Xiangyang Lin

Microwave-assisted pyrolysis of microalgae for biofuel production

The pyrolysis of Chlorella sp. was carried out in a microwave oven with char as microwave reception enhancer. The results indicated that the maximum bio-oil yield of 28.6% was achieved under the microwave power of 750 W. The bio-oil properties were characterized with elemental, GC-MS, GPC, FTIR, and thermogravimetric analysis. The algal bio-oil had a density of 0.98 kg/L, a viscosity of 61.2 cSt, and a higher heating value (HHV) of 30.7 MJ/kg. The GC-MS results showed that the bio-oils were mainly composed of aliphatic hydrocarbons, aromatic hydrocarbons, phenols, long chain fatty acids and nitrogenated compounds, among which aliphatic and aromatic hydrocarbons (account for 22.18% of the total GC-MS spectrum area) are highly desirable compounds as those in crude oil, gasoline and diesel. The results in this study indicate that fast growing algae are a promising source of feedstock for advanced renewable fuel production via microwave-assisted pyrolysis (MAP).

Catalytic pyrolysis of microalgae and their three major components: Carbohydrates, proteins, and lipids

To better understand the pyrolysis of microalgae, the different roles of three major components (carbohydrates, proteins, and lipids) were investigated on a pyroprobe. Cellulose, egg whites, and canola oil were employed as the model compounds of the three components, respectively. Non-catalytic pyrolysis was used to identify and quantify some major products and several reaction pathways were proposed for the pyrolysis of each model compound. Catalytic pyrolysis was then carried out with HZSM-5 for the production of aromatic hydrocarbons at different temperatures and catalyst to feed ratios. The aromatic yields of all feedstocks were significantly improved when the catalyst to biomass ratio increased from 1:1 to 5:1. Egg whites had the lowest aromatic yield among the model compounds under all reaction conditions, which suggests that proteins can hardly be converted to aromatics with HZSM-5. Lipids, although only accounted for 12.33% of Chlorella, contributed about 40% of aromatic production from algal biomass.

Fast microwave assisted pyrolysis of biomass using microwave absorbent

A novel concept of fast microwave assisted pyrolysis (fMAP) in the presence of microwave absorbents was presented and examined. Wood sawdust and corn stover were pyrolyzed by means of microwave heating and silicon carbide (SiC) as microwave absorbent. The bio-oil was characterized, and the effects of temperature, feedstock loading, particle sizes, and vacuum degree were analyzed. For wood sawdust, a temperature of 480°C, 50 grit SiC, with 2g/min of biomass feeding, were the optimal conditions, with a maximum bio-oil yield of 65 wt.%. For corn stover, temperatures ranging from 490°C to 560°C, biomass particle sizes from 0.9mm to 1.9mm, and vacuum degree lower than 100mmHg obtained a maximum bio-oil yield of 64 wt.%. This study shows that the use of microwave absorbents for fMAP is feasible and a promising technology to improve the practical values and commercial application outlook of microwave based pyrolysis.

Hydrothermal pretreatment of microalgae for production of pyrolytic bio-oil with a low nitrogen content.

Microalgae can be converted to an energy-dense bio-oil via pyrolysis; however, the relatively high nitrogen content of this bio-oil presents a challenge for its direct use as fuels. Therefore, hydrothermal pretreatment was employed to reduce the N content in Nannochloropsis oculata feedstock by removing proteins without requiring significant energy inputs. The effects of reaction conditions on the yield and composition of pretreated algae were investigated by varying the temperature (150-225°C) and reaction time (10-60 min). Compared with untreated algae, pretreated samples had higher carbon contents and enhanced heating values under all reaction conditions and 6-42% lower N contents at 200-225°C for 30-60 min. The pyrolytic bio-oil from pretreated algae contained less N-containing compounds than that from untreated samples and the bio-oil contained mainly (44.9% GC-MS peak area) long-chain fatty acids (C14-C18) which can be more readily converted into hydrocarbon fuels in the presence of simple catalysts.

Cultivation of a microalga Chlorella vulgaris using recycled aqueous phase nutrients from hydrothermal carbonization process

This study investigated the feasibility of using recovered nutrients from hydrothermal carbonization (HTC) for cultivation of microalga Chlorella vulgaris. Different dilution multiples of 50, 100 and 200 were applied to the recycled process water from HTC and algal growth was compared among these media and a standard growth medium BG-11. Algae achieved a biomass concentration of 0.79 g/L on 50 × process water after 4 days. Algae removed total nitrogen, total phosphorus and chemical oxygen demand by 45.5-59.9%, 85.8-94.6% and 50.0-60.9%, respectively, on differently diluted process water. The fatty acid methyl ester yields for algae grown on the process water were 11.2% (50 ×), 11.2% (100 ×) and 9.7% (200 ×), which were significantly higher than 4.5% for BG-11. In addition, algae cultivated on process water had 18.9% higher carbon and 7.8% lower nitrogen contents than those on BG-11, indicating that they are very suitable as biofuel feedstocks.

