Catalytic Organic Solid Waste Valorization Using Natural Gas

BioSYN’s process begins with a pyrolysis reactor that thermally degrades biomass pellets in the presence of natural gas. A catalyst is used for these reactions, and a combustor unit is used to regenerate and cycle the catalyst back to the pyrolysis reactor, like that of Fluid Catalytic Cracking technology. The desired products include condensable gases that are quenched to produce bio-oil, and non-condensable gases that are purified in the gas-cleanup units. These gases are reacted further in a Water-Gas Shift reactor to increase the hydrogen to carbon monoxide ratio. Light intermediate hydrocarbons are produced and upgraded in a series of catalytic liquefication reactors. Finally, the heavy hydrocarbons and separated into desired product streams using a 3-phase separator. Our major products from this separator include toluene and para-xylene. A recycle stream returns natural gas from the 3-phase separator to the pyrolysis reactor, which aids in cost saving and limiting greenhouse gas emissions.  

CYCLONES

Three cyclones are present in the BioSYN process: 

1. The products stream exiting the pyrolysis reactor is separated by the first cyclone into gaseous products and solids. The gaseous products contain both condensable and non-condensable gases, including aldehydes, levoglucosan, phenols, and other aromatics. Solids consist of the HZSM-5 catalyst coated in biochar (solid carbon). 

2. The second cyclone further separates solid ash from the product gases before they are transported for cooling to collect the bio-oil product. 

3. Char is fully oxidized from the surface of the catalyst in the combustor. The regenerated catalyst is fed to the third cyclone to remove flue gas, then circulates back into the pyrolysis reactor. 

The cyclones use centrifugal force to separate particulate matter from the vapor streams. Air enters tangentially at the top of the barrel and travels down the cone of the cyclone to create the vortex. The increase of velocity in the vortex results in a centrifugal force on the particle which allows the solid to be removed from the stream. At the bottom of the cyclone, an inner vortex is created reversing direction and exiting out the top as product vapour or flue gas. The particulate falls out the bottom of the cyclone and is collected or recycled back into the process.  

WATER-GAS SHIFT REACTOR

Non-condensable gases and water from the gas cleanup unit are fed into a High-Temperature Water-Gas Shift Reactor, which increases the conversion of high purity H₂ through the shift reaction from CO to CO₂. The reactor is being modelled as an adiabatic fixed bed to avoid overheating of catalyst due to exothermic reactions and improving the carbon conversion per catalyst weight. An iron-chromium oxide catalyst is being utilized due to its commonality in industry and size which limits the pressure drop across the bed while assuring a negligible mass transfer resistance.

CATALYTIC LIQUEFACTION REACTORS

Three reactors can be found in series to conduct the upgrading and liquefication of the syngas stream exiting the Water-Gas Shift reactor. The first reactor is a multi-tubular packed bed reactor that facilitates the Fischer-Tropsch and Methane Co-aromatization reactions using two separated catalyst beds – Co/ZSM-5 and Zn/ZSM-5 catalysts. A stainless steel exterior with almost 2400 internal tubes promotes heat transfer from the highly exothermic reactions to a cooling stream running counter-currently. 

The second reactor will be a fixed Cu/ZnO/Al₂O₃ bed to facilitate the methanol synthesis reactions. This set of reactions is important for the environmental contributions of the BioSYN process. By reacting the carbon dioxide and hydrogen found in the syngas stream to produce methanol, greenhouse gas emission rates of are greatly reduced and the removal of CO2 will also reduce the chance of equipment fouling in downstream process equipment.  

Finally, another fixed bed will be found in series where Aromatic Methylation reactions occur. This reactor uses a H/ZSM-5 zeolite to upgrade the intermediate methanol with aromatics produced in the methane co-aromatization to produce the desired liquid biochemical – toluene and para-xylene.  

With the impacts of climate change resonating around the globe, it is becoming increasingly important for industries to seek renewable energy and chemical production pathways. Toluene and para-xylene are valuable commodities in the chemical industry that can be used anywhere from a fuel additive in the transportation sector, to a solvent in pharmaceuticals. BioSYN provides a net low emission process to manufacture these marketable products, paving the way for a brighter future in alternative energy.

Bio-fuel production from various biomass feedstocks has the potential of causing indirect land use changes. Land previously used for food or other crops becomes repurposed to sustain the feedstock, meaning these crops must be grown elsewhere. This results in indirect environmental disturbances to clear and harvest additional land overall. BioSYN acknowledges this challenge and addresses it by sourcing feedstocks from residual forest waste of pulp mill operations that is otherwise burned or discarded. This extends our development of a low emission process upstream of our plant life-cycle.    

