A comprehensive multidisciplinary investigation on CO2 capture from diesel engine

Climate change and global warming are the visible consequences of the increased amount of carbon dioxide (CO₂) in the atmosphere. Among the various sources of anthropogenic CO₂ emission, the diesel engine has a significant contribution. The development of a reliable system to efficiently minimize CO₂ emissions from diesel engines to the safest level is lacking in the open literature. Therefore, a comprehensive multidisciplinary approach has been applied in this paper to investigate the efficacy of the post-combustion carbon capture (PCC) process for the diesel engine. The experiments have been performed on the exhaust of a direct injection diesel engine at five different brake powers with blends of aqueous ammonia (AQ_NH₃), monoethanolamine (MEA), N,N-dimethylethanolamine (DMEA), and 1-ethyl-3-methylimidazolium tetrafluoroborate (C₂mim BF₄) ionic liquid (IL) as an absorbent for CO₂ capture. The reaction mechanism of these absorbent with CO₂ are also studied by the geometrical, energetical, MESP, frontier molecular orbitals, and NBO analysis using the first-principles density functional theory (DFT) calculations. The maximum CO₂ absorption efficiency of almost 97% was achieved for the blend consisting of 67% of AQ_NH₃ and 33% of MEA. Moreover, AQ_MEA and blend of AQ_NH₃, DMEA, and C₂mim BF₄ ionic liquid showed 96% and 94% CO₂ absorption efficiency, respectively.

Pre-treatment of sugarcane bagasse with aqueous ammonia-glycerol mixtures to enhance enzymatic saccharification and recovery of ammonia

In this work, an efficient aqueous ammonia with glycerol (AAWG) method to improve the digestibility of sugarcane bagasse (SCB) was developed. Response surface methodology was utilized to optimize the AAWG parameters to achieve the maximum total fermentable sugar concentration (TFSC) and total fermentable sugar yield (TFSY). Under optimal AAWG conditions, 13.59 g/L TFSC (9.25% ammonia, 1.86 h, 180 °C) and 0.4449 g/g TFSY (9.51% ammonia, 1.78 h, 180 °C) were achieved, with delignification of 77.81% and 70.91%, respectively. Compared to pretreatment with glycerol or aqueous ammonia, the AAWG method significantly enhanced the enzymatic efficiency of SCB. The ammonia was recovered from the pretreatment liquid by distillation, and about one-third of the ammonia was retained. The overall results indicate that AAWG is effectively used as a pretreatment method for recovering ammonia, which would largely contribute to the economic benefits of biomass biorefinery.

Optimization of dilute sulfuric acid, aqueous ammonia, and steam explosion as the pretreatments steps for distillers' dried grains with solubles as a potential fermentation feedstock

Distillers' dried grains with solubles (DDGS) is the by-product of bioethanol production from starch-rich grains through dry-mill fermentation. In this study, dilute sulfuric acid hydrolysis, aqueous ammonia, and steam explosion as the pre-treatment methods were optimized. The central composite response surface methodology (RSM) design was used for optimization of dilute acid pretreatment, aqueous ammonia pretreatment. The steam explosion trials were evaluated. The results show that the dilute acid pretreatment at 121 °C is the most effective way of obtaining simple fermentable sugars (0.382 g/g DDGS). The levels of furfural and HMF was also 5.2 mg/g DDGS) and 1.6 mg/g DDGS, respectively, in the dilute sulfuric acid pretreated DDGS. On the other hand, maximum sugar yield for ammonia pretreatment was 0.129 g/g DDGS and 0.055 g/g DDGS for the steam pretreatment, while no significant amounts of furfural and HMF were observed for these two pretreatment methods.

Hybrid dilute sulfuric acid and aqueous ammonia pretreatment for improving butanol production from corn stover with reduced wastewater generation

An efficient hybrid pretreatment method was developed for butanol production from corn stover using dilute sulfuric acid (DA) and aqueous ammonia (AA). With the optimized AA concentration, treatment temperature and time of 10% AA, 80 °C and 24 h, the hybrid pretreatment could effectively dissolve hemicellulose and lignin with solid recovery rate of 37.45% and lignin reduction rate of 86.77% compared to those of 57.75% and 45.84% from single DA pretreatment. By washing 1 time after each step treatment, sugar yield and butanol production were increased to 401.76 mg/g-CS and 10.89 g/L from 346.04 mg/g-CS and 9.33 g/L obtained without washing. Compared with conventional single DA and AA pretreatment methods, wastewater generation was reduced to 0.83 L/g-butanol from 2.11 and 3.46 L/g-butanol, indicating this hybrid pretreatment could be an effective approach for improving butanol production from lignocellulosic feedstocks.

Local structures and the dissolving behavior of aqueous ammonia and its KCl and NH₄Cl solutions: A Raman spectroscopy and X-ray scattering study

The aqueous ammonia (5%-15%) and its KCl and NH4Cl solutions have been studied by Raman spectroscopy and X-ray scattering. The microscopic structures in these solutions were proposed. The addition of KCl reinforced the hydrogen bond between NH3 and H2O. On contrary, NH4Cl destroyed this interaction by forming hydrogen bond NH4(+)-NH3. This study gave an interpretation of the different dissolving behavior of KCl and NH4Cl in aqueous ammonia, which may have important implications in the separation of potassium and ammonium salt during the industrial production.

Pretreatment of sugarcane bagasse with liquid hot water and aqueous ammonia

Low water consumption operation (LWCO) can reduce the usage of water and energy input for the liquid hot water (LHW) pretreatment of sugarcane bagasse (SB) but causes great negative effects on the saccharification rate of xylose and enzymatic digestibility (ED) of cellulose. Therefore, a combined pretreatment with LHW and aqueous ammonia (LHWAA) was developed. ED of glucan and xylan is enhanced greatly resulted from the removal of hemicellulose and lignin after the LHWAA pretreatment. However, the intriguing results of low lignin removal and ED value were observed at the high reaction temperature of 180°C for the second step pretreatment of AA. It was proposed that lignin or pseudo-lignin droplet redeposited on the surface of residual solids might play a crucial role in determining the ED, so it is indispensable to make the enzyme access to the cellulose by the step of post-treatment with ultrasonic washing or hot washing. Coupled with the process of post-treatment and enzymatic hydrolysis, a high hemicellulose derived sugars recovery of 75.5% and glucose recovery of 87% was obtained for LHWAA pretreatment.