Mark R. Nimlos

Bio: Mark R. Nimlos is an academic researcher from National Renewable Energy Laboratory. The author has contributed to research in topics: Pyrolysis & Thermal decomposition. The author has an hindex of 55, co-authored 168 publications receiving 11685 citations. Previous affiliations of Mark R. Nimlos include California Institute of Technology & Colorado School of Mines.

Biomass recalcitrance: engineering plants and enzymes for biofuels production.

Abstract: Lignocellulosic biomass has long been recognized as a potential sustainable source of mixed sugars for fermentation to biofuels and other biomaterials. Several technologies have been developed during the past 80 years that allow this conversion process to occur, and the clear objective now is to make this process cost-competitive in today's markets. Here, we consider the natural resistance of plant cell walls to microbial and enzymatic deconstruction, collectively known as "biomass recalcitrance." It is this property of plants that is largely responsible for the high cost of lignocellulose conversion. To achieve sustainable energy production, it will be necessary to overcome the chemical and structural properties that have evolved in biomass to prevent its disassembly.

Computational Study of Bond Dissociation Enthalpies for a Large Range of Native and Modified Lignins

Abstract: Lignin is a major component of plant cell walls that is typically underutilized in selective conversion strategies for renewable fuels and chemicals. The mechanisms by which thermal and catalytic treatments deconstruct lignin remain elusive, which is where quantum mechanical calculations can offer fundamental insights. Here, we compute homolytic bond dissociation enthalpies (BDEs) for four prevalent linkages in 69 lignin model compounds, including β-O-4, α-O-4, β-5, and biphenyl bonds, with a large range of natural and oxidized substituents. These calculations include ab initio benchmark values extrapolated to the complete basis set limit and full conformational searches for each compound. The results quantify both the relative BDEs among common lignin bonds and the effect of native and oxidized substituents on the functional groups in lignin. These data yield insights into thermal lignin deconstruction for a large range of prevalent linkages and aid in the identification of targets for catalytic cleavage.

A Mechanistic Investigation of Acid-Catalyzed Cleavage of Aryl-Ether Linkages: Implications for Lignin Depolymerization in Acidic Environments

Abstract: Acid catalysis has long been used to depolymerize plant cell wall polysaccharides, and the mechanisms by which acid affects carbohydrates have been extensively studied. Lignin depolymerization, however, is not as well understood, primarily due to the heterogeneity and reactivity of lignin. We present an experimental and theoretical study of acid-catalyzed cleavage of two non-phenolic and two phenolic dimers that exhibit the β-O-4 ether linkage, the most common intermonomer bond in lignin. This work demonstrates that the rate of acid-catalyzed β-O-4 cleavage in dimers exhibiting a phenolic hydroxyl group is 2 orders of magnitude faster than in non-phenolic dimers. The experiments suggest that the major product distribution is similar for all model compounds, but a stable phenyl-dihydrobenzofuran species is observed in the acidolysis of two of the γ-carbinol containing model compounds. The presence of a methoxy substituent, commonly found in native lignin, prevents the formation of this intermediate. Reacti...

Mechanisms of glycerol dehydration.

Abstract: Dehydration of neutral and protonated glycerol was investigated using quantum mechanical calculations (CBS-QB3). Calculations on neutral glycerol show that there is a high barrier for simple 1,2-dehydration, Ea = 70.9 kcal mol-1, which is lowered to 65.2 kcal mol-1 for pericyclic 1,3-dehydration. In contrast, the barriers for dehydration of protonated glycerol are much lower. Dehydration mechanisms involving hydride transfer, pinacol rearrangement, or substitution reactions have barriers between 20 and 25 kcal mol-1. Loss of water from glycerol via substitution results in either oxirane or oxetane intermediates, which can interconvert over a low barrier. Subsequent decomposition of these intermediates proceeds via either a second dehydration step or loss of formaldehyde. The computed mechanisms for decomposition of protonated glycerol are supported by the gas-phase fragmentation of protonated glycerol observed using a triple−quadrupole mass spectrometer.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering.

Abstract: 1.0. Introduction 4044 2.0. Biomass Chemistry and Growth Rates 4047 2.1. Lignocellulose and Starch-Based Plants 4047 2.2. Triglyceride-Producing Plants 4049 2.3. Algae 4050 2.4. Terpenes and Rubber-Producing Plants 4052 3.0. Biomass Gasification 4052 3.1. Gasification Chemistry 4052 3.2. Gasification Reactors 4054 3.3. Supercritical Gasification 4054 3.4. Solar Gasification 4055 3.5. Gas Conditioning 4055 4.0. Syn-Gas Utilization 4056 4.1. Hydrogen Production by Water−Gas Shift Reaction 4056

Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review

Abstract: Fast pyrolysis utilizes biomass to produce a product that is used both as an energy source and a feedstock for chemical production. Considerable efforts have been made to convert wood biomass to liquid fuels and chemicals since the oil crisis in mid-1970s. This review focuses on the recent developments in the wood pyrolysis and reports the characteristics of the resulting bio-oils, which are the main products of fast wood pyrolysis. Virtually any form of biomass can be considered for fast pyrolysis. Most work has been performed on wood, because of its consistency and comparability between tests. However, nearly 100 types of biomass have been tested, ranging from agricultural wastes such as straw, olive pits, and nut shells to energy crops such as miscanthus and sorghum. Forestry wastes such as bark and thinnings and other solid wastes, including sewage sludge and leather wastes, have also been studied. In this review, the main (although not exclusive) emphasis has been given to wood. The literature on woo...