no catalyst, only SiC, only MCM41 catalysis and the catalytic effect was also investigated at different temperatures and different catalyst to feed ratios. In a downdraft system with a pyrolysis temperature of 550 °C, a catalyst to feed ratio of 1 : 2, and a catalytic temperature of 400 °C, 32.43% C₅–C₁₂ hydrocarbons and 41.10% mono-aromatics were obtained. The composite catalyst combined the catalytic effect of SiC and MCM41 because it increased the amount of C₅–C₁₂ hydrocarbons and decreased the amount of oxygen-containing compounds in bio-oil. After repeated uses, the composite catalyst still retained the catalytic properties.

Main flow chart of the pyrolysis process using SiC-MCM41 catalyst.

Catalytic fast pyrolysis of torrefied corn cob to aromatic hydrocarbons over Ni-modified hierarchical ZSM-5 catalyst

Catalytic fast pyrolysis (CFP) of torrefied corn cob using Ni-modified hierarchical ZSM-5 catalyst was conducted in this study. The prepared catalysts were characterized by N₂ adsorption and desorption (N₂-BET), X-ray diffraction (XRD), and temperature-programmed desorption of NH₃ (NH₃-TPD). NaOH solution treatment resulted in the lower peak intensities of hierarchical ZSM-5 catalyst in the XRD patterns while Ni modification improved the catalyst framework. In addition, NaOH solution treatment created some mesopores or macropores, but the incorporation of Ni reduced BET surface area and volume of micropores. Though the addition of Ni lowered the acidity of catalyst, Ni-modified hierarchical ZSM-5 catalyst led to higher yields and of aromatic hydrocarbons. What is more, hierarchical ZSM-5 catalysts significantly improved the selectivities of mono-aromatics. Kinetic analysis shows that CFP of torrefied corn cob was second-order reaction and the addition of Ni can obtain a lower activation energy compared with hierarchical ZSM-5 catalyst.

Intermittent-vacuum assisted thermophilic co-digestion of corn stover and liquid swine manure: Salinity inhibition

In this study, the effects of Intermittent-Vacuum Stripping (IVS) on activities of methanogenesis in co-digestion of corn stover with liquid swine manure (LSM + CS) under thermophilic anaerobic digestion (TAD) conditions were evaluated. A 65% methanogenesis activity inhibition was observed in pretreated LSM plus corn stover (pLSM + CS), while 60 and 165 mL/L/day CH₄ productions were achieved in pLSM + CS and LSM + CS, respectively. The high salinity condition (5.28%) after IVS pretreatment was considered the primary inhibitor in pLSM + CS, while the ammonia (≤600 mg/L), C:N ratio (15.52) and volatile solid loading rate (3 g/kg^-1·day^-1) didn't show a negative effect on CH₄ production. When salinities were increased from 2% to 4% and 8%, 50% and 100% inhibition were observed respectively. The butyrate accumulation was a potential indicator of the non-salinity-inhibition status for methanogenesis in TAD.

Evaluation of ammonia recovery from swine wastewater via a innovative spraying technology

An innovative spraying system for NH₄⁺-N removal and recovery was investigated under different pH, temperature, spraying frequency and rate by using spraying system. Results showed that NH₄⁺-N removal efficiency and mass transfer coefficient (K_La) value in swine wastewater (SW) remarkably increased with increasing of temperature, spraying frequency and rate due to promoting the diffusion of NH₃ molecules caused by increasing specific surface of SW molecule, and high shear force and temperature difference between SW and circulating heating tube. Considering the cost and discharge standard, the optimum parameters for NH₄⁺-N removal from SW using spraying system were alkaline, 0.24 m³ h^-1 of continuous spraying, and 45 °C circulating water, and the NH₄⁺-N decreased from 591.2 to 68.9 mg L^-1 (<80 mg L^-1) after 8 h treatment, and this value corresponded to 88.35% removal rate. Furthermore, over 85% recovery rate for NH₄⁺-N could be obtained through absorption of phosphoric acid.

