Is it possible to apply for a patent without the consent of co-inventors?

Yes, it is possible. Check out MPEP 1.45:
http://mpep.uspto.gov/RDMS/detail/manual/MPEP/current/d0e18.xml#/manual/MPEP/current/aia_d0e317823.xml
1.45 Application for patent by joint inventors.
[Editor Note: Applicable only to patent applications filed under 35 U.S.C. 111(a) or 363 on or after September 16, 2012*]
(a) Joint inventors must apply for a patent jointly, and each must make an inventor's oath or declaration as required by § 1.63, except as provided for in § 1.64. If a joint inventor refuses to join in an application for patent or cannot be found or reached after diligent effort, the other joint inventor or inventors may make the application for patent on behalf of themselves and the omitted inventor. See § 1.64 concerning the execution of a substitute statement by the other joint inventor or inventors in lieu of an oath or declaration.
(b) Inventors may apply for a patent jointly even though:
(1) They did not physically work together or at the same time;
(2) Each inventor did not make the same type or amount of contribution; or
(3) Each inventor did not make a contribution to the subject matter of every claim of the application.
(c) If multiple inventors are named in a nonprovisional application, each named inventor must have made a contribution, individually or jointly, to the subject matter of at least one claim of the application and the application will be considered to be a joint application under 35 U.S.C. 116. If multiple inventors are named in a provisional application, each named inventor must have made a contribution, individually or jointly, to the subject matter disclosed in the provisional application and the provisional application will be considered to be a joint application under 35 U.S.C. 116.