Microbial DesulfurizationCHBE446: Process Economics and Design 2

6 February 2014Heather Cook

Savannah GreenDave Weglein

Mike Wellen

Outline

• Introduction & History• Mechanisms• Current Uses in Industry• Major Challenges & Advantages• Current Research

Introduction: What is Microbial Desulfurization?

●Also known as Biodesulfurization (BDS)●Biological desulfurization process where

microbial catalysts are used to oxidize sulfur in crude oils

Introduction: Why is BDS important?

●Combustion of sulfur compounds leads to production of sulfur oxides ● High concentrations of sulfur oxides in the

atmosphere can lead to health issues such as asthma, bronchial irritation, and lung cancer

●Ability to “desulfurize compounds that are recalcitrant to the current standard technology in the oil industry” (Abin-Fuentes, et al)

New Regulations

• Sulfur content in crude oil ranges from 0.03% - 7.89%• Many crude oils are increasing in sulfur content

• Clean Air Act Amendments introduced by EPA in 1990 to restrict sulfur concentrations in fuels • Reduce annual SO2 emissions

BDS Overview

● Increased interest over last 20 years○ Desulfurizes wider range of compounds then

conventional hydrodesulfurization (HDS)● Three pathways

○ Kodama (destructive)○ Anaerobic (selective)○ 4S (specific oxidative)

● 4S is the most popular/effective

Mechanisms

Kodama Pathway

● Sulfur not selectively cleaved from dibenzothiopene (DBT)

• Carbon-carbon bonds broken

• Metabolize DBT’s & convert to water soluble compounds

• Water soluble products inhibits further microbial growth & DBT oxidation

Anaerobic pathway

• Anaerobic strain can degrade some of DBT

• Products: biphenyl & H2So Makes this a selective pathway

• Advantage:o Oxidation of hydrocarbons to undesired compounds

is minimal

• Disadvantage:o Reduced caloric content in fuelo Specific activity for most isolated strains are

insignificant for alkylated DBTs

4S Pathway● Carbon-sulfur bond selectively cleaved

Bacteria Used

4S Pathway Enzymes

• Reaction is energy-intensive and needs cellular metabolism

• The 4S pathway involves sequential oxidation of the sulfur part and cleaving of the C–S bonds

• Four main enzymes used in the 4S pathway

DszC Enzyme

• 45 kDa protein

• Catalyzes DBT->DBTO->DBTO2

• Step uses oxygen, NADH, and FMNH2 for activity

DszA Enzyme

• 50 kDa protein

• Transforms sulfone into sulfinateo Uses FMH2 as co-

substrate

• Step requires oxygen and NADH as wello Oxygen from

molecular oxygen

DszB Enzyme

• 40 kDa protein

• Final step in the reaction

• Rate limiting stepo Present in cells in smaller amount in cytoplasm

DszD Enzyme

• Uses FMN as a substrate

• Couples the oxidation of NADH to substrate oxidation

• Produces FMNH2 to allow DszC and DszA to work

Currents Uses in Industry

Thiopaq

• Biogas• Vent air

• Refinery Gas

• Hydrogen Sulphide

• 120 Installations World-wide

• Reduces to under 25 ppm

• Fluctuating Gas Flows

• Low maintenance

• Ambient Pressures an Temperatures

• Produces Elemental Sulfur

Benefits of System

• Deep H2S removal and recovery as elemental S, extremely low SO2 emissions are achieved

• Special costly equipment such as burners and reboilers are not required. The regeneration and sulphur recovery section always operate at atmospheric pressure and ambient temperature

• Reliability of a natural process coupled with the efficiency of dedicated engineering

• Simple process configuration- and control with stable operation

• Broad and flexible operating range with short system start-up times

• Expensive chemicals such as those required for liquid redox processes are not required. Only sodium hydroxide and nutrients are needed

More Benefits● Limited utility requirements

● Ease of operation. Produced biosulphur is hydrophilic and behaves like a relatively stable suspension without clogging or other nuisances

● Environmentally friendly process based on naturally occurring bacteria

● Inherently safe operation:

○ no free H2S downstream absorber

○ ambient temperatures for the whole system (solution temperatures of 25 – 40 °C)

○ bioreactor and sulphur recovery at atmospheric pressure.

