Nanocatalyst used for biofuel production from weed biomass -

Nanocatalyst used for biofuel production from weed biomass

          Weed (Biomass) from agricultural fields can be used to produce biofuels through nano catalysts enhanced gasification and process. Lignocellulosic part of weedy plants represents a potential alternative feedstock for economic production of bioethanol. Nanomaterials could be used as a catalyst to enhance the energy use efficiency and product quality. So, present study was conducted to produce bio-gas, bio-diesel and bio-char from mixed weed biomass of weeds like Carthamous oxyacantha, Asphodelus tenuifolius and Chenopodium album through gasification process using nano-materials as catalysts. Nickel and cobalt nano-particles were used as nanocatalysts to expedite the bio-chemical reactions for the generation of these products at lower temperatures i.e. (400 ℃) in a muffle furnace. Further, these products were characterized using GC-MS analysis. It was observed that biodiesel contained 65.47% esters, which indicates its better quality than the normally produced biodiesel having 15–20% esters contents. Similarly, GC-MS analysis of biogas produced from mixed weed biomass showed 3.76% Methane, 8.32% Propane, 50.16% Ethene, 3.12% Propyne and 34.64% Methanol. The present results clearly exhibited the improved product quality and better energy use efficiency in gasification of weed biomass for bioenergy production.

          The weed biomass of Carthamous oxyacantha, Asphodelus tenuifolius and Chenopodium album were collected. The weed flora was collected before the start of their reproductive growth to obtain raw material. The freshly collected weed biomass was kept in sun for 48 h for drying. The sundried weed biomass was oven dried at 64 ℃ till constant weight in drying cabinet to have a crushable dry biomass for onward gasification.

Preparation of cobalt nano-particles

          Cobalt nano-particles were synthesized through titration of cobalt nitrate Co(NO₃)₂ and sodium hydroxide (NaOH) using magnetic stirrer. About 4 g sodium hydroxide (NaOH) was mixed in 500 ml water in a beaker and the solution as then poured in burette. Then 2 g cobalt nitrate Co(NO₃)₂ was mixed in 100 ml water in another beaker. The beaker was placed on the magnetic stirrer and the burette was fixed on the stand near the magnetic stirrer. The opening of burette was opened to such an extent that (NaOH) was allowed to drop in beaker drop by drop to react with Co(NO₃)₂ and to increase the pH of solution. The pH of the reaction was noted frequently, at the pH of 10 the titration was stopped and the solution was washed with distilled water by adding water, rinsing the solution and then deponents were allowed to settle down and then water was removed carefully leaving the titrated cobalt nitrate mixture in beaker. This step was repeated five times and after that the titrated cobalt nitrate mixture was placed in the furnace in a china dish at 500 ℃ for three and a half hours. After that the mixture was carefully removed from the china dish and left to cool and finally grinded with the help of all grinding mill into nano size.

Preparation of nickel nano-particles

          Nickel nano-particles were synthesized through titration of nickel carbonate (NiCO₃) and sodium hydroxide (NaOH) using magnetic stirrer. For this purpose, 4 g sodium hydroxide (NaOH) was mixed in 500 ml water and the solution was then poured in a burette. About 2 g nickel carbonate (NiCO₃) was added to 100 ml of water in a beaker. The beaker was placed on the magnetic stirrer along with the burette fixed on the stand. The opening of burette was opened to such an extent that (NaOH) was allowed to drop in beaker drop by drop to react with (NiCO₃) and to increase the pH of solution. The pH of the reaction was noted frequently and at the pH of 10 the titration was stopped and the solution was washed with distilled water by adding water and rinsing the solution after which deponents were allowed to settle down for some time and then water was removed carefully leaving the titrated nickel carbonate mixture in beaker. This step was repeated five times and after that the titrated nickel carbonate mixture was placed in the furnace in a china dish at 500 ℃ for three and a half hours. After that the mixture was carefully removed from the china dish and left to cool and then was grinded with the help of ball grinding mill into nano size.