Fast microwave-assisted catalytic pyrolysis of sewage sludge for bio-oil production.

In this study, fast microwave-assisted catalytic pyrolysis of sewage sludge was investigated for bio-oil production, with HZSM-5 as the catalyst. Pyrolysis temperature and catalyst to feed ratio were examined for their effects on bio-oil yield and composition. Experimental results showed that microwave is an effective heating method for sewage sludge pyrolysis. Temperature has great influence on the pyrolysis process. The maximum bio-oil yield and the lowest proportions of oxygen- and nitrogen-containing compounds in the bio-oil were obtained at 550°C. The oil yield decreased when catalyst was used, but the proportions of oxygen- and nitrogen-containing compounds were significantly reduced when the catalyst to feed ratio increased from 1:1 to 2:1. Essential mineral elements were concentrated in the bio-char after pyrolysis, which could be used as a soil amendment in place of fertilizer. Results of XRD analyses demonstrated that HZSM-5 catalyst exhibited good stability during the microwave-assisted pyrolysis of sewage sludge.

Production of aromatic hydrocarbons by catalytic pyrolysis of microalgae with zeolites: catalyst screening in a pyroprobe.

Catalytic pyrolysis of microalgae and egg whites was investigated to evaluate the performance of different zeolites for the production of aromatic hydrocarbons. Three zeolites with different structures (H-Y, H-Beta and H-ZSM5) were used to study the effect of catalyst type on the aromatic yield. All three catalysts significantly increased the aromatic yields from pyrolysis of microalgae and egg whites compared with non-catalytic runs, and H-ZSM5 was most effective with a yield of 18.13%. Three H-ZSM5 with silica-to-alumina ratios of 30, 80 and 280 were used to study the effect of Si/Al ratio on the aromatic yield. The maximum yield was achieved at the Si/Al ratio of 80, which provides moderate acidity to achieve high aromatic production and reduce coke formation simultaneously. Aromatic production increased with the incorporation of copper or gallium to HZSM-5. However, other studied metals either had no significant influence or led to a lower aromatic yield.

Enzymatic hydrolysis of corn stover pretreated by combined dilute alkaline treatment and homogenization.

Corn stover, the most abundant agricultural residue in the U.S., is a potential feedstock for production of bioethanol because of its high content of carbohydrates, but an efficient pretreatment is required prior to enzymatic hydrolysis. In this study, a combination of NaOH treatment and homogenization was used as a pretreatment to enhance the enzymatic hydrolysis of corn stover. The combined pretreatment increased the enzymatic hydrolysis of corn stover five times compared to the control. The effectiveness of such pretreatment was found to be a function of NaOH concentration and particle size. Within the NaOH concentration range of 0.1 to 1.0 N, best performance of this combined pretreatment was achieved at 0.3 N NaOH. There is a significant cross effect of homogenization and NaOH treatment. Among the three particle sizes tested (the particle size was not directly measured; it passed through screens with openings of 2 mm, 0.707 mm, and 0.25 mm respectively), 2 mm was found to maximize the economic benefit of the pretreatment.

Liquefaction of corn stover and preparation of polyester from the liquefied polyol

This research investigated a novel process to prepare polyester from corn stover through liquefaction and crosslinking processes. First, corn stover was liquefied in organic solvents (90 wt% ethylene glycol and 10 wt% ethylene carbonate) with catalysts at moderate temperature under atmospheric pressure. The effect of liquefaction temperature, biomass content, and type of catalyst, such H2SO4, HCl, H3PO4, and ZnCl2, was evaluated. Higher liquefaction yield was achieved in 2 wt% sulfuric acid, 1/4 (w/w) stover to liquefying reagent ratio; 160°C temperature, in 2h. The liquefied corn stover was rich in polyols, which can be directly used as feedstock for making polymers without further separation or purification. Second, polyester was made from the liquefied corn stover by crosslinking with multifunctional carboxylic acids and/or cyclic acid anhydrides. The tensile strength of polyester is about 5 MPa and the elongation is around 35%. The polyester is stable in cold water and organic solvents and readily biodegradable as indicated by 82% weight loss when buried in damp soil for 10 mo. The results indicate that this novel polyester could be used for the biodegradable garden mulch film production.

Fast microwave-assisted catalytic gasification of biomass for syngas production and tar removal

In the present study, a microwave-assisted biomass gasification system was developed for syngas production. Three catalysts including Fe, Co and Ni with Al2O3 support were examined and compared for their effects on syngas production and tar removal. Experimental results showed that microwave is an effective heating method for biomass gasification. Ni/Al2O3 was found to be the most effective catalyst for syngas production and tar removal. The gas yield reached above 80% and the composition of tar was the simplest when Ni/Al2O3 catalyst was used. The optimal ratio of catalyst to biomass was determined to be 1:5-1:3. The addition of steam was found to be able to improve the gas production and syngas quality. Results of XRD analyses demonstrated that Ni/Al2O3 catalyst has good stability during gasification process. Finally, a new concept of microwave-assisted dual fluidized bed gasifier was put forward for the first time in this study.