Green Energy: Production of Alcohols from Switch-grassHaseeb Quadri

Tim Obrien

Tim Bannon

Catalina M.

Greg D.

March 9th, 2009

Professor Perl

Team Alpha Final Design/Engineering-Review

Abstract:

One of the greatest reductions of carbon emissions in the U.S. thus far has been the addition of alcohols to gasoline. Many states now mandate an addition of 10% ethanol to each gallon of gasoline sold. Most fuel ethanol is produced by the fermentation of corn. At the end of the 2006/07 crop year 2 billion bushels, approximately 19% of the US corn crop, were used for the production of ethanol. The increased demand for corn has put the energy industry in direct competition with the food industry. This has also increased the price to produce a gallon of fermented ethanol to $1.70 per gallon at the end of 2007. The catalytic production of alcohols via alternative feedstock can lower the cost of producing ethanol to a more competitive level allowing the process to be viable without subsidies from the government. Switch grass is a particularly attractive option as it can be grown on land unable to sustain food producing plants.

The gasification of switch grass and subsequent catalytic conversion of the synthesis gas leads to ethanol and higher chain alcohols. The process uses an indirectly heated gasifier which is known as the Silva Gas process to produce synthesis gas, or syngas. The syngas tars are destroyed catalytically through a two step process. The gas has the CO2 and sulfur removed, is compressed, and is then sent through a fixed bed reactor to produce alcohols. The K/MoS2 catalyst is selective towards ethanol and mixed alcohols, allowing greater flexibility should the market demand change to higher chain oxygenates. Recycling the methanol produced back to the reactor considerably increases product yields.

Executive Summary:

This work addresses the issue of alternative fuels, specifically the creation of alcohols from non-food sources of biomass. The entire world is focused on reducing our carbon footprint and moving away from the use of hydrocarbons for energy. Currently the government subsidizes the production of ethanol with a $1.00 credit per gallon. With the economy in a slump and the increasing mandates for using more bio-fuels, it is likely that the $1.00 credit will soon be rescinded. This creates a need for cost effective production of ethanol. The current goal is to find ways to produce ethanol for approximately $1.00 per gallon. At that cost a process can be profitable without the $1.00 per gallon credit.

This process design evaluation looks at the conversion of switch grass to ethanol via thermo chemical pathways. This report uses:

Currently established and published technology Indirectly heated gasification Catalytic tar destruction Amine absorption of CO2

Fixed bed catalytic conversion of syngas to ethanol and propanol Azeotropic distillation to produce fuel grade ethanol as specified by ASTM D 4806

This report shows that ethanol and other higher alcohols can be produced at the goal price. This report also indicates however that there needs to be a significant capital investment with paybacks longer than 2 years. This means that the conversion of biomass to alcohol will require technological improvements in order to increase the attractiveness of the process to investors.

Conclusions:

Appendices:

1. Process Flow Diagram showing the major components:

Conceptual Process Flow Diagram:

Detailed Process Flow Diagram:

Figure 3.1: PFD, Gasifier, Combuster, Tar removal unit

Figure 3.2: Waste heat recovery and Biomass Drying