Browsing by Author "Varma, Abhishek R."

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Mechanism-based thermodynamic analysis for one-step and two-step ethanol-to-1,3-butadiene conversion processes
    (American Chemical Society, 2024-11-27) Rahman, Md Ziyaur; Varma, Abhishek R.; Gadkari, Siddharth; Tawai, Atthasit; Sriariyanun, Malinee; Kumar, Vinod; Maity, Sunil K.
    Renewable 1,3-butadiene (BD) is essential for sustainability of the synthetic rubber sector. This work presents a comprehensive thermodynamic analysis for one- and two-step ethanol-to-BD conversion processes. The two-step process comprises ethanol dehydrogenation, followed by the condensation of acetaldehyde with another ethanol molecule into BD. The process involves a complex reaction network with a wide range of byproducts depending on the nature of the catalysts and operating conditions, lacking unique consensus on the C-C bond-forming mechanism. This study elucidates the temperature regime for the spontaneity of the reactions proposed in various mechanisms and side reactions based on the standard Gibbs free energy change. The equilibrium conversion and product selectivity were further calculated under a wide temperature and pressure range. The overall reaction in the one-step process is thermodynamically spontaneous above 417 K, while the first and second steps of the two-step process are spontaneous above 550 and 285 K, respectively. Excepting Prins condensation, other mechanisms lack the spontaneity of all reaction steps. The equilibrium BD selectivity is favorable at elevated temperatures and low pressures. The addition of acetaldehyde in the two-step process has a favorable impact with higher BD selectivity, the maximum being at a 1:1 molar ratio of ethanol/acetaldehyde. This study elucidates thermodynamic insights into existing mechanisms and drives the evolution of a feasible mechanism. This effort will eventually help design novel catalysts and optimized processes for sustainable biobased BD production using ethanol derived from renewable feedstocks, aligning with the global commitment to greener and resource-friendly chemical manufacturing.
  • Thumbnail Image
    ItemOpen Access
    Recent advances in fermentative production of C4 diols and their chemo-catalytic upgrading to high-value chemicals
    (Elsevier, 2023-10-13) Varma, Abhishek R.; Shrirame, Bhushan S.; Maity, Sunil K.; Agrawal, Deepti; Malys, Naglis; Rios-Solis, Leonardo; Kumar, Gopalakrishnan; Kumar, Vinod
    The current era is witnessing the transition from a fossil-dominated economy towards sustainable and low-carbon green manufacturing technologies at economical prices with reduced energy usage. The biological production of chemical building blocks from biomass using cell factories is a potential alternative to fossil-based synthesis. However, microbes have their own limitations in generating the whole spectrum of petrochemical products. Therefore, there is a growing interest in an integrated/hybrid approach where products containing active functional groups obtained by biological upgrading of biomass are converted via chemo-catalytic routes. The present review focuses on the biological production of three important structural isomers of C4 diols, 2,3-, 1,3-, and 1,4-butanediol, which are currently manufactured by petrochemical route to meet the soaring global market demand. The review starts with justifications for the integrated approach and summarizes the current status of the biological production of these diols, including the substrates, microorganisms, fermentation technology and metabolic/pathway engineering. This is followed by a comprehensive review of recent advances in catalytic upgrading of C4 diols to generate a range of products. The roles of various active sites in the catalyst on catalytic activity, product selectivity, and catalyst stability are discussed. The review also covers examples of integrated approaches, addresses challenges associated with developing end-to-end processes for bio-based production of C4 diols, and underlines existing limitations for their upgrading via direct catalytic conversion. Finally, the concluding remarks and prospects emphasise the need for an integrated biocatalytic and chemo-catalytic approach to broaden the spectrum of products from biomass.
  • Thumbnail Image
    ItemOpen Access
    Techno-economic viability of bio-based methyl ethyl ketone production from sugarcane using integrated fermentative and chemo-catalytic approach: process integration using pinch technology
    (Elsevier, 2024-04-24) Varma, Abhishek R.; Shrirame, Bhushan S.; Gadkari, Siddharth; Vanapalli, Kumar Raja; Kumar, Vinod; Maity, Sunil K.
    Butanediols are versatile platform chemicals that can be transformed into a spectrum of valuable products. This study examines the techno-commercial feasibility of an integrated biorefinery for fermentative production of 2,3-butanediol (BDO) from sucrose of sugarcane (SC), followed by chemo-catalytic upgrading of BDO to a carbon-conservative derivative, methyl ethyl ketone (MEK), with established commercial demand. The techno-economics of three process configurations are compared for downstream MEK separation from water and co-product, isobutyraldehyde (IBA): (I) heterogeneous azeotropic distillation of MEK-water and extractive separation of (II) MEK and (III) MEK-IBA from water using p-xylene as a solvent. The thermal efficiency of these manufacturing processes is further improved using pinch technology. The implementation of pinch technology reduces 8% of BDO and 9–10% of MEK production costs. Despite these improvements, raw material and utility costs remain substantial. The capital expenditure is notably higher for MEK production from SC than BDO alone due to additional processing steps. The extraction based MEK separation is the simplest process configuration despite marginally higher capital requirements and utility consumption with slightly higher production costs than MEK-water azeotropic distillation. Economic analysis suggests that bio-based BDO is cost-competitive with its petrochemical counterpart, with a minimum gross unitary selling price of US$ 1.54, assuming a 15% internal rate of return over five-year payback periods. However, renewable MEK is approximately 16–24% costlier than the petrochemical route. Future strategies must focus on reducing feedstock costs, improving BDO fermentation efficacy, and developing a low-cost downstream separation process to make renewable MEK commercially viable.