Post-Harvest Logistics and Co-Products

Purpose | Methods | Progress | Research & Results

Purpose

Guar and guayule are promising crops because they can be used to produce industrial products that have already been shown to be financially feasible: guar gum and hard rubber for tires. The long-term resilience of guar and guayule economies can be improved by developing additional and value-added products from other parts of the plants. For this reason, SBAR researchers in this component focus on co-products from guar protein and hulls, and from guayule resin and bagasse.

Growing guar and guayule in the field is the first part of the path to end-product sales. Since biomass quality is affected by time (time of harvest, storage time and conditions, transportation time), attention must be paid to how harvested biomass is handled between field and processing facility. Guayule rubber in the plant begins to break down after harvest, so there is limited time to get the materials from the field to the extraction plant. Biomass is also bulky and varies from batch to batch, which complicates harvesting, packing, loading and unloading, routing, processing, and selecting transportation mode(s). Post-harvest logistics modeling and testing will allow researchers and practitioners to identify the optimal strategies for harvest and collection levels, storage amounts, and transportation routes to meet demands in economically efficient and environmentally sustainable way.

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Methods

Biochemical Characterization of Guar and Guayule Bagasse

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Guar bagasse, mostly stems, collected from the field
Guar bagasse, mostly stems, collected from the field

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Bomb calorimeter used to measure bagasse energy content as higher heating value (HHV)
Bomb calorimeter used to measure bagasse energy content as higher heating value (HHV)

Bagasse refers to the residues from a product extraction from plant biomass, traditionally the fibrous material left over after the extraction of sugar from sugarcane. For guayule, the bagasse consists of the woody stem material left after resin and rubber extraction at the processing facility. For guar, bagasse consists of the plant stem, leaf, and bean pod material left on the field after combine harvesting. Bagasse has several potential applications: direct use as a solid fuel (i.e. guayule bagasse pressed into pellets for combustion in pellet stoves for heat), conversion to a liquid fuel through biochemical or thermochemical methods, return to the soil as soil cover/conditioner for nutrients and organic matter, incorporation into composite materials as a fibrous filler, etc. The characteristics and available amounts of each bagasse provides information about which application will be the most sustainable.

Characterization consists of several measurements to describe bagasse composition and properties: biochemical content by National Renewable Energy Laboratory methods for moisture, ash, extractives, hemicellulose and cellulose; elemental content by CHNS combustion and by acid digestion/inductively coupled plasma optical emission spectroscopy (ICP-OES); energy content by higher heating value analysis by bomb calorimeter, particle size distribution by sieving, and bulk density. 

 

About CHNS Elemental Analysis

CHNS is the most common form of elemental analysis, and is generally accomplished through combustion. This method allows for the rapid determination of carbon, hydrogen, nitrogen, and sulphur in organic materials. A sample is burned in an excess of oxygen, and various traps collect the combustion products: carbon dioxide, water, nitric oxide, and sulphur dioxide. The masses of these elements can then be used to calculate the composition of the sample.

 

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Conversion of Guayule Bagasse to Fuels

The baseline use for guayule bagasse is as a solid fuel, to be pelletized at the guayule rubber extraction facility, and then sold for use in pellet stoves. A goal of the SBAR project is to find higher-value energy products that can be made from the bagasse, preferably a liquid fuel such as a hydrocarbon mixture: gasoline, jet fuel (kerosene), diesel, etc.; or one of the shorter-chain oxygenated fuels: ethanol, dimethyl ether, butanol, etc. The yield and quality of the produced fuel depends on the composition of the feedstock, the conversion method, and the reaction conditions. 

Among the conversion technologies being investigated for guayule bagasse are enzymatic hydrolysis and sugar fermentation, anaerobic digestion, hydrothermal liquefaction, fast pyrolysis, gasification, Fisher-Tropsch synthesis, syngas fermentation, and hydrotreatment/catalytic upgrading. In the first two years, conversion will be studied through literature review and lab-scale experiments; in the last three years, partnerships with companies/organizations will be formed to conduct pilot/demonstration scale experiments to down select conversion technologies to those most ready for commercialization.

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Conversion of guayule bagasse to fuels chart
Conversion of guayule bagasse to fuels chart

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Model and Algorithm Development for Biomass Supply Chain

A biomass supply chain consists of several operational components: from biomass harvesting and collection, pre-treatment, storage and conversion, to transportation. This research includes the development of system-level logistics models, and the identification and evaluation of alternatives for production, harvest and collection, storage, and transportation routes to meet demands. The model brings biomass production, processing, and conversion to a wholly sustainable bio-economy system, as well as simplifying and streamlining the feedstock logistics. Compared to existing research, this project will improve the efficiency of designed algorithms to obtain the solutions for decision-making, increase the quality and accuracy of optimal solutions, enhance the robustness of decisions for the biomass supply chain, and ensure the flexibility and adaptiveness of models for studying in various scales and different regions.

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Progress Made Thus Far

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SBAR student – Meshack Audu – in a guar research field at the NMSU Agricultural Science Center in Clovis, New Mexico
SBAR student – Meshack Audu – in a guar research field at the NMSU Agricultural Science Center in Clovis, New Mexico

Progress in the first two years has included: visits to partner sites; collection and characterization of whole plant and post-processing fraction samples; preparation of literature review articles on biomass transportation optimization models and on biomass conversion methods; identification of new compounds in guayule resin; synthesis of guayule resin molecule analogs for bioactivity testing; identification of secondary metabolites in guayule under different growth conditions; and characterization of guar gum and microorganisms involved in guar nodulation.

 

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Research and Results

Posters and Presentations

Brewer Research Group SBAR

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