● Produced biosulphur is the basis for a range of new agricultural products designed to act as (ingredients for) liquid fertilizers and liquid fungicides

Steps of Process

• Sulfide rich solution loaded to flash drum• Loaded to bioreactor• Lean solution returned to absorber• Lean solution returned to absorber• Elemental Sulfur seperated out• Bioreactor contents are recycled over settler• Concentrated slurry dewatered in centrifuge• Filtrate is cycled back• Small slipstream of clear solvent

Industrie Eerbek

• Netherlands treats water from three neighboring paper mills

• Biogas used to produce electricity• 1% to 25 ppm• Thiopaq system was installed in 1993

Ben & Jerry’s

• Hellendoorn, Netherlands• Ice cream waste products converted into electricity• Desulfurized with Thiopaq• 40% of factory's energy requirements• Operational 2011

Cargill

• Starch processing company• Sulfate rich water treated with anaerobic bioreactor

Lenzig Ag• Viscose Fiber Production

• 2009 produced 568,600 tonnes

• Produces range of secondary compounds

• Some streams need to be discharged.

• SULFATEQ system installed in 2002

McCain

• Potato processing company• Receives biogas from anaerobic water treatment and

solids digester• To prevent corrosion of gas engine, Thiopaq converts

hydrogen sulfide to elemental sulfur• Longer life for gas engine.

Other Examples

• WaterStromen• Hulshof Royal Dutch Tanneries• Weltec BioPowr GmbH• Tempec• Nine Dragons• Smurfit Kappa

Challenges, Advantages & Current Research

5 Step Process

• Production of active resting cells with high specific activity

• Preparation of biphasic system containing oil fraction, aqueous phase and biocatalyst

• BDS of wide range of sulfur compounds at acceptable rate

• Separation of desulfurized oil fraction, recovery of biocatalyst and return to bioreactor

• Efficient wastewater treatment

Major Challenges

• Biocatalyst activity improvement

• Biocatalyst longevity improvement

• Phase contact and separation

• Process engineering research

Current Research

• Reduction in biocatalyst activity associated with the generation of the end product (2-hydroxybiphenyl)

• Increase of bacterial desulfurization rate through identification of certain genes

• Overexpression of FMN reductase

• Change in host strain for dsz genes

Advantages of BDS

• Requires less energy and hydrogen

• Operates at ambient temperature and pressure with high selectivity

• Decreased energy costs

• Low emissions

• No generation of undesired products

Questions?

ReferencesAbin-Fuentes, A., M. E.-S. Mohamed, D. I. C. Wang, and K. L. J. Prather.

"Exploring the Mechanism of Biocatalyst Inhibition in Microbial Desulfurization." Applied and Environmental Microbiology 79.24 (2013): 7807-817. Web. 6 Feb. 2014.

Mohebali, G., and A. S. Ball. "Biocatalytic Desulfurization (BDS) of Petrodiesel Fuels."Microbiology 154.8 (2008): 2169-183. Web. 6 Feb. 2014.

Ohshiro, Takashi, and Yoshikazu Izumi. "Microbial Desulfurization of Organic Sulfur Compounds in Petroleum." Bioscience, Biotechnology, and Biochemistry 63.1 (1999): 1-9. Web. 6 Feb. 2014.

Paqell | THIOPAQ O&G - Biological Gas Desulpherisation and Sulphur Recovery | Paqell."Paqell | THIOPAQ O&G - Biological Gas Desulpherisation and Sulphur Recovery | Paqell. Paqell BV, n.d. Web . 05 Feb. 2014.

Soleimani, M., Bassi, A., and Margaritis, A. 2007. Biodesulfurization of refractory organic sulfur compounds in fossil fuels. Biotechnol. Adv. 25(6):570-96.