Shengjun Luo

Efficiency of CO2 fixation by microalgae in a closed raceway pond

Microalgae contain about 50% of carbon, which means that a total of 1.83 ton of CO2 is needed to produce 1 ton of microalgae. The cost of CO2 supply for microalgal large scale cultivation should be considered and the low CO2 fixation efficiency by microalgae will lead to much more expenditure of CO2. In this study, a closed raceway pond was constructed by covering a normal open raceway pond with a specially designed transparent cover, which directly touched the surface of microalgal culture media. This cover prevented supplied CO2 escaping into atmosphere and thus increased the retention time of CO2. The CO2 gas-liquid mass transfer and CO2 fixation efficiency by microalgae in the closed raceway pond were investigated, and the model of CO2 fixation by microalgae was developed. Through the model, the CO2 fixation efficiency increased to 95% under intermittent gas sparging.

The thermophilic (55 °C) microaerobic pretreatment of corn straw for anaerobic digestion

Microaerobic process has been proven to be an alternative pretreatment for the anaerobic digestion (AD) process in several studies. In this study, the effect of thermophilic microaerobic pretreatment (TMP) on the AD of corn straw was investigated. Results indicated that TMP process obviously improved the methane yield. The maximum methane yield was obtained at the oxygen loads of 5ml/g VSsubstrate, which was 16.24% higher than that of untreated group. The modified first order equation analysis showed the TMP process not only accelerated the hydrolysis rates but also reduced the lag-phase time of AD process. The structural characterization analysis showed cellulosic structures of corn straw were partly disrupted during TMP process. The crystallinity indexes were also decreased. In addition, large or destroyed pores and substantial structural disruption were observed after pretreatment. The results showed that TMP is an efficient pretreatment method for the AD of corn straw.

Methane hydrate formation with surfactants fixed on the surface of polystyrene nanospheres

To improve the application of surfactants in methane hydrate formation, sodium dodecyl sulfate (SDS) was fixed on the surface of polystyrene nanospheres (named as SDS@PSNS). SDS@PSNS resulted in a shorter induction period of hydrate formation compared to SDS. With SDS@PSNS as a promoter, hydrates formed mainly at the bottom of the reactor with a much higher apparent density and higher methane consumption, and during the hydrate dissociation period, less foam was generated. In addition, the recycling experiments showed high stability and good recycling performance of SDS@PSNS in seven methane hydrate formation–dissociation cycles.

Preparation of –SO3−-coated nanopromoters for methane hydrate formation: effects of the existence pattern of –SO3− groups on the promotion efficiency

Sodium dodecyl sulfate (SDS) has been confirmed to be the most efficient promoter of gas hydrate formation; however, the foam generation during hydrate dissociation severely limits its application. In this study, the –SO3− group, similar to the hydrophilic group of SDS, was covalently fixed on polystyrene nanoparticles to prepare –SO3−-coated nanopromoters (–SO3−@PSNS) for methane hydrate formation. The existing form of –SO3− groups was controlled by varying the ratio of the hydrophobic and hydrophilic monomers during emulsion polymerization, which produced significant influence on the promotion efficiency. At the initial pressure of 5 MPa, when –SO3− groups existed irregularly with the macromolecules of –SO3−@PSNS in solution (–SO3−@PSNS-1), the growth rate was merely 8.02 ± 0.95 × 10−6 mol min−1 mL−1; however, when –SO3− groups were uniformly arrayed on the surface of the –SO3−@PSNS nanospheres (–SO3−@PSNS-2-3-4), the growth rate reached 18.08 ± 3.29–40.97 ± 2.89 × 10−6 mol min−1 mL−1. When nanopromoters with regularly arrayed –SO3− groups (–SO3−@PSNS-2-3) were used at the initial pressure of 6 MPa, the entire hydrate formation process was completed within 1–2 h and the methane storage capacity reached 142 and 137 v/v, indicating much better promotion compared to other common promoters, such as SDS, nanofluids, and activated carbon. Moreover, –SO3−@PSNS-3 resulted in no foam generation during hydrate dissociation and produced excellent recycling performance in 8 cycles of methane hydrate formation. Therefore, the –SO3−-coated nanopromoters developed in this study have significant potential in the industrial application of hydrate-based natural gas storage and transportation.

Grafting of nano-Ag particles on –SO3−-coated nanopolymers for promoting methane hydrate formation

Sodium dodecyl sulfate (SDS) has been reported to be the most efficient promoter for hydrate-based natural gas storage and transportation, however, foam generation during hydrate dissociation seriously affects its application. Nano-metal particles have also been demonstrated to be efficient promoters, nevertheless their poor stability is a serious problem. In this work, we first fixed –SO3− groups (similar to the hydrophilic group of SDS) covalently on polystyrene through soap-free emulsion polymerization to synthesize –SO3−-coated nanopolymers, and by tuning their morphology they existed as amorphous polystyrene macromolecules (–SO3−@PSMM) or uniform polystyrene nanospheres (–SO3−@PSNS). Afterwards, we grafted nano-Ag particles with the size of 2–5 nm on the –SO3−-coated nanopolymers through electrostatic adsorption and in situ reduction to prepare Ag&–SO3−-coated nanopolymers (denoted as Ag&–SO3−@PSMM and Ag&–SO3−@PSNS), which were then used for the first time to promote methane hydrate formation. When 0.5 mmol L−1 amorphous Ag&–SO3−@PSMM was used at an initial pressure of 6 MPa and temperature of 275.15 K, the induction period was 32.2 ± 7.9–60.8 ± 14.2 min, the growth period was 108.8 ± 8.2–177.1 ± 38.9 min and the methane storage capacity reached 143.9 ± 3.7–145.2 ± 1.2 v/v, whereas when the spherical Ag&–SO3−@PSNS was used at 0.5 mmol L−1, the induction period and growth period were 17.8 ± 2.8–38.5 ± 8.0 and 39.6 ± 2.8–42.1 ± 0.9 min, respectively; and the storage capacity reached 149.3 ± 1.2–151.3 ± 3.0 v/v, indicating that Ag&–SO3−@PSNS were much better promoters compared with Ag&–SO3−@PSMM. Moreover, Ag&–SO3−@PSNS exhibited excellent recycling performance for 10 cycles of methane hydrate formation–dissociation. To sum up, the Ag&–SO3−-coated nano-promoters developed in this work showed significant potential in achieving the industrial application of hydrate-based natural gas storage and transportation.

The thermophilic (55 degrees C) microaerobic pretreatment of corn straw for anaerobic digestion (vol 175, pg 203, 2015)

Chinese Acad Sci, Qingdao Inst Bioenergy & Bioproc Technol, 189 Songling Rd, Qingdao 266101, Shandong, Peoples R China