Production of bio-oil from agricultural waste by using a continuous fast microwave pyrolysis system

In this study, a continuous fast microwave-assisted pyrolysis system was developed to produce bio-oil, gas, and biochar from rice straw and Camellia oleifera shell. The effects of different pyrolysis temperatures (400 °C, 500 °C, and 600 °C) and feed rates (rice straw: 25, 45, and 66 g/min; C. oleifera shell: 100, 200, and 400 g/min) on bio-oil production were investigated. Experimental results showed that the yields of bio-oil (31.86 wt%) and gas (54.49 wt%) produced by the microwave-assisted pyrolysis of rice straw increased with increasing temperature. By contrast, the yields of bio-oil (27.45 wt%) and biochar (35.47 wt%) produced by the pyrolysis of C. oleifera shell decreased with increasing temperature. The contents of phenols, aldehydes, and alcohols in bio-oil produced from the shell were higher than those in bio-oil derived from rice straw.

Characterization of additional zinc ions on the growth, biochemical composition and photosynthetic performance from Spirulina platensis

In this study, the effect of various initial Zn²⁺ concentration additionally on microalgae growth and biochemical composition were investigated. The Spirulina platensis biomass of each concentration reached the maximum at the end of the cultivation. However, high levels could severely inhibit the growth of microalgae. Fluorescence activity occurred changes in response to heavy metal stress. Moreover, biochemical composition in Spirulina platensis altered under zinc stress, and the highest contents of phycocyanin (PC), Chlorophyll-a (Chl-a), Carotenoid and zinc accumulation were obtained. The proportion of saturated and polyunsaturated fatty acids increased constantly in response to Zn²⁺ exposure. Overall, this study indicated that the use of Spirulina platensis is a viable method for treating zinc containing wastewater and harvested microalgae can be processed into high-zinc products.

Improving hydrocarbon yield via catalytic fast co-pyrolysis of biomass and plastic over ceria and HZSM-5: An analytical pyrolyzer analysis

The excessive oxygen content in biomass obstructs the production of high-quality bio-oils. In this work, we developed a tandem catalytic bed (TCB) of CeO₂ and HZSM-5 in an analytical pyrolyzer to enhance the hydrocarbon production from co-pyrolysis of corn stover (CS) and LDPE. Results indicated that CeO₂ could remove oxygen from acids, aldehydes and methoxy phenols, producing a maximum yield of hydrocarbons of 85% and highest selectivity of monocyclic aromatics of 73% in the TCB. The addition of LDPE exhibited a near-complete elimination of oxygenates, leaving hydrocarbons as the overwhelming products. With increasing LDPE proportion, the yield of aliphatics and the selectivity of BTX kept increasing. An optimum H/C_eff of 0.7 was superior to that reported in literature. Mechanisms consisting of deoxygenation, Diels-Alder reactions, hydrocarbon pool and hydrogen transfer reactions were discussed extensively. Our findings provide an efficient method to produce high-quality biofuels from renewable biomass resources.

Silicon carbide foam supported ZSM-5 composite catalyst for microwave-assisted pyrolysis of biomass

Considering a series of issues facing the application of catalysts in large scale catalytic fast pyrolysis systems, a novel composite catalyst of ZSM-5 coatings on SiC foam supports was developed and tested for ex-situ catalytic upgrading of the pyrolytic vapors. Different configurations of catalysts placement were compared and the results showed the composite catalyst could significantly improve the bio-oil quality without significantly reducing the yield. The effect of catalyst to biomass ratio on the product yields and bio-oil composition was studied and the results showed that increasing catalyst to biomass ratio could improve the quality of bio-oil at the cost of its yield. In addition, the composite catalyst can maintain its activity until a catalyst to biomass ratio of 1/10, outperforming ZSM-5 in other configurations reported in literature. Furthermore, the composite catalysts could be regenerated and reused while well preserving its material properties and catalytic activity after seven reaction-regeneration cycles.

Correction: In situ plasma-assisted atmospheric nitrogen fixation using water and spray-type jet plasma

Correction for 'In situ plasma-assisted atmospheric nitrogen fixation using water and spray-type jet plasma' by Peng Peng et al., Chem. Commun., 2018, 54, 2886-2889.

