Gate Greenhouse Gas Research Articles

Magnesium production by molten salt electrolysis with liquid tin cathode and multiple effect distillation.

Low-cost clean primary production of magnesium metal is important for its use in many applications, from light-weight structural components to energy technologies. This work describes new experiments and cost and emissions analysis for a magnesium metal production process. The process combines molten salt electrolysis of MgO using MgF₂-CaF₂ electrolyte and a reactive liquid tin cathode, with gravity-driven multiple effect thermal system (G-METS) distillation to separate out the magnesium product, and re-use of the tin. Electrolysis experiments with carbon anodes showed current yield above 90%, while a yttria-stabilized zirconia solid oxide membrane (SOM) anode experiment showed 84% current yield. G-METS distillation is an important component of the envisioned process. It can potentially lower costs and energy use considerably compared with conventional magnesium distillation. Techno-economic analysis including detailed mass and energy balances shows that this electrolyte composition could lower costs by utilizing CaO, which is the primary impurity in MgO, as the Hall-Héroult process uses the sodium impurity in alumina. Analysis options include: raw material types (magnesite rock vs. brine or seawater), drying and calcining using electricity vs. natural gas, and carbon vs. SOM anode type. Using SOM inert anodes results in a cost premium around 10%-15%, mostly due to higher electrical energy usage resulting from membrane resistance, and reduces GHG emissions by approximately 1kg CO₂/kg Mg product. Capital and operating cost estimates, and cradle to gate greenhouse gas (GHG) emissions analysis under several raw material and process technology scenarios, show comparable costs and emissions to those of aluminum production.

Field-to-farm gate greenhouse gas emissions from corn stover production in the Midwestern U.S.

Measured field data were used to compare two allocation methods on life cycle greenhouse gas emissions from corn (Zea mays L.) stover production in the Midwest U.S. We used publicly-available crop yield, nitrogen fertilizer, and direct soil nitrous oxide emissions data from the USDA-ARS Resilient Economic Agricultural Practices research program. Field data were aggregated from 9 locations across 26 site-years for 3 stover harvest rates (no removal; moderate removal – 3.1 Mg ha−1; high removal – 7.2 Mg ha−1) and 2 tillage practices (conventional; reduced/no-till). Net carbon uptake by crops was computed from measured plant carbon content. Monte Carlo simulations sampled input distributions to assess variability in farm-to-gate GHG emissions. The base analysis assumed no change in soil organic carbon stocks. In all cases, net CO2 uptake during crop growth and soil-respired CO2 dominated system emissions. Emissions were most sensitive to co-product accounting method, with system expansion emissions ∼15% lower than mass allocation. Regardless of accounting method, lowest emissions occurred for a moderate removal rate under reduced/no-till management. The absence of correlations between N fertilization rate and stover removal rate or soil N2O emissions in this study challenges the use of such assumptions typically employed in life cycle assessments Storage of all carbon retained on the field as SOC could reduce emissions by an additional 15%. Our results highlight how variability in GHG emissions due to location and weather can overshadow the impact of farm management practices on field-to-farm gate emissions.

Greenhouse gas emissions and non-renewable energy use profiles of bio-based succinic acid from Arundo donax L. lignocellulosic feedstock

The European Union recognizes the priority of new bio-based industrial pathways, such as bio-based succinic acid (bio-SA). This study has investigated, through a life cycle method, the cradle-to-factory gate greenhouse gas (GHG) emissions and non-renewable energy use (NREU) of bio-SA from lignocellulosic giant reed (GR) feedstock grown on marginal lands in Southern Italy (GR bio-SA). The aims were to: (1) evaluate the environmental performance of the GR bio-SA and (2) discuss the GR bio-SA profile with respect to its fossil counterparts and alternative bio-SA routes. For 1 kg of GR bio-SA, the gross GHG emissions amounted to 3.9 kg CO2 eq, while through the inclusion of the biogenic C potentially stored in SA molecule (1.47 kg CO2 eq) and soil organic matter (0.44 kg CO2 eq), the final net global warming potential would be nearly halved. Similarly to current starch-based SA supply chains, the GR bio-SA showed: (1) better gross GHG profile compared to the fossil adipic acid (GHG emissions reduced by 55%) and (2) comparable net GHG emissions in comparison with petrochemicals SA and maleic acid. The total NREU for 1 kg of GR bio-SA amounted to 26.6 MJ, with reduced energy consumption by about 55–79% relative to fossil counterparts, thanks to the on-site energetic valorization of lignin and holocellulose residues with relatively high heating values. The soy protein concentrate and the inorganic chemicals used in the co-fermentation showed up the prevailing contributions to the GHG and NREU profiles of the GR bio-SA, suggesting the need to optimize nitrogen and carbon sources of the growth medium.