Gasification of mixed weed biomass

          Gasification of weed biomass was achieved in a muffle furnace in the presence of Nickel and Cobalt nano-catalysts at 400 ℃ without oxygen under a pressure of 1–5 bars to yield gaseous compounds i.e. (biogas), solid charcoal i.e. (biochar) and liquid extract i.e. (bio-oil). A composite sample of 100 g dried mixed weed biomass was prepared by mixing the dry biomass of three weeds in equal proportion (1:1:1). This sample was poured in a flask along with the nanoparticles of cobalt (0.5g) and nickel (0.5g) at the rate of 1% of the weight of weed biomass. The flask was placed in the muffle furnace at 400 ℃ for 2 h. The biogas and bio-oil samples were collected in a gas sampler and beaker respectively for further processes, which were kept at the upper opening site of L shaped glass tube and muffle furnace. After cooling the biochar samples were collected in a disposable jar.

Analysis of bio-gas

          The biogas sample was analyzed using Gas Chromatograph Mass Spectrometer.

Trans-esterification of bio-oil for the extraction of bio-diesel

          The 10 ml bio-oil obtained by gasification of weeds was placed in a dry beaker equipped with a hot plate magnetic stirrer and a thermometer. In another beaker, 30 ml methanol was mixed with the catalyst (KOH) in ratio 2.5% (0.75g) of the volume of methanol. Solution was stirred with hot plate stirrer until all the catalyst was dissolved (for about 1 h). Then bio-oil was mixed with the mixture of KOH and methanol with continuous agitation for 2 h at a temperature of 60 ℃. When the reaction was finished the esters and glycerol was separated with the help of separating funnel through sedimentation process to separate the mixture of biodiesel and glycerol obtained. Biodiesel was then washed several times with distilled water to take out the catalyst and unreacted methanol, until a neutral pH was obtained. Distilled water was added in the biodiesel in a beaker and left over for 5 min, after that again two layers of water containing unreacted methanol and catalyst and layer of biodiesel were developed later on the upper layer of water containing un reacted methanol and catalyst was spoiled carefully and pH of biodiesel was noted. This process was repeated until neutral pH was obtained. Finally, the translucent ester obtained was dried and the volume of the bio-diesel was recorded for further analysis.

Analysis of bio-diesel

          The sample of bio-diesel was collected and analyzed on Gas Chromatography Mass Spectrometer (GCMS) for its characteristics.

Analysis of bio-char

          The biochar prepared through gasification was also analyzed for its other characteristics like pH, EC, total organic carbon, organic matter content, nitrogen, phosphorous and potassium concentrations. The pH, EC, of biochar was determined by taking 1g of biochar and 5 ml distilled water mixture in a beaker. The mixture was shacked at 150 rpm for 30 min. Multimeter was used for analysis. The nitrogen content was determined using wet digestion and Kjeldahl technique. While Phosphorous contents was determined by spectrophotometer. Flame photo meter was used for potassium analysis.

Conclusion

          These results concluded that the nano-catalysts used in this study could improve the gasification process efficiency and product quality. Residual weed biomass could be used not only to produce biodiesel and biochar, but also for hydrocarbon-based fuel gases. The use of weed biomass as feedstock will also helpful for weed management and will decrease the competition of food crops to be used as feedstock for biofuel production. Quality of biodiesel produced from weed biomass is high as shown by its high viscosity and low sulfur contents. It indicates the great potential of this technology to be used to replace fossil fuels. It could be a cheap source of fuel compared to standard petro-diesel, however further studies based on life cycle assessment or techno economic assessment work are required to establish its cost effectiveness.  This technology can be very useful in global perspectives where most of the countries has already set targets to replace fossil fuels with alternative energy sources from 2025 to 2030.

Reference:

Ali, S., Shafique, O., Mahmood, S., Mahmood, T., Khan, B.A. and Ahmad, I., 2020. Biofuels production from weed biomass using nanocatalyst technology. Biomass and bioenergy, 139, p.105595.