Co-pyrolysis of microwave-assisted acid pretreated bamboo sawdust and soapstock

Fast microwave-assisted co-pyrolysis of pretreated bamboo sawdust and soapstock was conducted. The pretreatment process was carried out under microwave irradiation. The effects of microwave irradiation temperature, irradiation time, and concentration of hydrochloric acid on product distribution from co-pyrolysis and the relative contents of the major components in bio-oil were investigated. A maximum bio-oil yield of 40.00 wt.% was obtained at 200 °C for 60 min with 0.5 M hydrochloric acid. As pretreatment temperature, reaction time and acid concentration increased, respectively, the relative contents of phenols, diesel fraction (C12 + aliphatics), and other oxygenates decreased. The gasoline fraction (including C5-C12 aliphatics and aromatics) ranged from 55.77% to 73.30% under various pretreatment conditions. Therefore, excessive reaction time and concentration of acid are not beneficial to upgrading bio-oil.

Effect of combining adsorption-stripping treatment with acidification on the growth of Chlorella vulgaris and nutrient removal from swine wastewater

After swine wastewater (SW) was treated with adsorption-stripping stage, the concentration of NH₄⁺-N and Total phosphorus (TP) in SW significantly decreased from 598.04, 42.95 to 338.02, 8.36 mg L^-1, respectively. The concentration of heavy metals, especially Zn²⁺ (96.78%), decreased by the ion exchange of artificial zeolite (AZ). The acidification of SW could significantly improve the nutrient utilization efficiency and promote the growth rate of C. vulgaris due to the hydrolysis of macromolecular substances into smaller molecules usable for algae. By combining adsorption (Part I), stripping (Part II) and cultivation (Part III), the highest removal rates of NH₄⁺-N, TP, chemical oxygen demand (COD) and total organic carbon (TOC) from SW were 80.50, 96.90, 72.91, and 84.17%, respectively, and the OD₆₈₀ value was 1.129 (1.48 times of control) at pH 6.0. The combined system (Part I-III) can significantly enhance the removal efficiency of nutrient and biomass production by acidification.

Ex-situ catalytic upgrading of vapors from fast microwave-assisted co-pyrolysis of Chromolaena odorata and soybean soapstock

Fast microwave-assisted catalytic co-pyrolysis of Chromolaena odorata (C. odorata) and soybean soapstock with HZSM-5 as an ex-situ catalyst was investigated. Effects of catalytic temperature, feedstock: catalyst ratio and C. odorata: soybean soapstock ratio on the yield and composition of the bio-oil were discussed. Results showed that catalytic temperature greatly influenced the bio-oil yield. Co-pyrolysis of C. odorata and soybean soapstock improved the bio-oil yield, and the maximum bio-oil yield of 55.14% was obtained at 250 °C. However, the addition of HZSM-5 decreased bio-oil yield but improved the quality of bio-oil. Moreover, the proportion of oxygen-containing compounds decreased dramatically with the addition of soybean soapstock. The C. odorata: soybean soapstock ratio of 1:2 and feedstock: catalyst ratio of 2:1 were the optimal condition to upgrade the bio-oil. In addition, the resulted biochar contained various essential elements and could be used as soil repair agent.

Improving hydrocarbon yield from catalytic fast co-pyrolysis of hemicellulose and plastic in the dual-catalyst bed of CaO and HZSM-5

The high concentration of oxygenated compounds in pyrolytic products prohibits the conversion of hemicellulose to important biofuels and chemicals via fast pyrolysis. Herein a dual-catalyst bed of CaO and HZSM-5 was developed to convert acids in the pyrolytic products of xylan to valuable hydrocarbons. Meanwhile, LLDPE was co-pyrolyzed with xylan to supplement hydrogen during the catalysis of HZSM-5. The results showed that CaO could effectively transform acids into ketones. A minimum yield of acids (2.74%) and a maximum yield of ketones (42.93%) were obtained at a catalyst to feedstock ratio of 2:1. The dual-catalyst bed dramatically increased the yield of aromatics. Moreover, hydrogen-rich fragments derived from LLDPE promoted the Diels-Alder reactions of furans and participated in the hydrocarbon pool reactions of non-furanic compounds. As a result, a higher yield of hydrocarbons was achieved. This study provides a fundamental for recovering energy and chemicals from pyrolysis of hemicellulose.