Implications of dairy systems on enteric methane and postulated effects on total greenhouse gas emission

The effects of feeding total mixed ration (TMR) or pasture forage from a perennial sward under a management intensive grazing (MIG) regimen on grain intake and enteric methane (EM) emission were measured using chambers. Chamber measurement of EM was compared with that of SF6 employed both within chamber and when cows grazed in the field. The impacts of the diet on farm gate greenhouse gas (GHG) emission were also postulated using the results of existing life cycle assessments. Emission of EM was measured in gas collection chambers in Spring and Fall. In Spring, pasture forage fiber quality was higher than that of the silage used in the TMR (47.5% v. 56.3% NDF; 24.3% v. 37.9% ADF). Higher forage quality from MIG subsequently resulted in 25% less grain use relative to TMR (0.24 v. 0.32 kg dry matter/kg milk) for MIG compared with TMR. The Fall forage fiber quality was still better, but the higher quality of MIG pasture was not as pronounced as that in Spring. Neither yield of fat-corrected milk (FCM) which averaged 28.3 kg/day, nor EM emission which averaged 18.9 g/kg dry matter intake (DMI) were significantly affected by diet in Spring. However, in the Fall, FCM from MIG (21.3 kg/day) was significantly lower than that from TMR (23.4 kg/day). Despite the differences in FCM yield, in terms of EM emission that averaged 21.9 g/kg DMI was not significantly different between the diets. In this study, grain requirement, but not EM, was a distinguishing feature of pasture and confinement systems. Considering the increased predicted GHG emissions arising from the production and use of grain needed to boost milk yield in confinement systems, EM intensity alone is a poor predictor of the potential impact of a dairy system on climate forcing.

Dairy farm greenhouse gas impacts: A parsimonious model for a farmer's decision support tool

This study presents an analysis of the cradle to farm gate greenhouse gas footprint of milk. Compared with the detailed model, we aim to accurately represent the variations in carbon footprint across farms, while being more parsimonious in terms of data needs. The simplified model strongly reduces the farm-specific data requirement from 162 animal-rations in the detailed survey to 12 feed rations for lactating cows, while explaining 91% of the variability in feed print and 98% of the variability in total footprint across 531 farms. The additional 95% confidence interval on an individual farm footprint is less than 10%. Feed efficiency and manure management are key determinants of the footprint per kg milk. A 15% reduction in the average footprint can be achieved by a 10% reduction for the 50th percentile of the best farms and by a higher and targeted reduction for the less efficient farms.

Comparison of Twelve Organic and Conventional Farming Systems: A Life Cycle Greenhouse Gas Emissions Perspective

Given the growing importance of organic food production, there is a pressing need to understand the relative environmental impacts of organic and conventional farming methods. This study applies standards-based life cycle assessment to compare the cradle-to-farm gate greenhouse gas emissions of 12 crop products grown in California using both organic and conventional methods. In addition to analyzing steady-state scenarios in which the soil organic carbon stocks are at equilibrium, this study models a hypothetical scenario of converting each conventional farming system to a corresponding organic system and examines the impact of soil carbon sequestration during the transition. The results show that steady-state organic production has higher emissions per kilogram than conventional production in seven out of the 12 cases (10.6% higher overall, excluding one outlier). Transitional organic production performs better, generating lower emissions than conventional production in seven cases (17.7% lower overall) and 22.3% lower emissions than steady-state organic. The results demonstrate that converting additional cropland to organic production may offer significant GHG reduction opportunities over the next few decades by way of increasing the soil organic carbon stocks during the transition. Nonorganic systems could also improve their environmental performance by adopting management practices to increase soil organic carbon stocks.