A review on alkaline pretreatment technology for bioconversion of lignocellulosic biomass.

Lignocelluloses are often a major or sometimes the sole components in different waste streams from various sources such as industries, forestry, agriculture and municipalities. It represents an as-of-yet untapped source of fermentable sugars for significant industrial use. Many physico-chemical, structural and compositional factors hinder the hydrolysis of components present in the biomass to sugars and other organic compounds that can later be converted into fuels. During the past few years, a large number of chemical pretreatment methods including lime, acid, steam explosion, sulfur dioxide explosion, ammonia fiber explosion, ionic liquid and others have been developed for efficient pretreatment of biomass. Many pretreatment methods have shown high sugar yields i.e. more than 90% of the theoretical yield from lignocelluloses. In this review, we discuss various chemical pretreatment processes, feasibility of the processes at industrial scale in terms of the mechanisms involved, advantages, disadvantages and economic assessment. It is not possible to define the best pretreatment method as it depends on many factors such as type of lignocellulosic biomass, process parameters, environmental impact, economical feasibility, etc. However, some of these chemical pretreatments have disadvantages such as formation of inhibitory compounds especially furfural and 5-hydroxyl methyl furfural (HMF).

Importance of chemical pretreatment for bioconversion of lignocellulosic biomass

From lignin to valuable products–strategies, challenges, and prospects

Current advancement on the isolation, characterization and application of lignin.

A number of pre-treatment methods have been developed during the last few decades to overcome bio- mass recalcitrance. Although the mechanisms of these pre-treatments are different, the fi nal objective is the same - increasing cellulose accessibility to cellulase enzymes. Generally, pre-treatment is the process to disrupt the compact structure of lignocellulosic biomass and expose cellulose fi bers, which can be achieved by mechanical comminu- tion, chemical modifi cations of biomass compositions, biological degradation, or a combination of these methods. After pre-treatment, the accessible surface area is increased resulting in the enhancement of cellulose digestibility. In this paper, we review the recent progress of the fundamental researches of various biomass pre-treatment proc- esses, especially on how these pre-treatments alter chemical composition and physically change cell wall struc- ture. Understanding these changes would be helpful to further optimize existing pre-treatments, and would aid in developing novel pre-treatment methods.© 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Biomass recalcitrance. Part II: Fundamentals of different pre-treatments to increase the enzymatic digestibility of lignocellulose

The methods of pretreatment of lignocellulosic biomass using aqueous ammonia are described. The main effect of ammonia treatment of biomass is delignification without significantly affecting the carbohydrate contents. It is a very effective pretreatment method especially for substrates that have low lignin contents such as agricultural residues and herbaceous feedstock. The ammonia-based pretreatment is well suited for simultaneous saccharification and co-fermentation (SSCF) because the treated biomass retains cellulose as well as hemicellulose. It has been demonstrated that overall ethanol yield above 75% of the theoretical maximum on the basis of total carbohydrate is achievable from corn stover pretreated with aqueous ammonia by way of SSCF. There are two different types of pretreatment methods based on aqueous ammonia: (1) high severity, low contact time process (ammonia recycle percolation; ARP), (2) low severity, high treatment time process (soaking in aqueous ammonia; SAA). Both of these methods are described and discussed for their features and effectiveness.

Pretreatment of biomass by aqueous ammonia for bioethanol production.

The results of investigation and comparison of a series of transverse phase space painting schemes for the injection of the SNS accumulator ring is reported. In this computer simulation study, the focus is on the creation of closed orbit bumps that give desired distributions at the target. Space charge effects such as tune shift, emittance growth and beam losses are considered. The results of pseudo end-to-end simulations from the injection to the target through the accumulator ring and the Ring to Target Beam Transfer (RTBT) system are presented and discussed.

/pdf/transverse-phase-space-painting-for-sns-accumulator-ring-2l169q6wvl.pdf

Transverse phase space painting for SNS accumulator ring injection

The goal of the proposed National Spallation Neutron Source (NSNS) is to provide a short pulse proton beam of about 0.5 /spl mu/s with average beam power of 1 MW. To achieve such purpose, a proton storage ring operated at 60 Hz with 1/spl times/10/sup 14/ protons per pulse at 1 GeV is required. The Accumulator Ring (AR) receives 1 msec long H/sup -/ beam bunches of 28 mA from a 1 GeV linac. Scope and design performance goals of the AR are presented, other possible technological choices and design options considered, but not adopted, are also briefly reviewed.

Accumulator Ring Design for the NSNS Project

Beam properties resulting from transverse phase space painting for the injection of the Spallation Neutron Source (SNS) accumulator ring are summarized. The focus is on the creation of closed orbit bumps that give suitable distributions at the spallation neutron target, at the same time minimizing the beam losses through tail/halo formation. Related issues such as foil traversal rate and foil temperature/lifetime are also studied. Finally, injection mismatch is investigated for large linac emittance to reduce the beam loss through scattering.

/pdf/beam-properties-in-the-sns-accumulator-ring-due-to-5au476qi69.pdf

Beam properties in the SNS accumulator ring due to transverse phase space painting

/pdf/accumulator-ring-design-for-the-nsns-project-16sx59d8zk.pdf

Accumulator ring design for the NSNS project

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