Pine beetle kill is a considerable issue for the forestry industry in Prince George and is a culprit for dry debris that causes forest fires. Over the next 2 decades, there will be a large surplus of low-value wood waste from Pine Beetle kill, estimated at 11 million dry tons/year. The harvested “beetle wood” is of lower quality and will not meet the standards for traditional wood, pulp, and paper products, increasing the amount of waste on the forest floor that can be repurposed as a biomass feedstock. In addition to pulp mill forestry waste, BioSYN can harvest this wood as an additional feedstock to produce the same high-quality bio-oil. 

Conventionally, bio-oil is created by pyrolysis or gasification technology but contains large mass fractions of water and oxygen with a low hydrogen-to-carbon ratio. The implications of this are a reduction in heating value, stability, fuel efficiency, and increased corrosiveness. Additional upgrading processes are typically performed to increase the quality of the bio-oil, like steam reforming, hydrotreating, or catalytic cracking. These processes are not only costly but increase design complexity and carbon footprint.

BioSYN integrates methanolysis technology, where natural gas is fed into our wood pyrolysis reactor to both create bio-oil components and upgrade them in “one step”. Wood enters the pyrolysis reactor and heats rapidly to produce several oxygen-containing vapors. Instead of sending them downstream for upgrading, natural gas provides a reducing environment to strip away oxygen from these vapors and replace it with hydrogen. Thus, bio-oil exits the reactor at a higher quality without the need for additional upgrading equipment. 

Our process, however, doesn’t end there. Light gases that can’t be converted into bio-oil are taken downstream and converted into light hydrocarbons. Any methane leftover from pyrolysis is taken downstream with them and reacted further using methane co-aromatization technology. This innovation capitalizes on the synergistic effect between methane and light hydrocarbons under high temperatures to produce aromatic species like toluene. To increase safety in design, we have investigated a unique reaction pathway that can convert more toxic aromatics (like benzene) into comparably safer ones (like para-xylene) as a part of this step. Any methane still left unused is recycled back to the beginning of the process to limit greenhouse gas emissions and reduce operating costs. 

The entire BioSYN process operates under 0.5 MPa pressures, allowing for significant environmental, economic, and safety benefits compared to other biomass-to-biochemical processes.

BioSYN’s goal is to develop a process to lower the amount of greenhouse gas emissions, energy consumption, and cost of traditional aromatic production technologies. 

Currently, the Intercontinental and Canfor Pulp Mills in Prince George, British Columbia, burn off residual wood waste from operations as hog fuel, amounting to 225 thousand tons per year. Hog fuel waste can instead be repurposed as BioSYN’s feedstock, in addition to the 17 million dry tons of sustainable forestry available in British Columbia per year. Sourcing feedstock from residual forestry waste eliminates the GHG emissions that would otherwise be released from hog fuel burning, and natural decomposition of other disposed wood products from mills.

BioSYN’s strategic plant location near these mills significantly reduces our transport costs for feedstock and utilities costs. Canfor operates with a steam plant nearby that our facility can tie-into, discounting costs of process steam. Methane used in the process can also be sourced economically from environmentally sustainable methods, such as decomposition and fermentation of municipal solid waste. Our process can also be adapted to all forms of organic solid waste including municipal feedstocks from landfills, increasing the span of our technology to other areas of the world. 

An extensive literature review was conducted for every process reaction and piece of equipment for both the detailed design and general design to achieve the optimal efficiency, safety, and economic feasibility.

A simulation of our plant was generated using VGM Symmetry software. Multiple hand calculations were conducted for each piece of detailed design equipment to validate if the simulated Symmetry model that BioSYN developed was feasible. Process optimization techniques were executed to improve the accuracy of simulation results and refine design assumptions.

MATLAB code was developed for the three reactors in the BioSYN process to represent a dynamic model of the molar flow rate, pressure drop and temperature change along the length of the reactors using developed kinetic parameters.

All detailed equipment design has been cross-referenced with similar technology currently used in industry to ensure that our plant operates within realistic and practical bounds.

We have performed an economic analysis of our design to assess the feasibility of this innovative project. A capital cost estimation reveals that the total capital investment required to construct the plant is $47.7 million, with a discounted payback period of 5.2 years. We anticipate annual revenues of $37.8 million from our primary products of bio-oil, toluene, and para-xylene. Our analysis also shows a net present value of $49.6 million, indicating financial viability.